isaac asimov atom journey across the subatomic

7/26/2019 Isaac Asimov Atom Journey Across the Subatomic

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T

uraed b F ach

Journey Across the

Subatomic Cosmos


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USMC ASUlOY

( TRA TALL BKS DUN EW RK


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DUOPublished by the Penguin GroupPegin Books SA nc., 375 udso Steetew Yok ew York 10014 SA.Pegi Bks td 27 rigts Lanedon 8 Z glad

Penguin Bks Austalia Ltd RigwdVictia, AstaliaPenguin Bks anada td 280 Jon SteetMarkam Ontai aada 3R B4Pengui Books () td 18290 airau Rad,Ackand 0 ew Zeaand

Pegin Books td Registeed Oces:amondsworth Middesex gad

Fist pbished by Tman aey Books' Dtta impit f ew American Libarya divisio of Pengui Books SA ncDistibuted i aada by Mceand & Stewart c

First Prting May 19911 9 8 7 6 3 2 1

opyright igtfa nc 99ustrations cpyigt D Bac 991

Al rights eseved

LIBRARY OF CONGRESS CTOGiG-N-PUBCTON DTAsimov saac 192

Atm juey across te subatomic cosmos saac Asimovp m

"uman aey boksSB -525-2990-71 Atms ite

Q73A778 195397dc20

Pnted in the ited States of AmeicaSet in entuy xpaded

-2343P

itot imitig the rights unde copyight reserved above no pat of tis pbication may be eproduced, stored in o introduced into a retrieva system ortansmitted i ay fom, by any meas (electric mecanica potocpyingrecodig or otherwise) without the pro witte pemission o bot te copy

rigt wer and te above pubiser o tis book


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To Trman "Mac Tay

Who rprsnts ook puishing at its st


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CONTITS

APER OE

MATTER

vidi Matt

Elements 6

Amism Tiumphat 8

Th Raliy f Atms 13

Th Dincs Amn Atms 8


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APR O

LGHT

Parcls and Wavs 26

Th our Phnomna 3

Conns

Combinng h Phnomna 42

Exndng h Spctrm 47

viding Enrgy 2

APR HR

ELECTROS

ividing Elctrciy

CathodRay Paticls 66

Rays 6

Elctrons and Aoms 72

Ectrons and Quana 79

Wavs and Parcls 2

APR OUR

UCLE

Probing h Atom

Posivy Chargd Particls 6

Aomic mbrs

Spctra Lins


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CAPR FV

ISOTOPES

la n 122

la Vaitis 2

Halfivs 31

Conns

Sabl la Vaits 36

CAPR SX

EUTROS

Pns and Ens 146

Pts and ns 11

a Ratns 1

Aiial stps 164

CAR SV

BREAOWS

ass f 174

a issin 1

a sn 17

Bakwn Patils 14

IX


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CHATER EIGHT

ATATTER

Antiparics 22

Csmc Rays 26

Paricl Acclratrs 25

Baryns 2

CHAP NINE

EUTROS

Contnts

Savin th aws f Cnsrvatin 225

tctin th Annurin 232

tctin th utrin 235

Ohr Lptns 23

Unsabl Parcs 244

rin Variis 247

CHATR EN

TERACTOS

Th Srn nracin 253

Th Wak nractn 26

Th Elcrwa nractn 266


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nn

CAE ELEVE

QUAS

Th Hadron Zoo 27

Insd Hadrons 278

Quantum Chromodynamics 28

CHAPE WV

THE UNIVERSE

Th Mysry o th Missin Mass 29

Th End o h Unrs 298

Th Binnin o th Unirs 3

INDE 3

i


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n

ATTR

Dvdng Matr

Suos you had a lar ha o sma, smooth bblsthousands o thm. you had nothin bttr to do youmiht dcid to dd it nto two smalr has, aro-maty qual n si You could discard on o ths has,

th othr, and diid it n two aain O ths twostill smar has, you coud discard on and th othror urthr dison, and rat th rocss or and or.

You mht wondr how lon you coud that uForr? You now bttr than that. No mattr how larth ha was to bin with, you would ntualy b t

wth a tiny "ha mad u o just two bbls. This wouldhan surrisinly quicy. n you startd with a


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Atom

milion bbls, you woud b down to two bbls aftrabou twnty diisions f you diidd a ha of two b-

bs onc aain, you would nd u with on ha consistnof a sin bbl, and th am woud b or. You cantdi on bbl.

But wai You can. You could lac th bbl on ananil and ound it with a hammr. You would bra it uinto framnts and you could diid his ino smallr andsmalr has unti you wr down to a sinl framn.

You coul thn ound th framn ino dus and thndiid h ha of dust untl you ndd u wth a sn,hardy isibl dust aric. You could bra tha u, and on oin.

This is not raly a ractical am bcaus is ryhard o handl a an of dus and try o bra it u furthr

But you can min main that you can bra u hdus ino stil nr articls, which you can bra u ytrthr n t r nr. Now as yoursf: s thrany nd o this

It miht no sm li a ry imorant qustion orn a aricularly snsb qustion n that you cant ralytry th rimn in any ractical way. You nd yourslfdaln ry quicly with objcts hat ar oo small tos so ha you don n now whthr or not yourbrain th ha down any furthr. Nthlss, crainancint Gr hiosohrs asd thmsls his qusionand statd a chain of thouht hat is stil occuyn hns to his day twny cnuris latr.

Th Gr hiosohr ucus ( ..) is hst rson w now of by nam suosd to ha considrd this robm of didin mar, and to ha com toth conclusion ha h rocss could not contin forr. insistd ha soonr or lar, on had o rach a fra-mnt of matr so smal ha i coud not b bron down

into anythin smalrA younr man, mocrius 4637 .), was on

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Mar

o Luiuss uls. H atd th notion o amntso mar so smal as to b unbraabl H ald suh

ramns aomos whih in Gr mans "unbraabland suh a ramn has om o b ald an atom n En-lsh. To Dmorus, al mar onsisd o a oltion oatoms and i thr was sa btwn h atoms hat saontaind nothn (h oid).

Dmorius is suosd o ha writtn siy boosoundin hs horis, inludin his noions o wha w

now al atomism In thos days thouh whn thr wasno rntin and all boos had o b hand od hr wrhardly r ry many os; and, arty baus his iwswr unoular th boos wr not od many tims.Or h nturis many boos anishd. Non o Dmo-rtuss boos has surid.

Mos hilosohrs o th m lt ha it didn masns o suos hat som iny ndidual artil wasindiisib. Thy houht i mad mor sns to suostha rythin ould b bron u into smalr and smalrbits o mar, ndlssy.

In ariular, th Gr hiosohrs lato a. 234 ..) and Aristot (33 ddn at aoms.Baus thy wr th most roound and mntaly widranin o th anin hilosohrs thir iws tndd oarry th day. But th arumnt was not unanimous. Thnuntal Gr hilosohr Eurus (342 ..) oou atomism as h nral or o hs ahins. Eiurusi sosd o ha writn 3 boos (anint boos tndd

o b shor nidnaly, but non o thm has surd.Th mos imortan o th Eiurans in this on

ton was a oman, Titus Lurtius Carus 655 , usually nown smly as urtius. In 5 .. h ublishd alon om in Lain ntld D Rm Naura (atn orOn h Naur of Thngs) n i h laind th Eiuran

w o aomism in ra dtai.Th boo was ry ouar in its tim bu in lar

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Atom

cnturs r Christanity had rown oulr, Lucrtiuswas dnouncd or what was considrd to b thism.

ws no lonr coid nd what cois alrady istd wrdstroyd or lost. En so on coy only on) surdthrouh th Middl As and ws dscord in 47 Itws rcod and thn, hal a cntury atr, whn rintincm into us, ucrtiuss om ws on o th rst itmsto b rintd.

Th om srd throuhout wst Euro nd was

th chi sourc o nowld o th ancint thors otomism. Th rnch hilosohr Pirr Gssndi 5655), hain rd ucrtius, dotd th atomistic whims, and wrot it u rsuasily, thus sradin thdoctrin.

In all th two thousnd yars btwn Lucius and

Gassnd, howr, tomism ro nd con, ws simly asubct o ndlss discussion mon scholrs. Thr ws noevdn ithr or or aainst atomism. Varous schoarsacctd atoms or rctd thm, ccordin to which onto iw lasd thm bttr or smd mor snsibl.Thr was no wy oorcin on iw on somon who hld

th othr iw rmy. It ws a subct dcision andthr ws no run wth tastAbout ths tim, howr som scholrs wr bin-

nin to rorm rimnts; to st qustions to ntur soto sa and to study th rsults. In this wy, dnccould b producd that was scintcy "comlln; thatis t was idnc that comld othrs to acct oint

o iw that thy wr subctily aainst roidd thywr ntllctuly honst).

Th rst to rorm rimnts tht smd to ha connction wth th qustion o atomism ws th Britishscintist Robrt Boy 676), who was strony in-uncd by Gssnds writins, nd who was consquntly

an atomst.

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Mattr

n 662 Boyl mad us o a lass ub shad ih ltr Th short arm was cosd and h lon arm

on H ourd mrcury ino h onin and i lld hbottom, train ar in h closd short arm Boy hnourd addonal mrcury ino th ub h wih owhich comrssd th air in h short arm, dcrasin houm o h air as a rsult h doubld th hht oh mrcury column in th lon arm, h oum o air inth short arm was hald Whn h mrcury was rmodand th rssur rlasd h olum o air incrasd Thsinrs lationsh bwn rssur and olum has bncald Boys aw r snc

This bhaior o air undr rssur was asiy laind on mad us o atoms Suos h air is mad uo atoms that ar widy saratd wth nohn n b

twnas Dmocrius had sustd This would accountor h ac that a oum o ar wihs so much ss than thsam olum o watr or marbl whr h aoms miht bn conact) acin h ar undr rssur woud orc haoms clos tothr squn out som o th nothinnss so o sa and woud dcras h olum Rliin

h rssur would alow th atoms o srad outwardFor h rst im, aomism ban to ain an urhand Somon mih hin hat it wasnt snsib, or rhas that wasnt shc o suos h istnc oatoms bu on could not aru wth Boys rimnThis was scialy tru n hat anyon could run th -rimn himsl and com u wih th sam obsraons

I w mus acct Boyls rimn thn atomismors a sim and oical anaion o his ndins E-ainin h rsuls wihout aoms is much mor dicult

From hat oint on thn mor and mor scnistswr atomists, but th issu was not y comly sdWll t bac to th subc atr)


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Aom

Elemnts

Th ancnt Gr hiosohrs wondrd what th worldwas mad o Carly i was mad o nnumrabl tys othns, bu sciniss ha always th ur o simlyThr was h ln hror ha h world was mado som basic matria or som ry w basic matrials)o which ryhn ls was on ariation or anothr

Thals ca 646 s h rs Gr hilosohrsuosd to ha susd ha watr was h basic marial out o which rythin was ormd Anothr Anaimns 7 houht i was air Sill anohrracitus ca 347 thouh it was r and soon

Thr was no way o dcidin amon ths sustionsor thr was no ral dnc on way or anothr ThGr hilosohr Emdocs (443 stld thissu by comromis H sustd tha h world wasmad o sral dirn basic subsancs r, air warand arh To this Aristotl addd ahr rom a Grword or "bazin) as a scial substanc out o which huminous hany bodis wr comosd

Ths basic substancs ar calld mnts in Enlishom a an word o unnown orin W sil dscribstorms by sain o "h rain o th mns as watrours down, ar bows about and r bus as lihnn)

To hos ol who accd th notion o th arious

lmnts and who wr aomists mad sns to suosha ach mn was comosd o a drn ty o aomso that th world consstd o our drn tys o atomsalohr wih a th y or h hanly ahr

En wh only our tys o aoms, it was ossbl toaccount or th ra arty o objcts on Earth On only

had o imain that h arious substancs wr mad u

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Matr

of combnations of dirnt numbrs of dirnt yps ofatoms in dirnt arranmnts. Aftr al with ony

twntysi ltrs or wh jus wo symbols, a dot and adash, it is possbl to buid up hundrds of thousands ofdirn words in Enish alon.

Howr th doctrin of th four or lmnsban o fad n as aomism ban o mo ahad n6 Boy wrot a boo, Th Skptcal Chms in whichh too up th posion that it was uslss to uss a what

h basic substancs of h world miht b. On had todtrmn wha hy wr by primn. Any subsanchat coud not b bron down by chmica manipuationino any simpr substanc was an lmnt. Any substancthat could b bron down into simpr componns wasnot an lmn.

This s indispuab n principl but i is not niryasy in practc. Som subsancs canno b bron downinto anythin simplr and miht sm to b lmnts butthn h tim miht com whn adancs in chmistry willma it possibl to bra thm down. And aain whn onsubsanc s conrtd into anothr i isn alwys asy to

dcd which of h two is simplr.rthlss, binnin with Boyl and continun foror hr cnurs chmiss ha labord to nd sub-stancs that can b dntid as mnts. Eampls offamilar substancs tha ha bn rconizd as lmntsin hs way ar old, silr, coppr, ron, in auminumchromum, ad and mrcury. Gass such as hydron

nitron and oyn ar lmns. Air watr arth andr ar no mnts.

A h prsnt tim, lmns ar nown. Eihythr of thm occur nauraly on Earth in rasonabl quantitis, and th rmainin wnythr occur ihr in tracsor ony aftr hain bn manufacurd in a boraory

This mans hr ar dirnt typs of aoms nown.

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Aom

Atomsm Tumphant

Most substances as they occur on Earth are not elementsbut can be broen down into he varous elements tha maehem u Those substances that are u together out of acombination of eemens are nown as comounds (fromLain words meaning o ut ogether)

hemiss grew increasingy interesed n rying to de

ermine how much of each elemen might exist in a artic-uar comound eginning in , the rench chemsoseh ouis rous 2) wored on his roblemand made a crucial dscovery There is a comound we nowcall coer carbonate roust began with a ure samle ofthis substance and broe i down into the three elements

that made it u: coer carbon and oxygen He found in9, hat n every samle he wored with no mater howit was reared here were resent for every ve arts ofcoer (by weight) four arts of oxygen and one ar ofcarbon If he added addiona coer o he mixture inrearing coer carbonae the additiona coer was efoer If he began with a shorage of coer only he roorionae amount of carbon and oxygen combined wh to form coer carbonate and the rest of the carbon andoxygen was left over

rous showed that this was also true for a number ofoher comounds he wored with The elements of whichthey were comosed were always resent in dente ro

ortions This was caled the law of denite roortionsThe law of denite roortions oered srong suor

for atomism Suose for instance tha coer carbonaeis made u of lie grous of aoms (caled moecules fromLain words meaning a smal mass) each grou consisingof one coer atom one carbon atom and three oxygen

aoms Suose also that he three oxygen aoms aen


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In 1 799 Joseph Louis Proust broke w a re sample of a substance nto the three elements tht compsed t: copper, carbon, aoxygen. He foun tt n every sample worked th there were

present for every ve parts of copper (by weght) four par of oxygenand one part of copper. The atomc elements tt compose a compound are always present n dente poportons.

together are four times as heavy as the carbon aom and

that the coer aom is ve imes as heavy as he caronatom If every molecule of ha comound is made u ofthat combination then coer caronae would always bemade u of ve ars coer four arts oxygen and onear carbo

If it were ossible to include in the molecule V aoms

of coer or aoms of oxygen or only % of an atom of


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Atom

crbon, the roortons of the three substnces mght vrfrom smle to smle of coer crbonte. However the

roortons n vr Ths not onl suorts the de oftoms but Democrtuss suggeston tht n tom s ndvsble It exsts s n ntct ece or s nothng

The derence between the wor of emocrtus ndroust ws ths however: Democrtus hd onl suggeston roust hd nce Ths s not to be ten s men-ng tht roust ws necessrl greter or wser mn thn

emocrtus. roust hd the benet of twentone dd-tonl centures of thought nd wor tht he coud drwuon ou mght es rgue tht t ws much more re-mrbe tht Democrtus could ht on the truth so erln the gme)

Even wth evdence, roust dd not necessrl hve

t ll hs own w After l, t ws ossbe tht roustsnlses were wrong, or tht he ws so eger to rove hsown de tht he unconscous twsted hs observtons.Scentsts re onl humn nd such thngs hen.)

Another French chemst ude Lous Berholet(1481822), fought roust ever ste of the w He n-ssted tht his nses showed tht comounds coud bemde u of elements n vrng roortons. In 84 however the Swedsh chemst ns ob erelus 91848) begn metculous nses tht bced rousts no-ton nd roved to the chemc world tht the lw of defnte roortons ws rght.

At the sme tme the Englsh chemst ohn lton

166844) ws lso worng on the robem He foundtht t ws ossbe for comounds to be mde u of eements n wde derent roortons Thus n one gswth molecules mde u of crbon nd oxgen, the roor-tons were three rts crbon to four rts oxgen Innother gs, wth molecules mde u of crbon nd oxgen

the roortons were three rs crbon to eght rts ox

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Matter

ygen These however were wo dieren gases with twodierent sets of roerties and for each one the law of

dente roortions hed.alton suggested that n one gas the molecule wasmade of an aom of carbon and an atom of oxygenwhereas n the other t was made u of an atom of carbonand two atoms of oxygen It eventually tued ou ha hewas correct and he wo gases came o be called carbonmonoxide and carbon dioxide resecivey (The rex

mon is from he Gree word for "one and d is from theGree word for "wo)

aon found hs sort ofthng was true in oher casesand in 3 he announced ths as the aw of multile roortons He ointed ou ha this t the notion of atomsand was he who caled hem atoms deiberately going

bac to the old term as a ribute to emocriusaton sad ha o account for wha was being found

out about the roortion of elements contained n com-ounds one had to decide that each eement is made u ofa number of atoms a wh the same xed mass that dif-ferent elements have aoms of dieren masses and ha

molecules are made u of a small xed number of dierenintact atomsIn alon ublished a boo entiled New Sytem

of hemica Phioophy in which he gathered al of theevidence he coud nd in favor of atomsm and showed how al t ogeher Wih this boo alton estabished themodern atomc theorymodern as oosed to ha of he

GreesAs i haens the word theory is not roery under-

stood by he general ublic whch ends to hin of a theoryas a "guess. Even dicionaries do not roery describewha he word means o scentiss

Proerly seaing a heory is a se of basc rules

suored by a grea many conrmed observaons by many


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Aom

scieiss ha exais ad maes sesible a large umberof facs ha wihou he heory woud seem o be co

eced I s as hough he facs ad observaos are aumber of dos rereseig ciies ad les rerese-ig coury ad sae boudares dsrbued higgledy-ggledy o aer maig o sese A heory s a mapha us each do ad lie io he righ lace ad maesa coeced ad sesibe icure ou of i all

Theories are o ecessarily correc i every deai o

begi wih ad migh ever be erely correc i everydeai bu hey are suciey correc if hey are goodheories) o gude sceiss i udersadig he subeche heory deas wih i exorg furher observaiosad eveualy i imrovig he heory

Each of he basc rules Dao se u for his aomic

heory was o quite righ I ued ou eveually haa eleme could have aoms of dere mass ha woelemes mgh have some aoms ha were of he samemass ad ha o al molecules were made u of smalumbers of aoms Daos rules were suciely close origh however o be very useful, ad as chemss learedmore ad more abou aoms hey were able o correc herules as we shal see aer o

No sceic heory is isay acceed by scieissThere are always hose scieiss who are suscious ofayhig ewad his s erhas a good hg Theoriesshoud o side io acceace oo easiy; hey shoud bequesioed ad esed vigorously I hs way, wea sos

i he heory wil be ucovered ad, erhas sregheedAs i haeed some of he mos emie chemiss of

Dalos day were susicious of he ew heory bu iured ou o be so useful i helig o udersad heobservaos of chemisry ha chemis afer chems fellio ie ad he eire sciec world eveualy became

aomiss

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Matter

The Reay of oms

Howvr wl aomic hory word and howvr ngnosly it was imrovd and howvr it managd to ointh way to nw dscovrs, on disrbing fac rmaind:no on cold s atoms or dct thm in any way All ofth vidnc in favor of aoms was ndirct Yo infeetha hy xstd from this fac and euce tha hyxsd from hat obsrvation bt al of h infrncs andddcons might b wrong Aomc thory smd o st a schm hat word bt i mgh hav bn jst asml modl for somhng tha was actaly mch morcomcad Th woring mod of h im was analogosto ayng or wih chs Th chs can b sd to bt

wh and o show how mch mony is bng los and wonand wil b absolly accrat in vry waybt thoschis ar not mony Thy jst symboiz h mony

Sos thn ha th ida of atoms is mrly a casof laying chmisry wh chis Aomism word bt thatoms mry rrsntd a trh tha was mch mor

comicatd Thr wr som chmsts vn a hndrdyars ar Daon who wr catosly awar of hs andwho warnd agans taing atoms too liraly Us thmby a mans thy wod say, bt dont thin tha thy arncssariy raly hr in th sha of mint blliardbals n scinist who hoght ths way was h RssanGrman chmist ridrich Wilhlm Ostwald 853932).

Th answr to this robm had long bn on th wayhowvr and it stard with an obsrvaion that smdto hav nothng to do wih atoms by a scintist who wasn'tinrstd in atoms (Its mortant to rmmbr that alnowdg is of a ic and tha any obsrvaion can havan nxcd and srrising conncon to somhng tha

aarny has nohng to do wih i)

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T vibraion o a gn o pollen n waer deonses he oveen o he invisible olecules o wae suoundg

I 182 he Scottish boaist Rober Brown (1858) was using a microscoe o sudy ollen grains susended in water He noticed that each olen grain wasmoving slighy and erratically rs in one direction thei another as though i were shiverig He made sure

that this wast he resu of currets i the water or ofmotios set u by the fact ha he water was evaoratigrown concluded i had o be something else hat causedthe movement

rown tried other yes of olle foud that al of thegrains moved in this fashion, ad wondered ifit was because

he olen grains had he sar of ife i them He tried

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Matr

olen grains from herbariums grains ha were a leas acenury old. They moved in jus he same way. He wen

on o ry smal objecs in which here was no quesion offe exsingbis of gass coal or mealsand hey amoved. Ths came o be caled rownian moion and noone, a rs, could exlain .

In he 186s however he Scoish mahemacianames Cer axwell (183189) ried o exain he be-havior of gases on he basis ha he aoms and molecules

ha made hem u were n consan moion Such consanmoion of aoms had been suseced by eary aomiss buaxwel was he s o succeed n woring he heory oumahemaically. The way in which moving aoms and mo-ecues bounced o each oher and o he walls of a conainer as mahemaically modeled by axwell comleely

exlained he behavor of gases. I exained oyes lawfor insance.

axwels wor aso roduced a new undersanding ofemeraure for i urned ou ha emeraure was hemeasure of he average seed of moion of he aoms andmolecues mang u no only gases bu liqids and solids.

Even in solids where aoms or molecules are ozen in laceand can move bodly from one oin o anoher, hose a-oms or molecules vbrae abou heir average osiion, andhe average seed of vbraion reresens he emeraure.

In 192, he Swedish chems Theodor Svedberg(88419) oned ou ha one migh exlan rownianmoon by suosng ha an objec in waer is bombarded

om all sdes by movng waer molecues. rdinariy hebombardmen from al sides is equal so ha he objecremans a res. To be sure by sheer chance a few moremolecues migh srie from one direcon or anoher buso many molecules sre al ogeher ha a smal deviaionfrom exac equaliy (wo or hree ou of rillions) does no

roduce measurable movemen.If an obec susended n waer s very smal however

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Aom

he number o molecules sriig i rom al sides is comparaively small too and here is a smal deviatio that

might represent a airly large eect comparativey Theparticle responds o he push o a ew etra molecules romone particular direction by jering slightly in he direcono he push. In he et moment there are exra colisosin anoher directio and he particle is pushed in that newdirection. The parcle moves randomly and erratically inresponse o the random motion o the surrouding

molecues.vedberg was oy specuating, bu i 95 the

Germanwiss mahematicia Albert nsen (1891955)appied Mawells heory to he bombardmet o small particles ad showed quie concusivey tha those particleswould jggle eacly as the polen grains were observed to

do. In other words, he presened mahematical equatosthat described rowian moion.

In 198 the French physcist Jea apise errin(1870194) se about checing inseins equations againstacual observations. He placed a ne powder o gum resii water. here were no bombardment by water mole-

cues hen all o he particles o gum resin ough o havegone to he boom o the contaier ad remaned here. here were bombardmen some o he particles woud beiced upward aganst the pul o graviy To be surehose parices woud settle again bu hey would hen beiced up again too. ome tha were aready up wouldbe iced up stil urther

A any given me, the particles o gum resi would bespread upward. Most woud be at the bottom, but somewould be a little distance above a ew a greaer disanceabove sill ewer a sl greaer disace above and so on.

The mathematical equatio wored ou by nsteishowed what numbers o particles there shoud be at every

height depending upon the size o the partices and he

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Matter

sze o he aer molecules sriing hem. errn counedhe number o parces a various heghs and ound ha

hey olloed insen's equaion eacly From his hecalculaed ha size he aer moecues mus be and hasze he aoms ha made hem up mus be.

errn pubished his resus in 913. The aoms he hadcalcuaed ere roughly a hundredmllionh o a cenimeer across. u i anoher ay 1 million aoms placedside by sde oud srech across a cenimeer (25 millionaoms paced side by side ould srech across an nch).

Ths as he neares hing ye o an acual observaono aoms. I hey could no que be seen he eecs o heircollsions coud be seen and her acual size could nallybe ored ou. The mos hardnosed scieniss had o given. ven Osald admied ha aoms ere rea ha hey

eren jus maebelieve models.In 936 he German physcs rin Wilhelm Mueller

919) go he idea o a devce ha oud mae ipossible o magniy he poin o a ne neede o such aneen ha one coud mae picures o ih he aomsha compose i lned up as le luminous dos. y 155

such aoms coud acualy be seen.e peope sill spea o he aomic theo becauseha is ha isan inelecua map o large aspecs oscience ha can be nealy epained by he eisence oaoms. A heory remember is no a "guess and no saneand qualied scenis can doub ha aoms eis (Thisaspec o he proo ha aoms eis is aso rue o oher

elesabshed scienic heories. The ac ha hey areheories does no mae hem uncertain even hen variousne deails are sil under dspue. This is particuary rueo he heory o evoluon hich is under consan aacrom peope ho are eiher ignoran o science or orseho allo heir supersiions o overcome ha noledge

hey mgh have)

7


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Aom

The Dierence Amon Atm

I seems easoable o suppose ha if hee ae dieenypes of aoms hey mus die among hemselves, someho in hei popeies. f hs ee no so and if al aomsee idenial in he popeties, he hy should someaoms hen heaped ogehe fom god hle ohesfomed lead?

The aie Gees had hei geaes neleual suess i he developmen of a igoous fom of geomey,so i as aual fo some among hem o hn in emsof shapes he hey hough of he aoms maing up hei"eemens To he Gees, aoms of ae mgh be vieedas spheial bodies ha sipped ove eah ohe easly,

hh as hy ae poued Aoms of eath oud beub and sable so ha eah int o Aoms of eould be agged ad shap hih as ha made e sopainful and so on

The aien Gees also did no have que lea inhei mind ha one ype of aom did no hange ino anohe This as espeialy ue f you osdeed ha goldad lead ee boh vaiees in he mai of he elemeneath Pehaps i as only neessay o pul apat he eathaoms in lead and pu hem io aohe aagemen haoud mae hem gold o oe migh modify he eath aomsin ead o hage hem slighly ino a fom ha ould maehem gold

Fo abou o housand yeas, vaious peope, someof hom ee eanes ad seneminded hle a geamany ohes ee ouigh faes ad haaas epyng o hange base meals suh as ead io he obemeal god. This is aled ansmuaion, fom Lai odsmeanig o hange aoss. They aays faled

By he ime he moden aom heoy as advaned,

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th ncnt Grks, tms wtr mght w s spc

is tht sipp wtr r ch thr sy which ws why wtrpur

i seemed clear tha atoms were not only dieren romeach oher, but tha one type o aom could not be changedinto aother. ach atom was ed and permanen in its

properties, so tha an atom o lead could o be chagednto an atom o gold. (The time was to come, as we shalsee when hs was oud o be no quit ue, under eryspecal conditions.)

u dieren ypes o aoms are dierent rom oneanother, o just what does the dierece consist? Dalton

reasoned as ollows the water moecule is made up o


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Aom

eight pats oygen o one pa hydogen and if he molecueis made up of one aom of oygen and one atom of hydogen,

hen i must be ha the ndvidual oygen aom eghseight mes as much as he indivdua hydogen atom. (Tobe moe pecise, one should say hat the ndividual oygenaom has eigh times he "mass of he individual hydogenaom. The eigh of an objec s the foce ith hch theath atacts i heeas he mass of an object is oughyspeang, he amount of matte t conans. Mass is the

moe fundamena of he to concepts.)Of couse, Daton had no ay of noing he mass of

eithe a hydogen o an oygen atom but hateve i ashe oygen aom had a mass egh times hat of a hydogenatom. ou could say that a hydogen atom had a mass of , ithou saying 1 what ou could then say ha an oygen

atom has a mass of 8. (Acualy e no say he hydogenatom is daon, in hono of he scenst but it is cusomaysmply o leave t as )

alon ent o o ith compounds containing otheelemens and oed out a sysem of numbes epeseninghe elaive masses of them all He caled them atomc

weht and he em s sill used today even though eshould spea of atomic masses. fequently happens thascienss begin to use a pacua em and then decdethat anothe em oud have been bee, bu nd it s toolate o change because peope have gon fa oo accustomed to he pooe em. Well come acoss othe casesof he sot in hs boo)

The touble ih aons method of deemnngatomic eghts as that he as foced to mae assumptionsthat coud too easly be ong He assumed that a atemolecule consisted of one atom of hydogen and one of oygen but he didnt have any evidence fo tha.

In ha case one mus loo fo evidence. In 1800 the

itish chemist Willam Nchoson (17531815) assed an

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Mattr

lcic cunt though acdd wa and obaind bub-bs of boh hydogn and oygn oninud invstigaion

of his phnomnon showd that h volum of hydognfomd was jus wic that of th oygn although thmass of oygn libatd was ight tims h mass of thdoubl voum of hydogn

Why was twic h voum of hydogn poducd ascompad to oygn Coud i b ha th wa moculwas composd of two hydogn atoms and on oygn aominstad of on of ach ould it b that h oygn atomwas igh tims as havy as both hydogn atoms put to-gh o sin tims as havy as a singl hydognatom In oh wods if hydogn had an atomic wghof 1 was th atomic wigh of oygn 16 ah than 8

alton fusd to accpt this noion (It on happns

tha a ga scintis having takn a gan stp fowaduss to tak oh stpsas though th gat st othad haustd himand avs it to ohs to continu omach fowad)

In ths cas i was Bius who ook th fowadstp placing hydogn at and oygn at 16 continud

with oh lmnts and in 1828 pubishd a tabl of aomicwights tha was much bt han atons had bn omth wo of Bzlius i smd cla that vy mnthad a dint atomc wight and that ach aom of apaticua lmn had h sam aomic wight ( musmind you again ha ths conclusions vntually povdo b not qui igh but hy w na nough to igh

to b usful o chmiss fo nay a cntuy Evnuallyas mo nowldg was gaind hs viws w modidn ways tha sighy changd and immasuably stngth-nd th aomic thoy This impovmnt of thois hap-pns ov and ov and is th pid of scinc To supposhat his should not happn and that thois should b

absolutly coc to bgn with is to suppos hat a stai


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Aom

way streching upward for ve stories should consis of asinge vestoryhigh step)

Well, then, he volume of hydrogen produced whenwater is broken down by an elecrical current is wce hevoume of oygen ow do we know from this that hereare two hydrogen atoms o one oygen atom in he mole-cule seemed sensibe o Berzelius to suppose so, bu hedidn't know for sure It, oo, was an assumption, evenhough here was more evidence behnd t than here was

behind alton's assumption that here was one hydrogenaom and one oygen in he water moecule

n 81 the Italan physcist Amedeo Avogadro7761856) made a more general assumption e sg-gested that in the case of any gas a gven volume alwayscontains the same number of molecules If one gas has twice

the voume of another gas he rst gas has twice as manymolecues as he other Ths is caled Avogadro's hypothesis (A hypohesis is an assumpon tha is sometmes ad-vanced jus to see wha the consequences would be If heconsequences go against known observations then he hy-pothesis s wrong and i can be dismissed)

Naturaly, when a competent scientst advances a hy-pothess hat he thins mgh be rue, there s a good chance will turn ou to be true One way of testng Avogadroshypohesis for instance, is to sudy a great many gasesand to wor ou he number of each of he dieren ypesof atoms in the molecules of hose gases on he basis hatthe hypothesis is true

If one does that and ends by volatng known obser-vaions, or ends by producing a contradiconas when oneline of argument based on he hypohesis shows tha a par-icuar moecule must have a cerain aomc compostionand anoher ine of argmen shows i mus have a dierenatomic compostionthen Avogadro's hypohess woud

have to be hrown out


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Aogado's aw eqa oes of a gases nd na oons of epee a pesse onan ea nes of oees For exape, gh ake 1 ga of hydogen g o ahds aoon wod ake appoxaey 1 gas of oxygengas o ae an dena aoon o an eqa sze oh aoonswod onan appxaey he sa ne of oees

Actuay no one has eve found a case in whch Ao-

gado's hypothesis is tuy miseading and the theory is noonge a hypohesis but s cosideed a fact athough hereae conditions unde which i must be modied It is stialld Avogado's hypothesis howee because chemistsae so accustomed to caing it hat

One pobem howeve was ha when Aogado's hy

pothesis was st advanced vey few chemists pad ny


38/332

Atom

aenion to it They eithe didn't hea o it o dismissedt as eihe idiculous o unimpotant Even Bezeus ddn

make use o the hypothesis so hat his tabe o atomicweighs was wong n placesIn 1858 howee the Italian chemis Stanislao an-

niao (18691) came acoss Avogados hypothesis andsaw hat that was what was needed o make sense out oging out how many atoms o each element thee ween a compound and getting the coect gues o atomic

weighn 186 thee was a geat inteational chemica con-

gess whch chemists om al ove Euope atended (itwas the s o such inenationa congesses) At hatcongess annizzao convincingly eplained the hypothesis

This at once impoved the entie notion o atomicweigh About 1865 the Belgan chemist eanSevas Stas(1831891) pu ou a new table o aomic weighs hat wasbette than Bezelus's Foty yeas lae he Ameicanchemist Theodoe Wliam Richads (1868198) made evenmoe ened obsevations and got he vey best values one

could get beoe (as we shal see) he entie subjec o atomicweight had o be modied because o new dscovees ByRchadss time Nobe pizes wee being handed out ando his wo on aomic weighs he go the Nobe pze ochemisty in 1914.

As it happens the elemen wih the lowest atomicweight s hydogen I is atomic weigh is set abitaly

at 1 then he atomic weight o oygen is a ite bit lesshan 16. (That it is not eacty 16 is a point we wi consdelate on) Howeve oygen easily combnes wh a geatmany othe elements and i is much simple o compaethe atomic weght o some paticua element to oygenthan to hydogen It s convenient then o se oygens

atomic weight at some eact gue I shouldn be set at

4


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Mattr

bcaus tha would giv svn lmns atomic wghsoflss ha 1 which would b incovnit n maing chm-

ica calculaons. bcam customay th o st th aomic wightof oygn at actly 16 which mad th atomic wigh ofhydog us a lit bt gat han 1 That man hatno lmt had an atomic wigh of lss han Stas's liswas mad that way ad hat st th fashion. Howv hsituation has b chagd vy slighy in ct yas foasons hat wl b plaind lat)

If h lms a lsd n od of incasing atomicwights thn s possibl to aag hm n a athcomplicatd tabl ha dmonstats ha ctai poptsof h lmns pat hmslvs piodically f h tabis aangd cocy lmns wth simila poptis fal

ino th sam coumn. This s cald th piodic tabl, anda wokabl vson of it was st psntd by h Russianchmis Dmti I vanovich Mndlv (183419) i 1869.

Th podic tabl was quit nativ at s bcausMndv ddnt kow al of h mts. May had oty bn dscovd. In aanging h tabl so that simila

lmns w n h pop columns Mndlv wasfocd o lav gaps. H flt that hs gaps pstdundiscovd lmnts and, choosig h of thos gapssatd in 181 that thos undiscovd lmnts onc dis-covd woud hav cain poptis which h dscibdn dail. By 1885 all h mts w discovd andMdlv was povn pcisly coct i ach cas. This

od vy song poof that th piodic tab was a lgmat phnomo but no on coud pai wy wod. W will tu to this la on.)

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lGH

Paics and aves

If we ae pepaed o adm ha al mae s composed ofaoms, hen is easonabe o ask if hee is anyhing nhe wold ha sn' mae and heefoe, sn composedof aoms The s possibly ha migh sping o mind is

ligh has always seemed obvious ha ligh is immaeia

Solids and iquids can be ouched; have mass and heefoeweigh and ae up space Gases canno be fel in he sameway ha soids and lquds can bu a moving gas can be fel.We have al epeienced high winds and we wel know wha

a onado can do Then oo a wil ake up oom so ha ifan empy beake (acually full of ai) is plunged open end

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Ligt

down ino a tank of water the waer does not l the beaerunless somehow, the air is allowed to escape In 1643 the

aan physicist Evangelsta Torrcel (608164) showedtha ar had weight and that his weight coud suppor acolumn of mercury 6 centimeters (30 inches) hgh.

Light however has none of these properies. It cannotbe fe even hough the heat i might produce can. t hasnever been found o have percepible mass or weight andi does not appear o ae up space.

Ths doesn' mean that light was dsmssed as unimportant because i was insubsanal. The rst words of Godas given in he Bible are "e there be light Whas moreunder the name of re it was he fourth of the ancientEarthly elements on a par wih the hree material ones ofair, waer and earth.

Sunight was naturaly consdered to be light a ispures. I was whe light, unchanging and eea f sun-ight were made o pass through colored glass t would pickup the color of he glass bu that would be an earthlympurity. Again when obecs burned on earth and gaveo light ha lght might be yellow orange, or red n somecases if certain powders were cas nto the re mighteven burn green or blue. Bu agan these were earthlympurities ha gave rise o color.

The one coored objec ha seemed to be divorced fromanythng earthy was the rainbow, which was sucientlyaweinsprng to gve rise o myhs and egends. t washought to be he brdge beween heaven and earth used

by divine messengers (The Greek messenger of the godsis given he name Irs whch is Greek for "rainbow) Itwas also a divne guarantee hat he world would neveragan be destroyed by ood so that it appears at he endof rainstorms indcating tha God has remembered andstopped the rain.

n 1665 however, the English scienist Isaac Newton

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Atom

1621727) poduced his ow aibow. a daeed oom,he alowed a beam of sunlgh to ete though a hole i a

shutte and passed tha beam hough a heedimensionatiangula wedge of gass called a pism The beam of ightspead out and poduced a bad of colos on he white wabeyod the colos being ed oange yelow geen bueand violet in that odejust the ode i which hey occui the anbow

A ainbow we now now, is caused by suight passing

though the numeable doplets of an sl in he aiafte a ainshowe. These doplets have the same eec onligh ays as a glass pism.

Appaently then, sunlght is ot "pue light afte all.Is whiteness is meely the eec poduced o he eye bya mitue of al of these colos. By having the light pass

though a pism ad then pass though aothe pism heldi he evese positio he sepaaed coos wil ejoin andfom whte light agan.

In that these colos ae thooughy immateia, Newton caled the ainbow band a specum fom he anwod fo ghost. Newtons spectum ceaed a pobem,howeve. o the coos o be sepaaed on passing thoughthe pism, Newon believed each one must have its odinay staightlie pah bent (efacted) as it passed intoand ou of the glasseach coo ben to a dieent etet(ed the east and viole the most so that hey wee sep-aated and see each by itself when the beam hi the walWhat, the, coud ligh be made of that would account fo

the sepaato of light no a spectum?Newon was an atomst and so it natualy occued o

hm tha ligh was made up of tiy patces le the aomsof mate ecept ha the paces of igh dd not havemass. He had no clea oion howeve, as to how the pa-icles of coloed ight might de among themseves, ad

why some should be efacted by a pism to a geate eetthan othes.

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Ligt

urhermore when two beams o ligh crossed eachoher one remained unaeced by he oher I boh con-

sised o particles should not those particles colide andbounce o one another randomy so hat he beam wouldgrow uy and spread ouward ter colision?

The utch physicist hrisiaan uygens (16165)had an alternae suggestion e hought light consised otny waves In 68 he advanced argments or showingthat an enire seres o waves migh advance in what looked

lie a stragh line jus as a beam o particles would andtha wo beams, each made up o waves woud cross eachother wihout eiher being in he end, disturbed

The roube wih the wave suggestion was ha peoplethough o the ypes o waves produced in water such swhen a pebble is dropped ino a sil pond As hose water

waves expand hey end o move around an obstrucionsuch as a piece o wood (dracion) and join again on heother side In ha case wouldn ight waves curve aroundan obstrucion and cast no shadows, or a least y ones?Insead, as s wel nown igh casts sharp shadows i thelight source s smal and seady Such sharp shadows areexacly what you woud expect i ligh were a beam ominte parcles and hs was considered a strong argu-ment aganst waves

I is interesting to noe ha he Itaian physicis ran-cesco Mara Grimaldi (ca 168663) had noiced hat abeam o igh passing hrough wo narrow openings onebehind he other widened a litle bit indicating had

diraced outward very slighy as i passed hrough theopenings is observaion was published in 1665 two yearsater his deah bu somehow didn't arac attention (Inscence, as in many other ypes o human endeavor important discoveries or evens someimes get los in theshue)

uygens nevertheless showed that light i composedo waves, migh well have waves o dierent lengths Those


44/332

Atom

potions of ight wth th longst wavs would b lastfactd Th shot th wavs th gat th fac-

tion In this way, on could plan th spctum, n thatit might b that d had th longst wavs and that oangyllow gn, and blu w mad up of succssivlyshot wavs whl volt was mad up of th shotst

On th whol, as w look back on it, uygns had thbtt of th agumnt but Nwton's putation was gowng apdly (h was undoubtdy th gatst scintist who

had v livd) and t was had to tak up a position againsthm (Scintists, n that thy a as human as anyon s,a somtims swayd by psonaitis as w as by logic)

Thoughout th 170s thn, most scintists accptdth fact that ight consistd of littl particls This mighthav hlpd th gowth of atomism n connction with mat

t, and as atomsm gaind, that, n tu, stngthnd thpaticl viw of lght

In 181 howv th Englsh physicist Thomas Young(17782) pfomd a cucia pimnt lt lightfall upon a sufac containing two closly adjacnt slitsEach sit svd as th souc of a con of ight and thtwo cons ovlappd bfo faling on a scn

If light w composd of paticls th ovlappinggion should cv patcls fom both sits and bbight than th outlying gions that civd paticsom ony on slt o th oth This was not so What Youngfound was that th ovlappng potons consistd ofstpsbight bands and dim bands altating

Th smd no way of plaining this phnomnonby th paticl hypothsis With wavs howv thw no poblms If th wavs fom on slit w in phaswith thos fom th oth sit both ping pfct stpthn th ups and downs of on st of wavs (o th ins andouts) would b nfocd by thos of th oth st and th

oscilation of th two combind would b stong than ofith spaaty Bghtnss woud ncas

30


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Aom

ha w obsd would b acly wha would b -pcd of was

Bcaus on s of was infs wih and canclsh oh s in spcic placs hs bands a calld nfnc pans Such infnc pas a ob-sd whn on s of was on a calm wa sucoaps anoh Thy a also obsd whn wo bamsof sound (known o consis of was) insc ach ohTh wa nau of igh hus appad o b dmonsad

by Young's pimn (ahough as w migh pc hadidn man ha hos who blid in h patcl wsundd asilybcaus hy didn')

I was n possibl fom h widh of h infncbands o calcula h lngth of a sng wa of igh(walngth) I und ou ha igh was had ngths

n h nighbohood of of a cnim (o ofan inch) Th walngth of d igh was a lil onghan ha whil h walngth of iol ligh was a lilshot This mans ha a ay of igh an inch long wiha mo o lss 500 was nd o nd along hay I aso mans ha abou fy aoms can b placd ndo nd along a singl walngth of ligh

Tha plaind why igh cas shap shadows dspbing mad of was Was bnd aound obsacls onywhn h obsacls a no much long han h wa nqusion A wa woud no bnd aound anyhing sub-sanialy ong han isl Sound was a y ong andcan mo aound mos odinay obsacs

Almos anyhing w can asly s how s muchmuch long han a ligh wa so hs iualy no un-ing fo hm and h shadows hy cas a shap This a y sligh uing c how and wh hobjcs a qui smal h shadows dg is incind o bslighly y Tha plains h diacion c ha Gi-

maldi had discod 1 yas bfo Youngs mTh issu wasn sld how Popl nw of wo

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1 . Watr avs spr outard and t partcls oatr mov upan don n a drcton at gt angls to t drcton n c tav progrsss Ts typ o av s calld a trvr wve2 Sound avs also sprad outard but t partcls o ar movn an out n a drcton paralll to t drcton n c t avprogrsss. Ts typ s calld a lgituil wv.

type of wae There were water wae in wich the waepread ouward bu the patcle of wate moed up and

down in a diection a igh angle o the dection in whichhe wae progreed Thi i called a anee waeThere were alo ound wae in whch the wae alo peadouward but the paticle of air moed in and out in adirection paallel to the diection in which the wae po-greed Thi i called a longitudinal wae

Which of thee two decribe light wae? uygen


48/332

Aom

whn h aboad h wav hypohi migh havl ha ligh and oud boh big h cau o

pcpion houd b imia in nau Sound wa kowno b a ongiudial wav o h uggd ha ligh waa logudina wav oo oung wh h dmonadh wav nau o ligh ao hough o

Eai in 669 howv h anih chola EamuBaholin 1625698) cvd a apan cyal omIcland o a yp ow cald Iclad pa od ha

obc viwd hough h cya w n doubl aumd ha lgh pang hough h cya wa -acd a wo din ag o ha om mgd inon plac and h in a ighly din plac, poducinga doub imag

Baholn could no plain why hi hould b and

nih could Nwon o uyg Th phnomnon waho puhd o on d a mpoaly ipicabl(N o vyhig ca b paid a om paicula ago knowldg Th ony ibl hig o do o planwha you can and hop ha, a owldg advac hm will com wh h mpoaly unplanab can alob paid)

I 187 oung aizd ha doubl acio couldno b aily pland i lgh conid o paicl o olongudna wav coud b plaid qui aiy howv i ligh coid o anv wav

Th ch phyc Augun an nl 788827) adopd hi poin o viw ad wokd ou a caul

hoical udy o lgh a av wav on haplaind al ha wa known abou h bhavio o lgh aha im Tha ld i o h n ighy ya phy-ici w qui aid ha gh wa mad up o inyav wav ad ha ha wa h who o hanw

34


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Ligt

T ur Pnmna

is a answ ha s mpltly sasacoy and hissms spcialy u in scinc, wh vy answ smso uncov a mo sub qusion I w gran ha lighss in wavs, as sound and a disubd pond suac dohn h mains h pobm ha ligh wavs avlasly hough a vacuum whas sound wavs and war

wavs do noWa wavs is bcaus wa molcus mov up

and down gulaly I wa did no is hn nihwould wa wavs Sound wavs is bcaus ai mo-culs o h molculs o any mdium hough which soundavls) mov n and ou gulaly I ai o any oh m-

dum dos no is sound wavs woud no is ihIn h cas o lgh wavs howv wha s i ha is

moving up and down I can b any yp o odnay ma-, o ligh wavs can pass hough a vacuum wh,appanly h is no ma

Nwon had a simia poblm whn h wokd ou hlaw o univsal graviaion in 168 Th Sun hld h Eahin s gaviaiona gip acoss 150 million kiloms (3milion mis) o vacuum ow could h gaviaiona c,whav i was, avl acoss a vacuum

Nwon wondd , phaps vacuum was no alyntig bu consisd o a yp o ma mo subl hanodinay ma and ho no asily dcabl This

vacuum ma cam o b calld h, in homag o hah Aiso imagind as maing up h havny bod-is Th gravaional aacion puld a h h, andhs pul was conducd om on bi o h o h nunil, nally, h Sun was puling a h Earth

Phaps i was his h (o anoh yp) ha wavd

up and down as lgh passd hough I had o l al o

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Aom

spac bcaus w could s vn h mos disan sarsWha's mor i had o b so ad rard a yp of

mar ha i did no n any way inrfr wih h passagof h Earth or any ohr havnly body, howvr lighas i progrssd hrough spac rsnl suggsd hahr prmad h vry body of h Earh ad of all ohrhavly bods

Th paricls of hr howvr wh movd up musprinc a rsorng forc ha movd hm down pas

h quiibrium poin, hn up again. Th mor rigid a m-dium h mor rapidy i vbras up and down, ad hmor rapidly a wav progrsss hrough i

igh ravls a a spd of 22 kiomrs (18620mils) pr scond This was rs drmind vry appro-imay by h anish asronomr Oaus Romr (16

11) i 1676. To allow igh o ravl a such a spd hhr mus b mor rigid han sl.

To hav h vacuum mad of somhing so n ha iallowd bodis o pass hrough i fry and wihou ma-surab inrfrnc ad a h sam m so si as o bmor rigid han s was rahr puzzlig, bu scnissdidn sm o hav any choc bu o suppos ha hs wash cas

I addiion o igh and graviy, wo ohr phomnawr kown ha could mak hmslvs f across a vac-uum. Thy wr lcriciy and magnism Boh wr rssudid, according o radiion by Thals. H sudid acrain pic of iron or rs found nar h own of Mag

nsia o h asr shor of h Agan Sa I had hproprty of aracing pics of iron and h is supposd ohav calld i magnete lits (h Magnsia rock)Objcs wih h propry of aracing iro hav bcald magns vr sinc

Thals aso foud ha lumps of ambr (a fossiid

rsin), if rubbd aracd no ro paricuarly bu any

36


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Light

ligh obc. This dinc in bhavio mant h atac-ion was not ha of magnsm Th Gk wod fo amb

is lkron and vntualy this phnomnon cam o bcald lcicity as a consqunc.Somtm in h lvnth cnuy in hinabu

actly wh and by whom and und what cicumsancsis unknown was discovd that if a ndl mad ofmagntc o o of stl that had bn magnizd by bingsokd by magnic o was alowd o tu fly, it

would algn tsf noth and souh. In addition f th ndsw makd in som way it would b sn ha h samnd always tund noth.

That nd was calld th magnic noth pol and thoth h magntic souh pol. n 16 th nch scholaPtus Pginus 1) pimnd wih such ndls

and found ha th magnic noth pol of on woud battacd to h magntic souh po of th oh n thoth hand th magntic noth pos of wo magntidndls would p ach oth, as would h magnicsouh pols of th wo ndls In sho lik magnic posplld ach oh whi unlik magntic pols aacdach oh.

In 1785 th nch physics has Augusin d ou-lomb 176806) masud th stngth of h foc bywhich a magntic noh pol atacd a magnic southpo o plld anoth magntic noth po. foundthat th ataction o pulsion dclind as th squa ofth disanc th invs squa aw) Tha is, if you in-

casd th distanc to x tims what t was bfo, hfoc bwn h pos bcam lx x o lx what was bfo Whn Nwon dal wh gavitation in 687h showd hat th foc of gavtationa attaction folowdwhat was to bcom h invs squa law.

Thus h Moon is siy ims as fa om h Eahs

cn as th Eaths sufac is Th Eath's gaviaiona

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1

1 a 2 An unnzd rn dl wll ad hrh nrh r h uh l f a n On nd hwvrn wll rlld whl h hr wll a3 nlk l (N, S) a4 Lk l N, N S S rl

pul at th dtac f th Mn ny

f what it i n th Eath' ufc Nrthl thi pulli pprtinal h pduc f th tw ma inldand th Eath and Mn a mai that th Eath'gatainal pull ti ag nugh at th ditanc f thMn t hld th Mn i bit

F hat matt th Sun can hld th Eath in bi

ac a ditanc naly 400 tim that btwn th Eah

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Lgt

and the Moon. ndeed huge custes of galaies stetchingacoss mlions of ightyeas of space ae held togethe by

gavtatonal puls.Yet as it tuns out the magnetic attaction betweentwo magnetized needles s tillons of tlions of tilons oftmes as stong as the gavitational attacton betweenthose same two magnetized needles Why is it then thatwe ae so awae of gavitationa puls and hadly at alawae of magnetic pulls Why ae astonomical bodies hedtogethe by gavitation whie we neve hea of two bodiesheld togethe by some magnetic foce

The answe is that magnetism involves both an at-tacton and a epulsion both of equal intensity. Gavitationinvolves nly an attaction. Thee is no such thng as gav-tationa epulsion.

The wod is ful of magnets. As we shall see eveyatom is a tiny magnet. The magnets of the Univese aetued evey which way howeve and thee is as muchchance of epulsions hee and thee as attactions On thewhole the two cance each othe and by and lage we aeeft with a nivese in which thee is not much magneticattaction o epulsion oveal

Gavitation howeve invoing ony n attactonsimply ples up so to spea. Athough the eect of gavi-tational pul is so small as to be unnoticeabe fo odinayobjects o even fo mountains by the tme you have objectsthe size of the Eath o the Sun the gavitationa pul isenomous.

Stl magnetsm does pay its pat. Suppose you placea piece of st pape ove a magnetized steel ba. Scattesome on ings upon the pape and tap it. The tappingalows the lings to move and to tae up some natuapostion with espect to the magnet. When this is done theings aange themselves in a goup of cuved ines e

tending fom one pole of the magnet to the othe. Pee


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Aom

ginus had noicd his and in 1831 h Engish scinisMichal aaday (11186) considd h subjc

To aaday i smd ha h inunc o h magnschd ou hough spac in al dicions in a magnicld ha waknd wih disanc accoding o h invssqua law Though h ld on coud daw a as numbo lins magnic lins o oc) ha mad ou gionswh h sngth o h magnc ld was h samSuch lins w olowd by h ion lings and w hus

mad isibTha s why magnic ndls in a compass poin noth

and souh Th Eah is is a magn and h ndlsin up wih h magnic ins o oc ha go om on oEahs magnic pols o h oh Eahs magnicpos a ocad in h a noh and h a souh bu a

a considabl disanc om h gogaphic pos o oa-ion) A ga many oh acs abou magns can b -paind by h concp o h magnic ld and is ins ooc and aaday's noion has maind valid v sincTh a also gaviaiona and cic ds and linso oc h, oo)

Wha abou lccy by h way? Th Englsh phys-icis Wiliam Glbt ca 151603) ndd Thalsswo on cid subsancs H plaind in a boo hpublishd in 160 ha subsancs oh han amb wouldalso aac ligh objcs i ubbd Gilb cald al suchobjcs lcics

In 133 h nch chmis hals anois d is-

nay uay (1683) pimnd wh ods o glassand o sn boh o which coud b lcid, whnubbd, and mad capabl o aacng igh obcs Bohwoud hn aac smal bis o co which w in unlcid

A pc o cok lcid by gass woud aac a pic

o cok lcid by sn Two pics o co ach lc

0


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Ligh

id by glass would howv p ach oh; as wouldwo pics of co, ach lcid by sin ufay con-

cludd hfo ha h w wo yps of ciciyEach pld isf bu aacd h oh as in h casof h wo yps of magnic pols

Th Amican schola Bnjamin anlin (106170)oo his on sp fuh suggsd, in 1, ha hwas bu on yp of ccy, which all ma conainda nomal amoun of and whch was undcab If cain

objcs w ubbd, howv, hn som of h lcciywas movd whl f oh obcs w ubbd som wasaddd Thos objcs ha had an css migh b consid-d posivly chagd hos wih a dcincy w ngavly chagd

In such a cas a posvly chagd objc would aac

a ngavly chagd on bcaus conac woud allow hcss chag in h s o ow no h scond and maup h dcncy h Th wo woud cancl ach ohand lav wo unchagd objcs bhnd This was acuallyobsvd by anlin in hs pimns) n h ohhand, wo posiivy chagd objcs would pl ach ohas would wo ngavly chagd objcs bcaus in nhcas was h a chanc of chag owing fom on o hoh

I only maind fo anin o dcid which of hwo yps of cicaly chagd bods had h css andwhch h dcincy Th was no way of lling a him so anln chos abialy dcidd ha ubbd

glass had an css and shoud b considd posiiv ( + whl ubbd sins had a dcincy and shoud b consid-d ngaiv )

Ev sinc popl wong wih cic cuns havassumd ha cun ows fom posiv o ngaiv nfounaly anlin had had a fyfy chanc of gussng

igh and had los I was h od of sin ha acualy


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Atom

had th css so that th cunt ally ows fom ng-ati to positi That dosn't matt in ctcal ngi-

ning how Th suts a th sam whichdiction you imagn th cunt owing podd youstick by you dcison and dont chang you mind inmidcous

mbining the Phenmena

Th a thn, fou phnomna that can mak thm-sls flt acoss a acuum lght cticity magntismand gaitation Al fou might b pictud as makingus of th but a thy maing us of th sam th

o dos ach on ha an th of its own Th wasno way of tling but somtims lght was pctud aswas in th luminifous th fom a atin pssionmaning "ight caying Might th aso tun out to ban lctfous a "magntifous and a gaitifousth

To b su th dncs among th fou w notqually gat Light did not sm th to attact o plGaitation only attactd Elctcity and magntsm,how ach both attactd and pld and did so inmuch th sam way wth is pllng and unlis attacting f ths ast two on smd to as out of thoth

In 8, th ansh physcist Hans histan std(177785) was lctuing on th lctic cunt and, as admonstation it is not cla what h was tyng to show),h bought a compass na a wi though which an lcticcunt was owng To hs own pofound supis thcompass ndl actd at onc pointing in a diction at

ight angls to th ow of cunt Whn std sd


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Ligh

th ow of cunt th compass ndl vd and pointdin th opposit dicton, stil at ght angls to th cunt

owOstd was th st to dmonstat an intimat con-nction btwn cticity and magntism but did not po-cd in his nvstigations Oths who had of thdmonstaton did howv and at onc

In 182 th Fnch physicist omniqu Fanos A-ago 786853 showd that a wi caying an lcticcunt actd as a magnt and coud attact on lingssomthng it would no long do whn th cunt casdowng Bcaus th wi was copp this showd thatmagntism was not ncssaily an attibut of on onlybut might st in any matt Scintists bgan to spa oflctomagntsm

That sam ya anoth Fnch physcist AndMai Amp (17751836) showd that if two paalwis had cunt owing though ach in th sam dic-ton thy attactd ach oth if n opposit dictonsthy pld ach oth

If you twist a wi into a hli (th shap of a bd

sping) and snd a cunt though it, th cunt tavlsthough ach cuv in th hi in th sam dction Alof th cuvs attact on anoth and ach sts up a mag-ntc ld, vy on infocng all of th oths Th solnoid (coil of wi) thn acts l a ba magnt with a nothmagntic pol at on nd and a south magntic po at thoth

In 1823 th Btish physicst Wiam Stugon 783185) wappd wi about a shapd ion ba Th iontndd to intnsfy th magntic ld and, whn th cticcunt was tund on it bcam a supisingy stongctomagnt

In 829 th Amican physicist osph ny 797

1878) usd nsulatd w (to pvnt shotccuits) wap

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Aom

ping hundds of uns of i abou an ion ba, o poducan lcomagn ha could lif phnomnal wighs of ion

whn a cun was passd hough iFaaday hn considd h vs If lciciycould ca magnism migh no magnism ca lc-iciy H instd an odinay ba magn ino a hlix ofwi ha was nt conncd o any bay ha could satan lcic cun owing in i Th magn, nvthlsspincd such a cun whn h magn was pushd

in o pulld ou Th was no cun whn h magnwas moionlss a any poin insid h hlx Appanyh cun owd hough h w only whn h wicu acoss h magnic ins of foc owing in on dc-ion as h magn wn n and n h oh dicion as cam ou

In 831 Faaday wod ou a sysm whby a cop-p disc was und bwn h pos of a agn Anlcic cun was s up in h disc and owd coninuallyas ong as h disc und was an ot o p i uingbcaus i oo wo o push h dsc acoss h magniclns of foc As ong as his was don, howv by humano animal muscl o by falng wa o by h foc ofsam poducd by bunng ul, mchanical wo wasund ino lciciy

This im, i was Hny who vsd h siuaonTha sam ya h invnd h cc moo in whichh ow of ccy causd a whl o un

Al of hs discovs svd o lcify h wod

(in a ia as wl as a guaiv sns) and o al humansociy nomously To sciniss howv h mpotancof hs discovis was ha hy ncasingly dmon-sad h clos laonshp bwn lciciy and mag-nism

Indd h w hos who bgan o hin ha h

was a singl lcomagnic ld, on ha a ms,


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Light

showd ts lctcal fac to th wold ad a tims ismagtic fac This achd s clma wih h wo of

Mawl Bw 186 and 1873, h wokd out th mahmaca mplcatios of aadays notions of ds and linsof foc and of h appant conctio of lcic admagntic ds Mawl ndd by dvising fou compa-aivy smpl quaios (simpl o mahmaticias a aya) tha dscibd all know lcical and magic b-havio Thy hav bn kown v snc as Mawll's

quationsMawls quaions (whos vaidity is conmd by al

obsvatios mad sinc) show hat lctic lds and magnic lds cao st spaatly Th is indd oya combid lctomagnic d with an lctic compo-n and a magnc componnt a igh angls to ach

ohIf lcic bhavio and magntic bhavio w simila

in al spcts h fou quatios woud b symmticalthy would ist in two mioimag pais In on spchowv th two phnoma do not match ach oth Inlcical phnomna posiiv chags and ngativchags can ist indpndnty of ach oth A objcca b th posivly chagd o ngativly chagd Inmagnic phnoma on h oth hand th magntic polsdo no st spaatly Evy objct ha shows magnicpopts has a oth magntic po a o ocaon and asouh magnic pol a aoth locatio If a long magntizd ndl wih a oth magtic pol at on nd ad a

souh magntic pol a h oh s bokn i h middlth pols a nt isolatd Th d with th oth magnticpol isatly dvops a south magic po at h bakwhil h nd with th souh magntic pol dvops a othmagntic pol at th ba

Mawl includd this fac i his quaions which in-

toducd a no of asymmty This has always bothd

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Atom

sciists, in whom th is a stong div o smpicyand symmty This "aw in Mawl's quaions is som

thing wl tun to atMawll showd that om his quatons you can dm-onsat hat a oscilaing lctc d will poduc inv-itably, a oscillating magntic ld which wil n tupoduc aoh osclatig lctc ld, and so on ind-nity This is th quivalt o an lctomagntic adaonmovng outwad in wav om at a constant spd Th

spd o his adaion can b calculatd by takng h aioo cain units pssig magntic phnoma to othunits pssng cica phnoma This atio woks outo naly 3, kioms (869 mils) p scodwhch s th spd o ight

This could no b a coicidnc igh it appad

was an lcomagntic adiaon Mawls quaons thussvd o uy th o h ou phnoma known to passhough a vacuum lctcity magnsm ad light

Only gaviao maid outsd this uncaton Itsmd to hav ohng to do with th und th AlbtEnsin i 916 wokd out his gal thoy o lativ-ity, which mpovd on Nwo's concpt o gavitaton IEnsi's intptaon o gavity, which is now widyaccpd as ssnaly coc h should b gavitaoal adation i h om o wavs, anaogous o ctomagnic adiaon Such gavitatioal wavs howv amuch mo subtl and b, ad much mo dcult odtc, tha a lcomagnc wavs Dspi som as

alams hy hav not yt bn dctd a this momt owing, although vtualy no scnst i th d doubtsthat thy is

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Ligt

Extnding t Stm

Maxwel's equations set no liitations on the peiod o os-cilatons o the eld. Thee coud be one oscilation pesecond o ess so that each wave would be 300,000 kio-metes long o moe. Thee could also be a decilion oscilatons pe second o moe so that each wave would be atillonth o a tlionth o a centimete long. And thee could

be anything in between.ight waves howeve, epesent ony a tiny action

o these possiblites. The longest wavelengths o isibeght ae 00007 milimetes long, and the shotest waeengths o visble ight ae just about hal this length Doesthis mean thee is electomagnetic adiation we don't see

Though most o human hstoy the question as towhethe lght existed that coud not be seen woud havebeen consideed a contadction n tems. ight, by de-nition was something that could be seen

The GemanBitsh astonome Wiliam Heschel(173818) was n 800 the st to show this was not acontadiction ate al. At that time it was thought thatthe ight and heat one obtained om the Sun might be twosepaate phenomena. Hesche wondeed i heat might bespead out n a spectum ust as light was.

Instead, then o studyng the spectum by eye whichnoted only the lght Hesche studied it by themometewhich measued the heat. He paced the themomete at

vaious places in the spectum and noted the tempeatue.He expected that the tempeatue would be highest in themiddle o the spectum and that it would all o at eitheend.

That did not happen. The tempeatue ose steadiy asone pogessed away om the volet and eached its high-

est pont at the exteme ed. Astonshed Heschel won

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Atom

dd what would happn h placd th thmomtbulb ynd th d H ound to his v gat aston-

ishmt that th tmpatu os to a high g ththan anywh in th visib spctum Hschl thoughth had dtctd hat wavs

In a w yas howv th wav thoy o light wasstablishd and a btt ntptation bcam possiblSunight has a ang o wavlgths that a spad outby a pism Ou tina acts to wavlghs o light withi

ctan limits but sunlight has som wavs that a longthan that o th visib d and is tho to b oundbyod th d nd o th spctm Ou tia wont -spond to such long wavs so w dot s thm but thya th anyway Thy a calld inad ays th pcomng om a Latin wod maning blow o you mght

viw th spctm as goig om viot on th top to do th bottom

All ight whn t stks th skn is ith ctdo absobd Wh absobd its ngy spds up th mo-tion o th molculs i ou skn ad this mas its ltas hat Th log th wavlgth th dp it p-tats th skin and th mo asly absobd it is Hcalthough w ca't s th nad w can l it as hatand th thmomt o simila asons can cod t assuch

It woud hlp o cous t could b shown that in-ad ays w actualy mad up o wavs lik thos olight but wth long wavlngths On mght aow two

bams o iad ays to ovlap and poduc itncngs but no o woud b ab to s thm Phaps thycoud b dtctd by thmomt with th tmpatugoig up ach tim th instmnt passd though a"bight aa and going down ach tm t passdthough a "dmm on

n 1830 th talian physicist Lopoldo Nobili 8

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LTRAVE VLET BE GREEN YELLW RAG RD IFRARE

1 Infmred Light n 1800 when Willa Herschel placed his ther

oet i the dak aea beyond the ed end Q the spectu heas sused to eco th hghest tepemte.2 Ultmvolet Lght n 1 770 Ka Wlhel Scheele ond that papersoaked i slver nitmte solton dakened ost qickl when exposed to iolet lght n 1801 John Wlhel Rtter exposed th papern the dak aea beyond the olet and the paper rkened een orempdly.

85) ivnd a thmomt tha would do th job Ono his cowos was th Italian physicis Macdonio Ml-loni 18185) Bcaus glass would absob a gat dalo h inad ays Mlloni mad us o pisms omd ooc sa which is anspan to inad ays As a sult

intnc igs w st up and Nobili's hmom


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Atom

showd ha thy istd By 850, Mlloni had dmon-satd that infad ays showd al of th poptis of

igh wihou cptioncpt that thy could not b snwith th nakd yWha about th oth nd of th spctum wh violt

ight dpns into daknss That soy bgan in 6 whnth Ialian chmist Anglo Sala (1576167) noticd thatsiv nita a pfctly whit compound daknd onposu o sunligh This happns w now know bcaus

ight conains ngy and can foc apart th mocul ofsiv nitat poducing nly dvdd siv whch ap-pas black

About 1770, th Swdish chmis al Wlhlm Sch(171786) wnt ino th subjc n mo dtail makingus of th sola spctum which wasn known in Salas

tim H soakd hn sips of wht pap in soluions ofsilv ntat t hm dy and placd thm n vaouspas of th spctum H found that th sips of papdaknd last quicky in th d mo quckly as on wntfarth and farth fom h d and most quicky in hviol This happns (as w now know fo asons that wilb paind lat) bcaus ight ncass in ngy as ongos fom d o violt

Onc Hschl discovd nfad ays in 180 how-v it occud o h Gman chmist Johann WilhlmRitt (77681) o chc th oh nd of h spctumIn 1801 h soakd stips of pap in slv nia soutionand pad Schls pimnt cpt hat h placd

sips of pap bynd h viol wh no light was visiblAs h suspctd hy might th sips of pap dakndin this ightlss gion vn mo apidy than thy woudin violt ligh Ths psnd th discovy of ultaviotays wh h p s fom h Latin fo "byond

nfad and ultaviot adiation std jus a th

bods of th vsibl spcum Mawls quaons mad

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Light

t sm that th could b adiation fa byond th bodsIf uch adiaton could b found thn Maxwls quations

would b suppotd vy stongly fo without thm no onwould hav suspctd such adiaton mght xistIn 1888 th Gman physicist inich Rudolf tz

(185789) mad us of a ctangula wi with a gap int as a dtcting dvc st up an oscilating lctccunt n his aboatoy As th ctic cunt oscilatd,movng st ths way thn that, it should mt lcto-

magntic adiaton with th adiaton wav moving upwhil th cunt s gong on way and thn down whn itis movng th oth way Such an lctomagntic wavshould hav a vy long wavlngth bcaus vn if thoscillatng lctc cunt changs dicton vy smallfaction of a scond ight can mov quit fa btwn

changs's ctangula wi woud gan an lctic cunt

if th lctomagntc wav cossd it, and th would ba spa acoss th gap t got his spa In addtion,as h movd his ctangula wi h and th in thoom h got a spa wh th wav was vy hg o vylow but no spa wh it was in btwn In this wayh could map th wav and dtmin ts ngth

tz had discovd what cam to b calld adiowavs which ay fa byond th infad adiation andcould hav wavlngths of anywh fom cntimts tolomts

No on qustiond Maxwll's quations aft that f

th was a lumnifous th t caid cticity andmagntsm also If th was anoth th it istd onlyfo gavtaton

In 1895 by th way lctomagntic adiation wasdiscovd fa byond th ultavolt wit wavlngthsxcdingly smal; but w wil gt to that at aft w

consid a fw oth matts

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Aom

Dividing Enrgy

Elciciy magnism ligh, and gaviaion a all omso ngy wh ngy s anyhing ha can b mad odo wok Ths oms o ngy cainly sm dinom on anoh bu on can b und no anoh Asw hav alady sn lciciy can b ud ino mag-nism and vic vsa and a vbaing lcomagnic

ld can poduc lgh. Gaviaion can caus wa o al,wih h aling wa uning a ubn ha can oc aconduco hough magnc lns o oc o poduc lc-iciy Inconvsions o ngy and wok psn hd o hmodynamics

Such convsions a nv comply cin Som

ngy s always los in h pocss Th los ngy dosno howv, disappa, bu mas is appaanc as hawhich s sil anoh om o ngy. ha is akn inoaccoun hn no ngy is v oally os, no dos anyngy v appa ou o nowh In oh wods h o-a amoun o ngy n h Univs sms o b consan

This is h aw o consvaon o ngy, o h saw o hmodynamcs, which was naly pacd in com-pling ms in 187 by h Gman physicis mannLudwig dinand von lmholz (821189).

In a way, ha s h mos undamnal om o ngy,o any oh om o ngy can b convd mpllyino ha, whi ha canno b convrd complly no

nonha ngy o his ason, ha is h mos conv-nin phnomnon hough which o sudy hmody-namics a wod, by h way whch is om h G omovmn o ha

a had bn closy sudid by sciniss v sinch s uly pacical sam ngin had bn invnd in

1769 by h Biish ngin ams Wa (76819)

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Lig

Once the law of consevaion of enegy was undesoodhe study of hea became even moe intense.

Afte the adven of the steam engne thee wee twoheoes of the natue of hea Some scienists thought of as a type of suble uid that coud tave fom one pieceof mate to anothe. Othes thought of hea as a fom ofmoion of atoms and molecues moving o vibaing.

The latte suggestion o he kinetic theoy of heat(whee ineic is fom a Geek wod fo motion) was

naly establshed n the 186s as the coec one whenMawel and the Austian physcist udwig Eduad Boltzmann (18196) woed i ou mathematicaly. Theyshowed hat eveything ha was nown about heat coudbe nepeted saisfacoily by dealing wih atoms and molecues tha wee movng o vibating As in he case of

gases, the aveage speed (o bee "veocity) of motiono vbation of the atoms and moecues making p anytings he measue of its tempeatue if the mass of the aomsand moecules is also taken into accoun. The toa kneticenegy (whch taes into account both mass and veociy)of all of hose moving paticles is the total heat of hesubsance.

Naualy then, the code an object ges, the sowehe motion of is aoms and molecules Ifit gets cold enoughhe kinec enegy of the paticles eaches a minimum. Itcan then ge no code and the tempeatue is a absouezeo. This notion was st proposed and made cea in 88by the Bitish mathemaician Wiliam Thomson (8

19) bee known by hs ate title of Lod Kelvin Thenumbe of esus degees above absolute zeo is the ab-solute empeatue of a substance. If absolue eo is equao 23.15 is equal to 23.15 K (fo Kevin) o23. 5 A (fo absolue).

Any body a a tempeatue highe than ha of is

suoundings ends to ose heat as eectomagnetic adia

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Aom

ion The highe he empeaue he moe inese headiaio n 187 he Ausia physicis oseph Sefan

1835183) woed his ou exacly He showed ha heoal adiaion nceased as he fourh powe of he absolueempeaue Thus if he absolue empeaue was in-ceased wo imes say om 3 o ha is, fom27 C o 327 C) hen he oal adiaio woud be iceased2 x 2 2 2 o imes

Fomely abou 18 he Geman physcis Gusav

Robe Kichho 1821887) had esablished he fac haany subsance a a empeaue lowe han ha of is su-oudings would absob ligh of paicua wavelenghs,and would hen em hose same waveleghs when s em-peaue ose above ha of s suoundngs I folows haif a subsance absobs all wavelenghs of ligh a blac

body i ha i eecs none of hem) i wll emi allwaveenghs whe heaed

No objec acualy absobs all waveleghs of ligh inhe usual sense of he wod, bu a objec wh a smal hoei i does so afe a fashion Any adiaio ha ds sway no he hole is no iey o nd is way ou agai ands naly absobed n he ineio Theefoe, when such aobjec s heaed bacbody adiaional of he waveenghsshould come poung ou of he hole

This oio was s advanced by he Geman physcisWilhem Wien 828) n he 18s When he sudedsuch blacbody adiaon, he found ha a wde ange ofwavelenghs was emied as was o be expeced ad ha

he vey og and vey sho wavelenghs wee low n quaniy wih a pea somewhee i beween As he empe-aue ose Wie found ha he pea moved seadly in hediecion of shore wavelegh He anounced his i 185

Sefans law and Wi ens law ou expeiece Supposea objec is a a empeaue a lie highe han ha of

ou own body If we pu ou hands ea ha objec we

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Light

can fl a ttl wamth adiatng fom it. As th tmpatu of th objct ss, th adiation bcoms mo no-

ticab and th pak adiation is at a shot wavngth.A ttl of boiing wat wil dliv considabl wamthf ou hand s placd na it. If tmpatu is aisd stilhigh an objct wll vntualy giv o pcptibl adiaton at wavlngths shot nough to b cognid by outina as light W st s d ight bcaus that is thlight wth th longst wavlngth and s th st to b

mittd. Th obct is thn dhot Natualy most of thadiation is stil in th infad but th tiny facton thatcoms o n th visibl potion of th spctum is what wnotic

As th objct continus to is n tmpatu it glowsmo and mo bghty. Th colo changs too as mo

and mo ofth shotwav light is mittd As th objctcontinus to gow stil hott it bcoms n bight andth colo undgos anoth chang as mo and shotwavngths of lght a mittd Th glow bcoms mooang and thn ylow Evntualy whn somthing is ashot as th Suns sufac it is whithot, and th pak of thadiation is actualy in th visib ight gon f t gowsstill hott t bcoms bluwhit, and ntualy al-though it s bight than v (assuming w can look at itwithout dstoying ou ys in th sam instant) th paks in th utaviolt

Ths hatlight pogsson catd a poblm fo nin-tnthcntuy scintists bcaus it was dicult to mak

sns out of th pattn of backbody adiation. Towadth nd of th 80s th Bitish physcist John WilliamStutt od Rayligh (181) assumd that vywavlngth had an qual chanc of bing adiatd in black-body adation On that assumption h wokd out an qua-ton that showd quit wl how th adiation woud in

cas in intnsity as on wnt fom vy ong walngths

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Atom

to shortr wavlngths This uaon howvr didnt provid or a pa wavlngth to b ollowd by a dcin as

on approachd stil shortr wavngthsInstad th uaon impid tha th intnsity wouldconinu going up without lmi as th wavlngths gotshortr This mant that any body should radia chy nth short wavlngths gtting rd o all o its hat in ablas o vol utraviol and byond This is somtimscald th violt catasroph But th violt catastroph

dos not ta plac so thr mus b somhing wrongwith Rayighs rasonng Win hmsl workd out anuaton that would th dsrbuion o short wav-ngths o backbody radaon bu i wouldnt t h longwavngths t smd as though physcists could panhr hal o th radiaon rang but not th whol

Th problm was takn up by th Grman physicsMa Karl Ernst Ludwig Planck (18581) thoughtthr migh b somthing wrong wih Raylighs assumption hat vry wavlngth had an ua chanc o bngradiad n backbody radiaion What i th shorr hwavngth th lss th chanc o ts bing radiatd

On way o making this sm plausb s o supposthat nrgy s not continuous and cant b bron up intosmallr and smalr pics orvr Untl Plancks timh connuiy o nrgy had bn takn or grand byphysicists No on had wondrd i nrgy li mattrmight consist o tny particls that coldnt b dvddurthr)

Planc assumd ha h undamnal bit o nrgy wasargr and argr as th wavngth grw mallr andsmallr This mant that or a gvn tmpratur h radaion would ris n intnsity as wavngths grw shorrjus as th Rayligh uation ndcatd Evntualyhough or wavlngths shortr still th mounting siz o

h nrgy unt would incras th dculy o gting

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Ligt

ough gy to o plac i od to adia i. Thwould b a pak ad as th wavlgths coiud to d-

cas th adiaio would acualy dcli.As th mpau w up ad h ha gw mois, i wold b as o adat th lag gy utsad th pak would mov i th dico of sho wav-lghs ust as Wis law would qui I shot th usof th gy uis that Pac postulad complysovd th poblm of blackbody adatio.

Pack cald ths gy uis quata (quatum ith sigula) whch is a ati wod mag how muchWhat cotd aft al i h asw to h blackbodyadato puzzl was how much gy th is th quataof dit wavlghs of adiaio.

Plac advacd hs quatum thoy, ad h quao

t mad possib fo blackbody adiatio (which agdwith th actual obsvatios both fo og wavlgths adshot wavlgths) i 1900 This thoy povd so impo-tatfa mo mpoa ha Plack a th tim, couldpossbly imagthat al of physcs pio to 1900 is caldcasscal physics ad al of physcs aft 1900 is cald mod- physcs. Fo his wok o backbody adiao, Wicivd a Nob pz i 911 ad Plack civd o i1918

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lCiONS

Dvdng Elctcty

Ealy pimns on ciciy dal wih objcs hacad ah small lcc chags. n 176, howv huch physcs P van Musschnbok (1691761)woking a h Univsiy of ydn invnd somhng

cald h ydn ja in which a ga da of lccchag coud b pumpd.

Th ga h chag h ga h pssu fodischag. f a ydn ja is ouchd o som objc, hlciciy ows ino h objc and h ja is dischagdf ouchd o a human bing ha human can cv a

ow of lccy ha wl suly b painl)f a Lydn ja cas a suciny ag cic

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Etrns

chag, dct cotact d ot b mad Und such co-diios, if h ydn a mly appoachs an objct hat

wil dischag it h lctic chag can foc its way fomh Lydn a o th oh objct hough th intvnng ai

Th sut is a ash of light and a cac Th ight isnot th ctcity itslf ath, th lcticity, whatvt is has th ai as it passs hough and h ai gowsmomntaily hot ough to adat ligh Th ha aso -

pands h ai and af h dischag s compl h pandd a conacts again and h cacling soud sults

Som pop saw a similaiy btwn th ligh andcac of a dischaging yd ja and h ighting andhud h clouds dung a stom ould lghning andhud b th dschag of a gganc Lyd a aag

mt in th cloudsIn 152 Bjamin aln povd this was so by

yig a it n a thundstom, lading h chag of hlighig dow a cod and o an uchagd yd jaTh sultant chagd Lydn ja showd tha lctcyfom th sy had th sam popts as cticty po-ducd on Eah

But what abou th ctcty islf that hids isidh chagd body, o insd th ight poducd by hada On asw would b to dischag ctcty thougha vacuum i od to s what h ba lcicity loodli As aly as 6 an Eglsh physcist, woig wihchagd objcts fa lss nts than a Lydn ja maagd

o gt a dischag acoss a vacuad vssl, obaiigligh as h did so

I hos days howv vacuag a vssl was stilony mpfcy possib A mnant of ai woud b lfisid, ad tha would b nough to glow as a sul of hpassag of th cticiy It was o h lcticy itslf

I od to gt ba lcicity, two thigs w ndful

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1 If yo od see n to nes o the perspete nortng eetron the nes ght pper tny dot t tdstne

2 Een thogh they he hes ofeq t opposte gntden eetron hs ony '/897 the ss of snge proton

On was a ssl ha was so wll acuatd hat th tacsof ai insid would not b nough o intf with h

lctici. Th scond was a wa of focing lcici nquantit though a good acuum. A Ldn a might doh but its dischag lastd fo onl a momn. Was ha wa of kping th lctci going fo a considablpiod of tim

Th scond poblm was sold in 1800 b th Iaianphsicis Alssando Giuspp Volta (1751827).

showd tha lcicit coud b poducd whn two di-nt mtals w both dippd ino a salt solution. This wasaccompanid b a chmical action and as long as thchmical action pocdd lcicit continud to bpoducd. f som of th lctci was dawn o thougha wi, th ctici would ow though th wi as long

as it was bing poducd b th chmical actions.

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Etrns

As a sult it bcam possbl to hav an lctic cunt instad of my a stationay lctic chag To

poduc a ag lctc cunt, Vota mad us of a sisof twomta combnations with salt wat bwn Anyof a sis of simila objcts is cald a batty. Vota hadinvnd an lctc batty

As soon as Vola announcd hs dscovy, scntissbga constucing bgg and btt batts and withina gnaton aaday wokd out a mhod fo poducing

an lctic cunt much mo chaply by buing fulTh was thn no poblm of sting up ctc cuntswth nough foc to mov acoss a good vacuumif a goodvacuum coud b suppid

Th suppli was h Gman nvnto ohann in-ich Whlm Gissl 181187), who, in 1855 invntd

an ai pump hat was a makd impovmnt on al of thpumps usd pviousy Insad of using mchanical dvicsinvovng movng pats Gssl usd only sng and fallingvls of mcuy. Th mcuy tappd a b of ai withach chang in lv and movd it It was a slow pocssbut by h tim this mcuy ai pump was don ov pcnt of th a in a vssl had bn movd

Gissl who was an p glass blow blw vsslsthat had wo pics of ma sald no opposit nds, andths vssls

isaac asimov atom journey across the subatomic

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