causes of color scientificamerican1080-124

7/30/2019 Causes of Color Scientificamerican1080-124

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hat makes the ruby red? Whyis the emerald gren? On themost supercial level thesequestons can be given simpe answers.When white light passes through a ruby,it emerges with a disproportionate share

of longer wavelengths, which the eyerecognizes as red. Light passing throughan emerald acquires a dierent distri-bution of wavelengths, which are per-ceived as green. This explanation ofcolor is correct as far as it goes, but itis hardly satisfying. What is missing issome understanding of how matter alters the composition of the light it trans-mits or reects. Ruby and emerald bothderive their color from the same impuri-ty element: Why then do they dier sodramaticaly in color? What gives rise tothe ne gradations in spectral emphasis

that constitute the colors of materials?It turns out that the utimate causes ofcolor are remarkably diverse. An infor-mal classication I shall adopt here hassome 14 categories of causes, and someof the categories embrace several re-lated phenomena. With one exception,however, the mechanisms have an ele-ment in common: the colors come aboutthrough the interaction of light waveswith electrons. Such interactions havebeen a central preoccupatio of phys-ics in the 20th centry, and so it is nosurprise that explanations of color in-voke a number of undamental physical theories. Indeed, color is a visible(and even conspicuous) manifestation ofsome of the subtle eects that determinethe structure of matter.

Engy Ladd

The perception of color is a subjectiveexperience, in which physiological andpsycholgcal factors have an importantpart; these matters will not be taken upin detail here. It seems reasonable toassume, however, that perceived cooris merely the eye's measure and the

brain's interpretation of the dominantwavelength or frequency or energy of alight wave. The meaning of this assump-tion is clear in the case o monochromatic light, which has a singe, welldened

1

wavelength. The interpretation of lightthat is a mixture of many waveengths ismore complicated, but it is still the relative contributions of the various wave-lengths that determie the color.

Wavelength, frequency and energy

are alternative means of characterizinga light wave. Energy is directy propor-tional to frequency; both energy andfrequency are inversely proportional towavelength. In other words, high fre-quencies and high energies correspondto short wavelengths, as at the violet endof the visible spectrum. A common unitof measure for light waveengths is thenanometer, which is equal to a billionthof a meter. The energy of light is conve-niently measured in electron volts, oneelectron volt being the energy gained byan electron when it accelerates through

a potential dierence of one volt. Interms of wavelength human vision ex-tends from about 70 nanometers,where red light grades into infrared ra-diation, down to about 400 nanometers,at the boundary between violet light andultraviolet radiation. The same rage inenergy units runs from 1.77 electronvolts to 3.1 electron volts.

An important constraint on all interactions of electromagnetic radiationwith matter is the quantummechanicalrule that says atoms can have only cer-tain discrete states, each with a preciselydened energy; intermediate energiesare foridden. Each atom has a lowestpossile energy, called the ground state,and a range of excited states of higherenergy. The allowed energy states canbe likened to the rungs of a ladder, although their spacing is highly irregularLight or other radiation can be absorbedonly if it carries precisely the rightamount of energy to promote an atomfrom one rung to a higher rung. Similar-ly, when an atom falls from an excitedstate to a lowerlying one, it must emitradiation that will carry o the dier-ence in energy between the two levels

The energy appears as a photon, orquantum of ight, whose frequency andwavelength are determined by the energy dierence.

The states that are of the greatest in

terest in the analysis of coor representvarious possible energy levels of elec-trons. In atoms, ions and moecules eachelectron must occupy an orbital, whichdescribes a particuar geometric distri-bution of the electron's charge around

the atomic nucleus. The orbitals in turnare organized in shels. A further con-straint on the possible states of the atomis that each rung on the energy laddercan be occupied by oy a limited num-ber of electrons. In general, when pro-ceeding from the smallest atoms to theargest ones, electrons are added in se-quence from the bottom rung up. Twoelectrons l the rst shell; each of thenext two shels holds eight electrons.The electrons in any led or closed shelform pairs, and they have a notably sta-ble conguration.

A comparatively large quantity of en-ergy is needed to promote one of thepaired electrons from a closed shell tothe next vacant position on the ladder.The energy required for such a transi-tion can usually be supplied only by ra-diation in the ultravioet or even in theXray region of the spectrum; as a resultclosed shells have no direct inuenceon the colors of materials. Instead colorusually results rom transitions of un-paired eectrons, which are most oftenthe outermost ones. They are the va-lence electrons, the ones that participatein chemical bonds.

Aomic ansiions

Consider a vapor of the element sodi-um in which the density is low enoughfor each atom to act independently ofits neighbors. The sodium atom has 11electrons, but 10 of them lie in closedshells, and it is only the single valenceelectron that takes a direct part in theinteractions of the atom with light.When the sodium atom is in the groundstate the outermost electron occupies anorbital designated 3. The nexthigh-

est energy levels (the next rungs on theladder) are abeled 3P and 3P/, andthey lie at energies 2.103 and 2.105 elec-tron volts above the ground state. Theseare the smalest quantities of energy a

1980 SCIENTIFIC AMERICAN, INC


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CHAMELEONLIKE GEMSTONE seems to adapt its color to thespectum of the light with which it iumiated. The stone is aexandrite, which app red in the red- and yellow-rich light of a candle

ame or an incandcent amp but turns blue-green in sunlight or inthe light from a uorescent lamp. A1exandrite is a beryllium aluminate, BeAl204, but the color generated by chromium ions presentin he crystal impuii. Transitions between various eergy levels of unpaired electrons in the chromium ions are responsible for thecolo of several gemsto. The exact color pruc depends on the

chemical environment of the ions. For example, chromium ions giverise to the red of ruby and to the green of emerald under slightly dif-

ferent condiions. The environment of the chromum ions in a1exan-

drite is intermediate between that of ruby and that of emerald, andso the color is changeabe. Natl alexandrit are exceedingly rare.

This one is a synthetic crystal grown by Creaive Crystals, Inc" of

Concord, Calif. The photographs, which were made by Fritz Goro,

do not show the exact colors of the crystal becae the rponse of

photographic lm is somewhat dierent from hat of the human eye.



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sodium atom in the ground state can ab-sorb. hey correspond to wavelengthsof 5 89.6 and 5 89.1 nanometers, in theyellow part of the spectrum

Above the 3P orbitals are a multitudeof other excited states, where the elec-tron has a greater average distance fromthe nuceus and a higher average ener-gy. he number of such states is innite,but the interal between levels becomes

smaller as the energy increases, so thatthe series converges on a nite limit. orsodium the limit comes at 5.12 electronvolts, where the outermost electron is nolonger merely excited but is torn loosefrom the atom entirely; in other wordsthe atom is ionized.

Suppose a sodium atom is ionized,

BLACK BODY AT 57 D EGR EES C.

\

perhaps by a quantum of ultraviolet ra-diation, and the free electron ad th ionthen recombine Initially the electronmay occupy one of the higher orbitals,but it quickly falls to a lower energy lev-el If the descent were made in a singlestep, from the ionization limit to theground state, the atom would emit a sin-gle ultraviolet photon with an energyof 5.12 electron volts. A much lielir

route would pass through several in-termediate states, accompanied by theemission of a lowerenergy quantumat each stage. Not all such cascadesare possible; selection rules" determinewhich ones are allowed Most of the al-lowed pathways proceed through one ofthe 3P orbitals and thence to the ground

\ SOLAR SPECTRUM\- (AS MEASURED ON EARTH),

1 2 3WAVELEGTH (AOMETERS)

ULTRAVOLET V S BL E FRARED

0

0 W [ 0 t4 45 5 55 6 65 7

WAVELEGTH (AOMETER)

I I I I I 75 7 65 6 55 5 45

FREQUECY 1' HERZ)

I I 3 275 2 5 2 25 2 1 7 7

EERGY (ELECTRO VOLTS)

SPECTRUM OF SUNIGT closely matches the sensitivity o the eye; as a result light appears white

its spectrum reembles the solar one and other colors can be described by how

they depart rom the solar spectrum. The sun's radiation is approximately that o a black bodywith a temperaure o 5,700 degrees Celsius. The shape o a black-body spectrum is determinedentirely by the temperature becoming steeper and shiting to shorter wavelengths as the temperature increases. Thus as an object is eated its color changes rom black (no emission) to redto yellow to white and nally to pale blue. The spetrum can be measured in units o wavelength requency or energy which are merely alternative means o describing a light wave.



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sae As a resul quana f yellw lighwih energies f 2103 and 2105 elec-rn

vls are amng hse emied In-

deed, hese w lines are y far herighes in he specrum f amc sdi-um and a vapr f excied r inizedsdium glws righ yellw

The characerisic yellw radiance famic sdium can e served whena sal f sdium is heaed in a ame

h nugh vaprize sme f h a-ms In analyic chemisry his prper-y serves as he asis f he ame esfr he presence f sdium The du-le f yellw lines is als prminen inhe specrum f a sdiumvapr lamp,where he sdium ams are inized y ahighvlage discharge

Oher ams als yield disinciveemissin lines when hey are excied rinized and en allwed reurn hegrund sae; in each elemen, hwever,he spacing f he energy levels is dieren, and s he lr f he emied ligh

als diers In nen he srnges linesare in he red par f he specrum,wich accuns fr he red glw f nenlighs and signs The mercury am hasprminen lines in he green and hevile regins f he visile specrum,and cnsequenly a mercuryvapr lampgies lueinged ligh ha is decien in red and yellw Lasers whsewrking medium is a mnamic gas expli emissin lines f he same kind

Lighning and elecric arcs als deriveheir clr frm elecrnic exciainsf he ams in gases

Black-ody Radiaion

Sharply dened emissin and asrp-in lines are ypical f gases The specrum f ligh emied y a slid r aliquid is usually quie dieren, in hai exends ver a cninuus rage fwavelenghs

A universal frm f radiain frmcndensed maer is lackdy radia-in, which as a cninuus specrumwih a disincive shape Here lackdy refers simply an idealied ma-erial ha asrs all wavelenghs wih-

u favr ad is als a perfec emier fall wavelenghs (Real maerials all havelwer emissiviy, u many apprachhe lackdy specrum a high em-peraure) Such radiain has an impr-an place in he hisry f physics, sincei was hrugh an analysis f he lackdy secrum ha ax lanck deduced he quanum principle in 1900.He fund he culd explain he shapef he specrum nly y assuming hequaniain f energy

n ideal lackdy radiain hespecrum is independen f he chemical

cmpsiin f he emier and is deer-mined y a single parameer: empera-ure A aslue zer all he ams ccupy he lwes energy level availale,and n radiain is emied As he em-peraure rises sme ams are prmed

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excte stats, but the process s a anm r statscal one, and th atoms astbut ov a broad rang o nrges At any nt tmpatu th numbe of ccupd stats ncass gadually wth enrgy up to som maxmumvalue; thn t dclns agan hus thshape f th spctum s somht lthe prl of an ocan wav about tbeak The steepness of th wv and thpostn f th crst dpnd on th tm

peaue f the bodyA rom tempatu th thmal x

ctatns are cnnd to small nrgs,an raatn s emttd only n th nfrae When th tmpratu achsabout 700 egees Celsus th maxmumemssons ae sll n t nfad, but alttle vsble lght begns to appa; t speceptbl as a dul rd glow As thmpeatue rses futher th pa of themsson curv shfts to hgh ngsan shot wavlngths, s tht the obect glows bghtr an ts colo changsTh sequence of colors uns from d t

ange to yllow to wht to pal blue, naccor wth the colloqual dscptonsd hot," whte hot" and so on

In a log r o a candle ame ncanescent partcls of cabon gve radaton wth an ctv blackbdy temeatue f at most 1,500 degees C,where thelght ranges fm r t yelw The tungsten lament f an ncanescent lgh bulb has a tempeature fabu 00 egees an yels a warmellwwte A ash bulb whch caneac emperature f 4,000 egreesel a mwha moe accuate ver

n eTe lar sectrum has the apprxae m a blackbdy curve; sape etermne by the tempeatuea he surface f he sun, abu 570egees C The pectum has a bradeak centered near 2 electon vlts, 560 nanomts, a yellowgreen waveength The eye s most senstv t usths wavelength Inded, the concept fwhte sms to be condtne lagelyby the spctrm of aylght, whch somnatd by sola adaton Rughly spakng, lght s pecevd as bngwht f ts spctum rsmbls that ofsunlght; oth colos can be ne accodng to how thy dpat fom the solar spectum

Cysalfld Colos

When atms combne to fom a mleule r cnnse t fom a lqud o al, new mdes f exctaton ae ntuce mng them are mechancal vratn an rtatns that a not pssle a slate atom o example,e ats a atomc mlecule canlla f ey wee cnnect by a

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At xchge s desg pmented to tsd tac o a aceIt wo e this: Gases risingog he stack (up to1500 F are used to deiver"ee peheated to thee he rest is 5% esse oi eqed to heat theace Depending on how yo

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Fo gas transmissioncompies, process industiesand other operators of age

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12/32

little energy at the red en of the spectrum and gives pure water and ice a paebue ast. For the most part, however,the energy of vibrationa and rotationaexcitations is smal, and it is dissipatedas infrared radiation, or heat.

Anther consequence of the bindingtogether of atoms is a change in the stateof the valence eectrons. In an isolatedatom the valence electrons are unpairedand are the primary cause of color. In a

molecule and in many soids, on the oth-er hand, the vaence electrons of oneatom form pairs with the valence elec-trons of adjacent atoms; it is these pairsthat constitute the chemical bonds thathold the atoms together. As a result ofthis pair formation the absorption bandsof the vaence electrons are dispacedto ultraviolet wavelengths, an they areno longer available for the productionof color. Ony electrons in exceptionalstates remain to give rise to coloration.It is evident, however, that such excep-tional states cannot be too rare; if they

were, most molecules and solids wouldbe transparent to visible light.

One set of unusual electronic statesappears in the transitionmeta ele-ments, such as iron, chromium and cop-per and in the rareearth elements. Theatms of metals in the transition serieshave inner shells that remain only partlylled. These unled inner shes holdunpaired electrons, which have excitedstates that often fall in the visible spec-trum. They are responsible for a widerange of intense coors. For example,both ruby and emerald derive their col-

or from trace amounts of chromium.The basic material of ruby is corun-dum, an oxide of aluminum with theformua A. ure corundum is col-oress, but in ruby a briliant color re-sults from the substitution of chromiumions (r+++) for a few percent of theauminum ions. Each chromium ion hasthree unpaired electrons, whose lowest-possible energy is a ground state designated 4; there is aso a complicatedspectrum of excited states. All the excit-ed states are broadened to form bands,and they are also modied in anotherway by the presence of the crystal matrix. Although the identity of the statesis dened by the eectronic congura-tion of the chromium ion, the absoluteposition of each eve in the energy spec-trum is determined by the electric eldin which the ion is immersed. The sym-metry and strength of the eld are determined in turn by the nature of the ionssurrounding the chromium and by theirarrangement.

In ruby each chromium ion lies at thecenter of a distorted octahedron formedby six oxygen ions. The interatomicbonds in ruby are about 19 nanometer

long, and they have about percentionic character, which means that theelectron pairs that make up the bondsspend more of the time near the oxygenions than they do near the auminum or



13/32

chromium ios This strbutio of theelectroic charge gives rise to a comparativey strog eectric e, which iscaled the crysta ed or the igad eldWhe a chromium io is immersed ithis eld, three excited states of its upaired electros have eergies i the visible rage

The three excited states are desigated 2 4 ad 4 Selectio rues forbid a direct trasitio from the groud

state to the 2 eve, but both of the 4 leves ca be etered from the groudstate The eergies associated with thesetrasitios correspod to waveegthsi the violet ad i the yeowgree regios of the spectrum Because the leves are ot sharp lies but broad bads arage of wavelegths ca be absorbedHece whe white light passes through aruby it emerges depeted of its violet adyellowgree compoets Essetialyall red is trasmitted, alog with somebue, givig the ruby its deep red colorwith a slight purpe cast

Because of the seectio rules electros ca retur from the excited 4 levels to the 4 groud state oy throughthe itermediate 2 evel The iitialtrasitios from 4 to 2 reease smalamouts of eergy correspodig to i

frared waveegths, but the drop from2 to the groud state gives rise tostrog emissio of red light It shoudbe oted that this red light, uie thetrasmitted bads, is ot preset i thebeam origially icidet o the crystal;it is geerated withi by the process ofuorescece Ideed, the red uorescece of ruby ca be observed mostclearly whe the crysta is illumiatedwith gree or vioet ight or with ultra

vioet radiatio O the other had, theuorescece ca be queched by iroimpurities, which are ofte preset iatura rubies The ight o a ruby laserderives from red uorescece i sythetic rubies, which are free of iro

Ruy ad Emald

The subtlety of crystaled coorsca be made apparet through a compariso of ruby ad emerald The colorgeeratig impurity i emerad is agaithe Cr+++ io, ad it agai repaces alu

mium i smal amouts The similarityof the two substaces exteds further iemerad too the chromium ios are surrouded by six oxyge ios i a octahedra coguratio, ad the bod egthis agai about 19 aometer I emerald,

OOR NR n form n rytl wen n eletron te te le of dlodged on.In uorte, or lum uorde, te eletron ll te ny reted wen uorne on remoed. e eletron etrum of eted tte tt etend nto te rnge o blewelengt. e olor enter n uorte, w re lled enter, ge t urle ue. eorgnl rytl truture n be retored by etng, wereuon te olor fde. ere r loeletron nd "ole olor enter, were ngle eletron rter tn n entre on dled.

1

however, the fudametal crysta atticeis that of a berylium alumium silicate,BeSi d the most sigicatdierece is i the ature of the chemical bods, which are ess ioic by a fewpercet, so that the magitude of theeectric ed surroudig a chromiumio is somewhat reduced s a resut thetwo 4 leves lie at slighty ower eergies; the positio of the 2 bad is essetialy uatered The major eect of

these chages is to shift the absorptiobad that i ruby bocs gree ad yelow light dowward ito the yellow adred part of the spectrum The emeradtherefore absorbs most of the red ight,but the trasmissio of blue ad gree isgreatly ehaced

Curiousy uorescece i emerald isalmost idetica with that i ruby Thereaso is that the eergy of the 2 eveis scarcey atered by the reuctio ithe crysta ed The similarity of theuorescet emissios shows it is merely a coicidece that ruby has a red co

or ad aso red uoresceceItermediate i spectra copositiobetwee ruby ad emerald is the rare(ad therefore costy) gemstoe alexadrite gai the color arises from chromium ios that replace alumium, buti this case the uderyig crystal structure is that of a berylium alumiate,Be The crystal ed that sets theeergy scale of the chromium ios isstroger tha that i emerad but weaer tha that i ruby, with the result thatthe red ad gree trasmissio badsare quite evely baaced The earequaity of the two bads has a extraordiary cosequece i bluerichsulight the gemstoe appears buegree, but i the redder ight of a cade ame or a icadescet amp it appears red

Crystaled colors ca arise wheever there are ios bearig upaired electros i a solid quamarie, jade adcitrie quartz get their coors from amechaism similar to that i ruby ademerad, but the trasitiometal impurity is iro istead of chromium Maycompouds ad crystals i which thetrasitio metas appear as major co

stituets rather tha impurities are alsostrogly coored mog atura mierals i this category are the blue or greeazurite, turquoise ad malachite, iwhich the coor is produced by copper,ad the red garets, which owe theircoor to iro Most pigmets i paitsare trasitiometa compouds

Colo Cs

The physica mechaism resposiblefor crystaled coors is ot coedto electros i trasitiometa ios; i

deed, the electros eed ot be a itrisic compoet of ay atom excesselectro uattached to ay sigle atomwil suce if the electro ca be trappedat some structura defect, such as a miss



14/32

The GE COpuer RadoAt 6:00 AM s Sarer han you are

The Great Awakening from General Electric. Forstarters, it's smart enoug to let you set the timedrectly...no flippng around the clock.

You can program it to change statons for you. itwill rock you to sleep wt Strauss, switc to yournews staton, and wake you at :

Then it comes back on to wake up our better alto Beethoven at : All wth push-button ease.

When you orget to set the alarm ...The GreatAwakenng remembers to remnd you.

You can scan all the AM or FM statons by pressinga button or, to tune n one station just punch inte frequency o your choice n the kyboard.

You can also program up to six satons ito thememory. And recall any one with the touch of afinger.

For a lttle extra sleep, press the SnzAlarm Itlets you sleep an extra minute or an extra hour. You

tell the memory how long.

The Great Awakening is so smart t even tells ouwhen youve made an error But its easy tocorrect .ust press a button.

W g .



15/32

When it comes to people worldwide.choosing a high er- And best of all,fomance mcrocom- Digitl's micrcom-puter company, you puters are software-only have tw compatible. Whichoices. ==.".-. means you won'

A semiconductr company tat's ak- ever have o wrry bout sig youring is rst stab at the wrd of compuers. software investmet.

Or Digita. So iyou don't have millios to spend on

No one has mre time r mney behindresearch

and develpment, mayb youeir 16bit micros than Digital. Our LSI-1/2, realy don't have tw chices at all.LSI-1/23, PDP1V03, and FDP1V23 are Maybe you have just e .e resu tens of miions of dlars andhundreds f man-years of development. R22/65, Oe Ion Way,Theyre diect descendants f our incredi rlbor, A 01752bly successf PDP- fay of minicmputers And they're every bit as successfu ineir wn igh. With mre tan 100,000sold into the market nw more an urnext three cometitors combined.

It all means at wi Digital's high erformance crs, you get a head start noseconductor company can give you.

Like a broad range of micocomuterboards, boxes, systems, and deveopmenttools to work with. High performance software thats literaly eas ahead of the competion. backe by echncal consutaon and tr g om over 13 support

It tooke micomputercompto micrs ise



16/32

ng n an mpuity. , tabsnc f n ctn m a pai, canav t sam ct nmais f tisknd a cad c cnts F cts (fm t Gman F c

thug many c cnts knwn, t mcanism f cpuctin is undstd in ny a fw. O ts s th pup F cnt f uit, amnal tat xibits a gat vaity

ccnt activitis. Fuit is cacium ud, CaF , in wic ac cacium n is nmay suud byigt un ins n F cnt mswn a uin in is missing fm itsusual psitin. T ss f t uincan cm abut in sva ways bygwng t cysta in t psnc xcss cacum, by xpsing t cystat gngy adatin (wic can dispac an n fm its usual psitin by applyng a stng cti d (wicmvs uin by t pcss f ctyss. In d t psv t ctical nutaty f t cysta sm thngativy cagd ntity must ta upt psitin in t lattic ft vacant byt absnt un n. Wn t cags suppd by an lctn, an F cnt scatd. T ctn s bund in pacnt by a cntal nuclus, as n an atm an in, but by t cysta ld f al tsuunding ins. Wthin th d t canccupy a gund stat and vaus xcitd sta ts simila t ts n t tansitn mtals. T mvmnt f lctnsbtwn ths stats givs s bt tc and t uscnc.

T cl f smky quatz is attibut

d t a l cl cnt T basic attc f quatz is silcn dixid (Si,ut a pquisit t t fmatin ft cl cnt is t psnc f auminum mpuitis pacng a fw siicnns. Bcaus auminum as a vancf + and siicn a vanc f anaali mtal in a ydgn in mustb naby t maintain ctical nutaty. Quatz is amst aways cntaminatd with tacs f aluminum, but tatan wi nt giv is t c bcausth a n unpaid ctns T c cnt s catd whn t quatz is

xpsd f a fw minuts t intns Xays gamma ays, wn it is xpsd t w vs f suc adiativ ggic pids. T adiatin xps n ctn fm a pai f ctns in an xygn atm adjacnt t anauminum impuity, tby aving anunpad ctn in t bital. T absnt ctn is cad a , an tmanng unpaid ctn as a st fxcitd stats muc i that an xcssctn.

mtyst is ant fm quatzthat dvs its c fm a ccnt, but t impuity in is in at tan auminum. Ctain d bttsw mad f a glass cntaining inand mangans; aft many yas xpsu t intns sunigt t gass tunspup tug th dvpmnt f c

BENZNE

H( )

H

< :>

H

\ H H H HBENZEN

PI O RBITALS

CYSTAL VOLET

MOLECULAR ORBITALS describe paied electrons distributed over se\eral atom many toms; they often absorb strongly at isible waelenghs. The pair of electrons ht form chemical bond ordinrily absorbs only in the ultaiolet, but when alterntie congutionso the bonds spred the pai oe nube of toms, the excitation energy of the pi is re-duced. The comonest oleculr obitas that cuse coo re those ssociated with systems ofonjugated bonds (ltenating singe nd doube bonds) in orgnic comounds such s benzene By shifting three airs of eectrons in benzene the sequence o bonds is reersed. A betterwy o reesenting the structue of the molecule ( shows single bonds between ll the car-bon toms, with the ext three is of electons distributed throughout the molecule in "piorbitals. It is the i obitls tht e ctie in roducing colo. In benzene the excited states ofthe i obitals stil lie in the ultaiolet, ad so benzene is coloress, but in molecules with gerconugated systems, such s the dye crystl iolet the bnds are at isible waelengths. Thecolor is enhanced by chemical groups called uxochromes that donate and accept electons.



17/32

MINIMM }COW N ENERGY BELO BAND GAP OF0 ABSORBED COLORLESSCOCON BAND

> 4 PHOTONz0 c ( cw 3 w VIOLET YELLO z BLE w

i GREEN ORANGE z( 0c YELLO w 2 RE D 0 - 1 RE D ( cw z (w BA GAP }c,z z0 c _ 0 - FERMI LEVEL

NBR OF LECTRONS

CTRONIC STRUCTUR OF A MTAL tnge by an eentally contoban of alloe energy level Te ban lle from e gron tae up o an energy callee Ferm level all hger energy ae are emp an can herefore accep excte electronA coneqence of t electronc congraton a all wavelen of aaon can be aborbe from te nfrae ogh te vble o he ultavole n eyon materal tataborb lg of all colo mg be expec o appea black meal e no lack becaue anexcte electron can mmeaely eurn o ognal ae b eemttn a quanm wtte ame avelengt a te aborbe one Te meallc rface terefore gl reectve

(cwc

WW

EMPTY BAND

F[ DNMBER OF LCROS

(cww

BAND STRUCTUR OF A SMICONDUCTOR mla to tat o a metal ecet tat agap of forben energe earate e lle valence ban from te emty concto baTere terefore a mnmm energy at a qantm of raaton mt ave n orer to be aborbe namely te energ neee to promote an electron from te to of te valence ba to

te botom of te concton ban Te color of a pre emconctor etermne by temagnte of te ban gap f le n te nfrare all vble avelengt are aborbe ante materal black A gap energy n e vble regon allo ome color to be tramtteo tat te emconctor take on a color rangg from re to yello Wen te ga ergy n te ltravolet all vbe avelengt ae tanmtte a te materal colo

o cenes and is cad srtmtystglass T sa t s y 10mint xposur to t ts am-a ys eid y colt 60

Mos colo centrs r st f taeial is no eatd xcssy uoi aising he tmpratur mks tdisplaced oin ion mo, so tati evenall sums is org os-ion; he colo cen and t oor r

n abolishd Amyst w dchanges colo ecoming tr rnaz o a a eend quart Bohese colos eprsent t u ofion iho h amyst oor trn soe aerials vn ry ofn igh can caus color tr to fdo xaple som coorss top ane iadiaed o iduc a dp org-on in; h coor fads, owr, f-e n f days in sunligt Nturalaz o sae colo is qui stbl

Molula Oials

as poined o abo tat molces and solids h enc ctrosae paied in cmica onds ad esl hei excied sats a sftd ntohe ulaviolt Actuay ts s tru oyhen h paid ctros rm oned o a pariculr o tw twoaos In many cs t ctro ov ov longr istc t ang hogot mou o hougout mcroscop o a tn oud ls t gty, t gy nded to crt xt tt educd T tro r o

cpy molecur ort ( ot taoic obits), ty r rosbe for var s of oor au.

On mcansm y w moobias can contrut oor t trf of ctr r from o o tanohe bu sar prod ampl of t proc Lk u, pir s basd o orudum u o sigicant murts, ro ttnium bo ppr oso orally lld umum owenegy sa t ro form rof + an t ttum fomchag of + t tt ormhen an lcto trsfrr ro tion o itnium, o t ot oave a foa crg o rof abo o cro ot tive e cag trsfr rsions ca ro oro ha exends fom t yow toue d and eaves t sappr wt ep be colo

In a nbe of maers ro ren in bo is commo , + +and e+++ Charg sfr twese fos give is o coors r

o dp bue o blac, s t ckion o agneieMoecuaobi thory so appis

o he colos obseved in may orisbsances in hich caro toms (



18/32

HW TO B U

A EG.

Boeing is nw buldng an arplane that'll save mllins of galons of fuel: the new gnratn 77

Hw much wll it sav? 77 ying mlln mls a

ear wll save mllin gallns oful aall vr th arlane itwl lc.

Fl cnmy has alys bn an t an arlan d.N s m crcal than vr.

n ngr is Dg Mll. s scaltyis lmry dn a vlo.

Dug and th d nvlvd in the dvlt airplane wing that ha xclly ecient arynac. I

wuld nvr hav bn l Bing had nt bn t aprctng cs lwht crn-r d sh al l

Rsl: Th 7 wing wll tthe arla th r adying wth lss ful cthan any ala s z

Nw adyn, rals ad ns al h a l mtm t c a xl k m 7 a

th . t l cx d c cl k r



19/32

s g as a jdby a ys aag g addub bds whch a cad cju-gad bds Th bskw xap uch a cjugad y h x-cab bz g bu h a ayhes caus ach bd ps apa shad c g a pa ecs ach dub bd h adace sg bd h -

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A ube bgca pges h c xedd yss p -bas Ag he a h ge chphy pas ad he d heg-

b bd Ogac dyes py hsa chas The Scey Dyes ad Cuss ss8,000 such ubsaces

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20/32

Aneludee de ble sa.

Someday, p ulses f l ght mcarry voice a nd lesnsias rough glss bes n ocean or. An xpeenlas r couniatns lei eing ested in a iulateon nvironment at Bel Lbi H olm .J.

The o-in diter cble sol al th size o f the letundrs cabl now i use. Buhe exrimnal cabl canialy crry a least tic s

ma lo crcuismoreha 800

Di a rstmod o ca av nmad im Wr a

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Th aricil ocan beneahhe n of Bell Lb' Holmd

facilty cn smulate th yrzing teprtus ad1000-oundr-square-inchrss h occu under ormi ocea wate 'r

try ing o make cabl thaextremely reliable ad long-iveecause its expenie t pk pn epr e tht i lesner the oen s ufe nstrec ss huns mes of oen o.

Although us f n neelghtguide cable tll ners o e ae kng t et read hen he Bell Systemneeds it o meet yur gwin gtelcmmuntons nees

77

@Bll abotoriesKp ou outos sst

th st th wo



21/32

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22/32

WHT' BETTRTHANSPEDREDING?

PD RG( S P E E D P L U S C O M P R E H E N S I O N )

Speed Learning is replacing speed eading. It' sy to learn . . . lasts lifetime . . . applies t everythingyu read . and is the only accredited course wit the opton of college or contin uing educat ion credits

Do you have too much to read an oltte tme to read i? Do yu mentallyproounce each word s you read? Doyou frequently hve to go back and rered ods or hole paragraphs you justfnshed eadng? Do you have trubleconcentratg? Do you quicky fogemost of hat you read?

If you aser "yes to any of hesequestions - then hee at last is the practical help you've been aing forWhether you read for business or pleasue, school or colege, youbuld ecep. onl skils om ths major bakro eeve reading, ated by RusseStuffer the Unversy of Delaare

Not just "speed reading - bu speedreadnghinkingunderstanding

rememberingandlearning

The ne Speed Learning Programshos you stepbyprovenstep o oincease your readng sill nd speed, sou understand more, remember morend use moe of everthng yo redThe tyca emark made by te 5000so eades ho compleed he Speed

Leaning ogram as: Why didn'someoe teach me ths a long tme ago?They ee no onge held ack by thelack of skls ad poor reading habtsThey coud ead amost as fast as theycoud tkWha makes Seed Leani so succesf?

The ne pd eaing oam doesot offe you a ehash of the usual eyxe]cises, tmg devces, costy gadgetsyou've pobaby ha aot coneco th speed readg corses o evenred a foud ffectv

In st a fe spa ms a day ofasy ag a exctig ste, you

scove an etey e ay to ea ahk - a acal epatue fm ay

OLLG TS, You may obtain ull u fo couse( j completon , wheeve you eside. Cedts ofeed thoug Whtte Coege (Cal fona) Deta ls ncludedn you pogam.

ONTNUNG UTON UNTS_ Natonal Management Assocation, te wold's lageti o"odat ;On of pof";on manages awad CEU= for couse copeton EUs can appied toad te ceifcate n Management StudesOSSONL SOT SSpeed eaning s offeed intenatonally to membes of pofes

sona assocations such as: Ameican Chemica Socet, Founda

tion fo Accountng Education Institute of Electial andEectoncs Enginees and dozens moe Consut you EducationDiecto fo infomaton

USNSS NUSTY GONNTMany companies and goenent agencies offe Speed Leanngas a wholly-paid o tuiton emusement pogam onsutyou Taning o Pesonnel ecto fo deta ls

ing you have ever seen or heard aboutResearch shos that readng is 5 %thinkin and only 5% eye movemen Yetmos of today's speed reding programsspend ther tme teachng yo rapid eyemovemen (5% of the problem) ad ig -nore the most imporant p (5% think-ing. In brief, Speed Leaing gves youwat spee redng can't.

magine he ne freedom yo'll havehen you lea ho o dash hrough allpes of reading materil at least ice asfast s you do no, nd ith greatercomprehension i of being ble toge on op f he vaance of nespapers, magaznes d correspondence yuve red finshing smultingbook nd reining fcts and deals moreclearl nd ith greater accuracy thanever before.

ListenandIearn at your own pace

Tis is ricl, esyolea prorm h ll rk fr yo n mtero slo ede o ink o reo e eed eaing Program is sinifilly lnne ge o srey elp in spre minutes brings y echerossetes gies ou, instrucs, enorges , plinng meri s

read nteresting items taken from TieMagazine, Business Week, Wa SreeJournal, Family Cirle, Times admny thers, make the programstimulating, easy ad fun ad somuch more effective

Execuives, students, professoapeople, men nd omen in all aks oflife fom 5 to have benefted fom thsprogram Speed Leaig is a fly acceited corse costg oly 5 he pceof less effectve speed eading classoocourses No ou can exame the same,easy , practica and proven methos athome in spare time hotriskg a penny

You l be the at h qcy sproram l beg o eveo nthing and reag ss Af sting to jus oe cassette a a preface yo ill qucly se ho yo cacieve increases n both te s ahch you read ad the a yunderstand an emember

You must be delighd wih wh y

ee or ou p nhing Ex hsremarable pga f dys. If te end of that time yu n cn-vned tt you wld like t sSpeed Lening, simply etn h -

ga nd w nthigee th cn f lwp ice n cn tdit s

Note: Many companis and gov-ernment agencis hve uiionassistance plans fo moyeesproviding full o paial paymentfor college cedit prams.

In most cas, he entie cost ofyour S

Learning Pam

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23/32 1980 SCIENTIFIC AMERICAN, INC


24/32

ed. A excited states ie in a separateconduction band, which in the groundstate is entirey empty. Separating thetwo bands is a gap of forbidden energies.The division of the energy band has profound eects on the optica propertiesof a semiconductor. No onger can theeectrons absorb radiation of arbitrariyow energy; the minimum energy is theenergy needed to ift an eectron from

the top of the vaence band to the bottom of the conduction band.

The coor of a pure semiconductordepends ony on the magnitude of theenergy gap. If the gap is smaer than theowest energy of visibe ight, a visibewaveengths are absorbed. Smagapsemiconductors in which reemission isecient and rapid have a metaike uster, as siicon does, but other smaa

BAND-AP COLOS are obere i i emicouctig comou. Pure camium ule( ) a a ba-ga eergy o 2.6 electro olt, wit te relt tat oly iolet ligtca be aborbe; te material a te color comlemetary to iolet, amely yellow. I urecamium eleie ( ) te ba-ga eergy i 1.6 electro olt, o tat all iiblewaelegt are aborbe a te crytal are blac. e oter our material are miture oariou roortio o te two comou; tey ow a graiet i abortio, wit color romorage troug re. e comou are emloye a igmet uer te ame camium re.

he uncein scienceesite the increasin usefuness ofmathematics as a ractica too thetheoretica basis of this branch ofnoee is an inte ectua batteroun o f ierenteen contraictorieas escribin the ramaticchanes that hae occurre i n ourconcetion of mathematics i neeamines the im ications for scienc

an for human reason

LOSS OFINM lne

S SSBo 9-8-142 Mao AveeNew York N 16

l pb pat when over 35000 years agor-Magnn and NeanderthalMan may have lved at the metme. crucial momen in evoluon wh en tw o races battle for theirvery extence

THE C OF H

CV_-



25/32

RED LGHT BLUE LGHT WHTE LGHT

D FFRACTON GRANGo RED LGHT BLUE LGH WHTE LGHT

PHYSIA OPIS rovde te mot convenent nterretaton ofcolor genrated by everal mecanm tat nvolve a cange n tedre


26/32

seionduos ae bla A he oo-sie exee he band ga an be geaehan 'he highes eneg o visible ligh;in ha ase no visible wavelenghs anbe absobed and he aeial is oloess Diaond wih a band ga o eleon vols is one suh lagegaseionduo and is ansaen boho visible ligh and o a liied ange oulaviole adiaion

Wee he bandga eneg alls inhe visibe ange he seiondo hasa denie olo The eu oe in-naba whih has he oula HgS andis also known as he igen veil-ion) has a bandga eneg o 2 ele-on vos All hoons wih enegieshighe han his level ae absobed andonl he longes visible wavelenghs aeansied; as a esul innaba aeased The igen adiu ellow CdShas a band ga o 26 eleon vols andabsobs onl blue and vioe ligh; aehese wavelenghs ae subaed owhie ligh he olo eaining is e-ow The sequene o bandga oloso he salles ga o he lages isbla ed oange ellow ooless

Ahough agega seionduosae ololess when he ae ue hean ae on olo when he e"doed wih aes o an iui Thiui an be eihe a dono o l-ons o n aeo o hem; in ihease i inodues a se o eg sin he p eween he aen

and h onduion and Tansiioso o o he new leves equie a sm-e quani o eneg han ansiios

aoss ie gaIn diaond he eaeen o e

abon aos wih niogen eaes dono band abou eleon volsabove he aene band Niogen hasone eeon oe han abon and i ishese exa eleons ha o he dono and he noina eneg needed oooe one o he o he onduionband is fou eeon vols whih is sillin he uviole; he dono evel is suien wide howeve o soe violeligh o e absobed A a onenaion o one niogen ao e 00000abon aos diaond is elow; wihoe niogen i beoes geen

Boon has one eleon ewe hanabon and give ise o aeo ohoe eves in he band ga o diaondAn eleon an be exied o he valene band o ou one o hese holesThe iui leve is eneed ele-on vo above he valene band buexends a enough o absob soe ohe longe visible wavelenghs The bo-ondoe diaond heeoe aeasbue

I is wel nown ha doing also al

es he eeial oeies o seionduos aing ossible all he devieso soidsae eeonis Aong hesedeies ae ligheiing diodes andseionduo lases in whih an ele

y y k k w y

JACK DANIES MILLER spends a lot oftime just waiting for his ype of grainto coe n.

Wt needs is young, ce cor itno ccked cob t a moiture cou of undfourtee. And te suret y to t k o er wy off i noi. O c ,

b bt wen o boy do'tve o e But tey ov oo tnce toc. n c to tndr wy b1.

R O O

D

6Y RO

Te n n e s s ee W h s k ey Proof D is t l l ed and Bot t led by Ja ck Dan e l D s t l l e ry ,Lem Mot low , Prop . I nc , Rout 1 ynchburg (Pop 36 ) Tennsse 37352

G



27/32

more ouboutiqesin Caiforat Ui San FraicStanford CePalo Alto.

JACK DANELSUARE GLASS SETM ac

"k Dan l was o g a o o

squa bo l fo s wh sky ad a lwayswan d o av a ma c ng squa g l ass l s s f y squa g l ass (acw gs 14 ouncs ) s p c compan oo a bo l o f M ack 's ns s d soundd o mak d k ng a p l asu and o g n a l ds gn s f d on o good l oks ad u a b l y M y p c o a s of 4g asss oz . capac y ) nc l uds posag , ,

, , (Tennessee residents add % sales tax . ) For a colocataog fu l of o ld Tennessee i tems and Jack Dane 's

memoab l a, send \ to above add ess

1

trc curret populates excited states adte electros emit radiaio i retur-ig to te groud sate Doped semi-coductors ca also fucio as pos-pors, whic are materials that gie oigt wi g eciecy whe they arestimulated electrically or by some oer meas Phospors are te lumioussources i a uoreset lamp ad i thepcture tube of a teleisio se I a colorpicture tube three posphors are distri-

uted oer te surface wih emissios ared, gree ad blue waelegths Cer-tai compouds of te trasiio mealsalso act as posphors

Gomical Opics

I the peomea I ae describedso far color results either from te direct emissio of colored ligt or fromte selectie absorptio of some wae-legts ad trasmissio of ohers I ast group of colorproducig peom-e teractios of ligt wit matter

cage te directio of te light Te

cage i d irectio s te primry causof color refracto d drcto,were te magtude of t ectioca ary wt waelegt. te sctte rig of ligt from small partce te deectio of ay gie ry s ot determiisic fucio of waelegt, bu t teaerage itesity of te scattered igtdoes deped o waelegt. terferece gies rise to color roug a teractio of ligt wit ligt, but cage

direcio is eeded to eable oe beamof light to iterfere wit aoter

A te most fudameal lee teseprocesses ca be uderstood i terms ofelecroic exciaios mater Refractio for example resuls from a chagei speed whe ligh passes from oe me-dium ito aother he speed i each a -terial is determied by the iteractio ofthe electromageic eld of the radiaio wit the elecric carges of the elecros A aalysis o this id is alwayspossible but i is ofe too cumersoeto be ery iformaie hat is eeded

is a higher leel aalysis i is proid

NTURL DIFFRCTION RTIN i formed by cloely acked here in a yntheticoal The here conit of ilicon dioide and a little water embedded in a tranarent matrithat ha a imilar comoition but a lightly dierent inde of refraction The here have adiameter of about 250 nanometer Dierion of white light by the threedimenional diraction grating give rie to ectrally ure clor that glint from within an oal. The yntheticoal wa made by ierre ilon in France, who alo made thi canning electron micrograh.



28/32

y mt f mtr y t.

t y rfrtd, r t, y rrt rm u w mr y tr tt y r . ( gt p f gt, d t tttty try y r xd, ttd y uum y mtr mdum t pd wr.) y p u

drt udrt y m t t ry r f p w frt. w frt trk trprt urfquy, dg tr d wfr ppt dg r t urf t dg tt wd rt tuf d t rt f t w frt, t ry td twrd t rdur. g t d t ry t wy frm t rur.

mgtud f t drt w gt ry rfrtd dd t t w trk

urf. r y g f t dpd t rt f pd f g tw mtr. tur ut tt t rt, w rfrt dx, ry m fr wt t yfrt . mm t tr rt mum r frqu r y w fqu wt. u rft rug rr , m f w

tru rm rtt t mp r. pr f wt t r

t wt w dr y Nwt 1 r t wNwt w r rg t . dr f ut y frt wtr drt r ryt rp fr t r f rwd f tr rd y ru t u d t m. r u r, r f r, rtrt f dmd d, r xtt, f tr ft tr

rt mt. pr twy wm pm tp, mr d tr pt ym t g r rmt rrt, r t mrtrt f mg drt r.

rfr w rt tgtd dt y Nwt. t rd ytm f w wr tw wm t yd g w ww mptud t pt mpy um f t mtu f t rg w. u mrmt gtw pt t tw mpt, fw dr pt d tmrg g. r t tw mpt r , tt t k dy d, t w rfr t t t rt. r

x x Now al your bookstoreRADOM HOUSEPublisher of The Random House Dictionarof the Eng/ish Languag. Unabridged Edition

cdc W

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end for Kodak's ee science fairkt I can help pu you in he blue ribbon circle Because it shows how to ephotography for sandout projects. Learnhow to photograph before-and-aer sequence, growth progre, ackgroun,closeups, and much more

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29/32

he coponens ae o o phase heaves cancel and appea dak

Inefeence is oen oseved in hnanspaen ls hee pa of he lighis eeced he s suace and pa he second Whehe he eas ein-oce o cancel depends on he naeand hickness o he l on he angle oeecion and on he avelengh o heligh If he l has a unio hicknessdieen avelenghs eege a die-

en angles I he lae vaies in hick-ness hen a an given vieing angledieen colos appea a dieen posiions Ineeence in a hin anspaencicle gives se o he colos o soeeeles and eies A hin lae of oilon ae sls ih colo as a esl oe sae echanis

The a at

Diacion s he ending o speadng o a ligh ave a he edge o anopae osacle When he osacle is a

acoscopic ojec he eec is geneall a no one i ecoes ipoan hen he den sions o he osacleae copaale o he avelengh o helg As ig e expeced e agni

ELE AI FEE

AO A D I O; V BATAL

de o he eec hen ecoes songldependen on avelengh

Diacion is an ipoan cause ocolo in he scaeing of lgh sallpaicles Lod Raleigh shoed hahe inensi of he scaeed lgh is invesel popoional o he foh poe o he aveengh accodingl lelgh is scaeed ao fou ies asuch as ed ligh The dispai in scaeing eeciveness is appaen in he

daie sk Molecules ds and c-aon s n densi in he aosphee peeeniall scae le lgh so ha hesk appeas lue The diec ligh o hesun on he ohe hand is depleed olue and heefoe appeas eddish paiculal a sunise and sunse hen heligh us avese a geae deph ohe aosphee

The sae pocess can e deonsaed on a salle scale passing hieligh hough diled unhoogenzedilk hee he scaeing cenes aepaicles o a The id appeas lish

heeas he diecl ans ied ea iseddsh The lue sheen o oonsoneals ceainl coes o a siilapocess Scaeing o uch lage inlsons hch do no ale colo ac

couns o he paens in sa asa sapphie and in igesee qua

Inefeence and diacive caeinac in coinaion in a nal meanis o geneaing colo he iaon gaing Such a gaing is an aayo an euall spaced lines o poinin hich he spacing is no oo agen copason ih ligh avelenghsigh passing hogh he gaing is sca-eed in all diecions a each opening

and so aves o adjacen peningsineee Fo an one avelengh heeae angles a hich he ineeence isconscive; a all ohe angles heaves cancel one anohe The acuavale o hese angles depends onl one avelengh and on he spacing e-een lnes o poins on he gaingWhen hie lgh passes hough a di-acon gang o s eeced fo ieac avelengh s enhanced in a dieen se o decons Hence he ligh inan gven diecion is specall peand onochoaic as he gaing

s oaed a sees o seca coes inoveA dacon gaing can e ade

nscng ne lings on a glass plaeand a e naal sses also have he

ELET EXIAIO ADEEE FLAME A, AK

LIGHG GA DHAGE ME AER

RATI I EULEVIBATIO BUEGREEN N OF UE WAER AND IE.

AON -EAL PODUQUOIE PIGEN OE AER

OE PHOPH OE FLUOEENT ATEIA

AL-FELD L AITIO -EA IPU I EUB EEAL RE ANONE

OE AER OE FLUEENE

LO ETE

HARGE AFE

AIO BETWEE

MOLE ULAR ORB TALJUGAED BD

ETALI ONDUTOR

AN N ATERIALUE EU

HAVING ENERG BAND

DED EINDUO

DERVE EFRA

GEOEAL ADAEG

HIAL O

EFEREE

DFFRAO GRANG

CAUSES OF COLOR are claied i 14 categorie of ve broadtype All but oe of te lorcauig mecaim (vibratio of teatom i molecule) ca be traced to cage i te tate of te elec

AEH O QUARZ EER

AMEH GLA OE UEEE

BLUE APPHRE AGETTE

GA E O PANT AND ANIAL

LAP LAZUI FIREFIE

DE LAE E FLUOREENE

OPE LVER GL IN BA

L N GALENA NABA IAOD

BLUE DAD ELOW IAOND lGH

EIG DDE EIODUO AER

E HPH.

HE ABW "FIE GEONE

HATI ABEATO

BLUE F HE ED OF UNE

OOE TA APPHIE

L F IL O WATER EN OATING

OE IE OLO

OA QU D RTA O E IN ET OOR

to i matter. Electoic traitio are te mot importat caueof color becaue te eergy eeded to ecite a electo commoly fall i te rge tat correpod to viible wavelegt of ligt.



30/32

It 's virtualy mpossble to get tradespeopleto openy admit whch product n teir ndus

try is number one. But, judging by numbersalone, the Fdelity seres, in te past 8 monts,has become the most sought after cessgame throughout Europe, Great Britain adorth Amerca.

. D es pi te I t s Fl awApart from its numerous official to urnametwins and co mputer nte l gence, the or ignalFdelty ga me ha s offered a maor advantageover a other eectronic games. Namely tad the abil ity to be chalenged an occasionaly beaten at various leves y eapeope opponents Ths smpe actor hasmade t a challenge, rewarding astmeand an unsurpassed se-mprovement evce. But, t goofed sometmes. Not throughany fault o its own, ut becaus hman

oppon e n t e n th u sia sm .Last years mode requre ayer oenter h is mo ve from a keyboar. The payerpressed eys ke A2 to 3 an th en moveis piece accordngy. The machine rep ein ind a nd h e moved ts piece. The probemarose when the player ecame so enrossein te game that after ha vn g made an stutemove, he anticpated the machnes extmove When the F de ity Chal enger ep ewit a tartl ingly different response, one otwo tings the happened ither the humanwas so astonshed and absorbe n rehinking hs next move tat he s mpy oot tomove the machines pece entrely or heabsent-mindedly move the pece n accordance with h is own preconceve deas andignored te machines actua move.

.Compt blak k night attak whit ook 8 boa ghtInat.

Lighs-AcionSo Fdey emnate his human factor

The enus Osprn as no keyboardnstea ery que on he agnetizedayn oar as o tate d amp atts orner. h he ach ne wshes to move ie at quare mp hts. A seconde amp hts to te you where the piece

"Genius Offspring- The Next Generation

SnitivIsueWe've gone beyond computer brilliance

o increase playability' while everyone eseis still fumbling with breadboards.

should go These ights wont go out unti lte move s made. You move in the sme

manner. The new Fdelty senstve boardregisters where your pece was ifted fromand were it was plae

A Ma jo AdvanceThe improement o state pressuresensitive e eneath the layin oard.Smple? es. u aor vance n eectronc hess mes. ssene to mp rother ournament me e tys e t eau o h l omtiton ti onee th eatn ou oe.

eet he o wrwinno t oou o at t um on oic letro h es.

v o bril wihv v Th Sit h o emo e o er osit o. Justouh h rot yo h rte o o. o re th ook t on h o qure with yourhte ook ht omputersack ook que sh. ontnuny o esn h ea ( ) ymo eate the eraton o. ts tota exil ty ets you et u hyothetca encountersto tes esponse t ferent ees. You canchange ames stream or witch sdeswth the com pute to see how t would hand leyour d emma. You can ad pieces or takeaway the computers queen It is a superbteacher!

The remarable , Senst ive Cal lenger "8

ae to anayze over 3m il l on board positions. t masterfuly handles over one thouand oo openings and wi respond to anyevation. cademic openings as ici ianFrench Ruy opez an Queen Gambit Dened are just some of te challeges tokeep you on your toes.

Knows Every Rue in te BookThe Cha lenger 8 w l permt you to cateor perform an n Passant apture or do sotsef that s ts best move. When yourpawn has reached the e ighth ran t wi l eautomatical y raised to a Queen, un less youtel the computer to promote t to anotherpee. I t w tae on any player and sharpenh s s i l l s co n si d er a bl y . but it ont perm iti ega moves

Sound SignasYou just cannot bel ieve te chess Q . of t isphenomena unit The Sensit ve Ca lenger8 ha s a beep audi o feedbac which soun dsto acnowedge your move, and double

S SamolePresident, Fideity Electrois

beeps wen the computer has made itsresponse . At evel 1 its average response

tme s 5 seconds. t ourament Leve the Chal lenger maes hampionip decisions in just 3 mnutes.

Unbeaale in Price s Wel s PayBest of l , the Chess Cha lenger 8 is icrediby affordable. I t s ust $89 copete wth Stau nton deig ned peces ad ULapproed 1 1 0V AC adaptor.

A ieces are magnetied to stay whereyou pace them on the permanent, senitiedoa. The set s mounted n a simlatedwoodgrained housing which meares 1 x 1 0 x 2 The unit is baced by a 90damanufacturers iited parts ad labrwarranty.

Enjo Days t Or Expese t o yourself, the 8 is uetioy the nest cess computer you caeect ut i within 30 days you are notatisfe mply return t for a prot, uestions-ased refud.

C",DIT "D "D" '"J299r ::NOIS RESIDENT: 55524 YK

--------------Please send me Snsit ive Chsshal enger "8(s) a pus $400 forsiing and insu rance. I ino is res idenssales ax If no sisfi d, I can eurn i wi hin days fo a efund r ices s i h ly ihrbeynd coninenal US.o Enclosed please find check or mney order . Charge My Credit Card:o Aercan xpress Master Card Carteo BankAmercardVlSA Diner's Club BlancheCredit Card No.Expiration DateNameddress

City__StateZ p

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31/32

PGWTHOUT

CMRISEThere are some discp ines in whih oromse isnecessar. With the Br onica ETR-System, photography is no l ongeramong tem.

Begin ith t he professional shapnes o a 45 x 6cm egatvenearly 3-imes arger than 35mm . . n a camera nearly a small. Addthe convenience o f an automatic exposure prism fnder that seectsthe correct shutter speed for any aperture you hoose. And thecreative freedo of a lens syste rangng rom 40mm wde-angl e to500mm telephoto, incudin g zoom lenses and a unique perspectivecontol optic that brngs view camera-like movements to mediumformat. Eac ens has an eec tronicayaccurate eaf sutter forelectronic fash synch at ever shutter peed to 1500th. There's alsothe fexibiy of interchaneable maazies for 120, 220, 70m andPolaroid lms And vewfnder and accessory systems to eetvirtuay any photographc chal enge.

Bronca the camera system wtou t compromise, nocosts less . . so you need compromise no more! See it at yourBonica deaer. Or, write for LitPak P52. Marketed by Nikon PhotoDivision, Ehrenreich Photo-Optca Industres, Inc., Garden City, 115 30 [

imsios a t ig gr r for a optica gratg. r mp, t matria ca iqi rytas molculs ar stack wt sucirgularity to act as a iractio gratig Bcaus th spacig tw moculs ps o th tmpratur sos th color of th matria, a itca ploy as a tmpratur iicator Similar orr arrays of molcls prouc iractiogratig coori so buttris a tls. Spctracolors arisig rom iractio also appar wh a istat strtligt is sthrough th abric o a urlla orwh th surac of a phoograph rcor is iw at a glacig agl

Th prmit atural iractiogratig is th opal this gmstosphrs ma up o silico ioi aa littl watr ar closly pack i athrimsioal array with a spacigo about 0 aomtrs Th traspart or trasluct matri that llsth spac tw sphrs has a similarcompositio ut a slightly irt i of rractio. Wh wit light trs this hrimsioal iractiogratig, pur colors appar isi tsto t colors chag as t y ort sto is o. Th chaism ocolor prouctio i opal cam to urstoo oly i 964 w t structur was rst rsol wit t ctromicroscop Syttic opals wr crat ot log thratr

The Visble Spectrum

this catalogu of colors, wic surly ot complt, a scrimor ta a oz mchaisms Tca put ito roa catgoricitatios of r aoms a ios aibratios i molculs crystall fcts, trasitios btw stats o molcular orbitals trasitios i th rgyas o solis a cts itrprtthrough physical optics t may sm atraoriary coicic that suc airsity of phoa is copassi a a o walgths that is ot a ull octa wi it ay sm stil

mor rmarabl that this arrow ahapps to b ust th o to which thuma y is ssiti

Actually it may ot b a coicicat all So uch o itrst hpps ithis arrow rgio o h lctromagtic spctr bcas hs ar th walgth whr itractios o light witlctros rst bco iportat Waso lowr rgy aily stilat thotios o atos a olcl s a sothy ar usally ss as hat Raiatio o highr rgy ca ioiz atomsa prmaly aag molculs, s

that its cts s largly strcti.Oly i th arrow trasitio zo tw ths trs is h rgy flight wll t o th lctroic structr o attr



32/32

The 1 980 's are T e of l has v "BY E : p ! BYE - m y jou al v toprl compurs hs held ui t ne d alr in, w rytanmg rl i, BYE' s 1 60,0 t .Tr ntsis s E tlrgst tr gzn n th !

b klgl t 1 980' s kn t s rsntrs B s r rsng t t n r BE tlls t l s qrsfr rtl rss rWt l BE n xr-nt rgt n r t

1h sma ysms jua

wrd i cr c z ulo?,rbt ic, l be m g- - nd f Sai ts

Rv t expnd r knlg.S BYE!

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B . . B J I One year $ issues) Two years $3 hree years $6

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" qQ Address - -=--- 3 1

causes of color scientificamerican1080-124

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