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JANUARY 1940

DO NOT CONCENTRATE ON WARDo not concentrate your thoughts upon war subjects. You will find it very worrying and very bad forthe nerves.Read, write, sketch, paint, study your vocation; anything that will occupy your mind and your time. Makeuse of the long dark nights by concentrating upon something useful.During the last war many people learned how to write short stories etc., to -day a number of them areworld -famed authors.By becoming efficient in your vocation you can give the best service to your country and to yourself. Themore you increase your earning power the better it is for the country and for yourself personally.War or no war,.earning power always brings its possessor to the front. It is no use waiting for bettertimes: The ideal opportunity never arrives. We have to make the best of existing conditions. Therefore,delay is useless; it is worse, it is harmful.

YOU CANNOT MAKE MONEY BY SAVINGIf you save 10s. per week for 10 years you have only got £260, but if you spend 2s. 6d. per week for 12or 18 months on a correspondence course, you give your brains a chance to earn thousands of pounds,,.hen there is no need to save. Savings are likely to vanish, but earning capacity is a permanent investment.

DO ANY OF THESE SUBJECTS INTEREST YOU?Accountancy ExaminationsAdvertising and Sales ManagementAgricultureA.M.I. Fire E. ExaminationsApplied MechanicsArmy CertificatesAuctioneers and Estate AgentsAviation EngineeringBankingBlueprintsBoilersBook-keeping. Accountancy and

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If you do not see your own requirements above, write to us on

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STUDY AT HOME INYOUR SPARE TIME

..

CAN YOU CHANGE MYEXPRESSION ?

IF SO, YOU MAY BETHE ARTIST THATCOMMERCE IS WAIT-

ING FORJust try it for yourseliTrace or draw the outlineand then put in the features

There are hundreds of openings in connection withHumorous Papers, Advertisement Drawing,Posters, Calendars, Catalogues, Textile. Designs,Book Illustrations, etc.(g) per cent. of Commercial Art Work is done by" Free Lance Artists " who do their work athome and sell it to the highest bidders. ManyCommercial Artists draw " retaining fees " fromvarious sources, others prefer to work full-timeemployment or partnership arrangement. Weteach you not only how to draw what is wanted,but how to make buyers want what you draw.Many of our students who originally took upCommercial Art as a hobby have since turnedit into a full-time paying profession with studioand staff of assistant artists; there is no limit tothe possibilities. Let us send full particulars for aFREE TRIAL, and details of our course for yourinspection. You will be under no obligationwhatever.

ART DEPT 76.

LET ME BEYOUR FATHERLet me tell you howto make a success ofyour career.If your future is un-decided or appearsunsatisfactory, let ustalk it over together.I want to help, and itwill cost you nothingto get my help: youwill be under noobligation whatever.

I HAVE HELPED THOUSANDSOF OTHERS

And when I say thousands, I do not exaggerate,as I can produce well over 10,000 unsolicitedtestimonials from grateful students who,through our Postal Train-ing, have achieved theirlife's ambition.

EVERY DEPARTMENT IS ACOMPLETE COLLEGE: EVERYSTUDENT IS A CLASS TO

HIMSELF

--Dept. 76, THE BENNETT COLLEGE, SHEFFIELD

JOURNALISMShort -Story, Novel and Play

WritingThere I s money and pleasure i n Journalism and In StoriWriting. No apprenticeship, no pupilage, no examina-tions, no outfit necessary. Writing for newspapers,novels or pictures is not a gift: it is a science thatcan be acquired by diligent application and propelguidance. It is the most fascinating way of makingpastime profitable. Trained ability only is requiredwe do the training by post. Let us tel I you all about it.DEPARTMENT OF LITERATURE 76

If you attend to this now, it may makea wonderful difference to your future.

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January, 194) NEWNES PRACTICAL MECHANICS 145

Start right with a

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The DLP Machine is the best possible nuclaus of a workshop. Icomprises:-a Parallel Vice; Pipe Vice; Tubs, Roi ani Strip BenderCable, Rod and Pin Cutter; Punching Machine; Cabla Stripper; ScrewingMachine for threads up to 3/4 -in. Whit., %-in.,Gas and t -in. Conduit; Flatand Conical Anvils. The space required on your bench is only 12 -in. xs8 -in. Illustrated Folder on application.

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A Book of Vital Interest to all who Love Ships and the Sea

SHIPS AT WORKBy A. C. HARDY, B.Sc., F.R.G.S., A.M.I.Mar.E.

This splendid book describes the work carried on by theworld's sea -traders in times of peace and in the morestrenuous times of war.It takes you aboard the merchant ships of the nations-fromthe humble dredger to the largest ship in the world. Theauthor is a naval architect, and he shows the work of liners,coasters, tankers, trawlers, cable -ships, lightships and everyother one of the great family of vessels that make up a nation'slifeline. With illustrations of over 100 ships.

7/6 net, from cif booksellers, or by post, 8.-, from

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ENGINEERINGWORKSHOP PRACTICE

This up-to-date book provides a complete practicalcourse of instruction in every important branch ofengineering workshop methods, materials and equip-ment. It deals with the underlying principles, crafts-manship, machines, tools, measuring processes andmachining methods of to -day, and it will -prove indis-pensable to the engineer, draughtsman, mechanic,apprentice and engineering student. Its scope extendsfrom simple hand tools and machines to the latestelaborate machines and methods employed for mass -production purposes.

SOME OF THE SUBJECTSFiles, Chisels, Scrapers, Shears, Punches, Burnishers, Hand

Screw -cutting Tools, Spanners, Vices, Various measuringmethods. Verniers, Micrometers, Gauges, Optical Devices,Fluted and Twist Drills. Grinding Angles, Drilling Data,Small and Large Drilling Machines, Electric Drills, PracticalLathework in all its branches, Machining of Metals andSynthetic Materials. Tungsten -carbide and Diamond Tools.Lapping, Honing, Cleaning, Polishing and Rust -protectionof various metals. Grinding Operations and Machines,Milling Operations, Cutters and Machines. Planing, Shaping,Slotting and Broaching Operations. Special Machines forProduction Purposes. Plate and Bar Machines. Gears andGear cutting Methods. Templates, Jigs and Fixtures.Overhauling and Adjusting Machines, Millwright Work.Welding, Brazing and Soldering Metals. Forging Work.Sheet Metal Work. Foundry Work. Patternmaking Practice.Press Work. Engineering Steel and other Metals; theirProperties, Testing. Hardening, Tempering and Annealing.Engineers' Drawings. \Vorkshop Calculations, Data, Hintsand Recipes.

THE ILLUSTRATIONSThe book is lavishly illustrated so that the explanations

are rendered very clear with examples taken from actualworks practice in many instances. There are 24 full -pageplates and 877 line and photographic illustrations in thetext.

ENGINEERING POCKET BOOKIn order to make the work even more comprehensive, we

have brought out a pocket book, which is supplied free to allpurchasers. It contains many useful tables of Screw Threads,Tapers, Angles, Drill Speeds and Sizes, etc.

A FREE BOOKLETTo the Caxton Publishing Co., Ltd.,

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146 NEWNES PRACTICAL MECHANICS January, 1940

ENGLNEERS I,4. EQUIP YOURSELF FOR WORK OF

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QUALIFIEDMen with technical knowledge are as important as troopsand ammunition. For the country's immediate needs andyour own future gain you are urged to send immediately fora free copy of "ENGINEERING OPPORTUNITIES."Containing 268 pages of practical guid-ance, this book is, beyond argument, thefinest and most complete handbook onSuccessful Engineering Careers ever com-piled. It is a book that should be on thebookshelf of every person interested inengineering, whatever his age, position orexperience.The Handbook contains, among otherintensely interesting matter, details ofB.Sc., A.M.I.C.E., A.M.I.Mech.E.,A.M.I.E.E., A.M.I.A.E., A.M.I.W.T.,A.M.I.R.E., Civil Service and otherimportant Engineering Examinations; out-lines courses in all branches of Civil,Mechanical, Electrical, Automobile,Radio, Television and AeronauticalEngineering, Building, GovernmentEmployment, etc., and explains theunique advantages of our EmploymentDepartment.

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Special Notice-Price IncreaseREADERS will notice that the price

cf PRACTICAL MECHANICS has beenincreased to 7d. as from this issue. Thewar has produced its inevitable conse-quences for publications of the characterof PRACTICAL MECHANICS, and not theleast are the higher costs and the loweradvertisement revenues. On the costside, paper alone has risen by over60 per cent. since the outbreak of warand the possibilities are that prices willrise evert further.

In facing this problem we had thealternatives of reducing the size and thenumber of pages of the journal or in-creasing its price. In deciding on thelatter course we felt sure that our readerswould prefer it to the alternative of ajournal smaller in size and with fewerpages, for this would ,have meantsacrificing the services of contributorsand artists and the many specialfeatures which our readers so muchappreciate.

Our tens of thousands of loyalreaders will, we are certain, appreciateour difficulties, and continue to givePRACTICAL MECHANICS their valuedsupport and co:operation. They will,too, understand that the extra pennyrepresents only a proportion of the in-creased costs we have to bear. Ourreaders, we are confident, will appreciateour intention, in spite of the difficultiesof magazine production, to carry onthroughout the war, and we express thehope that the war will mercifully be ofshort duration.

Clubs for EngineersWHILST most other industries

have clubs, it is somewhat sur-prising that hitherto the engineeringtrade has been without them. I now seethat in some of the busy engineeringdistricts engineers are forming localclubs where they meet for discussions

PRACTICALMECHANICS

Editor: F. J. CAMM

VOL. VII. JANUARY, 1940. No. 76.

FAIR COMMENTBy the Editor

on engineering problems and to listento lectures. Many engineering firms arewilling to supply lecturers and to hireout instructional films. This club move-ment seems to be growing and I supposethat inevitably there will be a parentorganisation to link the various branches.In some of the industrial centresengineers have been having a flat timein the evenings owing to the black -out.The club movement provides them witha pleasant means of spending an eveningand meeting others with kindredinterests. It is a means, too, ofgaining knowledge and experience.

The Model of the " FlyingScotsman"

I REGRET that it has not been foundpossible to commence the series of

articles dealing with the 2 in. gaugemodel of the "Flying Scotsman." Thesewill, however, commence next month.The model has been built and thedrawings are being prepared from theactual model. It has passed its steamtests with flying colours.

New BooksWE shall shortly be publishing

from the offices of this journalthe Practical Wireless Short WaveManual-a complete treatise on theprinciples, design and construction ofshortwave receivers for mains andbattery operation. Another new bookshortly to be published is Watches-Repair and Adjustment, which deals ina practical way with every branch ofwatch repair and tuning. We haverecently published the seventh editionof the Practical Wireless Encyclopedia(formerly The Wireless Constructor'sEncyclopedia). A new edition of ModelBoat Building is in course of preparationand Motor Car, Principles and Practiceis on the stocks for publication early in

January. More Miles Per Gallon, whichcosts ls. from the offices of this journal,is a volume which every motorist willappreciate in these times of petrolrationing. This book covers the wholesubject of economical running, anddec13 with alternative fuels and methodsof improving petrol consumption. Weissue a catalogue of our technical booksfor engineers, mechanics, and electri-cians, and a copy will be sent free to anyreader upon request. A list of thechapters of each book is included.

NeW FeaturesI MAKE my annual request for readers

to let me know what subjects theywould like to form the subject of futurearticles. Last year I received an excel-lent response to my appeal and wasable to satisfy the requirements of alarge number of readers.

I should welcome a postcard fromyou detailing articles which you feelwould be of interest. I would, however,ask you to bear in mind that referenceshould be made to the indexes of pastissues so that you do not suggest asubject which has already been treated.Indexes for most of the past volumesare available at 7d. each.

Our Companion JournalsREADERS interested in motoring,

wireless or cycling should remem-ber that we issue from the offices ofthis journal the Practical Motorist,which is published at 3d. every Friday,and deals with all aspects of motoringand the motor car, especially from theowner's point of view; The Cyclist,every Wednesday -at 3d.; and PracticalWireless-the only weekly wireless jour-nal-at 3d. every Wednesday. Nextmonth I hope to make an interestingannouncement regarding another newjournal which will appeal especially toengineers.


The Principles of the Electric

A Model A Console will give every satisfactionhome. There is hardly a limit to the scope of

AN organ that is without pipes or windmay well indeed be called a newinstrument. The Hammond Organ

is not merely new; it represents in itself arevolution so far-reaching as to be quiteincalculable.

Science and the laws of dynamics havebeen so harnessed to the inventor's will thathe has created an ,instrument eminentlysuitable for the drawin,g,rooni ; yet, whenoccasion demands, powerful enough to fill acathedral with a tone of great sweetness. Itis remarkably adaptable for installationpurposes. The maximum floor spacewhich it needs never exceeds fouror five feet square.

The actual ' furniture " of theinstrument consists of but twopieces-the console and the powereabihet, which is connected to theconsole by a cable and can be placedin any convenient part of a room orbuilding. The number of cabinetsmay be multiplied for large build-ings, as required.

General ArrangementFig. 1 shows the various controls

marked. The pre-set keys are atthe left-hand end of each manual.The tremulant control is locatedjust above the pre-set keys. Imme-diately over the upper manual arefive groups of controls.

There are two groups of harmoniccontrols of nine draw -bars each, onthe left-hand side; these operate onthe upper manual. The two groupsof nine harmonic controls on theright operate on the lower manual.Between these groups are twoother harmonic controls ; theseoperate on the pedals.

The Pre-set Keys, Models A and BConsolesAt the left end of each manual is an

A Brief Description of

Tonal Combinations of an

The key at the extreme left, C, is the cancelkey, used only to clear the pre-set keys when twohave been depressed by mistake

The two pre-set keys at the extreme right, A -sharpand B, are really switch keys, When A -sharp isdepressed the organ speaks with whatever tonecolour is set up on the left one of the two harmoniccontrollers for that manual. When B is depressedthe organ speaks according to the right-handcontroller for that manual.

The intervening pre-set keys, C -sharp to A in-clusive, are each associated with a different ready -mixed tone quality set up before the organ isinstalled. These keys correspond to the pistons ona pipe organ. They are generally useful tonequalities. The artist may, however, substituteany other pre-set quality he prefers for any or allof them by a simple method fully explained in theoperating instructions.

The tone of the organ is changed from one qualityto another while playing, merely by depressinganother pre-set key.

The two manuals are really duplicates of eachother, each having its own pre-set keys and twoharmonic controllers.

It should be clear from the above that, beforein a small church or auditorium or in the playing, the organist must first depress one of the

music which can be played on this instrument pre-set keys associated with 'the manualon which he is about to play.additional octave of reverse colour keys-

that is. the naturals are black and the sharpswhite. These are the pre-set keys. Those tothe left of the lower manual are associatedwith that manual, those above with theupper manual.

When a pre-set key is depressed it staysdown. When a second key on the samemanual is depressed the first key springs upand the second remains down. Up, the pre-set key is "off"-not functioning. Depressed,it is " on." Only one pre-set key should bedepressed on the same manual at one time.

TREMULANT

CONTROL -1

The Pre-set PistonsOn the Model E Console, small pistons

(numbered 0 to 11) are employed, instead ofthe reverse colour keys. A label against eachpiston indicates the tone quality associatedwith it. The piston marked " 0 "is the cancel key and Nos. 10 and 11are available for any tone qualitiesthat may appeal to the organist by man-ipulation of the drawbars as explainedon the opposite page.

PRESET KEYS: C$ to A INCLUSIVE

HARMONIC CONTROLLERS FOR UPPER MANUAL

HARMONIC CONTROLLER FOR PEDAL KEYS

HARMONIC CONTROLLERS FOR LOWER MANUAL

STARTING SWITCH

RUNNING SWITCH

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[-CANCELKEYS

SWITCH KEY CONNECTING LOWER MANUAL TO ITS RIGHT HARMONIC CONTROLLER

SWITCH KEY CONNECTING LOWER MANUAL TO ITS LEFT HARMONIC CONTROLLER

SWITCH KEY CONNECTING UPPER MANUAL TO ITS RIGHT HARMONIC CONTROLLER

SWITCH KEY CONNECTING UPPER MANUAL TO ITS LEFT HARMONIC CONTROLLER

PRESET KEYS. C$ to A INCLUSIVE

Fig. 1.-A plan of Console A model. The pre-set keys are at the left hand of each manual. The tremulantcontrol is located just above the pre-set keys. Immediately above the upper manual are five groups of controls

January, I94u NEWNES PRACTICAL MECHANICS 149

Organthe Electrical Principles andIngenious Musical Instrument

The Harmonic ControllerThe Harmonic Controller is the device by

which the artist is enabled to mix the funda-mental and any or all of 8 different har-monics in various proportions. It consists of9 drawbars. The third drawbar from theleft controls the fundamental. Each of theother drawbars controls a separateharmonic as shown on the diagram. Eachdrawbar may be set at any one of 8different positions. If pushed all the wayin, against the console, the element it repre-sents is not present in the mixture. It maybe drawn out to 8 different positions. Theseare marked off on the -drawbar and may beread by the artists. Each position repre-sents a different degree of intensity of theelement it controls. When drawn out toposition 1, the element it represents will bepresent in the mixture with minimumintensity : when drawn out to position 2,with greater intensity, and so on, up toposition 8.

PEDAL PISTON INDICATORS

MANUAL PRI.SET PISTONS,

TRINULANT

caw TRDIULANT

Fig. 2. Mode! E Console showing themanual pre-set pistons, pedal piston indica-

tors and tremulant levers

A tone colour is logged by noting thenumerical position of the various drawbars.For instance, the tone set up in the diagramFig. 3 is known as tone 23,6444,222. After atone is so logged it may be made availableagain by setting up the harmonic controllerto that number.

The Electrical PrincipleWhen you pull out one drawbar of ti con-

troller and depress a playing key, a minutesingle alternating current generated in theconsole is carried flu -cough the cable to thepower cabinet. Here it is amplified by theuse of normal amplifying methods andcaused to operate standard speaker conesand produce audible sound. The characteris-tics of the minute current generated are suchthat the sound produced at the speakers is amusical tone perfect in pitch and free fromall overtones and harmonics. In otherwords, it is a pure fundamental tone.

To this the artist, by using the otherdrawbars, may add other pure tones whichare selected harmonics of this fundamentaland thus produce complex musical tones ofa wide variety of qualities. The quality of amusical tone depends upon its harmonic

Model E Console which canbe termed a professional organ -id's instrument. Whilst beingperfectly suitable for use-

content. This harmonic content is added tothe fundamental by combining the properminute electrical currents at the consolethrough use of the controls provided.

The GeneratorLet us now consider the generator,

located in the console, and see how it pro-duces the minute electrical t urrents whichcreate the musical tones. Refer to Fig. 7.A metallic plate (the tone wheel) about thesize of half a crown is arranged so that itwill rotate in close proximity to a per-manent Magnet. About the permanentmagnet is wound a coil. The illustrationclearly shows this arrangement of plate,magnet and coil. This plate is not circularbut has a number of high points equallyspaced around its periphery, as shown. Asit rotates it does not touoh the permanentmagnet, but these high points pass close to

SUB FUNDAMENTAL

SUB 3RD HARMONIC

FUNDAMENTAL

END HARMONIC

6TH HARMONIC

6131 HARMONIC5TH HARMONIC4TH HARMONIC

3RD HARMONIC

Fig. 3.-A harmonic controller. This is the device I!,which the artist is enabled to mix the fundamentalsand any or all of eight different harmonics in various

proportions

the magnet, Each time a high point passesthe magnet it varies the magnetic field' andinduces a minute flow of current in the coil.Should the tone wheel be rotated at such aspeed, for instance, that 439 high points passU. to magnet each second, a minute alter-nating current of a frequency of 439 wouldbe generated in the coil and flow in thecircuit with which it is associated. Such afrequency of 439 when converted into soundwould be New Philharmonic " Pitch_" A."

Now in the generator there are 91 suchplates, all permanently geared together anddriven by a constant -speed synchronousmotor. Their speeds of rotation and the

-in the home or in the smallest orlargest building, it is so equipped thatevery description of organ literature

may be played on it

number of high points on each are so cal-culated that each disc produces one of the91 frequencies necessary for the 91,pitcheswhich are ns d in the fundamentals andharmonic overtones.The General Electrical Operation

Ninety-one frequencies are thus con-tinuously available at the generator. Whena key is depressed it selects the proper fre-quency for the fundamental of the note itrepresents, together with the proper fre-quencies for eight harmonies of that note asset up on the harmonic controlleror on apre-set key. These frequencies then flowthrough the contacts made by the key, eachto its proper drawbar, of the harmonic con-troller. The position of the drawbar (whichis under the control of the artist) determinesthe intensity of each frequency. Afterleaving the harmonic controller thesevarious frequencies are superimposed uponone another, or mixed, and flow as a singlecomplex electrical wave to the preamplifier,also located in the console. From here thewave (amplified somewhat) flows throughthe connecting cable to the amplifierslocated in the power cabinet, where it isfurther amplified and caused to operate thespeakers.

DuntssiomPE AL (NIMMONS

CHORUS CONTROL

----STARTING SWITCH\ RUNNING SNITCH

Fig. 4.-The expression pedal indicators,chorus control and starling and running

switches


The swell pedal control is located betweenthepre-amplifier and the matching transformerIts operation varies the strength of the elec-tric wave flowing to the pre -amplifier but doesnot change any of its other characteristics.Varying the strength of this wave varies thevolume of the organ.

Notice that the operation is entirelyelectrical. No sound is created in the con-sole-only electrical wave forms. The musicfirst appears as sound at the power cabinet.

The above should serve to give an idea ofthe vast resources of the Hammond Organ.Within each tone family can be discoveredan infinite variety of qualities from whichthe player can choose ; he is not limited torelatively few in each family, but is enabledto create that special subtlety of tone -colourwhich he may want at a particular moment.It is this which makes the Hammond Organthe instrument upon which the artist -organist can best express his own indi-

. viduality.

The Harmonic Controller for the Pedal OrganHere the harmonic resources have been

combined into only two harmonic controls.The fundamental 16 ft. pitchand second harmonic areassociated with the left-handcontrol and produce the fun-damental depth to the pedal.The third, fourth, fifth, sixth,and eighth harmonics areassociated with the right-hand control to give higherharmonic quality variations,and a useful 8 ft. solo if usedwithout the left-hand control.

While the possible numberof pedal organ tone qualitiesis, of course, less than thoseavailable on the manuals,the player will find the vol-ume quality and tonal depthample to balance the manualcombinations that are used.

Fig. 5.-Graphs of the wave patterns ofstring and reed, pitch " .4." The stringquality is characterised by large upperharmonic development, and in the reedtone the upper harmonic development is

very heavy

4. Adjustable. With this piston thetwo pedal drawbars are brought intoaction and are used in the mannerdescribed in the foregoing para-graph.

Electrically lighted indicators just abovethe manuals show which of the toe pistons isin action.

Fig. 6 illustrates the position of these toepistons, the independent swell pedals andalso the 32 -note concave, radiating pedalclavier that is such an outstanding featureof the Model E.

The TremulantThe organist call adjust the degree of

tremulant to suit his own musical taste.

would correspond to approximately 32points on a pipe organ, only a few of whichare constructed with a range in excess of12 points.

The volume increase effected through theswell pedal is dynamically equivalent to apipe organ crescendo build-up. One notice-able and very desirable difference is theabsence of sudden tone quality changescharacteristic of the build-up of the pipeorgan to orchestral crescendos.

How to Make One Manual Louder than theOther (Models A and B)

Since the swell pedal operates equally onboth manuals and on the pedals, this balanceis maintained throughout the entire dyna-

mic range of the swell unit.When it is desired to make

Fig. 6.-Showing the toe pistons, the independent swell pedal and also the 32 -noteconcave, radiating pedals clavier that is such an outstanding feature of the Model E

The Toe PistonsSituated to the left of the expression

pedals of the Aiodel E Console are fourpistons which are placed in the correctposition for easy manipulation for the toe.

The standard settings are :1. FF-Adjustable from the back of the

organ as are the 18 pre-sets.2. MF-Swell and pedal.3. Great to pedal

(This piston is especially useful asit enables the organist to couple anyof the whole range of tone qualifiesavailable on the manuals to thepedals in 8 ft. pitch ; 16 ft. tone canbe added by using the first pedaldrawbar).

MAGNET

TONE WHEEL -,

COIL

When the knob is turned as far as possible tothe left, the tremulant is entirely off. As itis turned to the right (clockwise direction)the degree of tremulant gradually increasesuntil it reaches the maximum at the extremeright position. The white dot marker qn theknob indicates at a glance the degree oftremulant present.

The adjustable feature makes it possible -to have a mild tremulant for flute qualitiesand a more vibrant one for string qualities,etc.

The Model E Console has separate tremu-lants for each manual. These tremulants areadjustable as to intensity or amplitude.The Swell Pedal, Models A and B

The swell pedal, or expression pedal whichis of the balanced type, is located in thecustomary position and with it the volumeof the organ may be controlled over a widerange. It operates on the two manualsand pedal clavier, equally ; that is to

say, once the manuals and pedalsare balanced, they retain their relativebalance over the entire swell pedarange.

The dynamic range of the swell isstupendous. Technically, the powerratio of the swell pedal fully open tofully closed, is 50 decibels. In the mostcarefully constructed pipe organ swell

shades, the power ratioseldom exceeds 15decibels and is usuallyconsiderably less. Therange of 50 decibels

Fig. 7 .-T he synchronous motor and generatorkit which produces the minute electrical

currents which create the musical toms

one manual louder than theother, it is necessary only toselect a tone colour which issofter than the one beingused on the other manual,whether the softer tonecolour be identical in char-acter or different.

To select an identical butsofter tone colour, it isnecessary only to see that theharmonic controller for thatmanual is set with the draw-bars in the same relationshipto each other, but not pulledout so far. For example, tonenumber 23,6444,222 is of the

" same quality as 34,7555,333, but softer.You have simply pushed each drawbar in byone position.

This ability to make the same tone colourlouder or softer on one manual than on theother is of great advantage musically. Theswell pedal, operating equally on bothmanuals, changes the volume of bothequally without destroying the balancebetween them.

The volume of the pedals can be con-trolled over quite a wide range by the use ofthe harmonic controls associated with thepedals, in addition to the volume change ofthe swell pedal.The Swell Pedals, Model E

The Model E Console has the addedadvantage of independent swell pedals, eachof which affects its respective manual overthe wide dynamic range of which theHammond Organ is noted. The pedal con-trolling the Great manual also controls thepedal clavier.

The position of each pedal at any time isclearly shown by indicators situated on theright, above the upper manual.

Hammond a " Straight " OrganThe chief difference between the Ham-

mond and a pipe organ is that in theHammond organ the player is able tocontrol the precise amount of strength ofeach rank, which is obviously impossiblewith pipes, because a pipe must either beblown or left silent. To incorporate as manydifferent sizes of pipes for each rank of theharmonic series as are necessary to controlthe tone quality by harmonic changes alone,would require so many pipes that the -expense and difficulty of regulation andmaintenance would make it impracticable.


Fig. I.-The observer of a reconnoissance planeusing an aerial camera. The use of colour filmis revolutionising the art of camouflage detection

AERIAL photography for reconnais-sance purposes in war -time datesfrom the Great War of 1914-18, but

subsequent developments have been sorapid as to make cameras and films of thattime appear extremely primitive whencompared with modern apparatus.

In the meantime the world has seen theintroduction successively of super -sensitivepanchromatic (colour ccrrected) film, infra-red photography, direct colour photographyand television.Photographing Objects Beyond Visual Range

Each of these developments in its turnhas been applied to military uses by theleading rowers. The latest developmentof which we learn is the use of aerial tele-vision by the Italian Air Force. At themoment this is. admittedly rather in thenature of an experiment, but aerial photog-raphy using infra -red film has already provedits usefulness in recording objects manymiles distant or concealed by mist or fog.Enemy ships at sea can be spotted by theinfra -red camera when quite invisible tothe photographer and sometimes as faras r,0 miles away !Penetrative Powers of Infra -Red Rays

There is one very definite " snag " withinfra -red photography, however, and thatis that the film is not very sensitive and,therefore, requires longer exposures thanwith ordinary film. One of the characteris-tics of this film is the paleness with whichgreen foliage is recorded; but it also hascertain peculiar penetrative propertieswhich are probably not generally so wellknown. For instance, the rays apparentlypenetrate rayon or artificial silk but notreal silk; which recalls the embarrassingexperience of a young press photographerwho took a snap of the ladies of a certainrevue chorus. When the photo was sub-mitted for publication it was noticed thatthe girls, with one exception, appeared inthe print as though naked. The exceptionwas provided by the only girl of the troupewho was wearing real silk.Advantages of Colour Photography

For the detection of camouflage, however,infra -red photography takes second placeto colour photograph and the results from

New Methods ofCamouflageDetection

Cut Branches of Trees and SimilarDevices Are No Longer EffectiveCamouflage Against the Reconnais-sance Plane Equipped with the

Latest Photographic Apparatus

the latter are such that the camouflageexperts are being forced to devise newmethods of concealment. The old dodge ofcovering gun emplacements with torn -oftbranches of trees and shrubs is no longereffective against aerial photography, sincethe change in colour of the leaves whichoccurs a few hours after the branches havebeen cut can be detected by the colour fihnnow being used. In the last war very con-siderable use was made of cut foliage forconcealing ground objects and such camou-flage would remain effective for many daysunder ordinary observation, but with the aidof colour photography even the scorching offoliage by the blast from a concealed gun iseasily discernable on the film.

Objects Identified Only by Their ColourAerial photography cuts out the human

element in reconnaissance work by correct-ing and supplementing the memory of theobserver. On the other hand until theadvent of the colour camera successfulobservation and detection of military objec-tives was dependent on the perception ofthe observer himself, supplemented bymonotone photographs. It was discovered,however, that the identification of anobject might depend solely on its colour.This was proved by instances in which anobject which had been apparent to thehuman eye, had appeared entirely abSentfrom the negative of an ordinary black -and -white fihn taken at the same time.

As an example of the importance of colourin discerning objects, let us take the hypo-thetical case of two areas of contrastingcolour adjacent to one another. If the depthof twp of these areas be photographicallythe same, then a black and white photo willrecord the two colours by the same shade ofgrey. In other wcrds they will appear asone area without division.

Colour in Terms of Black and WhiteIt must be understood that colours which

are photographically of the same tone maynot necessarily be so visually ; thus, forinstance_ a certain blue may be darker intone than a red, but when photcigraphed,especially with ordinary non -panchromaticfilm, the tone values may actually bereversed, the blue reproducing as a lightershade than the red. With panchromaticfilm, on the other hand, the tone values arerendered approximately correctly.

The very fact that ordinary photographyoften tends to reduce contrasting colours tothe same tone, might very well prove usefulin detecting some forms of camouflage, par-ticularly of the type which endeavours tobreak up the outline of the object by bandsof contrasting colours such as that shownin Fig. 2. The reduction of the colours tohalf tones helps to clarify the outline. It isinteresting to note that in the early stages of"dazzle painting " used by the British Navy,and which, incidentally, was introduced todeceive the enemy as:regards the course andspeed of a vessel and not to reduce itsvisibility, that the use of a large range ofcolours was used. This was discontinued,however, when it was discovered that theGerman submarines were having theirperiscopes equipped with colour filterswhich neutralised the effect of the coloursand reduced them to a monotone. There-after, the colours employed were limited toblack, white and blue; the dazzle propertiesof this combination being unaffected by thecolour screens.Colour Camera at High Altitudes

Apart from the fact that the permanentrecord of a reconnaissance flight provided bythe colour camera has obvious advantagesover a memorised visual record, the cameraalso surpasses the human eye in its power ofdetection and resolution of colours and smalldetails. It is of particular advantage whenflying at high altitudes when the human eyeloses its power of discernment due to haze.

The colours of objects, which are easilyrecognisable' at low altitudes, becomeincreasingly difficult to detect as the planerises, and at 12,000-14,000 feet the coloursof objects commence to merge into a hazyblue. By the use of special correcting filtersthe colour camera can overcome this dis-advantage to a very large extent; as airexample, it is possible sufficiently to recordthe colours of cars in the street ! Againaerial colour photographs show clearly thecontrast in colour between the various typesof vegetation-the green of young corn asdistinct from the green of meadtw grass,and the brown foliage of a dead tree in aliving forest. By the use of multi -lenscameras large areas can be photographed atone shot and the films developed and piecedtogether at the base.Modern Methods of Camouflage

Parallel with the military research intoimprovements in colour phofography areexperiments being carried out on methods ofcamouflage. For instance, where the paint-


brush fails to disguise an object it is made toresemble something else, thus an innocent -looking cottage or farmhouse may hide apowerful anti-aircraft gun and its crew.The cottage may not necessarily be a real

black is practically invisible from the groundand may escape detection by searchlightsequally well. Camouflage for daylightoperations is not so simple, but the schemewhich has met with most success so farconsists in having the upper half painted indarl- hands and indeterminate shapes so

Fig. 2.-A typical example of a camouflaged aeroplana Junkers bomber. For daylight operations it is usual to paint the upper surfaces of a plane in darkcolours, as depicted here, with the underside a light tone, so that when viewed from above or below the outline of the plane merges into the background. Night

bombers have the wider surface painted dull black

one but may be a specially constructedset " built for the purpose. However,

large-scale troop movements, batteries oflarge guns and such distinctive objects asairports and harbours are extremely difficultto conceal from the air. In the case ofareas of easily recognisable shape such asaerodromes, attempts are made to alter

their appearance by marking the field insuch a way that it appears to be divided upinto a number of smaller areas.

Disguising Bomber PlanesAeroplanes themselves have also come in

for their share of camouflage, thus a nightbomber with the underside painted dull

as to merge into the general landscapewhen viewed from above, while the under.side is coated with a light-coloured paint oralternatively is given a highly polished met-allic finish, which although it does not mini-mise the risk of detection, serves to dazzlethe man at the range finder so that it becomesdifficult to determine the plane's altitude.

" SECOND YEAR ENGINEERING SCIENCE-MECHANICAL," by G. W. Bird,Wh.Ex., B.Sc., etc., revised by B. J.Tams, M.Sc.Tech., A.M.I.Mech.E. 246 pp.,230 illustrations. Pitman, 6s.ASECOND edition of this well -prepared

book has just been published, of whichthe first edition was published in 1934.

Since the first edition appeared a numberof minor corrections have been made and anew chapter-Strength of Materials-hasbeen added. The book was prepared tocover the Second Year National Certificatecourse, and various other courses of asimilar ature. This it does in a praise-worthy manner, for the contents are notwritten in dry -as -dust form, as are those offar too many text books. Instead, theauthors have added to the technical explana-tions descriptions and illustrations of theapplication of the technical points inpractical engineering.

This will have an especial appeal toyounger students, although very valuableto all readers. As a result of this form of

,BOOKS Ivor*

READING

treatment the book is a combination of agood text book and an interesting manual.It will commend itself to every student ofthe subject.

Especial reference should be made to theillustrations, both in line and half -tone,which are uniformly good." Silent Flight." By Ann C. Edmonds.

Published by Country Life, Ltd. 84 pages.Price 5s. Od. net.YOUNG persons of either sex who enjoy

outdoor life will find this entertainingbook very interesting reading. The author,a well-known girl' glider, has taught manyR.A.F. pilots and leading commercialpilots the art of gliding. The book tells

the story of how two young persons begantheir aerial knowledge by flying modelaeroplanes and eventually progress toactual gliding and flying. Several fineillustrations are a feature of the book.

" The Mechanic's Repair Shop Manual." ByHerbert J. Dyer. Published by PercivalMarshall & Co., Ltd. 116 pages. Price2s. 6d. net.HERE is a book written by a practical

fitter and turner for mechanics whorun their own workshops, and their assis-tants. The practical wrinkles described arebased on everyday repair -shop experience,and deal with repairs to ordinary engines,marine motors, and general mechanicalrepairs. The book is divided into fourteenchapters, covering, amongst other subjects :Removal of Studs and Screws ; Drawing OffFlywheels ; Lighting and Removing Valves ;Piston Troubles; Re -Metalling Bearings;Boring Jobs ; and Taking Up Slack Bushes.The book is illustrated with numerous linedrawings.


The Second Article of a New Series

Worksho

ONE method of cutting a series ofteeth around the edge of a gear wheelblank is to make use of a simple

rotary cutter driven at high speed by thespindle of a milling machine. The edge ofthe cutter can be shaped to give the correcttooth contour, according to the number ofteeth on the gear wheel.

The first cutter in Fig. 1 would be suitablefor producing a large gear wheel withapproximately 135 teeth, while the second

pinion with only 12 or 13 teeth. Normally,a set of eight cutters for each pitch, willcover all sizes of gears, but half sizes canbe obtained if necessary by the use ofspecial cutters. In use, the rotating cutteris moved across the face of the blank, whichis rotated through the required amountafter each cut.Involute Gear Teeth

The fact that in the case of involute gearteeth the shape or profile of the teethvaries according to the number of teeth onthe wheel, offers a simpler and moreaccurate method of producing the teeth asmentioned. On a small pinion having, say,15 teeth, the curvature would be fairlypronounced, as shown in Fig. 2. On alarger wheel, the curvature of the teethbegins to disappear, until in the case of a

PracticeNo. 2 .-Gear Cutting and

Grindi g

Cutting a spiralbevel pinionwith a Gleasonmachine in thefactory of theMoss Gear Co.

Ltd.

rack, that is, a number of teeth arrangedon a straight strip-the sides of the gearteeth would be straight.

From this it follows that a very simplemethod of producing the gear teeth isavailable. Fig. 3 shows that the cutter can

take the form of a rack with straight -sidedteeth. For accurate work the contour ofthe teeth of the master gear must beabsolutely exact. This is considerablysimplified at the outset, as it is a simplemanufacturing proposition to producestraight -sided teeth. The simple design ofthe cutter is, in fact, the keynote of thissystem of gear generation, as it is termed.

During the process of generation the rackis moved forward so that it engages withthe blank, which is rotated at the correctrelative speed. If the blank were not ofhard metal, the pressure of the rack wouldautomatically generate correct involuteteeth, as will be appreciated from theillustration. As the metal has to be cut,however, it is necessary to move the rackfrom side to side at the same time, so thatits teeth will cut or " plane " Correspondingteeth in the blank.The Rotating Cutter

An alternative method of producing gearteeth is to make use of a grooved, cylindrical

The Methods by which Gear Wheels are ProducedDepend not only on the Shape of the Teeth Them-selves but also on Manufacturing Considerations

INVOLUTE ,TEETHFORMED

ROTATINGCUTTER

LARGE GEAR BLANK

SMALL PINION

Fig. I.-A simple method of cutting gear teethby means of a rotating cutter with a tooth edge,carried on the arbor of a milling machine. Notethe different shape of cutter when dealing with

small and large wheels

CURVED FLANKS '

TO TEETH

PINION WITH 15 TEETHj-L-4-- CURVATURE LESS

GEARWHEEL 60 TEETH

STRAIGHT

RACK

Fig. 2.-With the involute form of gear tooth, principally used, the flanksof the teeth become less curved as the size of the gear wheel increases, until they

are straight in the case of a rack, or toothed strip

rotating cutter, known as a hob. Probablythe most readily usiderstood example is thehob shown in Fig. 4, which is used toproduce the worm on a worm wheel. Thehob, which in this case more or less resem-bles the worm with which the wheel iseventually intended to mesh, is gashedalong its length so that cutting faces areformed. With the worm wheel and the hobrotating at suitable speeds the bob isslowly advanced, so that cutting takesplace progressively until the required depthof thread is obtained. Sometimes separatehobs are used for the preliminary cuttingand the finishing operation.Making Bevel Gears

Bevel gears are, of course, widely u, ed

GEAR WHEELBLANK ROTATING

RACK CUTTER

INVOLUTETEETH GENERATED

Fig. 3.-A simply cut straight -toothed rack can be made to cut correctly curvedteeth in a circular blank. While the rack is moved forward into engagementwith the rotating blank, it is given a simultaneous side -to -side cutting movement


CUTTING EDGES

NORMA LHOB

WORM WHEEL HOB

Fig. 4.-During the process of hobbing thecutters shown are rotated against the edge of thegear wheel blank, which is turned during the

process so that teeth are cut

for back -axle drives, and for other applica-tions, such as driving overhead camshafts.There are objections to the old-fashionedstraight -toothed bevel gears, so that thespiral bevel is now almost universal.

There are three well-known methods ofcutting spiral bevels. In the first place, theend -mill process can be used ; the cuttingtool is .again driven by the spindle of amilling machine, and moves in a curvedpath, cutting curved flutes in the blank.This process, however, offers technicaldifficulties, and is normally limited to large -size bevels for industrial use, in which thepitches are coarse. Alternatively, straight-line bevel teeth may be planed at an angle.This, however, does not give correct results.

Double Helical DifficultiesDifficulty is sometimes experienced in

the production of double-helical gears, inwhich the gear teeth are cut in the formof a shallow " V." To -day hobbing may beused, two hobs being required for right-hand and left-hand teeth respectively. Itis impossible to hob a double-helical gearwith continuous teeth across the blank,however, as the two halves of the helicalsare separated by a gap which depends onthe diameter of the hobs used.

As the size of the hob cannot be reducedbeyond a certain point owing to technicaldifficulties, hobbed helical gears are oftenmachined with staggered teeth in order toovercome this difficulty. Staggering of theteeth becomes almost imperative, in fact, ifa narrow gear wheel is desired and thehobbing process is used. Continuous doublehelical gears, however, can be generated byusing two rack cutters of the type alreadydescribed, which generate accurate gearteeth, and move to and fro across the sur-face of the blank to the centre or apex ofthe teeth.

Under modern production conditionswhen single -helical or spur gears haveoften to be cut in compact clusters mounted,for instance, on a gearbox layshaft, andwhen internal teeth have to be formed atthe same time, as in the case of the engagingdogs on synchromesh gearboxes, a universalhigh-speed gear -shaping machine is usuallymore suitable for mass production whengears cannot be produced by hobbing orother methods of milling.

The cutter of a gear -shaping machine forthis type resembles a pinion, as will be seenfrom Fig. 5; this is very accurately made,and is frequently checked for truth. It ispassed rapidly backward and forwardacross the face of the gear blank in order tocut the teeth. Modern gear -shaping ma-chines enable as many as 600 strokes aminute to be made; in a typical instance,two complete turns of the gear blank aremade while the teeth are being cut, thetotal time taken to cut all the gears on alayshaft cluster being just over an hour.

Gear FinishingSurplus metal to the extent of approxi-

mately .002 in. is left on the flanks of thegear teeth to allow for finishing operations.Where the greatest possible silence ofoperation ierequired, the finishng of thegear teeth assumes considerable importance.One method is to make use of a speciallydesigned gear -finishing machine. A machineof the type used in one well-known motorcar works is illustrated in Fig. 6. Thecutter resembles the gear itself, but hashelical teeth which are slotted to their fulldepth. The teeth of the cutter, moreover,are ground to conform.with the convexityof the gear teeth, and the tool is thus saidto be of the enveloping generating type.

The gear is mounted on a mandrel and israised against the cutter, which rotates it.

HELICAL CUTTER

SPUR GEARCUTTER

11

HELICALGEARBLANK

Fig. 5.-Gear shaping machines are widely usedto -day. Various types of cutter similar to thoseshown are drawn backward and forward againstthe edge of the gear wheel blank, which is rotated

during the process

The cutter, which is not parallel to the gear,but at a slight angle to it, runs at a speedof 600 r.p.m., reversing its direction ofrotation at intervals of 10 seconds. Aftertwo runs in each direction the operation iscompleted and the cutter comes to rest.

UTTER WITHSLOTTEDHELICAL TEETH

HELICAL GEARTO BE FINISHED

Fig. 6.-A cutter provided with grooved helicalteeth rotates the gear wheel during the finishingoperations. The cutter is not quite parallel to thewheel, so that a sliding and cutting action takesplace between its teeth and those on the wheel

An alternative method of finishing thegears is to make use of a rack cutter of thetype already described. The work ismounted on an arbor, which is held betweencentres, and is lowered into contact withthe horizontal cutting rack. The fact thatthe gear wheel is at a slight angle to therack results in a fine shaving cut on theteeth of the gear as the rack is movedlengthwise while in mesh with the gearwheel.

A more compact machine of a similartype is one in which a circular involutetype of cutter is substituted for the rack.In this case the cutter axle is again atan angle to the work, so that a lengthwisesliding action takes place between thecutter and the gear teeth when they arerotated in mesh.

Heat TreatmentBefore the final finishing of the gears

takes place, the gear wheels are sent forhardening and heat treatment. As someslight distortion takes place, the wheels areoften run in a lapping machine, as shown inFig. 7. In some cases there are threelapping wheels, and in others only two ;the wheels are of cast iron, and are coatedwith an abrasive compound. The gearwheel to be lapped is engaged with thesewheels and is rotated at a speed of about180 r.p.m. At the same time it is movedbackwards and forward, or " stroked " atthe rate of approximately 90 times perminute.

After lapping has continued for about20 seconds the direction of rotation isautomatically reversed, so that the gearwheel is lapped under both driving andover -running conditions.

The laps themselves are braked byhydraulic means in order to provide a dragon the teeth. As a rule, a cast iron laprequires renewal after about 8,000 or10,000 gears have been dealt with.

Finishing is, alternatively, often carried out by grinding the gear wheels with theaid of rapidly rotating abrasive wheels,shaped to provide the correct tooth con-tour. Grinding wheels can, of course, beused for producing the gear teeth them-selves. The thread on a worm, for instance,is produced on a machine in which theworm is simultaneously rotated and movedalong its axis past an abrasive wheel, theedge of which has been trimmed to asection which will provide the required formof thread on the worm. The longitudinalmotion of the machine table, in unisonwith the rotation of the work, provides thescrew thread, in just the same manner as ona screw cutting lathe. A highly polishedsurface is subsequently obtained by runningthe worm with a wooden worm wheel towhich an abrasive lapping compound hasbeen applied.

PRACTICAL MECHANICSHANDBOOK

By F. J CAMMAn extremely valuable book, packed with factsand figures, tables and formulae for the mechanic,engineer and designer.From all booksellers 6, net, by post Gs. 3d. fromthe publisher George Newnes. Ltd. (Book Dept.),Tower House Southampton Street. Strand,W.C.2.

11111111111

LAPPING WHEELSCOATED WITHABRASIVE

-STROKING"MOVEMENT

HELICALGEAR TOTAPPED

Fig. 7.-The final finishing is often carried outby lapping the gear wheel in conjunction with twoor sometimes three cast iron wheels which arecoated with an abrasive compound. An end -to -end movement of the gear wheel is usually provided

in order to distribute the abrasive


A Turret Tool Holder forthe Lathe

By Fitting a Turret -Head to the Slide Rest, Much Time and Labourcan be Saved, Especially in Repetition Work Where Several Operations

have to be Carried out on one Chuck Piece FittingWHERE repetition work is to be

done in the lathe, and there areseveral operations on one chuckedpiece fitting, a turret -head to the

slide -rest is a time and labour-saving device.

USUAL TOOLHOLDER

Fig. 1.-A conventional type of top slide resttool holder

In the accompanying illustrations are shownmethods of applying such a head to anordinary lathe.

In Fig. 1 is shown a conventional typeof top -slide rest tool holder which has atool holding block bolted down by a singlestud and nut ; the stud is a fixture in thetop -slide. In the new arrangement thisstud is replaced by a new one and a cast-iron block is cast from a simple woodenpattern of the same shape and size as theblock, Fig. 2. It is bored centrally to fitthe upstanding stud or a longer and largerstud if necessary.

BoringFor boring it is chucked in the three -jaw

chuck and a drill is put through, fed alongby the back headstock barrel, or by theback centre if no drill -holder is availableto fit the barrel taper. In this case thedrill is centred at the end to hold on to theback centre and a lathe dog or carrier with

"a piece of gas barrel driven on its shankdepends between the lathe ways to preventthe drill turning. The arrangement isshown in Fig. 3.

The hole should be bored dead parallel.The block is then chucked on a mandrelbetween centres and faced flat each sideand turned along its outside diameter.While on the mandrel a line is scribed allround it at a height which will bring theline into the axial line of the lathe centres.To get this line, fit the upstanding stud inthe lathe top -slide in place of the tool postholding -down stud, and rotate the blockby hand meanwhile pressing it up (by thetop parallel slide) to a hardened andtempered cast steel pointer or scriber

JOG OPCARRIER..//

1A141.1,1.1,L1

TURRETBLOCK

running dead true in the lathe three -jawchuck. This will give the height for thecentres of the holes drilled radially aroundthe block to take the tools.

Divide this line around the block intofour, five or six equal parts and with a

drill running in thp three -jaw chuckdrill radial holes at each division. This isdone by feeding the block up to the drill bythe top -slide. Open these *-in. holesout to a size of hole which will be -decidedupon for our turret -head tools. The sizewill depend on the amount of room there isbetween the lathe head centre axial line andthe top surface of the top -slide. These holesshould go through the side of the block and

TURRETTOOL HOLDER

Fig. 2.-In this arrangement the bolting downstud is replaced by a new one and a cast ironpattern is cast from a simple wooden pattern of

the same shape and size as the block

terminate just clear of the central hole asshown in the sectional plan view, Fig. 4.

DrillingBefore drilling the holes in the centre

marked ring round the block, chuck theblock again on the mandrel on which it wasturned and, with a scriber bolted in the toolpost with its tempered point at lathe centreheight, scribe lines horizontally (they willbe vertical when the rig is in use) througheach centre mark for the tool holes, to thetop surface of the block (now standingvertical) without moving the block roundand, with the scriber still in the tool postat the correct height, scribe horizontallines across the face of the block from itsperiphery to the mandrel on which it ischucked. These lines will be, when theblock is in its horizontal working position,dead above the axial lines of each of theholes for the tools. With the block stillchucked on the mandrel scribe a circleon the top (now vertical) face of the block,at a distance / in. from its outer edge.This circle will intersect `he radial lines on

IiiI11011111111311111111111

-*GAS BARREL

Fig. 3.-A piece of gas barrel driven on its shank depends between thelathe ways to prevent the drill turning

LEVER NUT

Fig. 5.-Details of thelever nut

the top of the block and, at each intersection will be drilled and tapped holes forthe set screws which hold the tools in theholes in the turret block.

The size of these holes (like the size of thetool -holding holes), will depend on the sizeof our block and the clearance between thetop surface of the top -slide and the axialline of the lathe centres. Hexagon orsquare -head set screws can be used, butthey must have flat ends and must be casehardened at the ends which grip the tools.

Where we have an American type oflathe with a slotted pillar in a slot in thtop -slide as shown in Fig. 4, we shall haveto fit the centre stud in a manner differingfrom the arrangement shown *in Fig. 2, forthe English type of lathe. The method isshown in Fig. 4. A long central bolt witha square head to fit the slot is turned tofit the slot in the top -slide. It is "screw-eutto take a flat hexagon nut which will holdit down on the top -slide vertically and in afixed position in the middle of the slot inthe slide.The Turret

The turret cheese -shaped block will haveits central hole recessed underneath toclear the hexagon nut and the cheese -shapedturret will bed down flat on the top of thetop -slide. It will be held, when any of thetools are in working position. by a washerand a nut on the centre stud.

To avoid the necessity for using aspanner every time the capstan is turnedto present a new tool to the work, a levernut as shown in Fig. 5, can be used. It ismade by forging over a piece of east steelbar at one end so as to get double thickness

FLATNUT

DISTANCEBUSH

T HOLDER

AMERICAN TYPETOOL POST

Fig. 4.-An American type of lathe with aslotted pillar in a slot in the top -slide

for the length of thread and bending at anangle as shown. The bent -under part andthe upward bend of the handle will enablethe lever to clear the set screws on the topof the turret or a bush, thick, as shown,can be put on the holding -down lever nut toenable it more easily to clear the set -screws.

The turret can be used for tools for faceor side work. Sometimes a combinationof both will be used according to the classof work being undertaken.


Fig. 1.-An interesting example of areally large -surfaced photo -electric cell such

as Was used some ten years ago

WITHIN the last few years it hasbeen very apparent on all sidesthat the practical control of elec-

trons has become an applied branch ofengineering whose rate of development hasoutstripped even the wildest dreams ofearly pioneers. By harnessing the energyof the electron and making it do work, thephysicist has shown the engineer thatmaterial improvements may be effected inhis equipment if he studies the subject ofelectronics in its broadest sense. In anarticle of this length no attempt will bemade to deal exhaustively with the manyapplications but rather to select a few ofthe most important, especially that sectionof the subject which makes use of secondaryemission and electron optics. There is no" order of merit " for obviously that willvary according to which branch of engineer-ing is most eonctrned, but there are certainfundamental principles common to all andthese will be dealt with briefly in casereaders may have forgotten them.Proce >sps Involved

The various forms of electron tubes inwhich the motion of electrons moving fromone area to another is controlled by somespecified method, are really energy con-vertors. The thermionic valve, photo-electric cell, electron camera, gas dischargelamp, X-ray tube, mercury arc rectifier,and so on are but a few examples of thosein everyday use ; devices which have reallybecome so commonplace that they are oftennot recognised as electronic engineeringequipment. In ordinary circumstances,when a current of electricity is made toflow, the electrons have their movementconfined to fixed conductors, but underspecial conditions energy can be impartedto free them, and these free electrons thenbecome capable of carrying out other work.Certain known substances when heatedrelease electrons, photo -sensitive surfacesrelease electrons under the influence oflight, electronic bombardment of a surfacecan cause secondary emission, ionisationproduces free electrons from gases, andonce set free it is necessary to exert anelectrostatic or electro-magnetic controlaccording to requirements.Cell Limitations

One of the earliest forms of electronic energy convertors to be used scientificallywas the photo -electric cell, and the engineer-ing applications of this device have extendedenormously. The incidence of light on acathode enclosed in a glass container eitherevacuated or partly filled with gas accordingto the purpose to which it is to be applied,

Sensitivity ImprovementsTo obtain an increased output signal

under certain light activation conditions,one of the first methods used was to increasethe siz.e of the cell. This was carried to verywide limits and as an example of whatcould be done in this connection referencecan be made to Fig. 1 which illustrates acell considerably over 1 ft. in diameter.Difficulties were still encountered, however,and it was the harnessing of the principlesof secondary emission that brought aboutsuch a high gain in efficiency. In simplewords, secondary emission merely impliesthe process which takes . place when anelectron stream is allowed to strike one or

Some PracticalElectronic

By H. J. BartonBy Harnessing the Energy of the Electron and Making it do

Improvements May be Effected in his Equipment if he

causes electrons (minute particles of nega-tively charged electricity) to be releasedfrom the surface and these are attractedtowards and collected by an anode whichhas applied to it a positive potential withreference to the cathode. The degree ofemission is dependent upon the quantityof light to which the cathode is exposed andthis photo -electric principle has madepossible many modern developments, par-ticularly television. The limitations of thisdevice are associated with its varyingsensitivity according to the colour of theactivating light and also its relativeinsensitiveness to small quantities of light,30-50 microamps per lumen being an

1215C

An early form of multi- k 44 4 Ed I -I I

Figs. 2 and 3.-(Left) trOCTANDE

plier photo -cell showingthe cathode surface and multiplier cage. (Right) An explanatory diagram showing the stage by stage

multiplication of electrom which result ultimately in a very large output signal

s.

FMOTO - GLICTRICCATMODC,

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lo.UPAINATIONIJIICIZATinoCe CLMOTROmb

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average figure. In the case of the former,continued research is being applied todevelop types of surfaces which are applic-able to the infra red or ultra violet ends ofthe spectrum, while certain forms of caesiumcombinations have furnished a colourresponse which closely resembles that of thehuman eye and in this way, at least in so faras television is concerned, there is a bettermonochromatic rendering of colouredobjects.

AUXILIARYCATHODE

Fig. 4. - TluS2 electron stream

path and elec-tronic arrange-ment of a secon-dary emissivethermionic valve

more metallic surfaces which have beenspecially prepared. Each electron is thencapable of displacing from that surfacesecondary electrons varying in number from1 to 10 and if this effect is made cumulativeit is easy to see that the final current produced is increased enormously when com-pared with the magnitude of the initialelectron stream.

These secondary emission multipliers canbe made up in a variety of ways. In somecases the electrons are made to reciprocatebetween two parallel faces and at eachimpact secondary electrons are releasedwhich join the main stream and so ulti-mately builds up a large current which ispassed to the output circuit. Successiveimpacts directed against separate surfacesproduce the same cumulative result, whilein yet another form the electrons are guidedto pass through mesh grids where thesecondary emission multiplication is of theorder of three times per Stage.

An ExampleAs an indication of this last named

scheme being put into actual practice.reference can be made to Fig. 2 whichshows an early form of a compact multiplierphoto -electric cell. The individual multi-


Aspects ofEngineeringChapple, B.Sc., etc.Work, the Physicist has Shown the Engineer that MaterialStudies the Subject of Electronics in its Broadest Sense

plier grid stages are accommodated in thetubular metal shield shown with its barwindow at the base of the cell. In Fig. 3is a simple explanatory diagram whichtraces quite clearly how with five multipliergrids and one reflecting plate a singleprimary electron becomes 1458 electronsflowing into the output circuit resistance.The potential applied to , each stage isstepped up, and assuming that e "electrons are released from the photo-electric cathode by the incidence of a beamof light, each grid stage produces a triple

All the different forms of secondaryemissive multipliers have found applicationin various types of modern electronicequipment and many important advantagesaccrue when compared with the previousorthodox methods of valve amplifiers.Among these mention can be made of theabsence of microphony, extreme stabilityover long periods of times a greatly improvedsignal to noise ratio, and the maintenanceof high gains over a very wide frequencyrange (up to more than 10 megacycles, ifrequired).

Fig. 6.-The marked improvement on the design in Fig. 5 broughtabout by using one diode and three secondary emission valves

multiplication. After the fifth multipliergrid, each of which has a fine mesh texture,an accelerating voltage drives the streamthrough the wide meshed collecting grid soas to strike the reflecting plate, where theaverage multiplication is 6. The totalelectrons released by this final action arecollected as shown and so cause a magnifiedcurrent to flow through the output resist-ance.

0

- --

SOURCE OFELECTRONS

C.

FOCUSCO I LS

OBSERVATIONSCREENS

Fig. 7.-A simplified optical arrangement of amodern electron microscope

Thermionic Valves andSecondary EmissionFor a long time it was

found impossible to har-ness this important prin-ciple of secondary emis-sion in a direct mannerwith thermionic valves,but now even this diffi-culty has been overcomeand there are now on themarket valves which givevery high mutual con-ductances by making adistinct departure fromordinary valve practice.The original TSE4 PhilipsMullard valve now super-seded by the EE50 is acase in point. Shorn ofall the intricate construc-tional details, themethod of operation be-comes quite simple as canbe seen by referring toFig. 4. Electrons areemitted from the valvecathode C, are controlledor modulated by the firstgrid and after passing

through the auxiliary grid are madeto follow the dotted path shown, bythe combined action of the two screensSi and S2. These electrons pass through anopen meshed anode, strike the auxiliarycathode which has been made secondary .used, there is a limit to the degree ofemissive, and the re-sulting amplified elec-tron stream is collectedby the anode A, whichis really a continua-tion of the openmeshed anode.

By this single stageof multiplication theeffective gain is threeand it might well beasked if this improve-ment in valve tech-nique can be put topractical advantage.The answer is in theaffirmative as can beproved by referring toFigs. 5 and 6 whichillustrates a two yearadvance in television

Fig. 5.-The vision chassis of this set occupiesthe whole width of the middle shelf and embodies

eight valves

receiving design. The vision chassis occupy-ing the whole width of the cabinet on themiddle shelf of Fig. 5 used six high gainpentode valves, a diode and triode, whilethe sensitivity was of the order of milli-volt and a band width of approximately2 megacycles. While this design and layoutgave good results, a reference to Fig. 6shows the marked change brought about bythe use of secondary emission valves of theTSE4 class. The whole unit comprises timebase generator cn the extreme right,cathode-ray tube with deflecting andfocusing system in the centre, and visionchassis on the left. The last named chassisis far mere compact than its Fig. 5 pre-decessor, uses only three secondary emissionvalves and a diode, and provides increasedgain and band width, higher stability andimproved sensitivity. This single examplewill serve to show how quickly an electronicadvance is incorporated in commercialequipment to the advantage of designer Andpurchaser alike.An Electron Microscope

The principle of operaticn of an ordinaryoptical microscope is no doubt familiar tomost readers but in practice, since light is

FOCUS COIL

LENS

TRANSPARENTCATHODE

MOSAIC WITHBACKING PLATE

ELECTRON SCANNINGjez BEAM

AMPLIFIER

Fig. 8.-A pictorial example ofthe application of electronics toproduce a scientific instrument

ci y4

FINAL MAGNIFIL:PICTURE

158 - NEWNES PRACTICAL MECHANICS January, 1940

magnification which can be achieved forinvestigation purposes. It is for this reasonthat the subject of electronics has come tothe fore within the last two or three yearsand it has been established that magnifica-tions up to at least 100,000 times have beenachieved, which of course is far in excess ofanything undertaken optically. The baredetails of such a device are shown in Fig. 7.On the left at the point A is a cathodeproviding a source of electrons and theseare accelerated towards and focused downto a minute point on the slide carrier B.The object undergoing observation, oftensome form of extremely minute bacteria --

is held in place on this slide by a very thincollodion film and the image is producedinitially on the observation ,screen shown at(1. This can be either a fluorescent screen orphotographic plate as desired, but if furthermagnification is required then the finalobservation is undertaken at D. A combina-tion of electron lenses provided by electro-static and electro-magnetic means in con-junction with extremely high voltages(these sometimes reach 100,000 volts)makes this device an instrument of immensevalue for bacteriological investigation, andequipment has been built both on thecontinent and in the United States usingthese electronic prinCiples.

Other Electronic InstrumentsIn a much simpler form the same idea is

used for investigating the cathode emissionof a cathode-ray tube. It is just a case ofproducing an enlarged image of the cathodesurface on the fluorescent screen and forthis purpose an electro-magnetic tube has apositive potential. applied to the modulatorelectrode-something of the order of 200volts deperiding on the voltage normallyused for the anode itself. The modulatorand anode used in this way provide anelectrostatic lens system and if this is usedin conjunction with the focusing coil, whichis of course and electro-magnetic lens, bycareful adjustment a greatly enlarged imageof the cathode surface is seen on thefluorescent screen. The variation of emissionover the cathode may then be studied andthe necessary steps taken to improve this

so that the tube when used for ordinarycommercial purposes will give a muchbetter performance.

Yet another scientific electronic instru-ment which has been used successfully isshown in elementary form in Fig. 8. Herethe object to be examined is opticallyfocused on to an electron tube having atransparent photo -sensitive cathode. Thisproduces an electron image such that theelectron density at every point is directlyProportional to the light and shade of theoptical picture distributed over the wholesurface. This electron image is thenattracted towards and focused on to amosaic element screen which can be

Fig. 9.-An actual example of animage -convertor ta53 u;i71 a

opaque concave shaped cathode

scanned by a beam of electrons to producesignal currents on'a backing gauze. Theseare amplified and passed to the modulator'electrode of a standard cathode-ray tubeand by using the usual focusing anddeflecting system a magni-fied and bright visible imageof the original object is seenon the tube's fluorescentscreen. '

Image Convertor TubesAnother useful piece of

apparatus which is basedentirely on the principles ofelectron optics is the image -convertor tube which hasIts most important applica-tion in the infra red end ofthe spectrum. A small -practical example of thisdevice is illustrated in Fig.9 and in the spherical glasssection will be seen a disccathode. This is providedwith a uniform coating of photo -electricmaterial, while the surface is made slightlyconcave to prevent any form of pin cushiondistortion in the final observed picture.The picture undergoing observation isoptically projected through the thin glassspherical wall on to the opaque photosensitive surface. This produces the familiarform of electron image as was the case ofthe device described for Fig. 8 and byMeans of the metallised coating, to whichis applied .a positive potential and a

cylindrical focusing coil placed round theneck of the tube, a bright visible imageappears on the fluorescent coating appliedinternally to the glass wall at the right handend of the tube. No scanning is necessary,the device being a straightforward con-vert& of an optical image into a visibleelectron image which can be magnified andobserved section by section by adjustingthe current passing through the focusingcoil. If the photo -sensitive surface is maderesponsive to infra red rays, then anapparently invisible optical image projectedon to this surface becomes completelyvisible on the tube's fluorescent screen asa sharp, bright picture. This infra red rayinvestigation is important when, say,living bacteria need to be examined whichwould, be .damaged if subjected to visiblelight rays and its value in the medicalworld has already been made manifest.

A somewhat similar tube but capable ofproviding a larger picture and using atransparent cathode in lieu of an opaque

Fig. 10.-An image -convertor tube with a transparent cathodeset up for scientific .examination

one is shown in Fig. 10. On the right is theoptical projector, apparatus and at the endof the tube neck is the transparent photo-electric cathode on to which the picture tobe observed is focused. A large solenoidalcoil provides the electro-magnetic electronlens and this in conjunction with the highpotential anode connected to the terminalon the conical section of the tube is all theequipment required for this ingenious butrelatively simple piece of electronic appara-tus.

Tools in MiniatureModern machine tools have a special

interest in these days of mass -production onwork of national importance-munitions,aircraft components, guns, gauges and otherengineering products. Here is an attractiveset of machine tools modelled to a scale of1 inch to 1 foot and built specially to order.The model represents a workshop fitted upin the modern style with electric powertransmission for each individual model.Each of these machines was hand -made toscale and several were working replicas oftheir prototypes. They were constructedmainly from brass and brass castings andof the models illustrated the bed planingmachine and the capstan lathe were workingmodels, driven from a shaft as with the" real thing." Among other models youwill recognise are the radial drilling machine,Drummond gear cutter and milling machine. A set of machine tools modelled to a scale of I in. to I ft.


TOOLMAKING AND TOOL DESIGN 6.The Principles and Methods of Making Press Tools, Jigs, Gauges and Fixtures

By W. H. DELLERALTHOUGH what has been written

so far on the subject of drilling jigs,by no means exhausts the subject,

the writer is of the opinion that sufficienthas been said to enable the reader to havean accurate outline of the principles ofdesign suitable for handling work of ageneral character.

Each individual job will. of course, beconsidered on its merits from the point ofthe actual design of the jig, and once theelementary requirements are fully under-stood the designing offers abundant oppor-tunities in many cases for the inclusion of" snappy" ideas where warranted. Thisbeing so, simplicity should be the keynote,however, and the jig should not emergeas a device bristling with " clever " partscostly to make and no more efficient thansomething a lot simpler.

FixturesThe term jig is one that is often errone-

ously applied to a fixture. As statedearlier a fixture is purely and simply awork -holding device not equipped withcutter guides. When intended for use on amachine -tool table or lathe face -plate thebase of the fixture is provided with a key,or keys, or a circular register so that it canbe accurately disposed on the machinewithout prior indication or measurement,therefore the fixture is merely bolted downeach time it is used.

Fixtures are also employed for certainassembly operations, but in these circum-stances the point just mentioned does notapply.

Various types of work where fixturesmay be profitably employed for the pur-pose of carrying out the operations indicatedare illustrated in Figs. 30 to 35. Thatshown in Fig. 30 is a turning job which hasbeen machined at a previous operationconsisting of turning a male register andfacing the flange at the bottom. The nextoperation calling for a fixture is that ofturning and screwing the male thread,facing the flange and undercutting thethread. The requirements are, that thefaces of the flanges shall lie at 90 degreeswith each other and that the centre of thescrewed nose shall be at a pre -determineddistance from the face of the bottomflange. In passing, mention is made of thefact tlipt the same type of fixture which

.will be described would suffice if the anglebetween the faces is other than that men-tioned. Where this is so, it follows thatthe portion of the fixture on which thework is mounted will lie at an acuteangle in relation to the surface of the faceplate.

MILIEU

N1ILLED

I Previous Articles in this Seriesappeared in Nos, 61, 63, 64, 65

and 67

Milled WorkExamples of simple miffing operations are

seen in Figs. 31 and 32. The first one wouldbe milled with a gang of three cutters fromthe solid. The domed portion is " formed '

FIRST OPERATION FACE

Fig. 30.-A turning job which has been machinedat a previous operation

in the turning operation. In the secondexample the parts are turned .from squarebar material, the slot is then milled at oneoperation and the radius at the end of thefork at another. Both of these exanylesshould be held by

Figs. 34 and 35 (Left).-An assembly job and (right)

WELDED An assembly job of adifferent type

operations were being performed and dealtwith singly or in gangs of six or more atone pass of the cutters.

A broaching job is seen in Fig. 33. Herethe requirements are that the splines arecorrectly positioned in relation to the holein the small boss. In this instance thebroaching would be done after the boring,

l'"111111111111111111111!i111111111111111111iiii.

BROACHING OPERATION

Figs. 31 to 33 (Left to Right).-Two examples of simple milling operations and a broaching job

facing and drilling operations, the leverbeing positioned in relation to the broachteeth by means of a peg or pin passingthrough the hole in the smaller boss.

The assembly job illustrated in Fig. 34consists of a flange attached to a tube bymeans of welding. Here the washer wouldbe held in correct relationship with the endsof the tube and at the desired angle whilebeing " tacked at several points. Thewelding operation proper would be com-pleted with the work removed from thefixture. This practice should not be takenas a general rule for other types of workmight require to be more rigidly held thanis necessary in this instanee. Where thisoccurs allowance has to be made in theclamping arrangements for expansion andsubsequent contraction.

Assembly FixturesMany light assembly jobs are greatly

expedited by the employment of fixtureswhich are thus beneficial even where closeaccuracy of the finished product is com-paratively unimportant, but where closeaccuracy is demanded the use of a fixturefor the purpose is practically a necessity.

Jobs of this nature may consist of theassembly of several pressings by means ofrivets or spot welding. Smaller parts of thesame nature might be joined together byeyelets or hollow rivets. Holes in partsthus joined would for ease of manipulationbe relatively large in relation to the dia-meter of the rivet or other means of fixing.Therefore no reliance could be placed on theuse of the rivets for the purpose of initiallylining up the several components. Anassembly job of a different type is shownin Fig. 35. Here the end brackets areattached to the shaft or tube by means oftaper pins and the bell -crank lever in thecentre is free to rotate between a pair ofcollars similarly fixed. The essential featuresof this assembly are that the feet of thebrackets shall lie in one plane at a distance

apart to correctly maintain the requisitecentre distance between the fixing holes.Equally important is the disposition of thelever. Therefore even if the assemblyconsists of placing the parts in positionand taper reaming the holes, the bracketsrequire to be fixed down in their correctpositions and the lever also placed, beforeso doing and driving home the pins. It isonly by taking these precautions even withso simple a job that constant results willbe obtainable.

Handling MillingReverting to the question of milling,

the type of work shown in Fig. 31 presentsno difficulty as in this particular examplethe surfaces to be formed are lying in oneplane. In the second exa mple, however, thetrack of the machining is in two directionsat right angles with each other. This means


either locating from the slot, or from the square sides, to bring the work into correctrelation with the concave cutter whichforms the radius.

Where the milling operation consists offorming a square, or other head of similarbalanced section, such as may be formedby a pair of cutters, the point to be decidedif gang milling is to he adopted, is whetherthe work shall be partially rotated mechani-cally between each pass of the cutters tobring about the desired result, or to other-wise achieve the purpose by re -locatingthe parts after the completion of each cut.The partial rotation of each part, arrangedin line, simultaneously will invariablymean the incorporation of gearing for thepurpose. This point, coupled with the factthat collett type of work -holders wouldmost likely then be necessary, leads to theconclusion that such a scheme will be onet hat will be costly to produce, but this willnot prove it, disadvantage where the outlaycan be spread over a considerable quantityof parts. It- might be that the fixturewould prove, with the -provision ofdifferent sized shank -adapters or collets,suitable for the production of a range of

similar parts. In this case the expensewould be also warranted. An alternativearrangement is to have a fixture that iscapable of being indexed about a baseand upon which the components arearranged in such a manner, on the rotatableportion of course, as to permit their beingmaohined in several lines at once by meansof a gang of suitably spaced cutters. Afterone pass of the cutters the fixture is swunground to bring the unmachined portionsin line with the cutters. This is a schemewhich, is much simpler to carry out, butis one which, for obvious reasons, isunsuited for parts having long " shanked "portions below the milled surfaces.

Items having tapped holes in them couldnaturally he handled in a similar mannerby the provision of suitable mountingadapters.

While dealing with this class of milledwork mention should be made of the factthat there is a special horizontal type ofmilling machine that was developed formachining parts of a "special, headed bolt"nature. The milling is carried out on thecontinuous principle and the fixture em-ployed is really a portion of the machine.

Briefly, the work pieces, held by the shanks,are passed through the cutters by a rotarymotion imparted to the fixture. After thework has passed the cutters it drops fromthe fixtures and fresh work is inserted asthe empty " stations " reach the loading *position. A rough picture of how this isdone can be obtained by imagining thefixture as a pair of bevel wheels mountedside by side with their teeth facing. Theaxes of the gear shafts are arranged at suchan angle as to bring the tops of the teethtogether more or less at the point nearestto the cutters. The work is fed betweenthe teeth at the " open " side and is carriedround to the cutters by which time it isgripped in rolling contact with the flanksof the teeth. After the cutters are passed,the receding teeth of the gears will permitthe work to fall out down a chute. Actually,specially contoured plates are used insubstitution for the gears. It will at oncebe apparent that slots thus produced willnot be flat bottomed " but will be concaveto the extent of the radius from the centreof the fixture to the face of the cutter.This fact is one that does not prove objec-tionable on many classes of work.

THIS MONTH IN THE WORLD OF

SCIENCE ANDSteered by Television

"Eye"MR. U. A. SANABRIA, a Chicago

scientist, chief of staff of the AmericanTelevision Institute,` has supplied to theU.S. War Department plans for an aerialtorpedo steered with a television" eye."

A television transmitter is enclosed in thenose of the machine which televises thescene below the torpedo to a screen in thecontrolling plane. This formidable machineis described as " sd.explosive that it coulddestroy even a large battleship." Theinventor states that the torpedo is a smallstreamlined aeroplane controlled by a largeaeroplane from as far away as 100 miles.

World's Biggest WaterMain

WHAT is stated to be the largest watermain in the world has just been com-

pleted in Southern California. It is 242miles long and big enough to drive a carthrough most of the way. The system willsupply thirteen cities with 1,000,000,000gallons of water a day.

New Torpedo BoatANEW torpedo boat capable of cruising

at 22 knots for more than. 1,000 milesand safe from both mines and torpeclos wasrecently described by Mr. Hubert Scott -Paine, the speedboat designer.

More than £200,000 has been spent inresearch and construction of the boat andit has been presented to the British Navy.The boat has a draught of only 3 ft., andcan carry a crew of eight. It has a topspeed of 40 knots and carries four 18 in.torpedoes.

New Road LightingANEW type of neon light is being tried

out in Poplar which is invisible fromthe air. It shows a blue light to driverswhen on their right side of the road, and a1-ed light if they swerve to the offside.

A Kerb DetectorINVENTION B

-Collapsible DinghiesAIRCRAFT patrolling the North Sea

are fitted with special equipment forsafeguarding the crew in the event of theplane having to make a forced landing inthe sea.. It consists of a collapsible rubberdinghy which is carried in such a positionon the plane that it can easily float freeafter being automatically inflated from acylinder of compressed gas. The releasing

is actuated by sea water flowinginto an inlet pipe as soon as the planealights on the water. In this way the crewhave a means of keeping afloat until theyare picked up.

NewSteerableParachute

ANYONE whohas ever

jumped out of aplane and taken thebumps of TerraFirma as hisparachute draggedhim over the roughspots will appreci-ate this new steer- able parachutewhich is shown onthis page, beingdemonstrated byRaymond Mordersof Lancaster, PA.,U.S.A. Air, insteadof spilling outaround the edges asin regulation para-chutes, flows outtwo vents in therear of the para.chute. The opera-tor may swingaround by pulling ashroud line andclosing one of thevents.

ECAUSE he was continually scrapinghis wings and tyres on the kerb, a

watchmaker of Rochester, New York, hasinvented a device which lights a tiny redlamp on the instrument board when thecar gets too close to any object. The mostimportant part of the device is a delicatecoiled spring which closes an electriccircuit and lights the lamp when the caredges towards the kerb.

Mechanical Bird -ManAContinenta I inventor has produced aflying that can be strapped to

the body. It is powered by a two -cylinderengine and is controlled by two hand levers.The feet are placed on a special frameworkand the machine has a foot -controlled rudder,

The parachutist holding out his hand for a left turn


"MOTILUS" PEEPS INTO THEMODEL WORLD "IL

Well, Model Fans, this Monthwe Celebrate the Anniversaryof " Motilus " who joined us inJanuary Last Year. Despite theBlack -Out our Model Fan, withhis Camera and his Torch, hasbeen Prowling About, and hasFound out that Though Shops inLondon and the Provinces mayLook Dead from the Outside inBlack -Out Time, INSIDE they

are Hives of Industry !

Trix RailwayAHAPPY New Year to you, readers,

and here's hoping you are all keepingyour spirits up ! Your model spy

has not only visited shops in London andthe provinces, with their cheerful Christmasdisplays, but has also been conducted roundfactories devoted to model making. He hadthe opportunity of seeing units of the Trixrailway being produced in bulk and it wasindeed an impressive sight. Rack upon

The new Trix 4-4-0 L.M.S.locomotive

rack of Trix locomotive casings-goodslocos, passenger locos and accurate littlescale model trains-drying in all theirpristine glory in the special " ovens " forthis purpose. Huge power presses blankingand piercing the small units for rails, wagons,tenders, coaches-the finished units, hun-dreds at a time, being assembled neatly-asfor instance the bogie and wheels on atruck-the mechanism in an engine ! It allappeared most efficient to me and I thoughtof the lucky boys these holidays who wouldbe running them round their tracks. WhileI was there I saw the new 4-4-0 L.M.S.and L.N.E.R. locomotives in an advancedstage of construction and the illustrationshows you the finished L.M.S. locomotive.A smart little job don't you think ? Andnot expensive-two guineas !

Permanent WayMany model enthusiasts I know use many

hours of their Christmas holidays in re-arranging or adding to their track. Thelaying of permanent way is quite often ajob the model engineer likes to do himself,but for an exhibition layout it is a task fora scale track worker. My picture shows onelaying a left-hand turnout in scale modelpermanent way with scale spacing of sleepers

A salesman explaining the merits of a model road tractor

and keyed chairs-and by the way whileon the subject of chairs I have just learnt

that Basset-Lowke are now making a newslide -on chair with cast key at the sameprice, Is. 4d. per hundred, as their die-cast

Laying a left-hand turn out on scale modelpermanent way

keyless chair. They have also introduced aslightly heavier pattern with the cast key,and chemically coloured at Is. 9d. per 100.I examined samples of these new chairsand they ar,,, a good fit on the standardsection steel rail.Road Tractor

My tour of London's toy shops has shownme that despite the kiss of population toproVincial centres they did a brisk festiveseason trade, also that working modelswere still in the front rank of popularhobbies. He're I caught a technical salesmanexplaining the merits of a road tractor-actually a brother model to that describedby Mr. F. J. Camm not so long ago in thesepages, while high upon a special stand wasa 71 -inch gauge " Royal Scot," and lookingat this first-class engineering job so accu-rately modelled, I felt a twinge of jealousyat the person or persons unknown whowould own this monster model on theirgarden railway. When I become a wealthymagnate(!)-hope springs eternal youknow-that is the gauge I'll go in for-justlarge enough to haul twenty persons andwith a good run for a quarter mile of trackand 40 ft. radius curves.Repairing Models

I'm afraid if the present state of myrailway is anything to go by, it will soonrequire the services of a model hospital.I am initiating a young nephew into themysteries of gauge 0 " locomotives, buthe is unfortunately at the Stage of pouringsand in the mechanism ! Model railwaydealers take into account such imps ofmischief and practically every one has arepair department. Some firms like Bassett-Lowke, Ltd., undertake repairs on everytype and make of locomotive whether clock-work, electric or steam, low or high pressure.Others like Messrs. Trix, Ltd., have aspecialised service for dealing with theirown repairs. The man in charge of a repairdepartment seems to me to need variedand unique knowledge of the idiosyncrasiesof small model's, and like a doctor, must


A model torpedo boat destroyer

know where to look for the trouble, but-and here he differs from the physician-hecan often reach down a spare part from theshelf to replace a broken or damaged. limb.Testing tracks are an essential part of the" model hospital" where after overhaul thepatient can be put through his paces andthen officially discharged ! Those readerswho have models they prize and who cannotcarry out their own repairs should nottrust them to some local garage or a friendwho is a good mechanic. Like a motor caror a radio set they need specialised repairand should be sent to a firm of repute. Mypicture shows a Bassett-Lowke craftsmanresetting the valves of a steam Mogul loco-motive.

Models of RoomsWhen gazing at the interiors of those

exquisite models of rooms you sometimes

with the realism of the work on the ceilings,and the other day a friend of mine askedme how this work was done. Well, here isthe secret. The ceiling is placed upside

in situ. There is no need to give politiciansthis idea. They have already turned Europeupside down !

Torpedo Boat DestroyerParticularly topical at the moment is the

new set of parts brought out for making amodel torpedo boat destroyer. The lengthof the boat is 30 in., the decks are roughlycut to shape, the motor and stern tube arefitted and the hull is bored to take the

Resetting the valves of a steam mogul locomotive

rudder. Among fittings included are rudder,anchors, QF guns, ventilators, bollards,fairleads. mast, davits, lifeboats, torpedotube, as well as steering wheel and standardand the smart little engine room telegraph.These varied fittings can be disposed aboutthe decks at the discretion of the owner, whocan also, if he is keen on trying out herpaces, experiment with her electric propul-sion. The motor can be wired in variousways with flash lamp batteries. For instance,he can obtain a longer run by series winding,or a slightly higher speed by parallel wiring,though in this cas he must beware of over-loading the motor, which is only constructedto take 4 to 6 volts. The set of parts is notexpensive at 50s.

down and worked upon and completed inthis position before it becomes a fixture theright way up. What a joy it would be to

Modelling a room interior

decorators and designers to -day if theycould get at their work in this way insteadof the back -aching job of doing the work

4

141rY*T4V4:'ir

A magnificent model of the Coronation assembly of our present King


A SMALL STEAM

a

C. -MANGLE VALVE/15 174/2

3;

SAFETY VALVEtic /4S/2

, ............. ...... _.. ................. ......

lb"

12 -

Fig. I.-Longitudinalsection of boiler, on

centre line

I I 111111111111111T1111111TMFITT111/1111111111711TMTM11111

THE article published in our Novemberissue concerned an original designfor a single -acting horizontal model

steam engine, but, unless such a model isrequired to be kept solely for spectacularreasons, in a showcase or as a tableornament, alone it is of no practical use.In order to complete it and to drive it, aboiler, or, to give it its proper name, a steamgenerator is required.

As the engine was intended to be anexample of model -making suitable for thebeginner, I think it desirable that themaking of the boiler should be a job whichis also well within his capacity. To this endI have made both the design and construc-tion as simple, or nearly as simple, as theycould well be, consistent with good andquick steaming capabilities.

A plain cylindrical shell or drum boilerwith a fire beneath it would perhaps besomewhat easier to make, but it would bemore uneconomical in fuel and certainlywould not generate steam at the rate calledfor by the engine. By the way, I shouldstate that the boiler which I have shown inthe drawings illustrating the presentarticle is intended to drive the larger ofthe two engines, i.e. the one having the2 in. by 1 i in. cylinder.

Small EngineFor the small engine a smaller barrel

tube of, say, 2i, in. diameter by about 8 in.long can he used, with three or perhapsfour simple water tubes. These tubes caneach enter the boiler shell at both ends,being brought down to a lower level at thefront and sloping gradually up towardsthe chimney end. Other details such as thedimensions of the casing, the chimney, thegas, or alternatively methylated spiritburners, will all be in proportion.

The type of boiler here dealt with followssomewhat on the lines of the famousBabcock and Willcox steam generators;at any rate as regards general proportions

and external appearance. To make theresemblance complete, however, the rect-angular casing ought to be of brick orsomething which could be made to look like

y K W. wining

brickwork. Internally the combination of ashell with large "downcomer" tubes andangularly placed water tubes constitutes atype of model boiler originally designed

2.-End view of boiler

OILThe Steam Gener-ator Described

elow will be F oundSuitable for Drivingthe Steam Engine

ix Described in theNovember Issue

by Mr. Smithies, a well-knownmodel maker, nearly 40 years ago.It was primarily intended for loco-motives, and for simplicity,thermal efficiency and quicksteaming qualities has neverbeen beaten.

In Fig. i is shown a longitu-dinal section on the centre -line.Fig. 2 an elevation of what I,for convenience, call the front end,and Fig. 3 a plan of the shelland water tubes as viewed fromunderneath. In Fig. 2 the frontplate of the casing is supposedto be removed in order to show

the downcomer pipes and cross drum fromwhich the water tubes issue.

Main BarrelThe main barrel should be made from a

piece of seamless copper tubing 4 in. indiameter and 12 in. long, having a thicknessof not less than 11, inch bare, that is to sayabout No. 18 gauge. If it should be a full* in. it will not matter, but, as we are notgoing to work at a high pressure, No. 18will be quite strong enough. If, when buyingthe tube, one or both ends are notcut off square, the supplier should be askedto give you a sufficient margin over andabove the 12 in. to enable you to square tI eends.

The flanged end plates, since they willbe flat, may very well be a little thicker.say -& in. full or No. 16 gauge. In cuttingthese end plates circular allow at least

in. for flanging. Ti is flanging is done bybeating the metal over the edge of acircular thick plate of steel. a circularcast iron block or a piece of very hard wood.Obviously iron is, best and the simplestway to obtain what is necessary will be toturn a wooden pattern and get a castingmade at an iron foundry. The 'pattern, canbe in any suitable wood; several pieces ofplywood to make up a thickness of aboutit in. will be best of all possible materials.To the back of this a small cube of woodshould be glued and nailed, say about 11 in.square. This will result in the casting in aboss by which the plate can be held in thevice whilst flanging.

The Four StaysThe outside of each copper plate should

be marked out with compasses and asecond circle scribed for the lines of the fourstays which will pass through the boiler.The inner circle on each plate is dividedon its circumference equally into four,centre dotted and drilled it in. holes. Thetwo plates had better, perhaps, be clampedtogether for drilling, both at one time. Cut


00o

00

0C

Fig. 3,-An underneath view of the boiler

the two plates circular and then thoroughlyanneal by bringing them to a dull red heatand plunging in water.

Now lay one of them truly and centrallyon the cast iron flanging block and markthrough on to the iron the four holes. Centredot and drill the iron with the samedrill. It is now possible, by using fourmodel bolts in. diameter, to clamp one ofthe plates securely to the iron. Beforedoing this, however, it will be necessaryto check up the diameter of the iron castingso as to ensure that after the plate is flangedit will exactly fit the interior of the boilerbarrel tube.

The best thing to do, to make quitecertain of this, will be to turn the woodenpattern to a diameter of about Basi in. largerthan the inside diameter of the barrel andthis amount will allow both forshrinkage of the casting and themachining or filing of the edge.

Obviously the exact diameterwill be equal to that of theinside of the barrel less twicethe thickness of the plate.

FlangingHaving got the casting right,

bolt up one of the plates andcommence flanging. Begin bytapping down all round, a littleat a time, using a fairly lightflat mallet. Assuming that thecasting and plate are held inthe vice in a horizontal positionthe blows should be deliveredwith a dragging action down-wards and rather towards the outer edgesof the plate.

As the flanging proceeds there will be atendency for the edges to buckle and themetal to harden. Should it be found that itis becoming stubborn the plate should beremoved and re -annealed, after which itwill be found more ductile and flangingcan probably then be completed.

When both ends are finished the flangesshould be cleaned bright with emery clothand tinned with solder. The inside of thebarrel should also be tinned for a distanceof iE in. inwards from the ends. The flangedplate which is to be the front of the boilercan now be drilled and have the collars of the

SPIRITTAM(

T.

fittings-the water gauge and pressuregauge syphon-soldered in place, and atthis stage it may be as well to do the sameon the top of the barrel with the safetyvalve and wheel valve collars. Then insertthe plate in the barrel and tack it in twoor three places with a large soldering iron.

Riveting the PlateThis plate has now to be riveted. Divide

up the circumference as shown in Fig. 2,drill all the holes, clearance size, for -1ff in.copper snap -head rivets. These are insertedfrom the inside held up by a square barof iron clamped in the vice to form a "dolly,"cut off with pliers, if necessary, to therequired length and closed over with theball end of a ball -pane hammer. Each rivethead should he finished off neatly by a

24'

4

165 SM./CUTS. %%MICH

making joints in boilers such as this, and ifit were necessary to work our engine withhigh pressure steam I would advise thismethod ; but I consider that silver solderingin a boiler of this diameter and thicknessof plate is a job somewhat beyond the youngbeginner's abilities and perhaps beyondhis means. It will be obvious that fargreater heat is required, silver -solder isexpensive and a considerable amount of itwould be needed for the whole boiler.Water Tube Assembly

When we come to the water tubeassembly, however, silver soldering couldvery well he adopted but I do not think itwithin the scope of this article to tell howsuch soldering is done.

Many years ago I built a locomotive witha Smithies type boiler, nearly as large asthe one we are now dealing with, and everyjoint including those in the water tubeswere soft soldered. I never had the slightesttrouble with it. Being always careful neverto let water disappear out of the gaugeglass I never had a particle of solder melt.If the reader leaves a good heavy fillet ofsolder at every tube joint they will haveplenty of strength.

It will be best to drill, bend and joint thewhok of the tubes and down -comer pipesas a separate unit and then insert it in theboiler barrel before the end plates are putin; this will give an opportunity of slightlyexpanding the tubes and beading them over

Fig. 4.-Details of the gas burners

cup shaped "snap." This, the front, end ofthe boiler can be completed by sweatingwith solder, but it will be best to do thiswith the large copper soldering iron incombination with a blowpipe. The lattershould only be used to assist in raising thetemperature of the joint, letting the iron,well supplied with solder follow behind theblowpipe flame. If Baker's fluid is used as aflux well clean the inside of the boilerwith soda water before the other end isinserted. This other end will be dealt withexactly as the first.

A great many writers advocate and mostskilled model makers adopt brazing orsilver -soldering as a means of securing and

Fig. 5.-Methylatedspirit burners

N

q5_-

inside of the shell and at the same time willallow free passage for the holding -up iron,or "dolly," when riveting. The soldering ofthe water tubes can be done with the ironalone if it is a large one and thoroughly hot.The general arrangement and all bends ofthe water tubes are shown in Figs. I and 3.

The four longitudinal stays are of in.brass rod, screwed at the ends and fittedwith nuts. After insertion, and the nutsscrewed up, each stay end and its nut aresoldered over. The casing enclosing theflames of the firing burners and supportingthe boiler is made from any suitable sheetiron jointed where necessary at the cornersby bending a flange over and riveting.

The chimney can be of any heightwhich may be found convenient butshould be not much less than 12 ins.It can be rolled from sheet metalriveted and flanged at the bottomor made from a length of brass orcopper tubing with a separate ringof angle brass riveted at the base.

The adding of the water gauge,pressure gauge, steam wheel -valveand safety valve will complete theboiler. These fittings are all ofBassett-Lowke's make and the codenumbers shown on the drawingsagainst each item have been takenfrom the catalogue of Bassett-LowkeLtd. The reader will therefore have

(Continued on page 191)


4

LORDGORT

says:-" By means of BATTLE TRAININGthe young man who, on joining theArmy, is eager to learn his newprofession, can assimilate not onlythe essential elements of soldier-ing, presented in an attractiveform, but also something of thetraditions of the British soldier."

Published with the fullco-operation and sanctionof the War Office

BATTLE TRAININGIN WORD AND PICTURE

NIS SERIES IS PUELMEN BY ODOM N

WITH THE APPROVAL Of THE INN

TO -DAY, when a commission in the Army is open CO every man whoproves that he has reasonable ability and the gift of leadership, a publi-

cation to supplement the official manuals is required-something instructiveand absorbing, too.

BATTLE TRAINING IN WORD AND PICTURE is intended in the main forleaders of the smaller formations, from the Section or Platoon upwards, andfor those who hope to gain promotion to these commands. It dealsauthoritatively and interestingly with the problems that confront suchleaders on peace and war manoeuvres.

Ono of the features of the publication is an account of the operationscarried out between two imaginary warring states-Anglia and Humbria.Problems are set covering every situation, and solutions given.

WITH MAPS, DIAGRAMS, PHOTOGRAPHS, EXPLANA-TORY PICTURES, AND A FOREWORD BY LORD GORT.

BATTLE TRAININGIN WORD AND PICTURE

6d. of all Newsagents, Booksellers and Bookstalls. If you have anydifficulty, send 7d. to the Publisher, George Newnes, Ltd., Tower House,Southampton Street, Strand, W.C.2, and it will be posted by return.

THE GRAND XMASAND BIRTHDAY

DOUBLE NUMBEROF

"THE AERO MODELLER"is now on Sale

Price IfGiven away Free with above issue

FULL SIZE PLANS FOR BUILDING AFLYING SCALE MODEL OF

THE SUPERMARINE "SPITFIRE"ALSO A COPY OF THE AERO MODELLER

BUYER'S GUIDE ! !

GRAND DOUBLE

BIRTHDAY AND CHRISTMAS NUMBER

As well as the two free gifts mentionedabove, the December issue contains manyexcellent articles, plans and sketches, in-cluding full size plans and instructions forbuilding the Douglas Dive Bomber, a

flying scale model, an excellent article onThe Recent Trend of Fighter Designs,fully illustrated with drawings, and a finearticle by Capt. C. E. Bowden on PetrolEngined model flying boats and seaplanes.Get a copy of this magnificent issue straightaway, if you find difficulty send us yourP.O. for If- and we will send your copyby return, post free.

"THE AERO MODELLER,"Allen House, Newarke Street, LEICESTER

:66 NEWNES PRACTICAL MECHANICS January, 1940

CRACKEDWONDAR

WELD Domestic is a

liquid metallic preparation forthe repair of cracks and the elimination ofwater leakage in all types of domestic andcommercial hot water systems, boilers,tanks, radiators, etc. It is not a temporary measure, but an efficient andpermanent cure. You just pour it in and the crack is sealed permanently in 60minutes. Save time, labour, mess and expensive welding. Tried and tested by Railway

and Transport Companies throughout the country. Write forHOLT'S free booklet.

WONI11111 WELD PriceMC0EmSpTiel!

Domestic Size

BOILERS, TANKSand PIPES, etc.

PERMANENTLY REPAIREDin 60 Minutes

WITHOUT DISMANTLING

Obtainable from any Halford Cycle Co. 230 Shops or directfrom Sole Distributors :

DOUGLAS HOLT (Est.1919) Ltd., 9, Little Turnstile,Holborn, LONDON, W.C.1. Tel.: HOL. 4891 2 201 -

Just Published

NEWNES COMPREHENSIVE WAR ATLAS Contains eight pages of newest War maps, printed in fullcolours. These include the Western Front, with the Maginotand Siegfried systems clearly shown, and all other countriesinvolved in the conflict, together with countries whose frontiersadjoin or are close to those of the belligerents. Full information is given of the strengths of the Armies,Navies and Air Forces of the nations. Air distances are shown from all important towns andcountries in a radius extending from Baghdad to London.

1/.6

*

NET

*From all newsagents, bookstalls or booksellers, or by post117 from the publishers, GEORGE NEWNES, LTD.(Book Dept.), Tower House, Southampton Street, Strand,

London, W.C.2.

Keeps the Flag ofHumour Flying

6DJANUARY

IN THE POPULAR POCKET-SIZE

Order from your Newsagent To -day

YOU'LL enjoythe bright and

topical drawingsby such stalwartsas Hynes, EdgarNorfield and TomWebster, thewhole -page artphotographs, andthe snappy hu-mour of LONDONOPINION'S*witty writers.When you getyour copy guardit carefully-toprevent someother member ofyour family frommaking it hisproperty!

FREE SERVICEFOR READERSREADERS requiring information con-

cerning goods or services advertisedin PRACTICAL MECHANICSshould give names of Advertisersfrom whom particulars are desired.Any number of names may be includedand we will obtain for you catalogues,lists and any other information you maybe wanting. THERE IS NO CHARGEFOR THIS SERVICE.Readers desiring particulars from a number ofAdvertisers will, by this method, save time andpostage. If any Advertiser stipulates that stampsor postal orders are necessary before samples orcatalogues are sent, please enclose the necessaryamount with your instructions. You are cordiallyinvited to make full use of this Service.

ADVERT, SERVICE DEPT.,PRACTICAL MECHANICS,

TOWER HOUSE, SOUTHAMPTONSTREET, STRAND, W.C.2

Please obtain and send to me particulars fromthe Advertisers in your, January issue whosenames I give on list attached.

Advertiser I Page No. I Information Required

Attach sheet of paper, wills particulars, andyour name and address (written in BLOCKletters) with date, to this announcement.

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Men over 21 areurgently wanted forreserved occupationsas draughtsmen inElectrical,Mechan-ical, Aeronautical,Structural, andother Branches ofEngineering. Prac-

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SUCCESS-OR NO FEEIl e now Or vote copy of this remark-able publication It may well prove to be

the tilrntn5 Joist in your career.NATIONAL INSTITUTE OF ENGINEERING

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VARNENEstains andvarnishesin oneoperation

You will be far moreproud of your woodworkwhen it has that finehigh gloss finish whichVarnene gives.Varnene never becomestacky while working.Its stain sinks deeplyinto the wood leaving thevarnish to provide ahard gloss which will rotreadily chip. or scratch.

From Ha.ndicraLt Stores, Ironmongers,men. Grocers, and General Dealers. In DarkOak, Walnut, Mahogany, Light Oak, EhonyBlack and Clear (Colourless) Varnish.

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Designing Model BiplanesA Fascinating Type of Modelwhich has been Neglected inthe Belief that it is "Difficult"

and Incapable of Duration

THE biplane is a fascinating type omodel, but it has been sadly neglectedon account of a widespread belief

that it is " difficult " and incapable of gooddurations. Recent achievements, however,have surprised many, and induced them toconsider personal investigation. The follow-ing notes are offered to facilitate the process.

The subject will probably be viewed intruer perspective if the raison d'otre of the

full-scale biplane is first explained. Bydividing the required lifting -surface intotwo wings, and joining them with strutsand wires, the efficiency is reduced some-what, chiefly owing to the increased dragof the extra junction of wing and fuselage.But lighter spars can be used than wouldbe needed to prevent a monoplane wingfrom flexing. The reduced span and chord

Mr. Knight's" Kabix Minor,"3's oz multi -sided

fuselage biplane

allow the tail to be moved nearer the wingswithout reducing its effectiveness, and sothe fuselage can be shortened and furtherweight saved. Consequently, a greater loadcan be carried, or the original load carriedon less power and fuel, The reduced overalldimensions also improve the powers ofmanoeuvre.Rubber -Driven Models

These advantages do not apply to therubber -driven model. Bracing -wires wouldsoon come adrift in the rough-and-tumbleof pilotless flying, and without them anyappreciable thinning of the spars wouldresult in flimsiness. The fuselage cannotbe shortened without shortening the rubber -skein and reducing the duration. As for

Mr. Knight's Kittiia:ck" 5 oz cabinbiplane

manoeuvrability, this is of no value to themodeller.

Biplane lay -out, in fact, offers no advan-tages to the modeller. On the contrary,extra work and care are involved, whilethe performance tends to be reducedthrough the extra drag steepening theglide. The sole inducements are theattractive appearance, and-to those whofeel that way!-the satisfaction of tacklingsomething out of the commonplace.

But while a biplane model is handicappedwhen flown in competition with mono-planes, it ,has shown its ability to soar inthermals, and a biplane holds the Britishseaplane record of 6 minutes 54 seconds !

Lay -Out VariationsNumerous variations in lay -out are open

to the designer. For instance, the wingscan be equal in span, or unequal. (Whenthe area of one is more than twice that ofthe other, the machine is termed a ses-quiplane, and is not eligible for biplanecontests.) The upper wing can be mounteddirectly over the lower, or ahead, or behind.Certain features are helpful, and othersdetrimental: The scale -modeller may haveno choice, but the free-lance designer canselect those features which benefit modelstability and performance.

By way of example, centre -sectionstruts, supporting the upper - wing abovethe fuselage, are likely to come off badly

A petrol-engined biplane (9 cc. "Brown Junior") by Messrs. I. and W. Worden, of The Model Aircraft Clu5


An unstaggered biplane

(literally !), and it is better to deepen thefuselage sufficiently to fill the gap betweenthe planes, so that the upper plane canrest upon it, and the lower against thelower longerons. If the gap is less thanthe root chord there may be interferencebetween the air -flow under one wing andabove the other.

Cantilever wings, independent of strut-ting, are an excellent feature. But inter -plane struts improve the appearance. Inthe case of Mr. M. R. Knight's " KabixMinor " each strut plugs into a celluloidtube in the lower plane, and touches theupper plane without actual connection,thus avoiding damage in heavy landings.Another method is adopted in Kitti-hawk," each strut consisting of a balsa -faired paper tube, through which passes arubber -band linking small hooks on upperand lower planes. A hooked wire is em-ployed to thread the band through thetube.

Ideally, the wing -area should be aboutone -quarter more than for a monoplane, tocompensate for reduced efficiency, and thespan of at any rate one wing must besufficient to deal satisfactorily with torque.When the wing -area is restricted by, rule,as with Wakefield models, the biplane ishandicapped, for one is not making thebest use of the permissible area by dividingit into two parts.

F.A.I. rules limit the tail -plane area to33 per cent. of the wing -area. Despite thegreater wing -area of the biplane, the writerhail never found it necessary to use alarger tail -plane than for the equivalentmonoplane, probably owing to the greaterproportionate length of the model fuselage.

" Backward Stagger "As to line-up,place the Centre of Gravity

midway between the assumed Centre ofPressure of the two planes (33-40 per cent.across the chord), and place the thrust -line on the Centre of Resistance, thepproximate position of which can be

ascertained by drawing a front eleva-tion and connecting the wing extremi-ties by diagonals, as depicted in theaccompanying diagram.

Other line-up items vary accordingto the type of biplane. It is interestingto note that Mr. F. Rogerson's modelwith negative or backward stagger(upper plane leading -edge behind lowerleading -edge), which won the CanadianWakefield Cup in 1935, had bothwings set at 2 degrees positive to thethrust -line, and the tail -plane parallelwith and above the thrust. The

Backward or negative stagger

Forward or positive stagger

The centre of resistance ofph2nes, fuselage and com-

plete model

upper plane has about 6 degrees of dihedral,and the lower plane none. A slight increasein lower plane incidence, and 2 degreesor more of dihedral might prove advan-tageous.

" Unstaggered " Line -UpWhen no stagger is employed, mount

both wings at 3-31 degrees positive to thethrust -line, and the tail -plane at about1-11 degrees positive. Any stalling ten-dency can then usually be eradicated byincreasing the lower plane incidence.Difference in upper and lower plane inci-

dence is termed " decalage.' Use 6degrees of 'dihedral on the upper plane.and about 8 degrees on the lower.

" Slot " Line -Up !When there is an appreciable amount

of forward or positive stagger (upperleading -edge ahead of lower leading -edge), the upper plane should havethe greater incidence, say 4 degreesto the lower plane's 2 degrees. Thelower plane then helps to stabilise themodel, and the tail -plane area can bereduced. The upper wing can be given8 degrees of dihedral, and the lowerplane 6 degrees or even less.

Mr. S. R. Crow, who for long heldthe biplane record with this type, con-tends that it lends itself to a durationequal to that of the monoplane, or-wen better. His method is to relychiefly for lift on a large upper wingof high -lift section, and to use amplepower. A tail of lifting -section ismounted parallel with and slightlybelow the thrust -line. The model istrimmed to turn against the torque,and to have so flat a glide that it tendsto stall on power. By the staggeracting as a species of Handley -Page slot (so Mr. Crow suggests) thestaffing tendency is converted into asteep upward spiral which takes themodel to a great height, from whencethe flat glide adds materially to theflight duration.

CENTRE OF RESISTANCE OF PLANES

CENTRE OF RESISTANCE OFCOMPLETE MODEL

(Midwati between other two centres, theresistance of the undercarriageofFsetting that of tart)

CENTRE OF RESISTANCEOF FUSELAGE

Skybirds in WartimeA New Ship Series o Waterline. Scale ModelsMANY readers will be interested to

know t4ot Skybird modelling ismore popular than ever, despite

the war ; in fact, the war has given addedinterest to this most suitable and appro-priate indoor hobby of solid Scale ModelAeroplane construction. What could bemore interesting than to occupy both mindand hands assembling and painting modelsof Britain's air fighters-the " Spitfires,"" Hurricanes," " Blenhehns," etc.

Skybirds are known to many thousandsof keen modellers, and the Skybird Leaguefounded some seven years ago has playeda very important part in making the youthof this country air -minded. Many hun-dreds of the League members are nowserving their country with credit in the

R.A.F. Many letters and personal calls arereceived at League headquarters fromenthusiastic members who have switchedfrom modelling to the real thing. Leagueheadquarters report an influx of new mem-bers and regret that owing to the need faeconomy, and the censorship of our informa-tion relating to Service machines, the pub-lication of the monthly Skybird Bulletinhas been temporarily suspended. For, theinformation of modellers, we are pleased toannounce that all being well, the seventhannual rally and model competition willtake place as usual on or about Easter next.Now is the time to prepare those prize-winning models (newcomers will have theirchance now that the past winners are onactive service). Particulars of the corn -

petition and the models eligible can be hadfrom Skybird League Headquarters, 3Aldermanbury Avenue. London, E.C.2.Waterline Models

Ship model enthusiasts will welcome thenew ship series of cast Water -Line Scalenode's advertised in this issue. Thesemodels are marketed at very moderateprices by the manufacturers of the famousSkybird Aeroplane models, and can berelied upon for correctness of detail.

There is a special set of 11 models com-prising battleships, cruisers, aircraft carrierand destroyers, scale 150 feet -1 inch,price 4s. There is also a very comprehensiverange of practically every ship of theBritish Navy-scale 100 feet -1 inch.

The prices range. from 3d. each in thesmaller type submarine, patrol boats, etc.up to 3s. each for battleships and aircraftcarriers, and the Ark Royal is still withthis Fleet. Send stamps 11d, for price listto A. J. Holladay & Co., Ltd., 3 Alder-manbury Avenue, London, E.C.2.


Mackin

PLY WOOD PANELEASED UNDERCURTAINS

Fig. I.-A simple method of fittingpanels into the window frame

Out the LiwhitBLACK -OUT PAPERFOR FAN -LIGHTSONLY

RE PIECEOF PLY TO SECURESCREW

WASHERUNDER HEADOF FINE SCREW

PROXIMITYTOWOOEDGED OF

THE hurried black -out measuresadopted by many when the war firststarted, necessitating the free use of

drawing pins and sticky paper, must havetaken toll of the wood and paint work,whilst unless suitable frames have been

' made for erecting black -out paper, bothventilation and light have of necessity beenrestricted during the daytime.

It can be said that the ideal black -outscheme would be one which is easy to erectat dusk and remove in the morning.

Various methods suggest themselveswith a little careful thought, and the follow-ing notes may help those who find that theirschemes have either the above objections orexpense is of primary importance. The writer's method of fitting panels into

each window frame without marring thewoodwork with screws, etc., comprisessimply the location of rubber cabinet feetfitted close to the edge of the plywood panelsso that there is provided a fair amount ofoverlap, as shown in Fig. 1.

The PanelsNow, as each panel is cut accurately to the

size of the window frame, the overlap ofeach rubber will bind against the frame-work as the panel is worked into position.

Owing to the amount of side pressure onthese rubbers it will be necessary for washersto be included under the heads of the fixingscrews, to prevent the rubbers tearing them-selves free over the heads of the screwsafter considerable use.

To facilitate erection and removal,handles can be fitted to the panels.

Where possible, the panels should befitted so that they do not interfere with anyexisting curtain fitments, and by treatingeach window frame independently, it shouldbe possible in the majority of instances toease each panel under the casement curtains(see Fig. 1).

For opening type windows, it is onlynecessary to cut the plywood at the pointswhere the casement catches are located, butalthough the wood should be cut sufficientlyto allow each panel to be eased into position

y _Handyman')The Ideal Black -out Scheme is one which is Easy toErect at Dusk and as Simple to Remove in the Morning

/0

behind the catches, care will needto be taken to see that not toolarge a cut-out is made.

In such instances where thiscannot be prevented, a strip ofcardboard temporarily fitted overthe hole will suffice. A leather,felt, or cardboard flap permanentlyfixed to the panel at these pointswould, however, be the best plan.

Fan -Light WindowsFan -light windows should be

treated separately, using eitherwood panels as in the above in-stances, or simply black -out paperfitted in the manner illustratedin Fig. 1.

SEFUL GROOVECAUSED IN SLID-ING PANEL INTOPOSITION

METHOD TO ADOPT WHENRECESSING IS NOT CON-VENIENT

Fig. 2.-Grooves cut into rubbers asshown make an ideal method for holding

the panels in place

LOLL CAPER OROTHER FORM OF

DECORATION

.11q,

ALTERNATIVEMETHOD USINGBINDING STRIPS

Fig. 3.-Another method ofholding the panels in position. Toprevent them from looking unsightly the panelscan be covered with wallpaper to match the

walls of the room

So far one has seen how the frames can befitted without using hooks or screws in thewoodwork, but in instances where say, in thecase of the hall door, or where a number ofsmall panels would prove troublesome,exception to this need not prove unsightlyand little damage need result to the paint -work where occasional screws are used.

In this case, the rubbers are fixed withlong thin screws and washers directly to thewood, and positioned so that the panel maybe either slid or pressed into position ; thisis shown in Fig. 2.

An alternative way to erect panels easilyand quickly, is to make up a number ofplywood strips at the ends of which, and sothat they overlap, rubbers are fixed, thuseach strip, cut a trifle larger than the frame -

Fig. 4.-A novelfront door lockilluminating scheme

ALuY

work into which it is to be fitted, will nowbe held in position by the bowed stripbinding in the frame as illustrated in Fig. 3.Now with regard to incidental light pre-cautions and fitments. Fig. 4 illustrates arather novel front door lock illuminatingscheme. In this arrangement, it will be seenthat a " pea " bulb is neatly concealed andprotected under half a small tin lid fittedjust above the lock.

Novel Switching ArrangementThe construction needs little enlargement

here, and the rather interesting method ofswitching by the letter box flap will beeasily followed on referring to the wiringdiagram given in Fig. 5.

A separate switch behind the door makesit possible for the circuit to be put out of


commission during the day, to preserve, asfar as possible, the life of the pocket lampbattery. The tin cover could be painted tomatch the door.

The pea bulb is soldered permanently to

RIES CONNECTION

HALLLIGHT

/11\.\

E_ -

Fig. 6.-Detailsof the switching

arrangement

CONTACTS SHORTED'WHEN FLAP IS RAISED

NTACTS OF STRIP BRASS)

Fig. 5.-Wiring diagramfor the keyhole light

the inside of the tin by a thin brass stripwhich could be obtained from one contactof an old torch battery. The fine wires passthrough a small neat hole drilled in thedoor.

Another wise plan is to fix a switch overthe front door on the inside, so that when

ErTERY(4.54

the door is opened, the hall light is imme-diately extinguished before open to any

extent.A snap -action switch

FINE HOLE should be used and goodDRILLED INFRONT ODOR quality flex neatly cleated

along the door frame.The illustration Fig. 6

shows the essential details ofa suitable switching arrange.ment and it will be noticedthat here again good use is

made of one of the cabinet rubbers.A toggle switch, chosen from the Bulgin

range, is mounted on a strong bracket sothat the dolly is semi -recessed in the rubber,which_ is fixed to the springy bracket by a6BA nut, bolt, and washers.

The whole fitment should be suitablylocated as near to the corner-on the openingside-of the door as is possible, so thatbefore the door is clear of the jamb, theswitch is operated. Both the resilience ofthe rubber mounting strip, and the bindingof the rubber, ensures a minimum of wearwith a surprisingly light action free of anyfouling.

Fig. 1.-A camerafitted with the pistol

grip and trigger

WHEN a small folding camera isused for taking quick snaps,difficulty is often experienced in

handling the trigger release effectively.This is, in pocket cameras, invariably anintegral part of the lens mounting, and theconditions are very similar to those whichwould pertain if the trigger of a revolver ora rifle were fixed on the side of the foresight.The camera trigger in its usual position isreasonably satisfactory when the back ofthe camera is held hard against the bodyfairly low down, but used against the cheekor the forehead it becomes awkward andnearly impossible to operate without movingthe body of the camera. For this reasonalone, the grip and trigger described herehas proved exceptionally satisfactory. Thegrip enables a firm hold to be made on thecamera, which is not possible in the ordinaryway, owing to the irregular shape of thecamera body, whilst the trigger is situatedin the right place, contortions of the wristand fingers are absent, and, used with thecurling forefinger, no unsteadiness results.

General. ArrangementFig. 1, shows the general arrangement.

The grip or butt " A," is fashioned from asolid piece of hard wood, sandpapered and

Adaptin4 a Small CameraA Pistol Grip and Trigger for Small Cameras

enamelled black. Corrugations may bescored in the wood for a good gripping sur-face, but it will be found that this is hardlynecessary.

The actual dimensions are not given,because these will vary with differentmakes of camera and also the size of one'shand, but a piece of wood 5 -in. long and1 in. x 2f in., will be a reasonable basis for

G a large hand. The wood is shaped to fit thefilm chamber tightly as some support isobtained thereby, and the top should be justclear of the underside of the platform. Theshaped brass bracket " B " shown in detailin Fig. 2, which is secured by the two screwsto the butt, holds the device to the cameraby a stud. The bracket should be madefrom i-in. or On. brass sheet and is madeto fit flush in the wood of the butt, both ontop and down the sides. If the tubularnuts cannot be obtained or made, ordinaryscrews with thin nuts used on the left-handside of the butt or wood screws are just aseffective. In the last case, the holes in thebracket should be staggered to avoid thepoints of the screws meeting.

The TriggerThe stud " C " Fig. 1, and in detail in

Fig. 3, fits into the tripod socket, usuallytapped 1-whitworth, but may be a metricsize, and carries a round milled nut " D "and also forms the fulcrum for the trigger.The trigger" E," details in Fig. 4, is made intwo pieces, the extension " F " being solderedinto the slot across the top of the trigger,

Fig. 4.-How the triggeris made

which also fits the tongue on the stud. Thetrigger can be cut from a piece of brassOn. wide, I -in. thick and approximatelyWin. long, and the extension piece ofA -in. brass. The length of the extensionpiece will vary with different cameras. Thelength and the necessary curvature can beobtained in this way.

Adjusting the TriggersPull out the camera to its middle distance

according to the meter scale on the platform,and drill a hole through the platform directlybelow the trigger release lever. The lengthof the arm can then be measured from thishole. The connection between the twotriggers is made with a short length of finechain. This chain is hooked on to therelease lever and passed down through thehole drilled in the platform and then hookedon the trigger extension. The strength ofthe spring in the shutter has been found inthe four cameras which have been so fitted,to be sufficient to return the trigger to itsforward position, but if a very light loadedshutter is used, a short piece of watch springscrewed to the butt behind the trigger willbe all that is required.

The grip can be easily taken off the camerafor Parrying purposes, by releasing the chain,the lock -nut and unscrewing the stud

Fig. 3. -Right .details of the stud

=. 11 1111#

L.

Fig. 2.-The shaped brass bracket


Chemistry for BeginnersNo. 10.-Nitrogen and some of its simple Compounds. Easily -performed

Experiments which can be carried out in any Home Workshop

NITROGEN is usually termed an" inert " element, for the reasonthat when in the uncombined state,

nitrogen gas enters only with difficulty intothe majority of chemical reactions..

Yet, if we choose to regard the elementnitrogen in another light, we are at oncestruck by the fact that nitrogen is anythingbut an inert element. There are literallythousands of compounds in the constitutionof which nitrogen plays an exceedinglyimportant role. Nitrogen, for instance,imparts to many dyestuffs their colouringproperties. It gives to a multitude of com-pounds their characteristic odours-goodand bad-whilst, again, it confers uponanother host of compounds which we call" drugs " the peculiar physiological effectswhich render them so valuable to us. Andlastly, nitrogen is an indispensable con-stituent of all explosives. There is nouseful explosive which does not containnitrogen. Indeed, we may regard thesudden detonation of an explosive com-pound as a practically instantaneousliberation of nitrogen atoms, with theconsequent release of enormous quantitiesof energy.

Explosive CompoundsIn explosive compounds, the constituent

nitrogen atoms show a great antipathy toexisting harmoniously side by side. Theyare like quarrelsome people who are alwaystrying to separate and who fly off at atangent on the least possible pretext. Andwhen they do so, they invariably manage todisrupt completely the " house ' or chemicalmolecule in which they have been existing.This sudden disruption we call an explosionand, unfortunately, we are all only too wellaware at the present day of the highlydisintegrating and shattering effects of thismolecular commotion.

In this article, we cannot, of course, dealwith nitrogen in its explosive or other com-plex compounds. We must confine ourselvesto experiments on pure nitrogen, which is,of course, a colourless, invisible and in-odourous gas, and, also, to the preparationof some of the simpler, yet none the lessinteresting nitrogen compounds.

Nitrogen is a very abundant gas. It con-stitutes four -fifths of the total volume ofthe earth's atmosphere. Thus, in a roomfulof air, practically four -fifths consists of pure.nitrogen, whose main function is to act as adilutant of the oxygen.

Nitrogen is so called because it is a con-stituent of " nitre " or potassium nitrate(saltpetre), the word itself meaning " nitre -producer." The French call nitrogen azote,meaning " without life," because the gas isincapable of supporting respiration or com-bustion, and the Germans term it Stickstoff,or " suffocating stuff."Preparing Nitrogen

It is not difficult to prepare a quantity ofnitrogen in the laboratory. All we requireis a shallow basin of water and an invertedbell jar or even a glass jam jar, the latterbeing inverted under the water as shown inthe illustration. Within the inverted jar isplaced a small amount of red phosphorouswhich is contained in some receptaclewhich raises it omit of contact with thewater. The jar is raised, a light is applied

to the phosphorous and the jar is thenquickly replaced over it. The phosphorousburns with a yellow flame, emitting white

In this test tube are nitric acid and scrap copper.Nitric oxide gas -is liberated, and this, issuingfrom the end of the glass tube, combines withoxygen of the air, giving rise to reddish fumes of

nitrogen peroxide

clouds of phosphorous oxides. After a littletime, the flame of the phosphorous will goout, indicating that the oxygen within theinverted jar has all been used up. At this -stage, the remaining gas within the jarconsists of nitrogen.

Nitrogen prepared in this manner fromatmospheric air is never quite pure. Forone thing, the burning phosphorous in-variably becomes extinguished before thelast traces of oxygen have been used up,whilst, again, the nitrogen " within thejar will contain a trace of carbon dioxideand about one per cent. of argon and theother inert gases of the atmosphere."Still, however, for many purposes, nitrogenprepared in the above manner is pureenough.

Absolutely pure nitrogen, the so-calledchemical nitrogen," is best prepared by

heating in a flask fitted with a delivery tubedipping under water (see illustration) a con-centrated solution of ammonium nitrate,or, better still, a mixture of equal volumes dfconcentrated solutions of ammonium chlo-ride (sal ammoniac) and sodium (orpotassium) nitrite.

NH.4NO2->- 2H20 +N5Ammonium nitrite Water Nitrogen .

Nitrogen, as we have already read, is acolourless, odourless gas, which is a non -supporter of life and combustion. Perhaps,however, the latter statement should bequalified, for nitrogen gas will admit of acertain type of combustion in that whensome metals (notably magnesium, titanium,calcium and lithium) are heated in nitrogen

Practical Experiments for theHome Worker

Making pure nitrogen by heating a strongsolution of ammonium nitrite. The gas is collected

over Water

gas, they burn in the gas, forming, notoxides," but nitrides. Thus, when

magnesium is heated in nitrogen gas itforms magnesium nitride, Mg,,N2, a white,solid not unlike magnesium oxide.Lighter Than Air

Nitrogen is somewhat lighter than air, itsspecific gravity being 0.973 (air = 1).Hence, when a jar of nitrogen is turnedupwards, the nitrogen slowly rises out of thevessel.

Under the influence of the electric sparkand the electric flame arc, nitrogen will notonly combine directly with oxygen, formingthe various oxides of nitrogen (which can beconverted into nitric acid), but it can also bemade to combine with hydrogen, formingammonia.

These reactions, which, unfortunately,cannot be imitated on the small scale in thelaboratory, are exceedingly important ones,since they underlie the modern industrialprocesses of " fixation of atmosphericnitrogen " whereby the nitrogen of the air isutilised for the production of nitric acidand ammonia, these latter compounds form-ing the basis of explosive, fertiliser and otheressential chemical manufacture.

By heating calcium carbide in nitrogengas we obtain a compound called calciumcyanamide. CaCN,, which, under the name of


" nitrolim," is used as a fertiliser. Thus :-CaC2 + N5 =

Calcium Carbide NitrogenCaCN2

Calcium cyanamide CarbonIn order to make this calcium cyanamide,

the calcium carbide must be heated to whiteheat.

Calcium cyanamide, CaCN2, besides actingas a fertiliser, can also be used for generatingammonia. This is effected by passing acurrent of super -heated steam over thecalcium cyanamide, whereby calcium car-bonate (chalk) is formed:and ammonia gasproduced :-

CaCN2 31-120 =Calcium cyanamide Water

CaCO3 2NH3Calcium carbonate Ammonia

AmmoniaAmmonia, of course, is one of the

simplest yet one of the most important.compounds of nitrogen. Many of us are aptto think that the " liquor ammonia " whichwe buy at the pharmacist's is pure ammonia.Actually, however, this is not the case, forammonia itself is a gas which is extremelysoluble in water. It is, therefore, the watersolution of ammonia gas which is usuallyknown as " liquor ammonia " or just" ammonia."

Water will dissolve (at 0° C.) more thaneleven hundred times its volume of ammoniagas, and when the resulting solution isheated, the ammonia gas is given off. Thusa very simple way of making a quantity ofammonia gas consists in warming some ofthe " liquor ammonia " or " liquidammonia ' of the pharmacist. Thissolution, when at its strongest, has aspecific gravity of 0.882 (at 15° C.) and con-tains 35 per cent. by weight of ammoniagas.

Ammonia gas is commonly prepared inthe laboratory by heating any of theammonium salts, as, for instance, ammon-ium chloride (sal ammoniac) or ammoniumsulphate, with slaked lime or with causticpotash or caustic soda. Ammonia gas isabundantly disengaged, and, if required, itmay be dried by passing it over quicklime,but NOT over calcium chloride (which isthe more usual gas -drying agent in thelaboratory) since the gas forms a compoundwith calcium chloride.

Owing to its extreme solubility in water.ammonia gas cannot be collected overwater. If, however, a solution of ammoniais required, the ammonia gas should be ledinto the water by means of a funnel, asshown in the illustration. If this precautionis not taken and the gas is passed into thewater by means of an ordinary glass tube,the absorption cf the ammonia by thewater will probably be so violent that thewater will ascend the glass tube and besucked into the flask. Using, however, thesimple apparatus shown in the photograph,considerable quantities of ammonia solutionmay readily be made in the home laboratory.

Ammonia GasThe suffocating, pungent -smelling proper.

ties of ammonia are well known. Bothammonia gas and its solution in water arehighly alkaline. Mixed with acids, thesolution forms salts. Thus, when ammoniasolution and dilute hydrochloric acid aremixed, ammonium chloride is formed (insolution).

Many metals, such as magnesium andcalcium, when heated in dry ammonia gas,give rise to nitrides, just as they do whenheated in pure nitrogen gas.

Under ordinary conditions, ammonia gasis incombustible. If however, the air be

heated or the quantity of oxygen increased.ammonia gas can be made to burn with acharacteristic yellow -brown colour. Thisflame is best seen by bubbling a stream ofoxygen through a quantity of ammoniasolution which is being warmed in a flask.The gas issuing from the delivery tube of theflask will burn with the yellow -browncolour characteristic of combusting am-monia. If, again, a stream of ammonia gas

A glass jar inverted over a quantity of redphosphorus supported over a basin of water.When the phosphorus is ignited, it abstracts the)xugen from the enclosed air in the jar, leaving

nitrogen

is directed into the air -hole of an ordinarybunsen burner through which coal gas isflowing, the flame of the burning coal gaswill be coloured brown -yellow and willexpand considerably.

When dry ammonia gas is passed oversodium heated in a tube, a compoundknown as sodamide, NaNH2, is formed.

As we have already seen, nitrogen andoxygen can be caused to combine together

Preparing a solution of ammonia gas. A strongsolution of sal ammoniac mixed with lime orcaustic soda is heated in the flask, and the am-monia gas is abosrbed into water by passing itthrough the inverted funnel. This funnel is anecessary protection against the possibility of thewater rushing back up the delivery tube into the

heated flask and so breaking it

directly by means of the electric spark,Usually, however, the oxides of nitrogen.of which there are at least five, are preparedby roundabout methods." Laughing Gas "

The first of the oxides of nitrogen isnitrous oxide, N20, popularly known as" laughing gas," because, in a few cases,this gas, when breathed, has been known tocause great excitement on the part of theinhaler of the gas. This is the anaestheticgas which is so much used at the presentday by dentists for causing momentaryunconsciousness. It has a sweet, rathersickly smell and it is best made on the smallscale by heating dry ammonium nitrate.Since the ammonium nitrate, even whengently warmed, often gives rise to muchcrackling and slight semi -explosions, it isbest not to heat this salt in a glass flask.but to employ instead for the heating anenclosed metal vessel. The nitrous oxideevolved can be collected over hot water, butnot over cold water, for it is substantiallysoluble in the latter liquid. In its properties,it behaves very much like oxygen, many'strongly burning objects, when thrust intoa jar of the gas, still continuing to burnwith great brilliancy.

Another interesting oxide of nitrogen isnitric oxide, NO, which is best made byacting upon copper with nitric acid.

Nitric oxide is a pungent -smelling colour-less gas. When brought into contact withair, however, it combines with the oxygenof the latter, giving nitrogen peroxide,NO2, which is a reddish gas.

Thus, in the experiment illustrated in thephotograph on the previous page, a quantityof copper turnings contained in a test tube isacted upon by nitric acid. The test tube isprovided with a cork through which passesa short length of glass tubing. Nitric oxideis generated within the test tube, and thisgas remains invisible. On issuing from theend of the glass tube, however, it immedi-ately combines with the oxygen of the air,giving rise to brown or reddish -brownfumes of nitrogen peroxide :-

2NO + 02 = 2NO2Nitrid oxide Oxygen Nitrogen peroxide

In a similar manner, nitric oxide com-bines directly with chlorine to form nitrosylchloride. NOC1 :-

2N0 + 012 2N OC1Nitric oxide Chlorine Nitrosyl chlorid

An Orange -Yellow LiquidNitrosyl chloride is an orange -coloured,

pungent -smelling gas which, when passedthrough a U-tube immersed in a mixture ofice and salt or a similar freezing mixture.condenses to an orange -yellow liquid whichboils at a temperature of about -8° C. Ifnitrosyl chloride is passed into water, it isdecomposed into nitrous acid and hydro-chloric acid.

Nitrosyl chloride may also be preparedby gently heating a mixture of 1 part con-centrated nitric acid and 3 parts concen-trated hydrochloric acid. In this instance,chlorine is produced in addition to thenitrosyl chloride, but when the mixed gasesare passed through a tube immersed in afreezing mixture, the nitrosyl chloride con-denses readily, while the chlorine passes on.

By acting upon silver fluoride withnitrosyl chloride, a rare gas. nitrosylfluoride, NOF, is produced. The properties,however, of nitrosyl fluoride have been littlestudied.

Nitrogen peroxide, NO2, may be used toprepare an interesting compound known ascopper nitroxyl. In order to make this com-pound, all we need do is to pass a slow

(Continued on page 179)


urSteed for the Stage

TlE zoological record of the pantomimeincludes more than one cleverly imper-

sonated animal. Examples of this fact areDick Whittington's cat, the mascot of aLord Mayor of London, and the ass of AliBaba, the panniers of which became jewelcases. The artificial horse has frequentlycavorted on the boards.

This fictitious steed usually necessitatesthe employment of two men. According toan invention which has just been patentedin the United States, the amount of labourrequired in connection with a propertyquadruped will be reduced 50 per cent.The beast in question consists of a skeletonbody, which is carried on the back of theactor, who adopts a stooping posture. Aflexible covering represents the hide of theanimal. The front legs are artificial but theperformer uses his natural walking appara-tus as the hind legs. Consequently, his partmay have a kick in it.

Birds and BlackTHE Minister of Agriculture urges us to

cultivate every square yard of soilavailable. But, though we dig MotherEarth in the ribs with a spade and tickleher with a hoe, she will not laugh in aharvest unless we defend the seed sownfrom those tiny air-raiders-the birds.

An application has been made to patentin this country a method of rendering seedsunattractive to feathered thieves. For thispurpose crude tar has been used in the past;but it is affirmed that this expedient isliable to injure the seeds or to cause delayin their germination. The new invention isbased upon the belief that the wingedmarauders are not enamoured of seedstreated with carbon blacks. The processtherefore comprises the treatment of seedswith substances such as lamp black, gasblack or acetylene black, or a liquid com-position containing a proportion of carbonblack. It is stated that this method hasnot been found to harm or hinder the seedsin any way.

Deep black seems to be the pet aversionof the birds. How they must detest theblack -out!

Buried TreasureI N these days of bombs and bandits an

effective depository will make for thesecurity of money and valuables and there-fore for one's peace of mind. There is aparable of an unfaithful steward who buriedhis talent. It is possible now to follow hisexample but with a legitimate motive. Iam informed that, at low cost, one mayinstall vertically in the ground a home safewhich is operated only by compressed airand which has a set of three keys. Presum-ably such a safe could be constructed in amanner that would defy incendiary bombsand present a powerful obstacle even to theexpert cracksman.

Mechanical Sherlock HolmesTHE X-ray apparatus is eminently

useful in detecting the position offoreign substances. But it is costly andsomewhat cumbersome. A British patent

- has been applied for to protect a devicewhich will not only find, but will alsoremove, metal particles from human bodiesand those of animals. The inventionincludes a source of comparatively weak

usy Inventorsy Dynamo"

electric current, an indicator and a scissors -like arrangement.

A cynic may suggest that, in the dayswhen gold was in circulation, in the case ofa man swallowing a sovereign, such anappliance would have been unnecessary.The Chancellor of the Exchequer wouldhave got it out of him !

Anti,Butting HalterTHE mad bull which runs amuck may

now at least suffer some inconvenience.There has been contrived an anti -buttingdevice for farm animals. The inventioncomprises an appliance of halter -like form,one loop of which encircles the head of theanimal, while another loop surrounds itsneck. The halter contains an electricbattery, so that, when the animal butts, itreceives a shock. Though this is not enoughto electrocute the Creature, it is sufficientto cause the beast an unpleasant sensation,if it be too pushing with its horns. Thedevice can be applied to a cow or a goatas well as to a bull. A mild electric shockwould train the animal to check its impulseto place folk on the horns of a dilemma.It would doubtless be effective in modifyinga bull -fight.

Motor BootsA YUGO-SLAVIAN doctor has thought

out a contrivance for helping peoplewho literally wish to go the pace. He hasdevised an accelerating apparatus for the

The information on this page is specially supplied to"Practical Mechanics" by Messrs. Hughes & Young(Est, 1829), Patent Agents of 9 Warwick Court, HighHolborn, London, W.C.1, who will be pleased to sendreaders mentioning this paper, free of charge, a copyof their handbook, "How to Patent an Invention. '

feet, which is described as " the motorisa-tion of walking by means of motor -drivenroller -boots."

The idea of the invention consists inconnecting the drive shaft of a small motor-carried in a satchel on the back-to twoflexible shafts connected to the rear axles ofthe roller -boots. Thereby the power of themotor is transmitted to them and the bootsare thus set in motion. Started with theleft hand by means of a control wire, aftera few gliding steps, the motor attains fullspeed.

Mercury's RivalTHE motor boots, also by means of the

control wire, can be brought to astandstill. In an emergency a halt may becaused in the same manner as when one isskating on ice. The motorised pedestrian,in a moment, can become an ordinarywalker and vice versa. It should be men-tioned that between the motor and theback of the pedestrian there is an asbestos-plate to keep the heat of the motor from thebody. All the wheels are fitted with pneu-matic rubber tyres.

Should one become fatigued after walkinga long time with the roller boots, if desiredthey can be combined with a seat mountedon a wheel having a movable steering controLThis rest wheel, when not in use, is carriedfolded up hanging on the outside of thesatchel.

Verily, these motor boots will qualify

their possessor to rival lercury. themessenger of the gods, whose feet wereequipped with wings.

Shirt with Zip FastenersTHE evolution of male underwear during

the present century has not beencharacterised by much variation. Theaverage shirt is still planned to be put on ina manner calculated to ruffle the hair,although the American design, which isdonned like a coat, is not unknown on thisside of the Herring Pond.

I note that the British Patent Office hasreceived an application to protect a shirtof a new pattern. The usual frontal openingis superseded by an aperture in eachshoulder. This is opened and closed bymeans of a Zipp fastener. If wished, buttonscan be permanently sewn down the frontof the shirt, in order to imitate the custom-ary opening. It will be appreciated that,with a shirt of this description, the studscan be inserted prior to dressing. This willavoid the risk of dirtying or crumpling theimmaculate garment. Incidentally, it willprevent the wearer from becoming what isvulgarly termed " shirty."

To Stop "Laddering"THE ladder is considered by the super-

stitious as a source of ill luck. Misfortuneand the ladder are certainly associated inthe case of silk stockings. As far as theirhose are concerned, the ladies may indeedhave a run of bad luck.

Yet another process for checking runs inknitted wear has made its debut. It relatesto goods composed wholly or in part ofwhat are known as thermoplastic yarns.According to the complicrted verbiage ofthe abridged American specification, itincludes the step of applying heat at areasto form overlapping staggered spacedcharacters, through the medium of whichcontiguous filaments of the knitted wearare put in partial solution and coalescedthereby, forming a discontinuous band ofuntreated and treated areas at spacedpoints in the knitted wear.

If, without concentrated attention, wecannot unravel the procedure of thisprocess, we trust that, as a result of itsapplication, ladders in stockings will not,like Charley's Aunt, be still running.

Auxiliary Church SeatsACOLLAPSIBLE pew seat has beenpatented in the United States. This

provides auxiliary seats in church when thecongregation overflows the normal sittings.Adjustable seats at the ends of pews in theaisles are familiar but the new device, in thecase of each seat, furnishes kneelingaccommodation for the worshipper sittingimmediately behind.

It is hoped that this supplement to thepew will not collapse at the wrong moment.In the Middle Ages certain monks occupiedseats which they propped up with theirlegs. Consequently, if, through weakness ofthe flesh, they slumbered during the sermon,they, soon found themselves on the floor ofthe Sacred edifice.

Ideal RaincoatFOR a new process recently developed it

is claimed that it enables textile fabricsof all kinds easily to be made waterproofand stainless. The fabrics are rolled throughvats containing a synthetic solution, derived


from coke, limestone and salt. The coatingmay be crystal clear, white, translucent orany colour, and the fabrics can be printedover the coating. It is further assertedthat the fabrics remain odourless, washableAnd pliable in all sorts of weather. Strengthto the material is added by the coatingbut very little bulk. Lately, I am told,there appeared a man's raincoat made ofthis fabric, which weighed less than sixounces. It is affirmed that this coat can befolded and enclosed in an envelope smallenough to be carried in a pocket. Such aparagon of a raincoat should qualify onecheerily to face that mildest form ofadversity-the passing shower.

Dogs in War TimeNOW that the hounds of war have been

unleashed, it has been a problem toknow what to do with our canine friends.

In an air raid the dog might prove to bean encumbrance. Barred from a publicair raid shelter his position and that of hisowner would not be enviable.

To ensure the safety of her Pekinesedogs and puppies, one lady, residing in asuburb of London, has had built an enorm-ous wire spring erection like a mattress tocover the abode of her pets. She hassufficient faith in this construction tobelieve that at least incendiary bombswould bounce therefrom. And there issomething to be said for stout chain nettingas a protection against shrapnel. Likesand, it does not present rigid resistancewhich may cause an impact to bedisastrous.

By the way, a dog -breeder within myken sent eight dogs from the allegedLondon danger zone to somewhere inScotland, in order that they might be safefrom aerial warfare. The suburb of London

in which they lived has, up to the momentof writing, been completely immune,whereas a number of air raids with bombsfalling not far away have occurred in theneighbourhood to which the canine evac-uees were dispatched. Such is the ironyof fate !

WORKSHOP CALCULATIONSTABLES AND FORMULA

2nd Editionby F. J. CAMM

A handbook (baling with methods of calculation,solution to workshop problems, and the rules andformula' necessary in various workshop processes.It contains all the information a mechanic normally

requires.From all booksellers, 3/6 net,by post 3/9 from the publisher :

GEORGE NEWNES LTD. (Book Dept.),Tower House, Southampton St., London. W.C.2

A Novel Camera SightFitting a Head and Cross Wire Sight to a Hand Camera

THE standard- view finder fitted tomost hand cameras is a practicallyuseless fitment for the speed Worker.

It is only good enough if there is time tostudy the picture carefully and then onlygives an apprOximate idea of the positionof the image which will later appear on thefilm. It is rarely accurate, because beingso small, only giving a picture about 1/50of the size of the actual image, exactadjustment is nearly impossible. Further,no adjustment is made to balance anyalteration in the focal adjustment of thelens, and -although- the register may begood at 50 feet the error at five feet may belarge. Further, the picture being so small,

so _a well finished device was then made.The sight does not indicate the size of thepicture, but ensures that the object is inthe centre of the screen. Very little addi-tions have to be made to the camera andthe sight is easily assembled or dismantledfrom the camera for transport.The Sight Bar

Fig. 1 shows the general arrangement.Two fixings are required, one at the back ofthe camera and the other at the front. Thefront fitting is a sliding one to allow forfocusing adjustment of the camera. Thelength of the sight bar is governed by the

small objects at a distance become too tinyto observe. Thus an aeroplane at 200 feetcannot be observed with any certainty inthe view finder. Then the oblong pieces ofwire fitted to cameras and called directvision finders, although an undoubtedimprovement, are again not too accurate,they only giving the area of the picture andits approximate position.

Moving ObjectsIn order to get shots of birds on the

wing, or an aeroplane diving, or in fact anyfast moving object, another system offocusing the camera on the object andkeeping it there, rock steady and centralon the film is necessary. The bead andcross wire sight, used on aircraft guns, wastried out, at first by twisting pieces of wireon the camera, and in taking some shots ofmoving objects. These proved promising

Fig. 1.-The general arrangement of the sigh ingdevice

angle of the lens, but should be as long aspossible withimt coming into the field of thelens. The bar is made from 3/16 in. x3/16 in. brass bar, and is secured to the backbracket with a terminal nut, run on a pieceof 6BA studding tapped into the end of thebar. The back bracket, shown in detail inFig. 2 is made of 1/16 mild steel and issecured to the body of the camera with aterminal nut, on a short screw tapped intothe body of the camera with the head of thescrew inside. The bracket is slotted from thetop and is graduated on the front face toregister with a scratch line on the side ofthe sight bar.

The Front BracketThe front bracket, the design of which

will have to vary considerably with each

DEAD

SPRING PIVOT WASHER

Fig. 3.-Details of the back sight

camera, is fitted either with screws tappedinto the carriage front or gripped behindthe shutter casing. The top of the bracketcarries a square sleeve, made to be anaccurate sliding fit on the sight bar and issoldered to it. The back sight is shown indetail in Fig. 3. The sight bar is slotted sothat the back sight can be folded down outof the way when not required. The backsight can be of thin mild steel sheet pivotedand shaped as shown, the spring under-neath the bar, held by the screw tappedinto the bar, holding it either up or downsecurely, by pressure on the flats. The beadcan he a small ball of brass or a tiny blackglass bead, fitted on a spike filled at the tipof the vane. - The front sight consists of abrass ring or a piece of tube soldered to thefoot which is arranged with two flats topress against the spring as in the case of theback sight. The actual cross wires can bemade in several ways. They can be of 47 or48 SWG 'enamelled wire soldered across thediameter of the ring, or very fine scratchesmade across a piece of clear celluloid andfilled with Indian ink, or spider's web threadlaid down on a disc of glass.

Adjusting the SightHaving. made all the pieces, fit them to

the camera and adjust the sight in thefollowing way. Remove the back of thecamera and place a piece of grained glasson which are drawn fine pencil lines fromcorner to corner, into the back. Set up thecamera on a steady base and place a candleor a pocket lamp at a measured distancefrom the camera. Move the camera untilthe image is at the intersection of the lineson the grained glass. Then adjust the sightwithout moving the camera to get the beadat the intersection of the cross wires in thefront sight and dead in line with the object.Mark off the sight adjustment on the backbracket, and proceed to the next distance.If you require practice try shooting at atennis ball thrown into the air.

WASHER SP NC PIVOT

Figs. 2 and 4 (above).-The back bracket. (Right) The front sight


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176 NEWNES PRACTICAL MECHANICS Jan uary, 1940

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Practical Mechanics HandbookBy F. J. CAMM

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Fig. 1. (left)-Sword for catching a handkerchief. The blade is hollow and an elastic cord running through it brings the handkerchief out of the hilt to the point.Fig. 7 (right). Pistol with tube for vanishing various objects. Note how the secret container is palmed out

Weapons For WizardsIngenious Devices that help to make the Conjurer's Armoury Baffling and Surprising

THE sword illustrated in Fig. 1 wouldnet be of much use against an enemy.But for providing the conjuror with

a silk handkerchief whenever he wants it,it is perfect. A pass in the air and thehandkerchief appears on the tip of thesword.

The blade of the sword is hollow. Alength of strong cord elastic is attached tothe hilt just inside the hollow blade. Itpasses along inside the blade and out at thepoint, where it terminates in a small pointedhook. The hilt of the sword can be removedwhen the elastic wears out, so that a newpiece can be inserted. There is slight tensionon the elastic and this keeps the hooknormally drawn up against the tip of thesword. To prepare the weapon for use, asilk handkerchief is impaled on the hookand the elastic is drawn down until thehandkerchief can be concealed in the handholding the sword. The performer presentsto the audience only the side of the swordwhere the elastic is not visible. A sweeping

Fig. 2.-An improvedtype of foiled sword with

a false hilt

ETAILS OF CATCH

HANDKERCHIEFCONTAINER TO

OPEN

handkerchief is released and flies to thepoint, appearing to be caught on the sword.

An ImprovementFig. 2 shows an improvement to allow

the sword to be picked up at any timeduring the show without the necessity of

B Norm anHunter(The Well-known Conjurer of

" Maskelyie's Abisteries")

Further Articles on the Secrets ofConjuring will appear Regularlyand Exclusive_ly in this Journal

going off-stage to get the handkerchiefready in the hand. This consists of a tubeattached to the hilt of the sword and fitted

SEPARATE TIP

ELASTIC

END OF HOLLOWSWORD BLADE

Fig. 3.-This type ofsword is used for im-paling on the sword acard chosen by the

audience

with a cap. The cap is hinged and helddown by means of a small catch. The hand-kerchief, attached to the elastic, is tuckedinto the tube, the cap closed -and the catchfastened. In this state the sword may befreely handled and the handkerchief can bereleased at the right moment by pressure ofthe thumb on the catch.

The sword shown in Figs. 3 & 4 is adaptedfor quite a different purpose though the prin-ciple is similar Here, the trick consists ofimpaling on the sword, a chosen card, whenthe whole pack is thrown into the air.

The blade is hollow as before and isfitted with elastic which, however, _in thisease terminates in a metal tip which fits onthe end of the blade. The blade is triangularin section and the tip is cut off. The elasticemerges from the cut-off point and isfastened to the loose tip as shown. To thehilt of the sword is attached a kind offrame large enough to hold a card. Thecard has a slit cut in the centre throughwhich the tip of the sword is passed. Theelastic is then ,stretched and the card in-serted into the frame. It is an easy fit andneeds pressure of the thumb to retain it, ora small catch may be fitted if desired. Acard, duplicate of that on the sword, isforced by one of the methods alreadydescribed in this series. The card is shuffledback into the pack, which is given to aspectator. The sword is then brought for-ward and the performer stands in a fencingattitude with his right side turned towardsthe audience. In this position the handholding the sword completely screens thecard holder, on i he hilt. The spectator is

.

Fig. 4.-How the cardis held in position in the

hilt

ELASTIC

CARDL. -HOLDER

SWORD TIP

4,t


asked to spread out the cards in a fan andthrow them well up into the air. As theyscatter in a shower a lunge is made into theirmidst, the card is released and flies to thetip of the sword, where it appears to havebeen caught from the falling pasteboards.

Fig. 5.-A special typeof sword suitable for

"swallowing"

DRUM OFSPRING TAPE

RIGID STEEL. TAPE

SWORDHILT

Catching Three CardsThree cards instead of one may be caught

with this sword by making in the secondand third cards triangular holes of succes-sively larger dimensions. The three cards arefitted together in the same way as the singlecard. When released the cards fly to thepoint of the sword, one will settle downabout half -way along the blade and theother will slide almost to the hilt, owing tothe different -sized holes made in them.

Sword swallowing, though outside therange of ordinary conjuring tricks, can beeffectively imitated with the special swordshown in Fig. 5. The blade in this case is ofthin spring steel, exactly the same as thesteel tape measures which can be rolledinto a coil and yet will remain rigid whenpulled out. A sword of this type is quite asimple job to make. First a hilt is con-structed of wood with a metal guard.Within the guard the container of the steeltape is fitted so that the metal strip can bedrawn out through a slit in the properposition. With the blade pulled out to asuitable length the sword appears quiterigid yet it can be apparently swallowedwith ease by gripping the tip between theteeth and gently pressing the hilt down.The blade winds up in the hilt and conveysthe impression of passing down the throat.It is then withdrawn by reversing theaction.Catching Oranges

Fig. 6 shows a sword for catching orangesfrom the air. A metal arm is pivoted mid-way along the blade so that it can lie alongthe blade either towards the point ortowards the hilt. A spring is fitted whichkeeps the arm normally resting towards thepoint, but a catch is fitted to the hilt bymeans of which the arm may be held backin its reverse position. An orange is im-paled on the end of the arm and the arm isheld back against the hilt. Under cover of aslashing movement the catch is released,the arm springs rapidly over, bringing the orange to the point of the sword. If it isdesired to produce several oranges, the armis again swung back under pretence ofremoving the orange and an alreadypalmed orange is brought into view inplace of the one attached to the arm. Thispalmed orange is openly placed on aplate and the sword can then be used tocatch another, and so on.Magical Pistols

Now we come to magical pistols. The

device illustrated in Fig. 7 is an old, butstill very useful attachment to a pistol forthe purpose of apparently shooting themat some given target. It consists of a metaltube fitting snugly on to the muzzle of thepistol. To the tube is attached a metal

Fig. 6.-A swordfor catching oranges

in the air

-.. ....... ........."--HOW PIVOTED ARMSPRINGS ROUND

ORANGE HIDDENIN GUARD

funnel and fitting loosely in the mouth ofthe funnel is a metal cup. The completething is shown in section in Fig. 8. With thecup in position, the inside of which, as wellas the inside of the funnel, is painted deadblack, the pistol is brought forward and thearticle to be vanished is wrapped in paperor in a handkerchief and tucked into thefunnel. The conjuror then transfers thepistol from his left hand to his right,the right hand taking it by the mouth ofthe funnel, while the left hand moves someobject into position or else guides avolunteer assistant to where he is to standto fire the pistol. The pistol is then taken

Fig. 8.-An attachmentto a pistol for the pur-pose of apparentlyshooting oranges at some

given target

back again by the butt and the right handpalms out the loose cup by gripping theprotruding edge, as shown in Fig. 7. Thepalmed cup can then be passed off fqr thecontents to be placed in whatever apparatusit is eventually to be found while the pistolcan be harmlessly discharged and thefunnel shown to be empty.

Vanishing a WatchA very subtle vanish of, say, a watch,

can be managed by the use of this pistolfunnel as follows. A handkerchief isgathered up by the corners and tucked intothe funnel, the loose cup being inserted on

WINDING KNOB HOOK

Co SPRINGDRUM

RELEASECATCH

Fig. 9.-A pistol forvanishing a handker-

chief

top of it. A borrowed watch is wrapped ina duplicate handkerchief and tucked intothe funnel, really going into the cup. Thewatch and handkerchief are then palmedout and disposed of ready for the finish ofthe trick. After the pistol has been fired,the duplicate handkerchief is withdrawnand shaken out, proving that apparentlythe discharge of the pistol has shot thewatch off to its destination, but left thehandkerchief behind. By borrowing a whitelinen handkerchief in which to wrap thewatch and having another white linenhandkerchief, torn and with burned edgespreviously packed into the funnel, a gooddeal of fun can be had at the expense of theowner of the handkerchief. One whitehandkerchief is nearly enough like anotherfor the purpose of the illusion and the per-former can say, " Well, we can see what'shappened to the handkerchief, but the fateof the watch remains a mystery. Still,judging by this," holding up the damagedhandkerchief, "I don't think we need worrythat there is much of the watch left totrouble' about."A Variation

For visibly vanishing a watch from theend of a pistol, a device something like theorange -catching sword, but working' thereverse way, is used. The pistol has a springarm, pivoted part way down the barrel.There is a clip on the free end and this endis held against the muzzle by a catch whichis released when the trigger is pressed andthe arm swings round, bring the free endagainst the butt and out of sight of theaudience behind the hand of the performer.The watch is attached to the arm byslipping the loop of the watch into the clip.

A pistol for visibly vanishing a handker-

CUP

chief can be constructed in various ways.Fig. 9 shows details of a simple methodwhich can be attached to an ordinary cappistoL The pistol in this case is of theautomatic type and the attachment consistsof a length of tube soldered along the barrelon the side which it is intended to keepaway from the audience when using theweapon. In this tube is a spring roller,operating in much -the same way as a rollerblind. There is a wide slot in the outertubing and a sharp hook is fixed to thespring roller. The handkerchief to be

HOLE

SPRING

HOOK

CATCH CONNECTEDTO TRIGGER FORRELEASE

Fig. 10.-Another typeof gun for vanishing

a handkerchief

January. 1940 NEWNES PRACTICAL MECHANICS 179

stream of nitrogen peroxide over finely -divided metallic copper (prepared by thereduction of copper oxide in a stream ofhydrogen). The finely -divided copperrapidly absorbs the nitrogen peroxide, form-ing a brown compound, which is coppernitroxyl, Cu5NO5.

Copper NitroxylNow, when this copper nitroxyl is heated,

it is decomposed into metallic copper andnitrogen peroxide. Thus, if we enclose aquantity of copper nitroxyl in one limb of a

Fig. 11.-Cannon that vanishes handkerchiefs. The barrel contains a powerfulspring which winds up the silk

vanished is draped over the pistol and thecentre secretly engaged in the hook. Whenthe spring is released the silk is rapidlywound up inside the tube by the spring roller.

The ReleaseThe release is connected to the trigger as

shown in Fig. 9. At the butt end of thetube is a thumb wheel for winding theSpring and attached to this is a cog. Apiece of wire bent to form a lever is pivotedto the pistol so that it engages the cog andstops the spring unwinding. The other endof the wire is soldered to the trigger. Whenthe pistol is fired, the movement of thetrigger not only explodes the cap, but alsoreleases the spring and so causes the hand-kerchief to vanish.

A gun on a Blighty different principle isshown in Fig. 10. Here there is a powerfulexpansion spring in the barrel, to the endof which is fixed a metal plug with a hookto engage the handkerchief. The spring isextended by pushing a metal rod throughthe breech of the gun and a catch holds thespring extended at the muzzle. This catchis connected to the trigger so that firing thegun also releases the spring and performsthe vanish. The gun, having a long barrel,can be used for the disappearance of a fairlylarge silk handkerchief.

A card may be vanished by means of apistol similar to the automatic pistol forvanishing a handkerchief. In this case theslot in the tube covering the spring roller ison top, and is slightly longer than the widthof a card. A slot in the spring roller engagesthe edge of the card which is thus fixedupright on the barrel and is rapidly rolledround the spring roller when the trigger ispressed.

Miniature CannonSomewhat on the

same lines is theminiature cannon,shown in Fig. 11.Here the springroller is actuallyinside the barrel ofthe cannon andinstead of a bookbeing used to attachthe handkerchief,there is a hinged barwhich closes acrossthe handkerchief.When the cannonis fired the springroller inside thebarrel rapidly windsthe handkerchiefout of sight.

Another .cannon,to cause the dis-appearance of anumber of borrowedarticles, has an in-ner lining to the

barrel. This inner lining is closed at thebreech end and slides easily within the barrel.The breech of the gun proper is eitherhinged or made to slide hack. The articlesto be vanished are dropped into the barrelwhile the latter is moved to a- verticalposition. In this condition the breechis opened secretly, the movement beingconcealed by the sides of the guncarriage, and the inner lining drops

Figs. 12 and 13.-(Left) A bow andarrow fitted with afine wire. (Right)A bow that vanishesits arrow. Whenthe arrow is releasedit flys up into the

bow as shown

through into an open well in the table. Thebarrel with breech closed is then levelled.a little flash powder is put into the muzzleand fired, after which the barrel may beshown empty and duplicates of the vanishedarticles produced from whatever apparatus

it has previously been decided to aim themat.

Bow and ArrowFinally, here are two more primitive

weapons adapted to conjuring needs. Thebow and. arrow.

Fig. 12 shows a bow with an arrow fittedwith fine wires at each side. With thisweapon the conjurer can let fly the arrowbehind his back and cut a strip of paperheld some distance away. His aim need beonly approximate since the wires project-ing from the arrow will tear the paper if thearrow goes wide.

Fig. 13 is a bow that vanishes its arrow.The arrow is permanently attached to thebow, being pivoted as shown between twoshaped pieces of plywood which form thehow. The bow with arrow in position fOrletting fly is either brought on or picked upfrom a table near the rear of the stage. Thebowstring is of cord elastic and thisstretches instead of the bow itself pro-viding the spring. When the arrow isreleased, it flies up into the bow by theaction of a small spring. The trick is com-pleted by the appearance of a duplicatearrow in the target. This duplicate arrow ishinged by its point to the gold (or bulls eye)and rests in a slot running across the target.When the release is pulled the arrowsprings out at right angleS and appears tobe sticking into the target. The two piecesof apparatus can be tit d with a sheet ofglass between perfornier and target, thearrow apparently passing through the glasswithout damaging it.

SPRUNGPIVOT

HOW ARROWSPRINGS UPINTO BOW

ELASTICBOW STRING

CHEMISTRY. FOR BEGINNERS(Continued from page 172)

bent glass tube and seal both ends of thetube, the copper nitroxyl, when heated, willgenerate nitrogen peroxide within the tube,which, under the influence of -its owninternal pressure will condense to a liquidin the other limb of the tube.

Similar nitroxyls can be made with themetals iron, cobalt and nickel when in thefinely -divided state.

Incidentally, liquid nitrogen peroxide mayalso be prepared by heating dry lead nitrateand by passing, the evolved gas througha L' -tube cooled in a freezing mixture.

./

Nitrogen peroxide must always be kept inthe dry condition, for it is decomposed bywater into a mixture of nitric and nitrousacids.

The necessity of taking elementary pre-cautions when experimenting with ammoniagas is self-evident. In much the same way,the other gaseous oxides of nitrogen shouldnot be breathed in any amount. since theyare more or less poisonous. For thisreason, therefore, it is recommended that allsuch experiments by prepared either out ofdoors, or in a well -ventilated outhouse, orin a room whose door and window areallowed to remain open, thus setting up acurrent of air and enabling the room toremain continuously ventilated.


A Winch for GlidersThe Winch Described can be Firmly Held to the Ground with oneFoot, Leaving One Hand Free to Manoeuvre it, or to Play the Line

THE F.A.I. method of launching glidersnecessitates the use of a winch, andthe winch described here will be found

suitable for launching any model glider, andthe drum is fully capable of taking the 655 ft.of tow line, without any danger of it becom-ing entangled.

When launching gliders, it is necessary tohave a winch which is very strong and canbe easily manoeuvred.

Because of this, the winch which can beheld in one hand and wound with the otheris very difficult to handle even when only asmall glider is being flown.

It is far easier to have a winch of the typedescribed here, which can be firmly held tothe ground with one foot: leaving one handfree to manoeuvre the winch, or to play theline.

First OperationsObtain a piece of hard wood, approxi-

mately if in. x in. and round off theedges.

Then bend a piece of flat Mild steel, stripapproximately f in. x I in. to the shapeshown, and drill two f in. dia. holes at A andB.

Drill two f in. dia. holes through the pieceof hard wood, as shown on the drawing,arid file off any rough edges which areto be found.

Buy a winder geared approximately8-1.

A grinder without the grinding wheel,,,which can be purchased from any hard-'ware store is most suitable.

'Then cut a circular piece of wood 4 in.in dia. and I in. thick, and slightly roundthe edges.Two thin plywood sides approxi-mately 8 in. dia. should then be cut.Cement or nail these on each side of thecentre block, and make sure that there areno rough edges which could damage thethread.

Drill a A -in. dia. hole through the centreof the drum.

The DrumFit the drum on to the spindle of the

winder and then tighten up the nut on thethreaded end of the spindle. A washershould be fitted between the nut and thedrum. A second nut should then be fittedand tightened up to prevent the first nutfrom slipping..

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The metal foot rest can now be fitted tothe wooden shaft by slipping two f -in. boltsthrough the holes as shown, and tighteningthe two nuts on the outside. The windercan be firmly screwed on to the shaft at theheight most convenient to the flyer. Itis very helpful if the top of the shaft isshaped into a handle which can be easilygripped -

When using the winch, the flyer shouldput one foot in the metal foot rest and graspthe top of the shaft with one hand.

The other hand is used for turning thehandle of the winder.

As the glider gains height, the shaft can beslowly tilted backwards, and should theglider go to the right or left, the winch caneasily be turned in the same direction with-out having to stop winding in the line.

GUIDE

8 DIAWINDER (GEAREDAPPROX 8:1)

4*DiA.CENTRE

SHAFT APPROX Iyti"x 5/84'

Fitting a GuideIt is very helpful to fit a guide, for the

thread, to the winder as shown. This shouldbe bent from 16 s.w.g. or 14 s.w.g. Anythinner wire will have a great tendency tosway about, and will be of little use. Makesure that there is no chance of the threadbecoming entangled or damaged on theguide. This winder is easy to make and isvery simple to operate. "

The best method of fixing the thread tothe drum, is to pierce a small hole in one sideof the drum, pass the end of the threadthrough it and securely knot it on the out-side.

This obviates any chance of thethread slipping when tEe line is fullyextended.

Constructional details of the winch for launching model gliders

Jant.nry, I 31. ) NEWNFS PRACTICAL MECHANICS 181

MASTERS OF MECHANICSNo, ;2-THE WONDERFUL DOCTOR

The True Story of Roger It acon, First of the English ScientistsSOME three centuries ago there was

translated into English a book entitled" The Famous Historie of Fryer

Bacon," in which Roger Bacon, the famousFranciscan friar, was credited with havingbeen capable of all sorts of black magic.

In the " Famous Historic " weread how Bacon was able to summonstrange and beautiful music fromnowhere, and how, at his merebidding, a table could becomecovered with the richest andchoicest wines and fruits of theworld. Here, also, we read theabsurd story concerning " FriarBacon's Head," a brazon head whichRoger Bacon was supposed to haveconstructed and which was capableof speech.

And finally, in this supposedHistory, Bacon is made to end hisdeath in a cell after having madea bonfire of all his magical writingsand having duly committed thesecrets of his Art to the flames." His grave," the " Famous His-toric " concludes, " he digged withhis own nayles, and he was laiedthere when he dyed."

Man of Myster%Now, unfortunately, all this tissue

of nonsense has had its effect uponthe historical, or, rather, upon thequasi -historical character of RogerBacon, so much so that evennowadays he is commonly investedwith quite an unnecessary amountof mystery and glamour as if hehad constituted a sort of scientificRobin Hood or Friar Tuck.

It is only within comparativelyrecent times that the truth con-cerning Bacon has been ferretedout, mainly by means of a carefulstudy of those writings of his whichhave managed to survive the passing of time.Such studies show us that, far from being acharlatan, or a would-be common prac-titioner of so-called " black magic." Baconstands out in the annals of British scienceas almost a second Archimedes, and certainlyas the first English scientist and experi-menter of whom we have any record orpositive knowledge.

Roger Bacon, the Franciscan friar, wasborn near Ilchester, in Somersetshire, inthe year 1210 according to some authoritiesand in 1214 according to others. He seemsto have come from a very wealthy familywho sacrificed most of their fortunes' onbehalf of King Henry III in his strugglewith the Barons from 1258 'to 1262. Rogergrew up to be a studious youth, and, afterbeginning his stuei_.s at home at the age ofthirteen years, he proceeded to the Uni-versity of Oxford, where he came under thetuition of Edmund Rich (afterwards Arch-bishop of Canterbury), and also becameacquainted with another of Rich's pupils,one Robert Grosseteste, who subsequentlybecame Bishop of Lincoln.

Incidentally, it was this latter individualwho was originally connected with thefabulous story of the Speaking Head, thelegend becoming attached to Roger Baconat a later date.

The ClergyWe have now to bring to mind the fact

that in the days of Roger Bacon there wasno science at all worth speaking of in thewhole of Europe, let alone in England. Allknowledge was in the hands of the clergy,

Typical of ,the crude mechanical contrivances impnzed by RogerBacon is the old English waterwheel, a device which still has its uses

who, as perhaps was only to be expectedfrom the manner of their lives, fastened itdown to the study of theology and of the oldGreek and Roman philosophies. True it isthat there had flourished before the time ofBacon the renowned St. Thomas Aquinas(1125-74), one of the greatest and mostbrilliant intellects which the world has everseen. But Aquinas gave his life over to theformulation of a comprehensive system ofTheology and Philosophy, which, howeverexcellent it may be, did not, in any sense,attack the many practical problems whichwere waiting to be investigated in thedomain of what we now term " NaturalPhilosophy."

Nevertheless, at this time, the ancient" scientific " culture of the old Greeks beganslowly to spread throughout Europe, chieflyas a result of the writing of several Arabianthinkers, and for the development of thisscientific spirit of learning in Englandalmost in the very middle of the " DarkAges " we are indebted to a small group ofFranciscan Friars who were mainly led bythe previously mentioned Robert Grosse-teste, afterwards Bishop of Lincoln.

It was this little coterie which RogerBacon joined after he entered the Fran-ciscan Order at Oxford. He had thenstudied at the great University of Paris,

and, returning to Oxford in 1250, he seemsalmost immediately to have launched upona twenty -years career of experimentalinvestigation, for he tells us that during thatperiod he expended upon books and instru-ments no less than two thousand pounds,

the bulk of which was subscribed byinfluential friends.

A Career of ExperimentBacon, in setting off upon a career

of experiment, went directly counterto the prevailing notions of hisday. Right up to the dawn of theNew Learning and the birth of theScientific Era, it had been heldthat if it was not exactly morallywrong to perform experiments, itwas certainly totally unnecessaryto do so, for all the knowledgeattainable about the natural orderof things around us was containedin the writings of the Greekphilosophers, notably those ofAristotle. Thus if in those daysyou wanted to know how manyteeth an adult horse normallyhad, you endeavoured to lookup the problem in Aristotle. Youwould never, unless your wereahhost hopelessly degraded, referthe problem to an actual inspectionof the horse's mouth.

Incredible as it seems in ourpresent age, it was this slavish

otherancient philosophers which suc-ceeded in delaying the oncomingof experimental Science for manylong centuries.

Gradually, however, the urge toexperiment, the ambition to find outat first hand some of the essentialfacts concerning things around ussucceeded in overcoming the pre-vailing servitude to the works of the

Greek philosophers, and from this growingdesire for experiment came into existencethe first fundamentals of modern Science.

That Bacon was England's first experi-mental scientist there seems to be no doubt.In many ways, also, he was one of the firstmartyrs of Science, for, although he wasnot actively persecuted by the Churchauthorities of his day, he at least fell foulof them for a time and incurred their activedispleasure.

" Natural Science."Perhaps Bacon treated his fellow clergy,

or wrote about them, with a greater amount.of candour than of tact. He spoke so freelyon the prevailing ignorance of the timeand he became so enthusiastic in his devo-tion to what we call nowadays " NaturalScience " that he found himself inhibitedfrom lecturing to his students at Oxford.Later, in 1257, he was, by command of theGeneral of the Franciscan Order, sent to theParis House of the Franciscans and therehe remained under very close intellectualsurveillance for some ten years

Perhaps Friar Bacon would have stayedat Paris for the remainder of his life had itnot been for the fact that one Guy deFoulques, an ecclesiastic whom Bacon knewand who was unusually broadminded


became Pope in 1265, taking the title ofClement IV. Knowing the new Pope'sphilosophical inclinations, Bacon sent apetition to him from Paris, offering to writedown his own system of natural philosophyfor the benefit of the world. In the follow-ing year, Clement IV wrote to his " belovedSon, Friar Roger named Bacon, of the Orderof Friars Minor," and invited him to com-pose the projected works, which, withinanother eighteen months, were forthcomingunder the titles of "Opus Magnus," "OpusMinus," and " Opus Tertius," the latterbeing a sort of recapitulation of the twoformer " Works."

These works, in 1268, gained for Baconpermission to return to Oxford, which he didimmediately. Settled once again in Oxford,the Friar commenced an encyclopaedicwork, a " Compendium of the Study ofPhilosophy," which was published in 1271.But this, again, did not please the Oxfordclerics. Moreoever, his friend and protector.Pope Clement IV, died, and soon afterRoger Bacon was charged with dabbling inthe occult and magical arts. His writingswere condemned, and he was once moretaken to Paris. Here again, despite thefact that he was now 64 years of age, hewas again more or less confined to the ParisHouse of his Order, and, this time, theconfinement lasted for fourteen years.Nothing daunted, however, Friar Baconoccupied this long period in further studiesand in the composition of books on a widerange of subjects.

WaterwheelsWhen eventually he was allowed to return

to his beloved Oxford in 1292, Bacon wasnow an old, although by no means a brokenman. Returning finally to Oxford, he wrotea " Compendium of Theology." His listdays seem to have been spent in completetranquillity, and peace, and he died at theage of 79 on the 11th of June, 1294. Hewas buried in the Church of the Franciscansat Oxford, but all traces of his last restingplace have long since disappeared.

Bacon's contributions to early scienceand mechanics are many. He appears tohave been an authority on waterwheelsand windmills and on various types ofmachinery, although never, so far as we canascertain, did he hit even dimly upon theidea of the steam engine.Scientific Prophecy

Yet in his various writings, Roger Baconshows an amazing trait for scientificprophecy. R'ad, for instance, the followingpassage from one of his earliest treatises,' On the Marvellous Power of Art andNature "

" First, by the figurations of art, theremay be made instruments of navigationwithout men to row them, as great shipsto brook the sea, only with one man tosteer them, and they shall sail far moreswiftly than if they were full of men : alsochariots that shall move with unspeakableforce without any living creature to stirthem. Likewise, an instrument may bemade to fly withall if one sit in the midst ofthe instrument and do turn an engine bywhich the wings, being artificially composed,may beat the air after the manner of aflying bird."

Most people remember Friar Bacon forhis supposed invention of gunpowder. Itwould seem that Bacon actually madegunpowder and gave sundry demonstrationsof its exploding force (which, no doubt,by no means tended to disprove his claimof having nothing to do with the " BlackArts "). The more, however, we go into thecircumstances of Roger Bacon and gun-powder, the more we become impressed

with the idea that he was not the actualcreator or inventor of this material. Itwould appear that he obtained the basicidea of employing a mixture of nitre,sulphur and charcoal from some oldArabian alchemical work.

GunpowderBut Bacon made the best of his work on

gunpowder, and, as was the wont of histimes, hid the information concerning itin a great mass of wordy writing. Hesays :

From Salt Petre and other ingredientswe are able to make a fire that shall burn atwhat distance we please. Sounds likethunder, and corruscations, may be formedin the air, and even with greater horrorthan those which happen naturally; for alittle matter, properly dispersed, about thebigness of a man's thumb, makes a dreadfulnoise and occasions a prodigious corrusca-tion, and this is done in several ways; bywhich a city, or an army may be destroyedafter the manner of Gideon's Stratagem,who, having broke the pitchers and lampsand the fire issuing out with an inexpressiblenoise, killed an infinite number ofMidianites."

Bacon's little matter, properly dis-persed," has indeed in subsequent historycarried out the promise of this first investiga-tor of the powers of explosive substances.

OpticsOf the subject of Optics (which he called

" Perspective ") Bacon had a considerableknowledge. It is on the cards that heinvented and actually used a crude type ofmagic lantern or optical projector yearsbefore it was first introduced in theseventeenth century by Kircher, of Rome.Although Bacon did not invent the tele-scope, he did construct several types ofmagnifying glasses. It has been conjec-jured, also, that he had much to do with theintroduction of spectacles, for these nowa-days often indispensable aids to visioncertainly first became used in his time.

Although Bacon was not exactly a

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mathematician, his knowledge df mechanicsenabled him to devise many simple types ofinstruments and tools which were whollyunknown in his time. He dabbled inalchemy, but, so far as we can see, heproduced nothing worth while as a result ofhis chemical efforts.

Bacon's ClaimProbably Bacon's greatest claim to being

the " First of the English Scientists " restsnot upon the few scientific inventions orimprovements which he brought about, butupon his instigating in our country the truespirit of scientific investigation. And thisclaim still stands in spite of the fact thatfor a couple of centuries after Bacon's deathScience in England remained very much ata standstill.

Roger Bacon undoubtedly liyed before histime. His classification of the sciences into" perspeCtive (optics), astronomy, thescience of weights, alchemy, agriculture andmedicine " was undoubtedly a bold and arevolutionary one. So also was FriarBacon's conception of the elements ofnational prosperity and success-" a fertilesoil, busy workshops and easy conveyancefor men and commodities from one place toanother," a dictum which remains truedespite its six centuries of age.

The "Wonderful Doctor "When Roger Bacon died, his fellow clerics

and his pupils referred to him as the" Doctor Mirabilis," the " WonderfulDoctor," and such he undoubtedly was inhis lifetime. Now that the spurious auraof fanciful mystery and deceit has beenstripped away from the life -history of FriarBacon, we see him as one of the long line ofgreat Englishmen, a scientific and amechanistic pioneer, and, curiously enough,a strange forerunner of anotber Englishscientific thinker, Sir Francis Bacon, whowas born in London more than three and ahalf centuries after the decease of the" Doctor Mirabilis."

Both these Bacons adopted a similar anda fundamental attitude to scientific research,but if number and weight of works is anyreal measure of a man's true calibre, theolder Bacon, who remained throughout hislife a brown-habited friar of the Fran-ciscan Order, was by far the superior of thetwo.

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ADDRESSICS


CONNECTING RODPISTON ROD

Figs. I and 2.-Connecting rod andthe crank mechanism of a steam engine

Fig. 3.-Diagram showingthe forces producing side

thrust on a piston rod

WHATEVER the source of energyutilised for the performance ofmechanical work, whether it be

steam, electricity, internal combustion oranything else, some mechanics is usuallyneeded to convert that power into theform necessary for the particular type ofwork in hand. For instance, in the case ofthe ordinary steam engine the power issupplied in a reciprocating form, that is,by a piston which moves backwards andforwards, whereas it is usually required in arotary form. The necessary conversion istherefore carried out by means of a con.fleeting rod and crank.

Connecting Rod and Cranks SystemsAn illustration of the steam engine

system of conneetingrodAnd crank is givenin Fig. 1. The fact that steam is fed to boththe top and bottom of the piston alternatelynecessitates the use of a rod known as thepiston rod, which operates through a steam -tight gland in the end of the cylinder andtransmits the power from the piston to theconnecting rod. The piston rod is really anecessary evil, for it does nothing in itselfto convert the direction of the piston'smotion. It is employed merely to conveythe motion of the piston to the little endof the connecting rod, without allowing theescape of useful steam from the cylinder.Its external end slides between two guides.Of course, without these guides it wouldtend to warp or bend with each thrust ofthe piston. the greatest strain being when

Fig. 5.-The arrangement ofthe cranks in a 4 -cylinder engine(three -bearing crank shaft)

TransmissionAn Analysis of Some of the

etter-known Devices forTransmitting the Drive fromthe Source of Power to Work

It

the crank is roughly at right angles to theaxis of the cylinder. Fig. 3 shows how theforce of the piston and resistance of theconnecting rod resolve themselves into thisside thrust on the end of the piston rod, thusnecessitating the use of guides.

In the internal combustion engine, asemployed in motor cars, motor cycles andmodel planes and speed boats, the drivingforce is confined to the top of the piston,therefore the use of piston rod and guiderods, etc., is entirely dispensed with.Fig. 4 shows how the little end of theconnecting rod is pivoted directly inside thehollow piston.

This form of transmission can he madeextremely difficult especially if the mainbearings of the crankshaft and the big endof the connecting rod are carried on ballor roller bearings. It suffers, however,from that one disadvantage associated withall reciprocating systems, due to the weightof the reciprocating parts. This weight notonly reduces the speed of acceleration anddeceleration, but tends to produce vibration.Even with the weight of the piston andconnecting rod most carefully balanced bymeans of counterweights incorporated inthe cranks or flywheels, vibration is likelyto manifest itself at high speeds. Some -

Fig. 6.-Simple oscillating steam engine showingoverhung crank

times vibration " periods occur. Forexample, an engine will run quite smoothlyup to a certain number of revolutions perminute, say 3,000, and will then vibratebadly up to say 3,500 r.p.m.

Above this speed however, it will againrun smoothly. This phenomenon is oftendue to the " natural " frequency of thewhole unit coinciding with the frequencyof the reciprocations of the engine at thatcertain speed. It is analogous with theclassic example of the troop of soldiersmarching in step across a suspension bridgeand by reason of the rhythmic beat of theirfeet, coinciding with the natural period orfrequency of the bridge, causing it to

CONNECT/NOROD

Fig. 4.-Connecting rod and crank assemb.'y of anautomobile engine

oscillate violently in harffiony with eachstep.

Weight of Reciprocating PartsThe need for making the piston and

connecting rod as light as possible becomesvery apparent if you consider that quite ausual speed for an internal combustionengine is 5,000 r.p.m. and that this speedmeans about 167 upward and downwardmovements of the piston per second. Inother words, the piston is started andstopped 334 times per second. If you lookat Fig. 4 you will see the reason for this.At the instant depicted the piston is movingdownward. When half way down it will bemoving at its greatest speed, but this speedwill decrease rapidly until it reaches thebottom of its stroke, when for an infinitelyshort time it will remain stationary. Itwill then start on its upward journey untilit reaches half -way when it will once moredecelerate until it stops at the top of itsstroke. It then starts on the next down.ward stroke, and so on. Thus you see, thepiston actually accelerates twice anddecelerates twice ' in the course of onerevolution of the crank. Obviously, if thepiston and the connecting rod are veryheavy, the inertia to be overcome inalternately accelerating and deceleratingsomething like 300 times per second will be


of MechanicalPower

enormous. It speaks well for the skill. ofmodern metallurgists that alloys are available for piston and connecting rod construc-tion which are light enough and strong enoughto permit of speeds up to 10,000 r.p.m.

The design of cranks is by no meansuniform, and various types are employedin different mechanisms. In some cases thecrank is built up as in Fig. 2, in others itmay be a solid forging such as the crank-shaft of an automobile engine as shown inFig. 5, or again crank and flywheel may becombined as in Fig. 6. This last arrange-ment is commonly used for small modelsteam engines of the oscillating cylindertype, while Fig. 7 shows a motor cycleengine in which the big end, of the connect.ing rod bears on a crank pin joining thetwo flywheels.

Fig. 9.-Method of mountingtwo connecting rods on one crankwhen the cylinders are in line

(Right.) Fig. 7.-Twin fly -wheelswhich also form thecrank in a motor

cycle engine

The Eccentric Belt CamA piece of apparatus which is closely

allied to these crank devices is the eccentriccam. Builders of model steam engines andlocomotives will be quite familiar with this.

Fig. 10.-An alternative method

In aero engine design, where multi -cylinder power units are the rule, some veryelaborate connecting rod and crank assemblesare to be found. Fig. 8 shows the principleof the radial and rotary types of engine.Here several connecting rods operate on theone crank, and some ingenious methods areemployed to accommodate the big ends ofthe various connecting rods. A simpleexample of how more than one big endcan be accommodated on one crank, whenthe cylinders are in line, is shown in Fig. 9.This is the usual arrangement adopted witha " V " type twin -cylinder engine. Astirrup shaped big end is used for one of theconnecting rods. An alternative method isshown in Fig. 10. Of course, where it is notnecessary to have the cylinders in line, thebig ends may be placed side by side as inFig. 11. However, in the design of radialand rotary engines with perhaps fourteen oreighteen cylinders, the problem is not quitesosimple. Usually an elaboration of themethod shown in Fig. 10 is employed.

PAZVE CHEST

Fig. I 2. -An eccentric belt cam as usedfor operating steam engine values

Fig. 11.-To mount the con-necting rods side by side the

cylinder must be off -set

It is illustrated in Fig. 12 and is usually usedto carry out a reversal of the action perform-ed by the connecting rod and crank, thatis, it converts rotary motion into reciprocat-ing motion. In the steam engine it is usedto impart a backward and forward motionto the valve gear by utilising the rotation ofthe crankshaft. Keyed or otherwise fixedto the crankshaft C is a circular disc orcam E. This, as its name implies, is mountedeccentrically on the shaft so that as theshaft revolves the centre of the disc tracesout a circular path round the shaft. Ametal strap S encircles the eccentric, whichis able to rotate freely inside the strap. Asthis strap is an integral part of the eccentricrod R., the rotation of the eccentric causes

Fig. 8.-Principle of radial and rotary type engine

the rod to adopt a crank -like action and sopush the rod V backwards and forwards.This latter rod operates the valve. Thedotted lines in Fig. 12 show various positionsof the eccentric and rod in the course of arevolution of the crank.

The circular belt cam of the steam engineis but one of circular cam devices usual forconverting circular motion into reciprocat-ing motion and vice versa. The cams usedto operate valve gear of automobiles areeither pear-shaped or else squarish, as inFig. 13. The object of a cam is to oven andclose its associated valve at the appropriatetimes during the explosion cycle. The idealto be aimed at is the sudden opening of thevalve to its full open position at just theright instant; the retention of it in thisposition for a certain period, during whichtime the gases are entering or escaping fromthe cylinder ; and then its instant closing.The " square " cam conforms to theserequirements. For about 180 degrees of itsmovement its contour is circular, and whilethis part passes under the tappet T thevalve remains closed by reason of the valvespring S.

However, as soon as the " hump " of thecam arrives in the second drawing in Fig. 13the tappet is suddenly pushed upward andopens the valve. This then remains openduring the passage of the hump " of thecam, after which the valve is instantlyclosed again by the force of the spring.Needless to say, with a " square" cam thewhole mechanism is inclined to wear morerapidly than when a pear-shaped one isused, owing to the fact that a very strongvalve spring is needed to induce the tappetto follow the violent contour of the cam,especially when it is rotating at speed. Withwear the valve gear becomes noisy as wellas losing its efficiency. For this reason cam,of the pear-shaped type are usually employed for the engines of touring cars. 0.

Fig. 13.-Internal combustionengine valve gear, using camsfor converting rotary into re-

ciprocating motion


course, with pear cams the valves do notopen and close quite as rapidly as efficiencydemands, but they are quieter in operationand wear better.

Other Cam MechanismsSome interesting, though less well known,

cam devices are shown in Figs. 14-17. Thefirst one is a face cam mounted on the endof a rotating vertical shaft. In the exampleshown, two separate earn contours areincorporated on the face of the one discat the head of the shaft. Bearing on thesetwo cams are two rockers pivoted at A andB respectively, and each is fitted with tinyrollers to reduce friction. As the shaftand cams rotate, so the two rockers moveup and down, thus converting rotary intoreciprocating motion.

The heart cam and the drum cam shownin Figs. 15 and 16 respectively are both of

Fig. 14.-Face camfor convertingrotary into recipro-

cating motion

the positive motion type, no springs beingrequired to make the reciprocating elementfollow the contour of the cam. They areboth designed to convery rotary motioninto irregular reciprocating motion.

The device shown in Fig. 17 is somewhatsimilar to that eccentric belt cam of Fig. 12.It employs a circular eccentric cans, butthus dispenses altogether with a connecting

Fig. 18.-Swash plate for operatingsteam engine valve gear

Fig. 15.-Heart cammechanism

Fig. 16.-Drum cans for con-verting rotary motion intoirregular reciprocating motion

rod. The circular motion of the cam shaftis converted into an irregular backwardand forward motion by the rotation of thecam within the rectangular shaped yoke.The Swash Plate Device

A device which is very similar to a facecam is illustrated in Fig. 18. It is known asa swash plate, and consists of a' circular

metal disc mounted concentrically on ashaft, but tilted at an angle to its axis. Itis sometimes used for operating the valvegear of certain steam engines where thevalve chest is mounted on the top of thecylinders and the valve works parallel withthe axis of the crankshaft. This is illustratedin Fig. 18. As the crankshaft rotates, so theawash plate rocks from side to side andoscillates the lever. The upper end of thislever is attached to the valve spindle by asimple link mechanism which conveys areciprocating motion to the spindle.

A description of the various types ofgears, clutches, ratchets and other mechan-isms associated with the transmission ofmechanical power will be dealt with in alater article.

The awash plate has also been used inplace of a crank in both internal combustionengines- and various pump devices. In

Fig. 17.- Another cam device

these mechanisms a number of verticalcylinders are arranged in circular formationwith their connecting rods bearing on thesurface of a swash plate whose axis isparallel with that of the cylinders. Com-pared with the orthodox crank, this arrange-ment is somewhat inferior, as considerablefriction is introduced at the contact of theconnecting rods with the swash plate.

NEW INVENTIONSTo Keep the Head On

MOST people who have occasion to usea brush or broom, have experienced

the nuisance of the head coming off thehandle. An inventor, impressed with thefact that previous attempts to ensure anindissoluble union have been futile, has sethimself the task of nullifying this tendencyto divorce. The common mode of attach-ment consists in driving a nail through thebrush head and the handle. It appears thatthe hole in the brush head is usually tooshallow, causing the nail to have only aprecarious hold on the handle.

To remedy this defect, the inventor inquestion has combined in a brush head andhandle two screws. One of these screws hasa hole bored through its head. This isscrewed into the head of the brush approxi-mately parallel to the handle. The secondscrew is inserted through the hole in thefirst screw and screwed into the handle atright angles to its longitudinal axis. Theresults should be that the head and handlelive together happily for ever after.

RoundaboutsTHE evolution of the roundabout from

the primitive merry-go-round to thelatest gorgeous development, has shownmany variations. To heighten the enjoy-ment derived from this rotating source of

amusement, by providing means givingnovel sensations, is the declared object of arecent invention of the roundabout type.The new excitement is obtained by tworoundabouts revolving in juxtaposition. Asa consequence, the enchanted passengers onone will receive the impression that theyare rushing to an inevitable collision withthe delighted riders on the other. It isstated that the best effect is produced byby rotating the two roundabouts in oppositedirections. The sequel is a thrilling circulartour.

Lather and GritFOR cleaning very dirty hands somethingmore powerful than ordinary soap is

required. The average lathering soap hasthe drawback that it will not remove thestains from the skin. On the other hand-in fact, on both hands-a sand -containingsoap, which has the grit to rub out dirt,lacks lather.

To obviate these defects, an inventor hasproduced a soap tablet consisting of twoparts, one of lathering soap and theother containing sand. The characteristicfeature of this tablet is that the sand -con-taining part is located in a depression formedin one of the large sides of the latheringsoap. Consequently, the former part has aborder of lathering soap.

One advantage of this tablet is that,

owing to the roughness caused by thepresence of the sand, the soap is not so slip-pery as the average cake.

The villain in the melodramatic thrillerwho soaps the stairs would not find this par-ticular soap effective for his nefarious pur-pose. And, though its obliterating power isalmost omnipotent, I am afraid it wouldfail to remove the incriminating stains onLady Macbeth and Bill Sikes.

To Salve an AeroplaneIMMEDIATELY prior to the war, an appli-

cation by a German citizen for a patentrelating to aircraft was published by theBritish Patent Office. His invention con-cerns the movement or removal of damagedor disabled aeroplanes. lf, whilst landing,an aeroplane breaks its undercarriage, or ifit is fitted with a retractible undercarriagewhich cannot be moved because it isjammed, the plane is forced to land on itsbody. The salvage of the machine thenpresents difficulties, owing to the factthat damage may be caused to the frame-work.

To cope with the task of lifting an aero-plane in the aforementioned predicament,the inventor's idea is to raise the machineby means of inflatable receptacles of apliable material. These are placed betweenthe plane and the ground. The inflationexerts a lifting pressure directly upon, andover an extensive area of the surface ofthe structure. This invention is, in prin-ciple, a pneumatic jack.


A DICTIONARY OF

MetalsBismuth.-Metallic element. Chemical sym-

bol, Bi ; At. No. 83 ; At. Wt. 208 ; M.P.`269°C.; B.P. 1420°C.; Sp. Gray. 9.823;Sp. Ht. .0305; Coef. Exp. .00001333;Therm. Cond. (Silver -100) 1.8 ; Elec.Cond. at 0°C. (Mercury -1) .8676.

Chief ores : Bismuth Ochre, Bi203;Bismuth Glance, Bi2S3. It occurs mainlyin the free metallic condition.

Metallic bismuth was known by thealchemists, but was frequently confusedwith antimony and/or zinc. The metalwas, perhaps, first scientifically studiedby an Englishman, J. H. Pott, in 1739.its name is supposed to be derived fromthe German, weissmuth, white matter, inreference to its now well-known whitecarbonate.

Bismuth is a white, lustrous metalhaving a very faint reddish tinge. It isextremely brittle and is a poor conductorof heat and electricity. Alloys readilywith other metals, and imparts to themthe proPerties of hardness and low -tem-perature fusibility. Hence. it is used agood deal in the making of such alloysas Wood's metal, etc. " Fusible metals "of this type are used as safety plugs insteam boilers, in fire -alarm apparatus

The fracture begins at the surface of the metal

and Their Alloys(Continued from page 126 of last month's issue)

and in other devices. Bismuth alloys arealso used for the snaking of metallic casts.Chemically, bismuth is fairly reactive, itsbest-known compound, bismuth car-bonate, being a popular medicinal sub-stance. In most of its properties, bis-ninth is similar to antimony.

Bismuth Amalgam.-A thinly fluid amal-gam prepared by adding mercury tomolten bismuth. Almost any proportionsof these two ingredients may be used.Bismuth amalgams, on account of theirfluidity, are useful for filling very delicatemoulds. Other amalgams are, also,rendered more fluid by adding to thema small proportion of a bismuth amalgam.

Bismuth amalgam is sometimes usedfor silvering glass globes and similararticles.

The amalgam will pass throughchamois -leather like mercury. The drops,however, are pear-skaped and not per-fectly globular as in the case of 'puremercury.

Bismuth Bronze.-An alloy sometimes usedfor 'mirrors and lamp reflectors onaccount of the very high polish which it

LIST OF ABBREVIATIONSThe following abbreviations are used throughout

this Dictionary :At. No. .. .. Atomic NumberAt. Wt. .. .. Atomic WeightM.P. .. Melting PointB.P. Boiling PointSp. Gray. .. Specific GravitySp. Ht... .. Specific HeatCoef. Exp. .. .. Coefficient of ExpansionTherm. Cond. .. .. Thermal conductivityElec. Cond. .. Electrical conductivity

takes. Composition : copper, 52 ; nickel,30; zinc, 12; lead. 5 ; bismuth, 1 parts.

Bismuth Purissimum.-Name sometimesgiven to refined bismuth metal of from99.85 to 99.98% purity.

Black Antimony.-See Yellow Antimony.Black Arsenic.-Also known as beta "

arsenic. Obtained by the slow condensa-tion of arsenic vapour. It occurs as ablack powder or a brittle, glassy -lookingmass which, when heated to s 360°C.,passes into the ordinary " grey " or

metallic " arsenic.Black Tin.-Strictly speaking, this is not

a metal. It is the name given by minersto tinstone (tin ore) to distinguish itfrom tin metal which they called " Whitetin."

-Blister Copper.-Name given to metalliccopper after it has been roasted in areverberatory furnace. It has then ablistered appearance.

Blister Steel.-A certain type of raw steelwhich has been cooled very slowly and

Three stages in the growth of afracture in a brass rod which hasbeen subjected to intermittent stress

which

The fracture deepens

presents a warty or blisteredappearance, the blisters " having beenformed by the efforts of gas to escapefrom within the metal.

Block Tin.-Name given to ingots of casttin. These are usually cast in granitemoulds.

Blowhole.-An air -hole in a metalliccasting.

Blue Gold.-(a) A gold -iron alloy containingfrom 25% to 33.3% of iron.(b) A colloidal solution of gold preparedby reducing a solution of gold chloridewith hydrazine hydrate. It possesses abluish colour.

Blue Metal. -A name for impure copperobtained during the -process of coppersmelting. " Blue metal " contains from55% to 66% of metallic copper mixedwith copper and iron sulphides. It has apeculiar bluish colour.

Bob Brass.-See Ferrule Brass.Bobierre's Metal.-This is ordinary brass

consisting of 66 parts of copper and34 parts of zinc. Introduced by M.Bobierre in the last century as a sheathingfor ships.

Boroto Metal.-A tin -lead -antimony white -metal in which colloidal graphite isincorporated. Of American origin, ithas a Brinell hardness of from 17-25, andis employed as a self-lubricating bearingmetal.

Bottger's Amalgam.-An electric amalgamused in frictional machines. etc. Com-position : zinc, 2; mercury, 1 parts.

Bottoms Copper.-The copper which hassunk to the bottom of the smeltingftirnace. It is the least pure of the massof metal in the furnace and it usuallycontains tin, lead and antimony, andsometimes traces of silver and gold.

Bourbon Metal.-An alloy composed ofequal parts of tin and aluminium. Itsolders readily.

Brass.-A generic name given to alloys ofcopper and zinc. Common brass (oreast brass) contains 2 parts of copper andI part of zinc.

Brass has been known from earlyages. Its name is supposed to be derivedfrom the Anglo-Saxon word braes-afire -produced metal.

The various brasses are describedunder their individual names.

Brazing.Soldering with a brass alloy.Brazing Brass.-A brass alloy having a low

zinc content. It possesses a red colourand is used for brazing purposes. Com-position : copper. 86.75; zinc, 12; lead,1.25 parts.

Brazing Metal.-This term is usuallysynonymous with brazing brass.

The fracture almost complete

Brazing Solder.-A variety of brass con-taining copper, 50%; zinc, 50%. Isusually cast in iron moulds havingtransverse and longitudinal ridges, sothat the cake of brass can be brokenup into small rectangular pieces. These


pieces are then heated in a furnace andafterwards powdered in an iron mortar.The solder is used for uniting Aron andbrass.

Brearley Steel.-An original type-of stain-less steel discovered in 1913 by Mr.Harry Brearley, of Sheffield. It is ahigh chromium steel and it was firstmade available for cutlery' purposes aboutthe middle of 1914.

Brightray.-A nickel -chromium alloy ofhigh corrosion' resistance.

Brinell Hardness Test.-A standardised testof metal hardness. It is made by indent-ing the smooth surface of the metal undertest by means of a hardened steel ball(usually 10 mm. in diameter) by sub-jecting it to a pressure or load of 300kilograms for a soft metal and 3,000kilograms for a hard metal. For veryhard materials, a 2 mm. diameterdiamond sphere is used.

By means of a lens, the diameter ofthe indentation in the metal surface ismeasured, and this is used as a meansof calculating comparative hardnessnumbers-Brinell Hardness Number.

Bristol Brass.-This is the same as Prince'sMetal, which see.

Britannia Metal.-This is, in reality, tinhardened with from '5 to 10%' of, anti=:mony. It frequently contains a smallamount of copper. Typical comp?sitionis : tin, 140 ; antiniony, 8 ; copper, 3 parts.An increase in the amount of copper hasthe effect of colouring the metal.

The average M.P. of the above alloyis 250°C. It is much used as the basemetal of plated goods of the ornamentaltype.

Brittleness.-A metal which, easily breaksupon the application of a sudden shockor one which fractures readily when sub-jected to a hammering or compressingforce is considered to be brittle. Metalsare usually increased in brittleness bythe presence of impurities; within them.Thus, phosphorus in iron renders themetal brittle or " short."

Crystalline metals are usually brittle,because of the feeble degree of cohesionbetween their component crystals.

Distinguish carefully between brittle-ness and hardness of a metal. The twoterms are by no means synonymous.Thus for example, Manganese steel ishard, but it is not brittle. Metallictellurium is brittle but it is not hard.

" Brocade."-A type of bronze powder con-sisting of coarse metal flakes preparedfrom the waste of metal -leaf factories.

Bronze.-The name given to a large classof copper -zinc -tin alloys. Approximatelimitating proportions of these con-stituents are : copper, 70-90%; zinc,1-25%; tin, 1.18%.

Such bronzes are much used formaking castings, coins, ornaments, etc.

Bronze has been known from veryancient times.

Bronze Powders.-These are used for coatingmetallic and non-metallic objects in orderto impart to them a decorative appear-anc,e. They have the following averagecomposition: copper, 64-83%; silver,4.3.4.5%; tin, 8-8.7%. The lower gradesof bronze powders contain up to 13%of zinc, which whitens them considerably:

Brown Gold.-An alloy containing 20 partsof gold, 4 parts of copper.

Buflokast.-An iron -silicon alloy of Ameri-can origin. It is non -corrosive and issimilar to Tantiron, -which see.

CCadmium. - Metallic element. Chemical

k'symbol, Cd.; At; No. 4S; At. Wt. 112;M.P. 320.2°C. ; B.P. 745°C.; Sp. Gray8.6603'; Sp. Ht. .0548; Coef Rxp..00003323, Therm. Gonda (Silver-WO)20.06. ; Elec. Cond. at 0°C. (Mercury -1)13.46.

Occurrence : Mainly in zinc ores.Cadmium never occurs in Nature in thefree state.

Cadmium was discovered by F. Siro-meyer in 1817 in a specimen of zinccarbonate, the name " cadmium." beingcoined from the term cadmic fossilis, bywhich zinc ore was then known, theancient Greeks having, during theircivilisation. known zinc ore as " cad-meia."

Cadmium is a bluish -white metal,closely related to zinc on the one handand to mercury on the other. It tar-nishes superficially, and is fairly reactivechemically, one of its chief compounds,cadmium sulphide, CdS, being extensivelyemployed in the paint industry as agolden -yellow pigment.

Cadmium metal is ductile, and can berolled into sheets and drawn into wire.It 'has been used to some extent as aplating metal. Cadmium -is also used inthe' making of fusible alloys and certaincasting metals.

Cadmium Amalgam.-Amalgams of mercuryand cadmium readily crystallise. Theycan be made in almost any proportions.They are tin or silver -white in colourand, when heated, become soft and canbe kneaded. These amalgams are usefulas metallic fillings and stoppings for avariety of purposes.

When mercury is completely saturatedwith cadmium, the. resulting amalgamhas the composition : mercury, 78.26%,cadmium, 21.74 parts. This amalgam istin -white, crystalline, and, although it issomewhat brittle, it softens, like allcadmium amalgams, when heated, somuch so that it can' be kneaded like wax.This amalgam is sometimes used bydentists for filling teeth.

Cadmium Copper.-A copper - cadmiumalloy containing either 0.5% or 1% ofcopper. Retains a maximum conductivitywith an increased tensile strength, andhence is in demand for the manufactureof overhead electric lines, power cables,etc. It was first introduced in 1920 andhas an approximately 50% greatertensile strength than ordinary hard -drawn copper wire.

Caesium.-Metallic element. Chemicalsymbol, Cs; At. No. 55 ; At. Wt. 133 ;M.P. 28.5°C; 670°C. ; Sp. Gray. 1.903 ;Sp. FR. .0522 : Coef. Exp. .000345.

Discovered by Robert Bunsen andG. Kirchhoff (1860) in certain springwater containing lithia. Given the name,caesium, from the Latin, caesiu8, sky-blue, in respect, of the blue light emittedby its incandescent vapour.

Occurrence': in certain mineral waterscontaining lithia, sodium, etc. Also insome rare minerals.

Caesium is a silvery -white, ductilemetal, which is soft enough to be cut witha knife, like cheese. It is the mostelectro-positive of metals. Exposed toair, it rapidly becomes covered with afilm of oxide, and hence must be pre-served belcw the surface of oil. LikeSodium and potassium, it energeticallydecomposes NI ater with the evolution ofhydrogen gas and the production ofcaesium hydroxide: If placed in anatmosphere of dry oxygen, caesium willspontaneously take fire.

Within the last few years, caesium'has come into prominence as a light-sensitive metal in the manufacture ofphoto -electric cells, ," caesium cells"

' being Particularly infra -red sensitive.' Calcium.Metallic element. Chemical

symbol, Ca; At. No. 20; At. Wt. 40;M.P. 780°C. Sp. Gray. 1.52 ; Sp. Ht:.152 ; Elec. ,doncl. at 0°C. (Mercary = 1)12.5.

Discovered in 1808 by H. Davy. Namederived from the Latin; calx, lime, sincecalcium is the constituent metal of limeand limestone. Occurrence : in lime-stone, chalk, marble, calcspar. CaCO3.

A white, lustrous metal, having a slightyellow tinge. Has a strong affinity foroxygen, becoming coated with an oxidefilm when exposed to air. Decomposeswater with evolution of hydrogen andformation of calcium hydroxide, Ca (0112).In general properties, calcium closelyresembles barium and strontium. Whenheated in nitrogen, forms calcium nitride,Ca3N2. Calcium metal is fairly soft andmalleable. Usually preserved under oilor naphtha.

Calcium metal can be made to formalloys with aluminium, lead, antimony,sodium, potassium and zinc, as well asseveral amalgams with mercury, butneither the metal nor its alloys haveany special uses.

Calcium Lead.-Lead containing a .smallpercentage of metallic calcium to hardenit.

Camelia Metal.-A white metal used forpivot bearings in machinery and forsimilar purposes. Composition : zinc,10.2%-; copper, 70.2%; tin, 4.25%; lead,14.75%; iron, 0.55%.

" Carat " Gold.-The amount of gold inalloys is conventionally expressed inRafts per 24, these parts being termed

carats." Thus pure gold is' 24 caratgold," whilst a gold alloy containing18 parts of gold and 6 ,parts of silver(or copper) constitutes " 18 -carat gold."Similarly, " 9 -carat gold " contains 9pails of gold and 15 parts of other metal.

The word " carat is supposed to bederived from the Greek, keration, signify-ing a bean or a seed used for weighinggold.

Carbon Bronze.-An anti -friction bearingmetal containing a trace of carbon.Composition : copper, 75.47%; tin,9.72%; lead, 14.57%; carbon, 0.1%.

Carbondale Silver.-A variety of nickelsilver. Composition : copper, 66 ;18; zinc, 16.

Carbon Steel.-Roughly speaking, steelis an intermediate material between castiron and wrought iron, the latter beingthe purest form of iron commerciallyattainable.

Cast or pig iron contains about 3%of carbon. Wrought iron contains about0.06% of carbon. Between these twolimits comes " steel," a form of ironcontaining dissolved or alloyed carbon." Carbon steel," therefore, is nothingmore or less than " ordinary " steel, theword " carbon " being employed todistinguish the metal from the nowadaysnumerous " alloy " or " special " steelswhich contain other alloying metals inaddition to carbon. " Carbon " steel,therefore, is the " old-fashioned " type,of steel.

A " hard " carbon steel contains about1%of carbon, whilst a " soft " steel ofthis type has a carbon content of about.,.1%.

(To be continued)

January, 1940 NEWN ES PRACTICAL MECHANICS 189

oAeuit QUERIESENQUIRIES

a:,41114

Re -silvering a MirrorCAN you tell me how to re -silver a looking

glass?-A. L. (Bristol).THERE are three general chemical

methods of silvering glass. Of these thefollowing, known as the Rochelle saltmethod, is the most readily worked foraverage purposes.

Make up the following solutions :-Solution 1.

Silver nitrate 0.5 gram.Rochelle salt 0.7 Boil andWaWr 250 cos filter.

Solution 2.Silver nitrate 2.5 grams.Water 25 cosTo Solution 2 add strong ammonia drop

by drop until the precipitate formed justdissolves. After this, add one or two dropsof weak silver nitrate solution until theliquid just becomes cloudy again, Thendilute the solution with 250 cos of water.

For use, the above two solutions (whichshould be freshly prepared) should be mixedin equal amounts and instantly poured overthe surface of the glass. For this purpose,the latter should lie in a perfectly clean dish.Silvering will take place immediately andwill be completed within about five minutes.

Before silvering, the glass should be verycarefully cleaned, preferably by rubbing itover with nitric acid. It should then bewell rinsed. Just before silvering it isadvisable to immerse the glass in a strongsolution of stannous chloride for a fewminutes and, afterwards, to rinse the lattersalt away.

Distilled water should be employed formaking the solutions.

The whole secret of successful silvering is(a) thorough cleanliness of all vessels andsolutions, (b) cleanliness of the glass surface,and (c) accurate making up of the solutions.If you have not engaged in this workpreviously, it would be advisable for you toperform a few experiments in glass silveringbefore embarking upon it for a seriouspurpose.

Repairing BakeliteCAN bakelite be repaired so as to retain

its insulating properties and if so howcan this be achieved ? Also, what is thevoltage required to produce a spark of onecentimetre?-L. D. (Carlow).

THE possibility of satisfactory repairsdepends largely on the size of the

article and the nature of the break. If thearticle has not become distorted or warpedthrough the fracture and the edges are quiteclean and close fitting apply a little of thecement sold as " Certofix " on both sidesof the broken part, allow it to become tacky,.and press together with a clamp until hard.

Bostick " is another useful cement, andrather a better insulator. Replying toanother question, the voltage required tospark across a distance of one centimetrewill depend upon the shape of the terminalpoints, the atmospheric pressure, and on the

A stamped addressed envelope, three pennystamps, and the query coupon from the currentissue, which appears on page iii of cover, must beenclosed with every letter containing a query.Every query and drawing which is sent must bearthe name and address of the sender. Send yourqueries to the Editor, PRACTICAL MECHANICS,Geo. Newnes, Ltd., Tower House, Southampton

Street, Strand, London, W.C.2.

temperature. Between two insulatedspheres of 20 mm. diameter at 25 degrees C.and 76 mm. barometric pressure, a dis-charge spark will take place across a distanceof 4.2 millimetres with a potential differenceof 10,000 volts between the spheres. At20,000 volts the sparkover will cross a gapof 8.6 mm., and at 30,000 volts 13.7millimetres. From these three points a curvecan be plotted showing the probablebehaviour for higher or lower pressures.Fuller particulars can be obtained fromBritish Standard Specification No. 358 of1929, obtainable from 28 Victoria Street,London, S.W.1.

Winding for Synchronous ClockMotor

I WISH to know how to decide on thenumber of turns and gauge of wire to use

on a small synchronous multi -polar electricmotor of sufficient power to drive a clock.

I have planned to use an iron disc rotorof 1 in. diam. and having 30 teeth. The coilwould be 1114, in. long and have its poles termi-nating in 8 teeth on each side. The currentis A.C. 220 v. 50-60 cycles. -A. C. (Mul-lingar).YOU omit to state what train of gears

you are contemplating, but probablyhave realised that the clock would not keeptime on frequencies of both 50 and 60cycles, it must be designed definitely forone or the other. The 30 -slot rotor of 1 in.diameter need not be more than in. thick,but should be built up of thin stampings,not from the solid. The same applies to thestator having eight slots on .each pole face.If you intend this to be plugged in directon a 220 volt circuit you must be preparedto wind the coil with extremely fineenamelled copper wire such as No. .45SWG,and if this is a first attempt at winding itcannot be recommended as it would tax theskill of quite an experienced winder. As analternative it is suggested to run the clockfrom a bell transformer secondary, at say12 volts, in which case a suitable windingwould consist of 1 oz. of No. .38SWGenamel covered copper. Cotton coveringsare quite inadmissible owing to the in-creased space factor they require. Withenamel coverings 2.4 times as many turnsas cotton covered wire of this gauge can begot into the same winding space.

Fireproofing CanvasCAN you tell of a reliable solution for

making canvas fireproof. Can paperalso be made fireproof ?-W. M. (Eltham,S.E.9).IN two gallons of hot water dissolveI approximately 1 lb. of alum. With aclean brush, spread this mixture (prefer-ably hit) all over the canvas and on both

sides so that it is thoroughly impregnated.When dry, rub the canvas over with a cleanrag in order to remove any of the alumpowder which may be adhering to itssurface. The canvas will now be fireproof.

Another solution having the same effectis made by' dissolving 10 parts of sodiumtungstate in 100 parts of water.

Paper and other materials can besimilarly fire -proofed by immersion in theabove solutions.

Actually, the above fire -proofed "materials will often smoulder slowly if theyare ignited, but, usually, the smouldefingarea will pot spread itself.

Running Motor on Reduced VoltageI HAVE a Spartan refrigerator-com-

pressor type-with a one -sixth h.p. motor.1,440 r.p.m. 1.9 amps at 220 v. A.C.

I now want to run this off 240 A.c. mains.I take it that the coil resistance of themotor is 220/1.9 = 115 ohms. and that if Iput a resistance of about 10 ohms in the leadfrom the wall plug to the motor it willreduce the voltage at the motor from 240 to220.

How do I do this ? I have some 24 gaugeEureka resistance wire, and I wound 10ohms. on to a former, but the wire tot veryhot through overloading. What is the rightwire, and how much shall I need ?-N. L.(Middlesex).I T is a little difficult to advise in the

absence of further particulars as to thetype of motor. If it is a series motor of thecommutator type and you wish to dissipatethe difference of voltage between 240 and220, that is 20 volts, when the motor istaking its normal current of 1.9 amperes, allyou need is a small additional resistance incircuit of 20/1.9 = 10.5 ohms. No. .23SWGEureka resistance wire will carry thiscurrent without excessive temperature rise,if freely ventilated, and has a resistance of1.487 ohms. per yard, so that the length ofwire required to give the required 20 voltsdrop would be 20/1.487 = 13i yards.approx. This should be wound on aninsulated metal tube of about 14 in.diameter, mounted vertically and protectedwith a ventilated cover. If the motor is ofthe induction type, however, the proposedresistance may not he entirely satisfactory,since these motors take such a heavy start-ing current in order to develop normaltorque that the additional resistance incircuit would cause an abnormal volt -dropat the terminals and probably prevent themotor from starting up. The impedanceof the windings is mainly composed ofinductance with a very low ohmic resist-ance, in this type of motor, hence yourcalculation of the motor resistance wouldnot apply. If the suggested resistance doesnot enable the motor to start up the bestalternative will be to put in a small auto -transformer input 240 volts output 220volts, short -rated at 10 amperes, and con-tinuously rated at 2 amperes.

Bengal MatchesCOULD you kindly give me some

information about the following :-How Bengal matches are manufactured ?How enamelled show signs are manu-

factured ?How mechanical tin toys are coloured or

painted ?-P.O. (Co. Clare).

BY" Bengal Matches " we presume that

you mean those which burn with acoloured flame, usually a red or a greenflame. These matches contain the ordin-ary safety -match " mixture," i.e., thematcher kre tipped with a mixture con-


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taining potassium chlorate, potassium bi-chromate, red lead and antimony sulphideand they are inflamed by rubbing on a sur-face (usually the side of the matchbox) pre-pared with a mixture of red phosphorous,antimony sulphide and a little glue to actas a binding agent. The matches are" coloured " by adding to the match -headmixture a quantity of barium nitrate (whichwill colour the flame green) or strontiumnitrate (which colours the flame red). Like-wise, sodium nitrate would colour the flameorange, whilst traces of copper salts wouldimport a blue-green colouration to it. Thepreparation of these matches is not withoutdanger and should not be undertakenexcept upon a very small scale.

Enamelled show signs are nowadaysmanufactured in many different ways.Usually, however, the clean iron surface hasspread upon it the glazing compositionwhich is either. printed on in the form ofletters or designs or else laid on by hand.This glazing mixture, may, of course, he ofany colour. Thus, for instance, a sign con-sisting of black lettering on a white back-ground would have its black letters appliedfirst, the surround subsequently beingwhitened. Finally, of course, the preparedsheet is " fired " for a definite time at ahigh temperature in a muffle furnace,wherein the glaze fuses and afterwards setsto a hard glassy film.

The mechanical toys which you refer toare usually hand coloured with ordinaryenamel paints. If, for instance, you applysoap and water to any ordinary painted toy,the colours can usually be removed quitereadily. Workers in the toy trades, par-ticularly in foreign factories, become veryadept at painting large numbers of thesetoys at a rapid rate.

Egg TongsI HAVE produced a pair of egg tongs, made

of wire. TI e feature is the novel way inwhich the egg is picked up.

When the tongs are gently pressed intothe egg, they automatically grip it and holdit securely.

A slight pressure on the sides of the longs,releases the egg.

Do you think that the idea is fit subjectfor a patent. If not, can it be protected l'ysome other means ?-V. W. (Surrey).

THE improved device for handling eggs,if novel, appears to form fit subject

matter for letters patent, but withoutfurther particulars or a sample of the in-vention, it is not possible to express adefinite opinion. It may be that protectionfor the device could be obtained by regis-tration as a design. The cost of registeringa design is less expensive than a patent, butthe protection given is not as broad as apatent.

In some eases it is possible to obtain botha patent and a registered design for adevice, but all devices are not capable ofregistration as designs.

American PatentsN a recent issue you state in one of the

I " Replies " that an American patentMUST be filed within 12 months of theEnglish patent application.

Does this mean that a patent devicewhich has proved to be successful, but onlyafter 18 months exploitation here, cannot bepatented at all in U.S.A. by its originalBritish owner ?-G. B. (Sunderland).

ACCORDING to the U.S. Patent Law aninvention to be patentable must be

novel. An invention is not considered novel(1) If it has been known or used by othersin the U.S.A. before your invention or dis.

covery thereof; (2) if it has been patentedor described in any printed publication inthe U.S.A. or in airy foreign country beforeyour invention or discovery thereof, ormore than twti years prior to the applica-tion for the patent; (3) if the invention hasbeen in public use cr on sale in the U.S.A.for more than two years prior to your,application unless the same is proved tohave been abandoned; (4) if an applicationfor patent for the invention has been filedin a foreign country more than 12 monthsprior to the application in the U.S.

It may be taken as correct that unless aninventor applies for a U.S. patent within12 months from the date of the applicationor the date of filing of his British patentapplication, on the supposition that suchpatent application is the first that is filedin any country for the same invention, thenno patent will be granted on such a U.S.patent application.

It is, however, true that if it be possibleto delay the sealing of the patent on theBritish application until after a U.S.patent has been issued on the late filing, i.e.after 12 months of a U.S. patent application,a U.S. patent will be granted on suchapplication. In practice, however, this ishardly ever possible, since the sealing of theBritish patent can only be delayed for adefinite time, which is almost certain to beexceeded. before it is possible to obtainissuance of the U.S. patent.

It will thus be seen that the statementthat a U.S. patent application must befiled within 12 months of the British patentapplication, is correct for all practicalpurposes.

Petrol Vapour LampCAN you give me any constructional

details of a petrol vapour lamp? I re-quire one for use in a garage.-A. R.(Chesterfield).

APETROL lamp works on the principle ofan incandescent mantle being heated by

the non -luminous flame produced by petrolvapour burning in a current of air. Forthis purpose, petrol from a suitable con-tainer is allowed to flow through a needle -valve or other suitable regulator to aspecially devised burner over which is sus-pended an incandescent mantle of the usualtypeIn.

order to start the lamp, it is necessaryto heat the burner. This is effected bypouring a small quantity of methylatedspirit in a cup -like channel former aroundthe burner. When the spirit is ignited, itwarms the burner and conduit thereto,with the result that the slowly flowingpetrol is gasified and mixed with air inwhich condition it is combusted, therebyheating the mantle and so exciting it to acondition of incandescence.

We fear that you will find it a verydifficult job to construct an incandescentpetrol lamp for yourself and, if possible,we would suggest your purchasing .a second-hand lamp of this type, since then youwould not risk disappointment. If, how-ever, you desire to try your hand at makingthese lamps (the majority of which, webelieve, are subject to patent protection)your best plan will be to procure a suitablecontainer for the petrol. This should have afilling' orifice and cap at the top and alength of piping should lead out from it atthe base. This piping (which must have init some type of regulating valve) com-municates -with an upright iron tube havingat its upper end a circular burner of theBunsen type over which the mantle may befitted and held securely. Around the pipejust below the burner, you will find it

January, 1940 NEWNES PRACTICAL MECHANICS 19i

necessary to fit some type of race or channelin which to pour the methylated spiritnecessary for the starting of the lamp.

Some petrol lamps operate under pressurewhich is generated by means of an auxiliaryhandpump fitted to the petrol container.The construction of these, however, isbeyond most amateurs, unless, of course.an ordinary spirit stove of the Primus "type is adapted for the purpose.

Firms manufacturing petrol lamps do notsupply parts other than replacements. Youmight, however, try the following firms forsupplies : Messrs. J. M. & D. Hunter, 41Slaney Street, Birmingham ; Messrs. Spencers(London), Ltd., 5 and 6 London Street,Paddington, London, W.2. ; Messrs. M.Howlett & Co., Ltd., 140 Hockley Hill,Birmingham.

Designing a SolenoidI WISH to construct a " Solenoid " similar

to that used for gearchanging on theAmerican " Caddillac " car some years ago,and capable of pulling or pushing a rod witha force of 10 lbs. Can you inform me ifthere is a " formula " for determining thesize and length of wire required, and thenecessary voltage and amperage of current.I want to use a car type battery if possible.

Is there any book covering the constructionof Solenoids -J. M. (York):THE design of a solenoid to give a

definite pull over a definite distance isa matter depending so much upon the spaceavailable that no general rules can be laid

down. The. tractive effort or pull when thefixed and movable iron cores are in actualcontact is calculable from the formula :

B2 x A2 (in square inches)Pull in lbs. ..

72,134,000B being the induction or flux density in linesper sq. in., but this figure is very difficult toobtain in practice, as the magnetic leakageis a variable quantity and varies with everychange in the length of the air gap betweenthe cores. It is impossible to go into thematter fully in the space of a letter, butsome assistance will no doubt be derivedby studying the articles entitled " Electro-magnetic Devices t" by A. H. Avery, whichappeared in The Model Engineer for April23rd and 30th, 1936 and also May 7th and21st of the same year. There is no publica-tion dealing exclusively with Solenoids.You may be able to see a copy of Prof.S. P. Thompson's The Electromagnet "at some technical library, but this has longbeen out of print.

PRACTICAL WIRELESSENCYCLOPAEDIA

7th Edition

6f-, by post 616from Geo. Newnes Ltd., Tower House,

Southampton Street, Strand, W.C.2

A SMALL STEAMBOILER

(Continued from page ILA)

no difficulty in choosing suitable fittings.Working Pressure

The working pressure of our boiler isintended to be 30 lb. per square inch. NowI want to give the reader a method of settingthe safety valve so that this pressure shallbe determined before steam is raised in theboiler for the first time.

The aperture or diameter of the bore ofthe safety valve is in. (.25 in.). This figuresquared and multiplied by .7854= .0491square in., or for convenience we will callit .05 square in. Thirty pounds multipliedby .05 equals 1.5 lbs. which is the actual

- pressure of steam on the under side of thevalve tending to -lift it. Now all that it isnecessary to do in pre-setting for thispressure is to insert a short piece of rod ofsteel, brass or wood up under the valve,letting it be a nice easy fit in the hole andprojecting an inch or so. Hold the safetyvalve over a spring balance or scales. Pressthe whole body of the valve down on thescale by means of the rod and adjust thenuts until the valve is seen to just lift offits seat when the scales are reading exactly

lbs. Then lock the nuts and the valveis set approximately if not with exactitude.

I have said that the boiler is finished, butit is recommended that the inside of theeasing be lined with asbestos cardboard;this will prevent some loss of heat byradiation. The top of the boiler may verywell be lagged, also with asbestos, and,for the sake of appearance, this shouldagain be covered with thin sheet metalwhich may be painted and held down bybrass (bands.Firing Arrangement

The last item to be dealt with is thefiring arrangement. Gas will be found byfar the most convenient fuel, and it may bethat the reader will save himself some work

by being able to find a gas ring of convenientsize and shape ; or it may he possible toadapt ready-made burners from a gasPre, the grill of a gas cooker or utilise thelower part of .a Fletcher pattern soldering -iron -heater. Failing all these, burners canbe made in accordance with the accompany-ing drawing Fig. 4.. using iron tubing withsaw -cuts made across it and stock patternbrass taps for the gas jets. The "Y" pieceof pipe can be soft -soldered together.

If no gas is available methylated spiritis a simple alternative. Burners and lamphaving asbestos wicks are shown in Fig. 5.The burners are made from 1- in. diameterbrass or copper tube flattened to oblongform. The boiler and engine may verywell be mounted side by side upon a ply-wood base board which should be protected,underneath the boiler, by an iron platescrewed down over a thick piece of asbestoscard.

The steam,connection between the wheel -valve and he engine will be by * in.diameter copper pipe and the exhaustfrom the slide valve cover -plate by I in.pipe, which it will be advisable to takeinto the fire casing and bend in such amanner that it points upwards, centrally,at the base of the chimney, just as theblast pipe. does in the smokebox of alocomotive.

It may be remarked that no provisionis made for feeding the boiler with water.Actually I think that a pump is scarcelyneeded ; for one filling through a funnelinserted in the safety valve hole, byunscrewing the valve, will be sufficientfor a very long run of the engine ; probablyas long as is desired, but if a greater periodthan about an hour is wanted withoutcooling off the boiler and refilling then ahand pump can be mounted on the base-board, or a small pump be driven by aneccentric off the engine crankshaft. Ineither case a check valve will he neededon the boiler, and, all things considered,I do not think it will be worth while toprovide a pump.

BARGAINS BY ELECTRADIXH.T. TRANSFORMERS. Steelclad, as illus., 200 watts, 50 cycles.10,000 v.. 40/-. 400 watts, 4,000 volts.60/, 220 volts /300-0-300 volts 60 ma..78 v., 21 a., 58 v.. 10 a..1.8:-, E.H.I.Mains- Rectifier Transformers 120volts 20 ma. output. 8 8. H.M.V.Transformers any A.C. Mains input.350-0-350 volts 80 ma.' 4 volts 2amps. and 4 volts 3 amps.. 8.6.TRICKLE. 200/240 v. to 2 a.. and 8 v.

a.. 7/6. Mains 110/220 v.. to 150 v.30 Ma., and 4 v. 1 a. and 4 v. 3. a.,4.13.INTERFERENCE FILTERS. inPolished walnut case, 71 x 6 x 3. L.F.

or H.F. smoothing, 15!-.L.F. Transformers and Chokes. all sizes.FERRANTI. Type 0.P.M., etc. SingleRatios 27.1. 3.1. 38/I, 5/6 each. Output for50 m.a.,6,-. 3 Ratio Ferranti 31-71-10 t0,1,or 4-7-10 to 1. 61. Push -Pull 3 ratio, 100ma.. 7,-. Loud Speakers, etc. List 17/.Sale 10 High Ratio Microphone TranS-former. 100 1 Ratio, 4/6. 30/1 ratio. 12/6.Special P.A. Speech Transformer, 10!6.

B.T.H. Bakelite 4 to 1 Intervalve, 5/,CHOKES. 30 Hy. 50 100 m.a.,4 -. t amp. ditto, 1.0;-. H.F.Chokes L. and S.W.. 1 6.MOTORS FOR A.C. MAINS. Repulsion,self-starting. 1/60 H.P. with pulley. Type 50,1.500 revs.. 18/8. Ditto, Type 36. 1;25 H.P.G.H.C., 3.500 revs..27 6. Enclo. Induction 1/10H.P. Motors, 2,500 revs., 35 -. Self-starting.

H.P.. 1.425 revs..491-. etc.. etc. D.C. MainsMotors, 1/40 H.P., 110 or 220-v. series, TypeKB., 1,750 revs., 15/-. Ditto. G.E.C. 230-v..2000 revs., 16/-. Croydon 1/12 H.P., 110 and220-v. shunt. 1.700 revs...30 -.

GENUINE E.D.C. ROTARYCONVERTERS. For A.C.Receivers on D.C. 230 v. A.C.output. All in silence cabinet.with filter. All sizes in stockfrom 50 watts to sets for tele-viso rs of 450 watts.D.C. MAINS MOTOR DENS.D.C. D.C. 220 v. to 30 v. 10amps.. £719/-. M.G. Cromp-

ton. D.C./D.C. 100 vlts.to 17 volts 6 amps..£45am7p6s..,200g5. Ev.sttroo M.G.

ditto to 6 volts 1 amp.45/-. Motor Genera-

r6so foramps.

l. outputs upto

ALTERNATORS. 200 DalSelf -exciting Alternator,TYPE` 52A. A most perfectly -made A.C. generator. 500cycles 10 volts 20 amps., eight71 lb., in aluminium cover.Belt or motor drive. and fullyguaranteed. With quite asmall transformer, H.T. vol-tage up to 6.000 volts may be obtained. smoothed andrectified for plate H.T. Cost 030, and are given away at23/10/- cash with order.SELENIUM CELLS. ' Light sensitive resistance, goldgrids. moisture -proof. L. to D., ratio 5 to 1. Mounted inbakelite, 10,-. Super Model in Oxybrass body withwindow 013.C0001'ROL BY RAYS. We have some £5 Photo Cells forTalkies. Light Tests. Timings Controls. etc.. at bargainPrices. Vacuum cells. Response to light 50 micro -amps.per lumen. R.C.A., 25;-.: Holders. 1/ Electric Cells, self -generating on Micro -Ammeter or Micro. Relay. 11 in. x

in..21/6. Beck Prisms. 5 6.LOW COST SOUND RECORDING. Blanks now 33 per

dozen. Electric FEIGH sethas ball -bearing centregear box and geared tra-verserod. Set with Track-ing Gear, Pick-up andTone -arm fitted diamond,3716. Tracker gear only.less Pick-up and Tone -arm, is 216. DiamondCutter Needles fit all pick-ups. 71. 6 in. Blank Discs.3.3 dozen. Sample with

record one side 1/-. Post free. Complete Acoustic Set,de Luxe,111/-, No. 2,10/6; Junior Type. 5/6 each complete.AMPLIFIERS for Record boosting. 21 watts undistor-ted output from mains. Steel clad chassis with metalcover. O.CRYSTAL SETS. Buy one now, you may want it oneday. No battery or valves wanted. Efficient reception.7.6 each. PhOnes 4 /6.

PHONES. For all purposes. Tableor wall, house or office 'phones, from10/-. Headphones. Pocket type W.D.leather Headbands, 31 pr. SullivanRadio Aluminium Headbaffils, 3/9 pr.4,000 ohm SIW lightweight Head-thones, 5.- pr. 13.T.H.. 6'-., Browns.

DIAL TUNING. 10 -point Finger SwitchDials. As illus.. usedon G.P.O. AutomaticTelephones. Thesehave spring drive.governor; clutch andcontacts inside. Price 21.

WIRE WOUND POWER RESISTANCES. 5 -watt 8,000ohms, 10 ma.. 10d. 5 watt Potential Dividers, tapped50,000 ohms, 16. Mains Transformers, 3/6. 1 -mid. Con-densers. 4d.

3 9 MILLIAMMETERS. New. Wherethe lob calls for something simplewithout calibration for tuning orgalvo for testing. Back of panel type.as illus., 8m.a. full scale. Plain scaleand 1 in. needle with mica panel, backlamp and bracket. Neat and compact.Can be used as voltmeter with extraresistance. Great bargain at 3'9post free.

Send for "Radio Electrical" Scientific Illus. Lisl ' V." Free

ELECTRADIX RADIOS218, Upper Thames Street, London, E.C.ti

'Phone : Central 4611


AUTHORITATIVE

TRAINING

in WartimeIn peace -time the T.1.G.B. home -study coursesprovided first-class technical education. Forseveral years past the pass percentage ofT.I.G.B. Students at Professional EngineeringExaminations such as A.M.Inst.C.E.A.M.I.Mech.E., A.M.I.E.E., A.F.R.Ae.S..C. and G., etc., has not once been lower than96%-and no fewer than 22 FIRST PLACEShave been gained. In War -time the advantagesof T.I.G.B. Training-free from black -out andtravel difficulties-are most marked. To -day,The T.I.G.B. courses are the ideal method ofqualifying quickly for the great range of postsbeing offered by Industry and the Govern-ment to technically trained engineers, theneed for whom needs no over -stressing. WriteTO -DAY for "The Engineer's Guide toSuccess," containing the world's widest choiceof engineering courses covering all branches andrecognised qualifications. Mention branch, postor qualification that interests you. TheT.I.G.B. guaranteestraining until success-ul for the one fee.

The TechnologicalInstitute ofGreat Britain218 Temple Bar HouseLondon - - E.C.4

(Founded 1917)20,000 Successes

An Absorbing HobbyBUILDING A STUART MODEL ISAN ENGROSSING PASTIME, ANDTHE RESULT A CONTINUOUS

PLEASURE

We illustrate

STUART

NO. 10.High Speed

Steam Engine.

Bore 41".

Stroke 71".

Each set is quitecomplete-drawings andinstructions areincluded.

If you have a lathe-The rough castings 8/6

If not-Fully machined set - - 19/6Ditto, with all holes drilled

and tapped - - - 25/ -

This and many other Stuart engines arefully described in the 72 -page CATA-

LOGUE No. 3, 6d. post free.

STUART TURNER LTD.HENLEY- ON -THAMES

BUY, EXCHANGE OR SELLTOOLS-Continued

40 New Improved Machine Vices, 21" wide steelfaced jaws, I" deep, opens 3r. A necessity to allmechanics. Clearing while stock lasts, 4/9 each. -Burke.

56 Sets Starrett Pattern Yee Blocks and Clamp. Twovee blocks and one clamp. Accurate and first-classfinish. Present-day priA over 12:-. Gifts at 5/6 set.-Burke.

Hexagon Dies Nuts, less than half price to clear.Very useful in any repair shop. In the followingthreads only : Whitworth, B.S.F., and AmericanFine S.A.E. Sets E' r, r, r, r, 1", 101set of nine; ditto f" to r, cis set of seven; ditto i" toA", 3/9. Special offer, three sets j" to 1" 271. Ilercheap.-Burke.

46 Sots Whit. Dies and Taps, Etc. Five. 1", tomtitdies, cutting 1". ", r, r. Whit., complete withset of five t tper taps, one I" all -steel die stock, and oneadjustable tap wrench. Very attractive liargain, 8/6set; also a few sets in Brass 26 Threads, same price.Sets of Whit. Taps, seconds, or Plugs, 2/9 get. Nostock of seconds or plugs in 26 thread.-Burke.

U Sets 1" Round Otis, t", r -1 B.S.F.,"! 4", in .S.Y.or S.A.E., _clear 2/9 set. No taps available in thesesizes. 1' Die Stooks, 1/9 each.-Burke.

148 Sets ir Split Dies, cutting I", A-, I", Whit.only. Complete with taper taps, stock and tapwrench. A very useful bargain, 4/6 set. Second orPlug Taps, 1'3 set.-Burke.

750 Only H° Split Dies, cutting 0, 1, 2, 3, 4, 5, 6 B.A.:31-. tt". In Whit. or B.S.F.

Also 32", k", i" by 40 threads. We parchtisledthis stock when prices were low. Secure supplies now.Si. each, 5 6 per dozen.-Burke.

1,200 Small Taps, 2, 4, 6 B.A., r, -6,' Whit.taper second; or plugs, 4d. each, 3/9 dozen; " "Whit.. 7, 5, 10 B.A., 6d. each.-Burke.

300 Large Taps, -4f" r Whit., 9d. each; . 1 -:i", 1,6: ", 2/-; 1", 2/6., Also r and r B.S.F. :it 1 6and 2 - each. Gas Tape, A", ed.; V. 9d.; 1 3:2-, 11: I", 2'6 each. -Burke.

300 Best Carborundum Wheels, approx. 3I" diam1" or r thick, I" hole, suitable for small tool or drillgrinding, 9d. each.-Burke.

2,000 Fine Emery Wheels, 2' to ar diam., Ile toI" thick. Very useful for grinding cutters, taps, etc.Given away price, 2 9 per dozen. Cost ad. to 1/6each.-Burke.

21 any lot. Eight lots St -Below.

:'" Toolholder, with four H.E. Tools,

Adj. Boring Tool, with II.R. Tool,

to p," Silver Steel, I 3 pieces. 13" long.

r to r Silver Steel, 4 lb., 2" to 4" loth.

500 Ass. Brass and Steel Screws, etc.

100 Steel Hex. Bolts and Nuts, I" to r.

16 H.S. Drills, .:31.2" to A-.

Slitting Saws, five " to V thick, 1" hole.

Two dozen Fine Odd Thread Taps to I".

Three dozen Tungsten Hack -Saws to 12".

18 Grinding Wheels, ," to 1" diant.

Three H.S. Tap Fluting Cutters, I i" diam.

One dozen Ass. Files, 4" t 12".

Dozen Toolmaker's Needle Files, indispensable.

Best Carborundum Wheel, 7" by liy 1" hole.

200 Springs to approx. 6" long.

El Orders Carriage Paid, except abroad. Moneyrefunded if not satisfied with any of the above bargains.

J. BURKE, 30, TRIPPET LANE, SHEFFIELD, 1

SITUATIONS VACANTDRAUGHTSMANSHIP. Men over 21 wanted

for reserved occupations. Thousands of openings in allbranches of Engineering, Governtrient Service, etc. Noexperience required. FREE details of rapid prepara-tion and employment service for these vacancies frontNational Institute of Engineering (Dept. 372), 148Holborn, London, E.C.I.

CHEMISTRY EXPERIMENTSFOR BLACK -OUT EVENINGS

Post Free OFFEROf SAMPLE PARCELcontaining manyuseful pieces of

CHEMICALAPPARATUS

219Write G.:. for

FREE PRICE LISTof other Sets.

BECK (=m.Al,

60 l':h 3I.Ne:10-da 4.13Booklet, "Experiments in Chemistry." ad. P.O.

Priao.2 -3-

MachineVice 11,

The ' ADEPT' Bench Hand ShaperLength of stroke of nun. ins.; Length of..rose travel of slide, a ins.: Site of Taint-11, ins. - 4 Ins.; Rise and fall of Tall' -2 ins.; Vertical feed of tool slide. If ins..Maximum distance between tool and table.3 ins.; Weight, 18 lbs. Also the .Adept'

No. 2B.H, Shaper, stroke.Pei w

ManefocirioefF. W. POEMS'.

STREET. SIIEFFI

BARGAIN OFFERINSTRUMENT WIREAt Halt OrdinaryPrieel

Price per lb. for Double Cotton Covered.25 SWG 1/8. 28 SWG 2,2. 30 SWG 2/10.32 SWG 3/4. 34 SWG 3/10. 36 SWG 4/9.

Price per lb. for Double Sill, Covered.26 SWG 2/8. 28 SWG 2/10. 30 SWG 3/2.32 SWG 3/8. 34 SWG 4/8. 40 SWG

Postage 6d. Reels and Winding, 6d. per reel.SPLIT PHASE A.C. MOTORS

1425 r.p.rn. All voltages.Ideal for workshop use,L aches. Blowers. Heavyduty rating. No radiointerference and silent.

h.p. 55/-; 1'3 h.p., 65/-;h.p. 781-, plus 10 per cent.

Other motors from 16/6.Universal, Capacitor,Repulsion. Low prices.

Leaflets Low voltage Trans -free. formers, secondary tap-

pings 10-20-40 volts 6'6. Post Pd.L. WILKINSON, 204 LOWER ADDISCOMBE ROAD, CROYDON

CHARGE YOUR L.T.AT HOME Battery Charger

just plug-in, lit itch Or., that's all !

l'rices: 2v., I amp, 12,6; 2 amps, 18/6; tiv., I amp,15/-. Car Battery Models: 6v., 2 amps, 25/-;12.v., 30/-. Commercial Charger for 1-14, 2v.cells, 0-3 ammeter, Low, Medium, High taps, 50/-.Larger Models, 75,', 90/-. All have Metal Rectifiersand strong steel cases. Send :;d. for REAL PHOTOand FREE TRIAL terms.

BRIGHTON RADIO SERVICE,34 Middle Street, Brighton.

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BUY, EXCHANGE OR SELLAdvertisements are accepted for these columns at 3d. per word (minimum 12 words at 3s. -advertisements of less than 12 words arecharged at the minimum rate of 3s.) subject to a discount of 2.1% for 6 consecutive monthly insertions or 5% for 12 consecutive monthlyinsertions. TERMS :-Cash with order. Cheques, Postal Orders, etc., should be made payable to George Newnes, Ltd. The Proprietorsreserve the right to refuse or withdraw advertisements at their discretion. All advertisements must be received on or before the 5th of themonth preceding date of publication and should be addressed to the Advertisement Manager, " Practical Mechanics, George Newnes

Ltd., Tower House, Southampton Street, Strand, W.C.2.

CANOESBOATS AND CANOE KITS. Hobby for long

evenings. Prices unaffected, few bargains. Metacraft(P) Christchurch, Hants.

METAL WORKMAKE METAL TOYS. Easy, profitable with

"Success" Moulds. List Free. Complete trial mould1/6. - -Lee's, 1 Birkin Avenue, Nottingham.

MICROSCOPYMICROSCOPIC OBJECTS, unmounted

prepared. Assorted packet, 2/-.-Leng, " Elhanan,"Brierley Road, Bournemouth.

MODELSEVERYTHING FOR electrical rewinds and repairs

Screws, nuts, and washers for model engineers. Listsfree. -Lumen Electric Co., Litherland, Liverpool, '21.

PERFECT USED RAILWAY BARGAINS(Gauge " 0 "). Send 4%cl. for our catalogue. -Below.

FOR mix RAILWAYS. Some special locomotivesand wooden coaches; list 1%d. Exchanges. Georges',11, Friars Street, Ipswich.

JUBILEEWORM DRIVEHOSE CLIPS

The long -life clip withthe ever -tight grip.

The Beat KnownFor Radiator Joints,Air, Oil, and WaterHose Joints.

We guarantee a TightJoint.

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L. ROBINSON & CO.,25 London Chambers,GILLINGHAM, KENT.

u s e

"Easily the Best SolderingFluid Obtainable." Thisstatement by a regular userof "BAKER'S" expresses thegeneral opinion of the Motorand Engineering Trades.Sold in 6d., 1'. and lib tins.

also in bulk.

SIR W. BURNETT CO._tH M [CIAO LIMITEDGREAT WEST ROAD ISLIWORill..MIDnE.SE%

OUR ADVICE. BUREAU

COUPONThis coupon is available until January alst, 1940,and must be attached to all letters containingqueries, together with 3 penny stamps. A stamped

addressed envelope must also be enclosed.PRACTICAL MECHANICS, JAN., 1940.

WIRELESSRADIO BARGAINS, 2 valve kits 15s. 8d., imme-

diate delivery. -Buckle, 63, Avenue Approach, BurySt. Edmunds.

PATENTS AND INVENTIONSHAVE YOU a sound, practical invention for sale,

patented or unpatented? If so, write CharteredInstitute of American Inventors, Dept. I6 -C, Wash-ington, D.C., U.S.A.

PHOTOGRAPHYPHOTOGRAPHIC MATERIALS. Plates, films,

mounts, chemicals. Interesting money -saving listsfree.-"Kimber's," 105 Queens Road, Brighton.

STAMPSFREE!! Twenty Unused Colonials. "Neurope,"

1%d. Fifty for 1/1 yel.-G. H. Barnett, Limington,Somerset.

WATCHMAKINGWATCH & CLOCK REPAIRERS. Send 3d. for

complete list of material and tools.-Blakiston & CoAinsdale, Southport.

MISCELLANEOUSCASTING MOULDS for Lead Soldiers, Indians'

Animals, etc. Sample mould, 2/9. Catalogue stamp. -Industries 2, Waldegrave Park, Twickenham.

TELESCOPES, MICROSCOPES, ScientificInstruments, etc. Send for lists. Sale or Exchange. -C. V. Bolton, F.S.M.C., 49a Leigh Road, Leigh, Lanes.

HALLICRAFTERS Sky Buddy, S.19, £7 orexchange for 5.10 meter battery superhet.-George,15 Garsdale Road, Peckham, S.E.15.

BE TALLER II Extra inches count Details6d. stamp. -Malcolm Ross, Height Specialist, Scar-borough.

in. WINFIELDFOR VALUE AND RELIABILITY

As illustrated £10 - 10 -0or by 12 monthly payments of 18:4

3 in. B.G.S.C. Lathes from E4 - 10 - 0

The Winfield Mfg. Co.`tigNeGS tiAtiks

CUT THISPractical Pen Coupon Value 3d.

Send five of these coupons with only 3/- (and 2d. stamp)direct to the Fleet Pen Co., 119, Fleet Street, E.C.4.By return you will receive a handsome lever self -fillingFLEET B.F. PEN with solid gold nib (fine, medium, orbroad), usually 10/0. Fleet price 4/3, or with 5 couponsonly 3/-. De Luxe Model, FLEET SELF -FILLER,2/- extra.

(Dept. 358), 6

MISCELLANEOUS-Cont.LIGHT BRASS AND ALUMINIUM CAST-

INGS made and turned (for inventors by blue printsif necessary). Strictly confidential. -Donovan Bros.,"Ronkswood," Llanbradach, Caerphilly, Glam., SouthWales.

MUSICAL INSTRUMENTSBAND GUIDE. Hints on the Bugle, Drum, Flute.

Staff Parade formation, etc. Free, post paid. -Potter's (Manufacturers), West Street, London, W.C.2,

TOOLSBRAND NEW POWER TOOLS of quality,

10 -inch bandsaws, 54s.; Jigsaws, 22s. 6d.; BenchDrills, 11s.; Circular Saws from 25s.; 3 -inch S.C.Toolroom Lathes, from £4 5s. New 1 -inch chromium -plated, Micrometers, 12s. 6d.; Electric Drills, 37s. 6d.;Grinders. -John P. Steel, Bingley.

GRAYSON'S Glass -boring Outfits and TubeCutters avoid risk. -Below.

DRILLS, Taps, Dies, Files, Chisels and Punches.Best quality at keenest prices. -Grayson & Company.300 Campo Lane, Sheffield.

MYFORD LATHES have no equal for sturdinessand value. Lists free. Delivery anywhere. Terms sts Iavailable.-Nuttall's, 20 Albert Street, Mansfield.

MASTER THE PIANOEasily, Quickly, EnjoyablyTo learn to play really beautifully isnot difficult -It is easy -with properteaching! Even if you start at middleage, not knowing a note. I CANTEACH YOU to play so that your

friends will want you always. I willsend you by POST. Sun -clear. FascinatingLessons from ordinary musical notation.no freakish methods, enabling you toread and play at sight any standard musi-cal composition. 1 have taught over51,000 adult pupl's during 35 rears. andI DAN TEACH YOU, and I guarantee toplease and even surprise you with yourrapid progress. Send p.c. for FREE BOOK

"Mind. Muscle and Keyboard."and form for free advice.

Say Moderate. Elementaryor Beginner.

Mr. H. BECKER,B,a14/6 by BirM

rai weal,9, Fleet Street, E.C.4.

Easily made from ourcastings 12,6 per set.Complete Enginesready to run from

£3 15s.J. HALLAM & SON

Upton, Poole,Dorset.

MINIATURE PETROL ENGINES . . . forAeroplanes and Speed Boats. 1 to 15 c.c.

Send 3d. for particulars.

MAKE MORE MONEY£3 to £6 weekly can be earned at home In a wonder-ful business of your own. No matter where youlive you can commence to make money in yourspare or whole time. No risk, canvassing or exper-ience required. A wonderful opportunity for anyonewishing to add pounds to their income. Particulars,stamp.BALLARD, York House, 12 Hambrook Road,

LONDON, 8.E.25.

Ali apptications respecting Advertising in this Publication should be addressed to the ADVERTISEMENT MANAGER .GEORGE NEWNES LTD.Tower House, Southampton Street. Strand, London W.C.2. Telephone : Temple Liar 4.163

1

GAMAGESend for copies ofGamages ToolBargain Leafletsfor Metalworkersand Woodworkers

FIRST QUALITY, HEAVYWEIGHT3 in. SCREWCUTTING LATHES(BACK GEARED, GAP BED), SLIDING, MILLING, SURFACINGAn opportunity to secure a high-grade lathe at a remarkably low

price. Be advised and order now while stocks are available.SPECIFICATION:-

Exceptionally strong headstoek with adjustable bearings.Heavy, solid bed ensures accurate work. Machine cut changewheels for all English threads. Saddle and slide have largebearing surfaces, and the tailstock is of right design. Swing oversaddle 41 in., over bed 6 In., over gap 8 in. Diameter of mandrelI in., mandrel nose in. x 12 threads. Mandrel and tailstockbored in. clear. Centres No. 1 Morse taper. leadscrew in. a8 T.P.I. Cone pulleys 31 in., 3i in., 21 in. x in.

2 in., overall length 27 in., weight 52 lb. Com-. IBack gear ratio 30 to 20, distance between centres

lete with face late. and ten change wheels.

Or DELIVERED on FIRST of SIX MONTHLY PAYMENTS of 14'9Carriage (outside our extensive delivery area) :1,6 extra England and Wales.

BRITISH MADETHROUGHOUT

TABLE VICES

withSteel -lined

Jaws andCoveredScrew

Ifigh-grade Vices in thesizes

11 in. Jaws. Weight 21lb.Post 6d.

21 in. Jaws. Weight 4 lb. 3/11 Post2;',, in. Jaws. Weight 5 lb. 5/- Post Bd.

BOXES 0 12ASSORTED FILESThe best and cheapest way to buyFiles. Britishquality.Sizes 6 to 12 ills. for

Post 9d.Also sizes 4 to 8 ins. 12 for 2,11.

Post tid.

Suitable for Very Fine Work

Constructed on orthodox lines. Overall length, 124 in. Length of bed, 8 in. Maximumdistance between centres, 01 in. Height of centres .un gap, 1. The nose of thesolid mandrel is # In. x 20 threads. Bearings adjust,tile for I ompound sliderest has yes slides with jibs and adjusting screw **lockof the sliding barrel type and is held in position 1), set,lniver plate, 11 in. in dia. Cone pulleys, lg in. x 1 it dia. tpe. in. or in. rotted belting. Weight, 8 10. ,

Carriage 1/6 England or -Wales.Foot Motor, 18 6. Set of Six Tools, 3/3; Belt, 518.

iv PLAINGAP BEDLATHE

with CompoundSlide Rest

SURFACE

GAUGESAccurately made.Fitted with lineadjustment device.Overall height 12 in.Diameter of base,31 inches.

Post list.

HEAVY DUTYAIR COMPRESSORSA first-class compressor at amost competitive price. f in.bore, 'kin. stroke. Splashlubricated, sealed crankcase.Diameter of flywheel 9 in.Weight 34 lb.Carriage1/6 Eng-land or

Wales.

63'Also large:and morepowerfulmodelwith 2 in.bore,2ln.

stroke,64.17.6

or £1Deposit.Balancein SixMonthly

Paymentsof 14 3

GEAREDMINIATURE

A.G. MOTORS (51 cydes)Will work through any -suit. -able transformer. Rating 12to 14 volts continuous totwo minutes at 24 volts.Incorporating bi-metal ther-mal cutout and automaticclutch to avoid breakageunder sudden stoppage. Re-versing switch, self-lubricat-ing bearings. Rotors eed noload) 2,000 r.p.m.Output spindlespeed 58 r.p.m.All brand new,andremarkable value. Post 6d.Illustration iR approx. one-

third (whorl

BRITISH

MADE-SUPER

QUALITY

ELECTRIC

SOLDERING

IRONS

A flue tool with a six months'guarantee against electricalbreakdown. Length 12 in.Fitted with a 6 oz. copperbit, loading 80 watts. Com-plete with twyards of twinIlex and adaptor.Exceptional value.Please state voltage. Po., 61

POLISHING, BORINGand

GRINDING HEAD

British made and offered at muchbelow original price. Height 7 in.Total length of spindle, 10 in. Chuckcapacity, 1 in. Weight 7 lb.Also available for grinding wheel -oily, and without a heck and tapered

-Muffle, at same price.

SET OF

HIGH-

GRADE

TAP

HOLDERS

With six collets for taps to-tif in. Excellent work-

2n

manship and out-standing value.

Post 6d.

STOCKS AND DIES by Russell Manufacturing Co.A SUPER SET ---- Adjustable dies in 21 in. diameter

collets cutting 1, 1%. R,

and in. Whitworth Threads witha taper tap to each size. Completewith die holder and tap wrench.['ached in a strong wooden box.

Carriage (outsidenee extensive deliver',

a, , a - England or Wales.

OR DELIVERED FOR 23/- DEPOSITBALANCE IN SIX MONTHLY 17'3PAYMENTS OF

Heavy Duty Block Type

CondensersI MED. Capacity.tages up to 1,000A.C. or 2,000D.C. Tested to1,000 volts D.C.Dimensionsapproximately41 in. wide, 9 in.overall height,

in. thick, Bake-lite ease. To becleared at all enor-wous lion.

216Pik! ad.

Suitable for vol-.

DAMAGES, HOLBORN, LONDON, E.C.1 Phone your order: HOLbo. i City Branch: 107 Cheapside, E.C.2

Published about the 30th of each month by GEORGE NEWNES, LIMITED, Tower House, Southampton Street, Strand, London, W.C.2, and Printedin England by THE SUN ENGRAVING CO., LTD., London and Watford, Herts. Sole Agents for Australia and New Zealand-Gordon & Gotch, Ltd. Sole Agentsfor South Africa-Central News Agency, Ltd. Subscription Rates : Inland and Abroad, 8s. 6d. per annum. Canada, 8s. per annum. Registered at the G.P.O.

for transmission by Canadian Magazine Post.t

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