,,six ,,lectures ,,on ,,light ,,deliv]$ ,,9 ,,! ,,unit$ ,,/ates ,,9 #ahgb-ahgc ,,by ,,john ,,tyndall1 ,d4,c4,l41 ,,ll1,d41 ,f4,r4,s4 ,,late ,,pr(essor ,,( ,,natural ,,philosophy ,,9 ,,! ,,royal ,,in/itution ,,( ,,great ,,brita9 ,illu/ration3 ,sir ,?omas ,laur5ce ,,pra ,p9x ,h5ry ,adl>c4 ,sc4 ,signature3 ,?omas ,"y ,london3 ,longmans ,co4 ,,six? ,,impression ,,longmans1 ,,gre51 ,,& ,,co4 #ci ,,pat]no/] ,,r[1 ,,london ,,new ,,york ,,& ,,bombay #aijf ,,preface ,,to ,,! ,,f\r? ,,edition4 ,9 ^! ,lectures ,i h s\ght to r5d] cle> a difficult b pr(\ndly int]e/+ subject4 ,my aim has be5 n only to describe & illu/rate 9 a famili> mann] ! pr9cipal laws & ph5om5a ( light1 b to po9t out ! orig91 & %[ ! application1 ( ! !oretic conceptions :i* und]lie & unite ! :ole1 & )\t :i* no real int]pretation is possible4 ,! ,lectures1 z /at$ on ! title-page1 7 deliv]$ 9 ! ,unit$ ,/ates 9 #ahgb-c4 ,i /ill reta9 a vivid & grateful remembrance ( ! cordiality ) :i* !y 7 receiv$4 ,my scope & object are briefly indicat$ 9 ! ',summ>y & ,conclusion1' :i*1 z recomm5d$ 9 a =m] edition1 might be1 n unfitly1 read z an introduction to ! volume4 ,j4,t4 ,,alp ,,lusg53 ,octob] #ahhe4 ,,cont5ts4 ,,lecture ,i4 ,introductory ,uses ( ,exp]im5t ,e>ly ,sci5tific ,notions ,sci5ces ( ,obs]vation ,k ( ! ,anci5ts reg>d+ ,light ,defects ( ! ,eye ,our ,in/rum5ts ,rectil9eal ,propagation ( ,light ,law ( ,incid5ce & ,reflection ,/]ility ( ! ,middle ,ages ,refraction ,discov]y ( ,snell ,p>tial & ,total ,reflection ,velocity ( ,light ,roem]1 ,bradley1 ,f\cault1 & ,fizeau ,pr9ciple ( ,lea/ ,action ,desc>tes & ! ,ra9b[ ,newton's ,exp]im5ts on ! ,composition ( ,sol> ,light ,8 ,mi/ake reg>d+ ,a*romatism ,syn!sis ( ,:ite ,light ,yell[ & ,blue ,lights produce ,:ite by _! ,mixture ,col\rs ( ,natural ,bodies ,absorption ,mixture ( ,pigm5ts contra/$ ) ,mixture ( ,lights ,,lecture ,,ii4 ,orig9 ( ,physical ,!ories ,scope ( ! ,imag9ation ,newton & ! ,emission ,!ory ,v]ification ( ,physical ,!ories ,! ,lum9if]\s ,e!r ,wave-!ory ( ,light ,?omas ,"y ,fresnel & ,arago ,conception ( ,wave-motion ,int]f]5ce ( ,waves ,con/itution ( ,s\nd-waves ,analogies ( ,s\nd & ,light ,illu/rations ( ,wave-motion ,int]f]5ce ( ,s\nd ,waves ,optical ,illu/rations ,pit* & ,col\r ,l5g?s ( ! ,waves ( ,light & ,rates ( ,vibration ( ! ,e!r-p>ticles ,int]f]5ce ( ,light ,ph5om5a :i* fir/ sugge/$ ! ,undulatory ,!ory ,boyle & ,hooke ,! ,col\rs ( ?9 ,plates ,! ,soap-bubble ,newton's ,r+s ,!ory ( ',fits' ,its ,explanation ( ! ,r+s ,ov]?r[ ( ! ,!ory ,diffraction ( ,light ,col\rs produc$ by ,diffraction ,col\rs ( ,"m-(-,pe>l4 ,,lecture ,,iii4 ,relation ( ,!ories to ,exp]i5ce ,orig9 ( ! ,notion ( ! ,attraction ( ,gravitation ,notion ( ,pol>ity1 h[ g5]at$ ,atomic ,pol>ity ,/ructural ,arrangem5ts due to ,pol>ity ,ar*itecture ( ,cry/als consid]$ z an ,introduction to _! ,action ^u ,light ,notion ( ,atomic ,pol>ity appli$ to ,cry/all9e ,/ructure ,exp]im5tal ,illu/rations ,cry/allization ( ,wat] ,expansion by ,heat & by ,cold ,deportm5t ( ,wat] consid]$ & expla9$ ,be>+s ( ,cry/allization on ,optical ,ph5om5a ,refraction ,d\ble ,refraction ,pol>ization ,action ( ,t\rmal9e ,"* ( ! ,beams em]g5t f ,icel& ,sp> ,pol>ization by ord9>y ,refraction & ,reflection ,depol>ization4 ,,lecture ,,iv4 ,*romatic ,ph5om5a produc$ by ,cry/als 9 ,pol>iz$ ,light ,! ,nicol ,prism ,pol>iz] & ,analyz] ,action ( ,?ick & ,?9 ,plates ( ,sel5ite ,col\rs dep5d5t on ,?ickness ,resolution ( ,pol>iz$ ,beam into two o!rs by ! ,sel5ite ,"o ( !m m ret>d$ ?an ! o!r ,recomp\nd+ ( ! two ,sy/ems ( ,waves by ! ,analyz] ,int]f]5ce ?us r5d]$ possible ,consequ5t ,production ( ,col\rs ,action ( ,bodies me*anically /ra9$ or press$ ,action ( ,sonor\s ,vibrations ,action ( ,glass /ra9$ or press$ by ,heat ,circul> ,pol>ization ,*romatic ,ph5om5a produc$ by ,qu>tz ,! ,magnetization ( ,light ,r+s surr\nd+ ! ,axes ( ,cry/als ,biaxal & ,uniaxal ,cry/als ,grasp ( ! ,undulatory ,!ory ,! ,col\r & ,pol>ization ( ,sky-light ,g5]ation ( ,artificial ,skies4 ,,lecture ,v4 ,range ( ,vision n comm5surate ) ,range ( ,radiation ,! ,ultra-violet ,rays ,fluoresc5ce ,! r5d]+ ( invisible ,rays visible ,vision n ! only ,s5se appeal$ to by ! ,sol> & ,electric ,beam ,heat ( ,beam ,combu/ion by ,total ,beam at ! ,foci ( ,mirrors & ,l5ses ,combu/ion ?r\gh ,ice-l5s ,ignition ( ,diamond ,se>* = ! ,rays "h effective ,sir ,william ,h]s*el's ,discov]y ( d>k ,sol> ,rays ,invisible ,rays ! ,basis ( ! ,visible ,deta*m5t by a ,ray-filt] ( ! ,invisible ,rays f ! ,visible ,combu/ion at ,d>k ,foci ,conv]sion ( ,heat-rays into ,light-rays ,caloresc5ce ,"p play$ 9 ,nature by ,d>k ,rays ,id5tity ( ,light & ,radiant ,heat ,invisible ,images ,reflection1 ,refraction1 ,plane ,pol>ization1 ,depol>ization1 ,circul> ,pol>ization1 ,d\ble ,refraction1 & ,magnetization ( ,radiant ,heat ,,lecture ,,vi4 ,pr9ciples ( ,spectrum ,analysis ,prismatic ,analysis ( ! ,light ( ,inc&esc5t ,vap\rs ,discont9u\s ,spectra ,spectrum ,b&s prov$ by ,buns5 & ,kir*h(f to be *>act]i/ic ( ! ,vap\r ,discov]y ( ,rubidium1 ,csium1 & ,?allium ,relation ( ,emission to ,absorption ,! ,l9es ( ,fraunh(] ,_! ,explanation by ,kir*h(f ,sol> ,*emi/ry involv$ 9 ?is ,explanation ,f\cault's ,exp]im5t ,pr9ciples ( ,absorption ,analogy ( ,s\nd & ,light ,exp]im5tal ,demon/ration ( ?is ,analogy ,rec5t ,applications ( ! ,spectroscope ,summ>y & ,conclusion ,,app5dix4 ,on ! ,spectra ( ,pol>iz$ ,light ,measurem5t ( ! ,waves ( ,light ,,index ,,on ,,light ,,lecture ,i4 ,,introductory ,,uses ,,( ,,exp]im5t ,,e>ly ,,sci5tific ,,notions ,,sci5ces ,,( ,,obs]vation ,,k ,,( ,,! ,,anci5ts ,,reg>d+ ,,light ,,defects ,,( ,,! ,,eye ,,our ,,in/rum5ts ,,rectil9eal ,,propagation ,,( ,,light ,,law ,,( ,,incid5ce ,,& ,,reflection ,,/]ility ,,( ,,! ,,middle ,,ages ,,refraction ,,discov]y ,,( ,,snell ,,p>tial ,,& ,,total ,,reflection ,,velocity ,,( ,,light ,,roem]1 ,,bradley1 ,,f\cault1 ,,& ,,fizeau ,,pr9ciple ,,( ,,lea/ ,,action ,,desc>tes ,,& ,,! ,,ra9b[ ,,newton',s ,,exp]im5ts ,,on ,,! ,,composition ,,( ,,sol> ,,light ,,8 ,,mi/ake ,,z ,,reg>ds ,,a*romatism ,,syn!sis ,,( ,,:ite ,,light ,,yell[ ,,& ,,blue ,,lights ,,produce ,,:ite ,,by ,,_! ,,mixture ,,col\rs ,,( ,,natural ,,bodies ,,absorption ,,mixture ,,( ,,pigm5ts ,,contra/$ ,,) ,,mixture ,,( ,,lights4 #a4 ,introduction4 ,"s twelve ye>s ago ,i publi%$1 9 ,engl&1 a little book entitl$ ! ',glaci]s ( ! ,alps1' &1 a c\ple ( ye>s subsequ5tly1 a second book1 entitl$ ',heat a ,mode ( ,motion4' ,^! volumes 7 foll[$ by o!rs1 writt5 ) equal pla9ness1 & ) a simil> aim1 t aim be+ to develop & deep5 sympa?y betwe5 sci5ce & ! _w outside ( sci5ce4 ,i agre$ ) ?\ghtful m5#a :o deem$ x good = nei!r _w to be isolat$ f ! o!r1 or unsympa!tic t[>ds ! o!r1 &1 to less5 ?is isolation1 at lea/ 9 "o dep>tm5t ( sci5ce1 ,i sw]v$1 = a "t1 f ^? orig9al rese>*es :i* h be5 ! real pursuit & pleasure ( my life4 ,! works "h ref]r$ to 71 = ! mo/ "p1 republi%$ by ! ,messrs4 ,appleton ( ,new ,york1#b "u ! auspices ( a man :o is untir+ 9 8 ef=ts to diffuse s\nd sci5tific k among ! p ( ! ,unit$ ,/ates2 ^: en]gy1 ability1 & s+le-m9d$ness1 9 ! prosecution ( an ardu\s task1 h won = him ! sympa?y & support ( _m ( u 9 '! old c\ntry4' ,i allude to ,pr(essor ,y\mans4 ,q z rapidly z 9 ,engl&1 ! aim ( ^! works 0 und]/ood & appreciat$ 9 ! ,unit$ ,/ates1 & !y br\ght me f ?is side ( ! ,atlantic innum]able evid5ces ( good-w4 ,ye> aft] ye> invitations rea*$ me#c to visit ,am]ica1 & la/ ye> 7#ahga7 ,i 0 hon\r$ ) a reque/ s cordial1 sign$ by five-&-tw5ty names1 s di/+ui%$ 9 sci5ce1 9 lit]ature1 & 9 adm9i/rative position1 t ,i at once resolv$ to respond to x by brav+ n only ! disquiet+ oscillations ( ! ,atlantic1 b ! f> m disquiet+ ordeal ( appe>+ 9 p]son be=e ! p ( ! ,unit$ ,/ates4 ,?is invitation1 convey$ to me by my accompli%$ fri5d ,pr(essor ,lesley1 ( ,philadelphia1 & prec$$ by a lett] ( ! same purport f y\r sci5tific ,ne/or1 ! celebrat$ ,joseph ,h5ry1 ( ,wa%+ton1 desir$ t ,i %\ld lecture 9 "s ( ! pr9cipal cities ( ! ,union4 ,?is ,i agre$ to d1 ?\gh mu* 9 ! d>k z to a suitable subject4 ,9 answ] to my inquiries1 h[ev]1 ,i 0 giv5 to und]/& t a c\rse ( lectures1 %[+ ! uses ( exp]im5t 9 ! cultivation ( ,natural ,k1 w\ld mat]ially promote sci5tific education 9 ?is c\ntry4 ,& ?\gh su* lectures involv$ ! selection ( weighty & delicate in/rum5ts1 & _! transf] f place to place1 ,i det]m9$ to meet ! wi%es ( my fri5ds1 z f> z ! "t & means at my disposal w\ld all[4 #b4 ,subject ( ! ,c\rse4 ,s\rce ( ,light employ$4 ,exp]im5ts h two great uses--a use 9 discov]y1 & a use 9 tuition4 ,!y 7 long ago def9$ z ! inve/igator's language address$ to ,nature1 to :i* %e s5ds intelligible replies4 ,^! replies1 h[ev]1 usually rea* ! que/ion] 9 :isp]s too feeble = ! public e>4 ,b aft] ! inve/igator comes ! tea*]1 ^: function x is s to exalt & modify ! exp]im5ts ( 8 pr$ecessor1 z to r5d] !m fit = public pres5tation4 ,?is second>y function ,i %all endeav\r1 9 ! pres5t in/ance1 to fulfil4 ,tak+ a s+le dep>tm5t ( natural philosophy z my subject1 ,i propose1 by means ( x1 to illu/rate ! gr[? ( sci5tific k "u ! guidance ( exp]im5t4 ,i wi%1 9 ! fir/ place1 to make y acqua9t$ ) c]ta9 elem5t>y ph5om5a2 !n to po9t out to y h[ ! !oretical pr9ciples by :i* ph5om5a are expla9$ take root 9 ! human m9d1 & f9ally to apply ^! pr9ciples to ! :ole body ( k cov]$ by ! lectures4 ,! sci5ce ( optics l5ds itself p>ticul>ly well to ?is mode ( treatm5t1 & on x1 !re=e1 ,i propose to draw = ! mat]ials ( ! pres5t c\rse4 ,x w be be/ to beg9 ) ! few simple facts reg>d+ light :i* 7 kn[n to ! anci5ts1 & to pass f !m1 9 hi/oric gradation1 to ! m ab/ruse discov]ies ( mod]n times4 ,all our notions ( ,nature1 h[ev] exalt$ or h[ev] grotesque1 h _! f\ndation 9 exp]i5ce4 ,! notion ( p]sonal volition 9 ,nature _h ?is basis4 ,9 ! fury & ! s]5ity ( natural ph5om5a ! savage saw ! transcript ( 8 own v>y+ moods1 & he accord+ly ascrib$ ^! ph5om5a to be+s ( l passions ) himself1 b va/ly transc5d+ him 9 p[]4 ,?us ! notion ( causality--! assumption t natural ?+s did n come ( !mselves1 b _h unse5 antec$5ts--lay at ! root ( ev5 ! savage's int]pretation ( ,nature4 ,out ( ?is bias ( ! human m9d to seek = ! causes ( ph5om5a all sci5ce has sprung4 ,we w n n[ g back to man's fir/ intellectual grop+s2 mu* less %all we ent] ^u ! ?orny discussion z to h[ ! grop+ man arose4 ,we w take him at t /age ( 8 developm5t1 :5 he became possess$ ( ! app>atus ( ?\ght & ! p[] ( us+ x4 ,= a "t--& t hi/orically a long "o--he 0 limit$ to m]e obs]vation1 accept+ :at ,nature (f]$1 & conf9+ intellectual action to x alone4 ,! app>5t motions ( sun & />s fir/ drew t[>ds !m ! que/ion+s ( ! intellect1 & accord+ly a/ronomy 0 ! fir/ sci5ce develop$4 ,sl[ly1 & ) difficulty1 ! notion ( natural =ces took root 9 ! human m9d4 ,sl[ly1 & ) difficulty1 ! sci5ce ( me*anics _h to gr[ out ( ?is notion2 & sl[ly at la/ came ! full application ( me*anical pr9ciples to ! motions ( ! heav5ly bodies4 ,we trace ! progress ( a/ronomy ?r\gh ,hipp>*us & ,ptolemy2 &1 aft] a long halt1 ?r\gh ,cop]nicus1 ,galileo1 ,ty*o ,brahe1 & ,kepl]2 :ile f ! high table-l& ( ?\ght occupi$ by ^! m51 ,newton %oots upw>ds l a peak1 ov]look+ all o!rs f 8 dom9ant elevation4 ,b o!r objects ?an ! motions ( ! />s attract$ ! att5tion ( ! anci5t _w4 ,light 0 a famili> ph5om5on1 & f ! e>lie/ times we f9d m5's m9ds busy ) ! attempt to r5d] "s acc\nt ( x4 ,b )\t exp]im5t1 :i* belongs to a lat] /age ( sci5tific developm5t1 little progress c\ld be "h made4 ,! anci5ts1 accord+ly1 7 f> less successful 9 deal+ ) light ?an 9 deal+ ) sol> & /ell> motions4 ,/ill !y did make "s progress4 ,!y satisfi$ !mselves t light mov$ 9 /raight l9es2 !y knew also t light 0 reflect$ f poli%$ surfaces1 & t ! angle ( incid5ce 0 equal to ! angle ( reflection4 ,^! two results ( anci5t sci5tific curiosity con/itute ! />t+-po9t ( our pres5t c\rse ( lectures4 ,b 9 ! fir/ place x w be useful to say a few words reg>d+ ! s\rce ( light to be employ$ 9 our exp]im5ts4 ,! ru/+ ( iron is1 to all int5ts & purposes1 ! sl[ burn+ ( iron4 ,x develops heat1 &1 if ! heat be pres]v$1 a high temp]ature may be ?us atta9$4 ,! de/ruction ( ! fir/ ,atlantic cable 0 probably due to heat develop$ 9 ?is way4 ,o!r metals are /ill m combu/ible ?an iron4 ,y may ignite /rips ( z9c 9 a c&le flame1 & cause !m to burn almo/ l /rips ( pap]4 ,b we mu/ n[ exp& our def9ition ( combu/ion1 & include "u ?is t]m1 n only combu/ion 9 air1 b also combu/ion 9 liquids4 ,wat]1 = example1 conta9s a /ore ( oxyg51 :i* may unite )1 & consume1 a metal imm]s$ 9 x2 x is f ?is k9d ( combu/ion t we are to d]ive ! heat & light employ$ 9 our pres5t c\rse4 ,! g5]ation ( ?is light & ( ?is heat m]its a mom5t's att5tion4 ,be=e y is an in/rum5t--a small voltaic batt]y--9 :i* z9c is imm]s$ 9 a suitable liquid4 ,an attractive =ce is at ?is mom5t ex]t$ betwe5 ! metal & ! oxyg5 ( ! liquid2 actual comb9ation1 h[ev]1 be+ 9 ! fir/ in/ance avoid$4 ,unit+ ! two ends ( ! batt]y by a ?ick wire1 ! attraction is satisfi$1 ! oxyg5 unites ) ! metal1 z9c is consum$1 & heat1 z usual1 is ! result ( ! combu/ion4 ,a p[] :i*1 = want ( a bett] "n1 we call an electric curr5t1 passes at ! same "t ?r\gh ! wire4 ,cutt+ ! ?ick wire 9 two1 let ! sev]$ ends be unit$ by a ?9 "o4 ,x gl[s ) a :ite heat4 ,:5ce comes t heat8 ,! "q is well wor?y ( an answ]4 ,suppose 9 ! fir/ in/ance1 :5 ! ?ick wire is employ$1 t we p]mit ! action to cont9ue until #ajj gra9s ( z9c are consum$1 ! am\nt ( heat g5]at$ 9 ! batt]y w\ld be capable ( accurate num]ical expression4 ,let ! action !n cont9ue1 ) ! ?9 wire gl[+1 until #ajj gra9s ( z9c are consum$4 ,w ! am\nt ( heat g5]at$ 9 ! batt]y be ! same z be=e8 ,no2 x w be less by ! precise am\nt g5]at$ 9 ! ?9 wire outside ! batt]y4 ,9 fact1 by add+ ! int]nal heat to ! ext]nal1 we obta9 = ! combu/ion ( #ajj gra9s ( z9c a total :i* nev] v>ies4 ,we h "h a beautiful example ( t law ( con/ancy z reg>ds natural en]gies1 ! e/abli%m5t ( :i* is ! greate/ a*ievem5t ( mod]n sci5ce4 ,by ?is arrangem5t1 !n1 we are able to burn our z9c at "o place1 & to exhibit ! effects ( its combu/ion at ano!r4 ,9 ,new ,york1 = example1 we may h our grate & fuel2 b ! heat & light ( our fire may be made to appe> at ,san ,francisco4 ,illu/ration3 ,fig4 #a4 ,remov+ ! ?9 wire & atta*+ to ! sev]$ ends ( ! ?ick "o two rods ( coke we obta91 on br++ ! rods toge!r 7z 9 fig4 #a71 a small /> ( light4 ,n[1 ! light to be employ$ 9 our lectures is a simple exagg]ation ( ?is />4 ,in/ead ( be+ produc$ by t5 cells1 x is produc$ by fifty4 ,plac$ 9 a suitable cam]a1 provid$ ) a suitable l5s1 ?is p[]ful s\rce w give u all ! light necess>y = our exp]im5ts4 ,& "h1 9 pass+1 ,i am rem9d$ ( ! common delusion t ! works ( ,nature1 ! human eye includ$1 are !oretically p]fect4 ,! eye has gr[n = ages t[>ds p]fection2 b ages ( p]fect+ may be /ill be=e x4 ,look+ at ! dazzl+ light f our l>ge batt]y1 ,i see a lum9\s globe1 b entirely fail to see ! %ape ( ! coke-po9ts :5ce ! light issues4 ,! cause may be ?us made cle>3 ,on ! scre5 be=e y is project$ an image ( ! c>bon po9ts1 ! :ole ( ! glass l5s 9 front ( ! cam]a be+ employ$ to =m ! image4 ,x is n %>p1 b surr\nd$ by a halo :i* ne>ly oblit]ates ! c>bons4 ,?is arises f an imp]fection ( ! glass l5s1 call$ its sph]ical ab]ration1 :i* is due to ! fact t ! circumf]5tial & c5tral rays h n ! same focus4 ,! human eye lab\rs "u a simil> defect1 & f ?is1 & o!r causes1 x arises t :5 ! nak$ light f fifty cells is look$ at ! blur ( light ^u ! ret9a is suffici5t to de/roy ! def9ition ( ! ret9al image ( ! c>bons4 ,a long li/ ( indictm5ts might inde$ be br\ght aga9/ ! eye--its opacity1 its want ( symmetry1 its lack ( a*romatism1 its p>tial bl9dness4 ,all ^! tak5 toge!r caus$ ,helmholt to say t1 if any optician s5t him an in/rum5t s defective1 he w\ld be ju/ifi$ 9 s5d+ x back ) ! sev]e/ c5sure4 ,b ! eye is n to be judg$ f ! /&po9t ( !ory4 ,x is n p]fect1 b is on its way to p]fection4 ,z a practical in/rum5t1 & tak+ ! adju/m5ts by :i* its defects are neutraliz$ into acc\nt1 x mu/ ev] rema9 a m>vel to ! reflect+ m9d4 #c4 ,rectil9eal ,propagation ( ,light4 ,elem5t>y ,exp]im5ts4 ,law ( ,reflection4 ,! anci5ts 7 aw>e ( ! rectil9eal propagation ( light4 ,!y knew t an opaque body1 plac$ betwe5 ! eye & a po9t ( light1 int]cept$ ! light ( ! po9t4 ,possibly ! t]ms 'ray' & 'beam' may h be5 sugge/$ by ^? /raight spokes ( light :i*1 9 c]ta9 /ates ( ! atmosph]e1 d>t f ! sun at 8 ris+ & 8 sett+4 ,! rectil9eal propagation ( light may be illu/rat$ by p]mitt+ ! sol> light to ent]1 ?r\gh a small ap]ture 9 a w9d[-%utt]1 a d>k room 9 :i* a little smoke has be5 diffus$4 ,9 pure air y _c see ! beam1 b 9 smoky air y c1 because ! light1 :i* passes unse5 ?r\gh ! air1 is scatt]$ & reveal$ by ! smoke p>ticles1 among :i* ! beam pursues a /raight c\rse4 ,! foll[+ in/ructive exp]im5t dep5ds on ! rectil9eal propagation ( light4 ,make a small hole 9 a clos$ w9d[-%utt]1 be=e :i* /&s a h\se or a tree1 & place )9 ! d>k5$ room a :ite scre5 at "s di/ance f ! orifice4 ,e /raight ray proce$+ f ! h\se1 or tree1 /amps its col\r ^u ! scre51 & ! sum ( all ! rays w1 !re=e1 be an image ( ! object4 ,b1 z ! rays cross ea* o!r at ! orifice1 ! image is inv]t$4 ,at pres5t we may illu/rate & exp& ! subject ?us3 ,9 front ( our cam]a is a l>ge op5+ 7,l1 fig4 #b71 f :i* ! l5s has be5 remov$1 & :i* is clos$ at pres5t by a %eet ( t9-foil4 ,prick+ by means ( a common sew+-ne$le a small ap]ture 9 ! t9-foil1 an inv]t$ image ( ! c>bon-po9ts />ts =? ^u ! scre54 ,a doz5 ap]tures w give a doz5 images1 a hundr$ a hundr$1 a ?\s& a ?\s&4 ,b1 z ! ap]tures come clos] to ea* o!r1 t is to say1 z ! t9-foil betwe5 ! ap]tures vani%es1 ! images ov]lap m & m4 ,remov+ ! t9-foil altoge!r1 ! scre5 becomes uni=mly illum9at$4 ,h5ce ! light ^u ! scre5 may be reg>d$ z ! ov]lapp+ ( innum]able images ( ! c>bon-po9ts4 ,9 l mann] ! light ^u e :ite wall1 on a cl\dless day1 may be reg>d$ z produc$ by ! sup]position ( innum]able images ( ! sun4 ,illu/ration3 ,fig4 #b4 ,! law t ! angle ( incid5ce is equal to ! angle ( reflection has a be>+ ^u !ory1 to be subsequ5tly m5tion$1 :i* r5d]s its simple illu/ration "h desirable4 ,a /raight la? 7po9t+ to ! figure #e on ! arc 9 fig4 #c7 is fix$ z an index p]p5dicul> to a small look+-glass 7,m71 capable ( rotation4 ,we beg9 by receiv+ a beam ( light ^u ! glass :i* is reflect$ back along ! l9e ( its incid5ce4 ,! index be+ !n turn$1 ! mirror turns ) x1 & at ea* side ( ! index ! incid5t & ! reflect$ beams 7,l o1 o ,r7 track !mselves ?r\gh ! du/ ( ! room4 ,! m]e inspection ( ! two angles enclos$ betwe5 ! index & ! two beams suffices to %[ _! equality2 :ile if ! graduat$ arc be consult$1 ! arc f #e to m is f\nd accurately equal to ! arc f #e to n4 ,! complete expression ( ! law ( reflection is1 n only t ! angles ( incid5ce & reflection are equal1 b t ! incid5t & reflect$ rays always lie 9 a plane p]p5dicul> to ! reflect+ surface4 ,illu/ration3 ,fig4 #c4 ,?is simple app>atus enables u to illu/rate ano!r law ( great practical importance1 namely1 t :5 a mirror rotates1 ! angul> velocity ( a beam reflect$ f x is twice t ( ! reflect+ mirror4 ,a simple exp]im5t w make ?is pla94 ,! arc 7m n1 fig4 #c7 be=e y is divid$ into t5 equal p>ts1 & :5 ! incid5t beam & ! index cross ! z]o ( ! graduation1 bo? ! incid5t & reflect$ beams are horizontal4 ,mov+ ! index ( ! mirror to #a1 ! reflect$ beam cuts ! arc at #b2 mov+ ! index to #b1 ! arc is cut at #d2 mov+ ! index to #c1 ! arc is cut at #f2 mov+ ! index at #d1 ! arc is cut at #h2 f9ally1 mov+ ! index to #e1 ! arc is cut at #aj 7z 9 ! figure74 ,9 e case ! reflect$ beam moves ?r\gh twice ! angle pass$ ov] by ! mirror4 ,"o ( ! pr9cipal problems ( sci5ce is to help ! s5ses ( man1 by c>ry+ !m into regions :i* c\ld nev] be atta9$ )\t t help4 ,?us we arm ! eye ) ! telescope :5 we want to s\nd ! dep?s ( space1 & ) ! microscope :5 we want to explore motion & /ructure 9 _! inf9itesimal dim5sions4 ,n[1 ?is law ( angul> reflection1 c\pl$ ) ! fact t a beam ( light possesses no weight1 gives u ! means ( magnify+ small motions to an extraord9>y degree4 ,?us1 by atta*+ mirrors to 8 susp5d$ magnets1 & by wat*+ ! images ( divid$ scales reflect$ f ! mirrors1 ! celebrat$ ,gauss 0 able to detect ! slighte/ ?rill ( v>iation on ! "p ( ! e>?'s magnetic =ce4 ,by a simil> arrangem5t ! feeble attractions & repulsions ( ! diamagnetic =ce h be5 made manife/4 ,! m9ute elongation ( a b> ( metal1 by ! m]e w>m? ( ! h&1 may be s magnifi$ by ?is me?od1 z to cause ! index-beam to move ?r\gh #bj or #cj feet4 ,! l5g!n+ ( a b> ( iron :5 x is magnetiz$ may be also ?us demon/rat$4 ,helmholtz long ago employ$ ?is me?od ( r5d]+ evid5t to 8 /ud5ts ! classical exp]im5ts ( ,du ,bois ,raymond on animal electricity2 :ile 9 ,sir ,william ,?omson's reflect+ galvanomet] ! pr9ciple receives "o ( its late/ & mo/ important applications4 #d4 ,! ,refraction ( ,light4 ,total ,reflection4 ,= m ?an a ?\s& ye>s no /ep 0 tak5 9 optics beyond ?is law ( reflection4 ,! m5 ( ! ,middle ,ages1 9 fact1 endeav\r$1 on ! "o h&1 to develop ! laws ( ! univ]se priori out ( _! own consci\sness1 :ile _m ( !m 7 s occupi$ ) ! conc]ns ( a future _w t !y look$ ) a l(ty scorn on all ?+s p]ta9+ to ?is "o4 ,speak+ ( ! natural philosoph]s ( 8 "t1 ,eusebius says1 ',x is n ?r\gh ignorance ( ! ?+s admir$ by !m1 b ?r\gh contempt ( _! useless lab\r1 t we ?9k little ( ^! matt]s1 turn+ our s\ls to ! ex]cise ( bett] ?+s4' ,s also ,lactantius--',to se>* = ! causes ( ?+s2 to inquire :e!r ! sun be z l>ge z he seems2 :e!r ! moon is convex or concave2 :e!r ! />s are fix$ 9 ! sky1 or float freely 9 ! air2 ( :at size & ( :at mat]ial are ! heav5s2 :e!r !y be at re/ or 9 motion2 :at is ! magnitude ( ! e>?2 on :at f\ndations is x susp5d$ or balanc$2--to dispute & conjecture ^u su* matt]s is j z if we *ose to discuss :at we ?9k ( a city 9 a remote c\ntry1 ( :i* we nev] he>d b ! "n4' ,z reg>ds ! refraction ( light1 ! c\rse ( real inquiry 0 resum$ 9 #aajj by an ,arabian philosoph] nam$ ,alhaz54 ,!n x 0 tak5 up 9 succession by ,rog] ,bacon1 ,vitellio1 & ,kepl]4 ,"o ( ! mo/ important occupations ( sci5ce is ! det]m9ation1 by precise measurem5ts1 ( ! quantitative relations ( ph5om5a2 ! value ( su* measurem5ts dep5d+ greatly ^u ! skill & consci5ti\sness ( ! man :o makes !m4 ,vitellio appe>s to h be5 bo? skilful & consci5ti\s1 :ile ,kepl]'s habit 0 to rummage ?r\gh ! obs]vations ( 8 pr$ecessors1 to look at !m 9 all lights1 & ?us di/il f !m ! pr9ciples :i* unit$ !m4 ,he _h done ?is ) ! a/ronomical measurem5ts ( ,ty*o ,brahe1 & _h extract$ f !m ! celebrat$ 'laws ( ,kepl]4' ,he did x also ) ,vitellio's measurem5ts ( refraction4 ,b 9 ?is case he 0 n successful4 ,! pr9ciple1 ?\gh a simple "o1 escap$ him1 & x 0 fir/ discov]$ by ,willebrord ,snell1 ab\t ! ye> #afba4 ,less ) ! view ( dwell+ ^u ! ph5om5on itself ?an ( introduc+ x 9 a =m :i* w r5d] subsequ5tly intelligible to y ! play ( !oretic ?\ght 9 ,newton's m9d1 ! fact ( refraction may be "h demon/rat$4 ,i w n d ?is by draw+ ! c\rse ( ! beam ) *alk on a black bo>d1 b by caus+ x to m>k its own :ite track be=e y4 ,a %all[ circul> vessel 7,,rig1 fig4 #d71 half fill$ ) wat]1 r5d]$ slightly turbid by ! admixture ( a little milk1 or ! precipitation ( a little ma/ic1 is plac$ ) its glass front v]tical4 ,by means ( a small plane reflector 7,m71 & ?r\gh a slit 7,i7 9 ! hoop surr\nd+ ! vessel1 a beam ( light is admitt$ 9 any requir$ direction4 ,x imp+es ^u ! wat] 7at ,o71 ent]s x1 & tracks itself ?r\gh ! liquid 9 a %>p bright b& 7,o ,g74 ,mean:ile ! beam passes unse5 ?r\gh ! air above ! wat]1 = ! air is n compet5t to scatt] ! light4 ,a puff ( smoke into ?is space at once reveals ! track ( ! incid5t-beam4 ,if ! incid5ce be v]tical1 ! beam is unrefract$4 ,if oblique1 its refraction at ! common surface ( air & wat] 7at ,o7 is r5d]$ cle>ly visible4 ,x is also se5 t reflection 7along ,o ,r7 accompanies refraction1 ! beam divid+ itself at ! po9t ( incid5ce into a refract$ & a reflect$ portion4#d ,illu/ration3 ,fig4 #d4 ,! law by :i* ,snell connect$ toge!r all ! measurem5ts execut$ up to 8 "t1 is ?is3 ,let ,a ,b ,c ,d 7fig4 #e7 repres5t ! outl9e ( our circul> vessel1 ,a ,c be+ ! wat]-l9e4 ,:5 ! beam is incid5t along ,b ,e1 :i* is p]p5dicul> to ,a ,c1 !re is no refraction4 ,:5 x is incid5t along m ,e1 !re is refraction3 x is b5t at ,e & /rikes ! circle at n4 ,:5 x is incid5t along m' ,e !re is also refraction at ,e1 ! beam /rik+ ! po9t n'4 ,f ! ends ( ! two incid5t beams1 let ! p]p5dicul>s m o1 m' o' be drawn ^u ,b ,d1 & f ! ends ( ! refract$ beams let ! p]p5dicul>s p n1 p' n' be also drawn4 ,measure ! l5g?s ( o m & ( p n1 & divide ! "o by ! o!r4 ,y obta9 a c]ta9 quoti5t4 ,9 l mann] divide m' o' by ! correspond+ p]p5dicul> p' n'2 y obta9 precisely ! same quoti5t4 ,snell1 9 fact1 f\nd ?is quoti5t to be a con/ant quantity = ea* p>ticul> sub/ance1 ?\gh x v>i$ 9 am\nt f "o sub/ance to ano!r4 ,he call$ ! quoti5t ! index ( refraction4 ,illu/ration ,fig4 #e ,9 all cases :]e ! light is incid5t f air ^u ! surface ( a solid or a liquid1 or1 to speak m g5]ally1 :5 ! incid5ce is f a less highly refract+ to a m highly refract+ m$ium1 ! reflection is p>tial4 ,9 ?is case ! mo/ p[]fully reflect+ sub/ances ei!r transmit or absorb a portion ( ! incid5t light4 ,at a p]p5dicul> incid5ce wat] reflects only #ah rays out ( e #a1jjj2 glass reflects only #be rays1 :ile m]cury reflects #fff ,:5 ! rays /rike ! surface obliquely ! reflection is augm5t$4 ,at an incid5ce ( #dj1 = example1 wat] reflects #bb rays1 at #fj x reflects #fe rays1 at #hj #ccc rays2 :ile at an incid5ce ( #hi1 :]e ! light almo/ grazes ! surface1 x reflects #gba rays out ( e #a1jjj4 ,?us1 z ! obliquity increases1 ! reflection f wat] approa*es1 & f9ally q ov]takes1 ! p]p5dicul> reflection f m]cury2 b at no incid5ce1 h[ev] great1 :5 ! incid5ce is f air1 is ! reflection f wat]1 m]cury1 or any o!r sub/ance1 total4 ,/ill1 total reflection may occur1 & ) a view to und]/&+ its subsequ5t application 9 ! ,nicol's prism1 x is necess>y to /ate :5 x occurs4 ,?is leads me to ! enunciation ( a pr9ciple :i* und]lies all optical ph5om5a--! pr9ciple ( rev]sibility4#e ,9 ! case ( refraction1 = in/ance1 :5 ! ray passes obliquely f air into wat]1 x is b5t t[>ds ! p]p5dicul>2 :5 x passes f wat] to air1 x is b5t f ! p]p5dicul>1 & accurately rev]ses its c\rse4 ,?us 9 fig4 #e1 if m ,e n be ! track ( a ray 9 pass+ f air into wat]1 n ,e m w be its track 9 pass+ f wat] into air4 ,let u pu% ?is pr9ciple to its consequ5ces4 ,suppos+ ! light1 in/ead ( be+ incid5t along m ,e or m' ,e1 7 incid5t z close z possible along ,c ,e 7fig4 #f72 suppose1 9 o!r words1 t x j grazes ! surface be=e ent]+ ! wat]4 ,aft] refraction x w pursue say ! c\rse ,e n''4 ,conv]sely1 if ! light />t f n''1 & be incid5t at ,e1 x w1 on escap+ into ! air1 j graze ! surface ( ! wat]4 ,! "q n[ arises1 :at w occur suppos+ ! ray f ! wat] to foll[ ! c\rse n''' ,e1 :i* lies beyond n'' ,e8 ,! answ] is1 x w n quit ! wat] at all1 b w be totally reflect$ 7along ,e x74 ,at ! "u surface ( ! wat]1 moreov]1 ! law is j ! same z at its upp] surface1 ! angle ( incid5ce 7,d ,e n'''7 be+ equal to ! angle ( reflection 7,d ,e x74 ,illu/ration3 ,fig4 #f ,total reflection may be ?us simply illu/rat$3--,place a %ill+ 9 a dr9k+-glass1 & tilt ! glass s t ! light f ! %ill+ %all fall ) ! necess>y obliquity ^u ! wat] surface above x4 ,look upw>ds ?r\gh ! wat] t[>ds t surface1 & y see ! image ( ! %ill+ %9+ !re z brightly z ! %ill+ itself4 ,?ru/ ! clos$ end ( an empty te/-tube into wat]1 & incl9e ! tube4 ,:5 ! incl9ation is suffici5t1 horizontal light fall+ ^u ! tube _c ent] ! air )9 x1 b is totally reflect$ upw>d3 :5 look$ d[n ^u1 su* a tube looks q z bright z burni%$ silv]4 ,p\r a little wat] into ! tube2 z ! liquid rises1 total reflection is aboli%$1 & ) x ! lu/re1 leav+ a gradually dim9i%+ %9+ zone1 :i* disappe>s :olly :5 ! level ( ! wat] )9 ! tube rea*es t )\t x4 ,any glass tube1 ) its end /opp$ wat]-tight1 w produce ?is effect1 :i* is bo? beautiful & in/ructive4 ,total reflection nev] occurs except 9 ! attempt$ passage ( a ray f a m refract+ to a less refract+ m$ium2 b 9 ?is case1 :5 ! obliquity is suffici5t1 x always occurs4 ,! mirage ( ! des]t1 & o!r phantasmal appe>ances 9 ! atmosph]e1 are 9 "p due to x4 ,:51 = example1 ! sun heats an expanse ( s&1 ! lay] ( air 9 contact ) ! s& becomes light] & less refract+ ?an ! air above x3 consequ5tly1 ! rays f a di/ant object1 /rik+ v obliquely on ! surface ( ! heat$ /ratum1 are sometimes totally reflect$ upw>ds1 ?us produc+ images simil> to ^? produc$ by wat]4 ,i h se5 ! image ( a rock call$ ,mont ,tombel9e di/9ctly reflect$ f ! heat$ air ( ! /r& ( ,norm&y ne> ,avran*es2 & by su* delusive appe>ances ! ?ir/y soldi]s ( ! ,fr5* army 9 ,egypt 7 greatly tantalis$4 ,! angle :i* m>ks ! limit beyond :i* total reflection takes place is call$ ! limit+ angle 7x is m>k$ 9 fig4 #f by ! /rong l9e ,e n''74 ,x mu/ evid5tly dim9i% z ! refractive index increases4 ,= wat] x is #dh1 = fl9t glass #chda'1 & = diamond #bcdb'4 ,?us all ! light incid5t f two complete quadrants1 or #ahj1 9 ! case ( diamond1 is cond5s$ into an angul> space ( #dgbb' 7twice #bcdb'7 by refraction4 ,c\pl$ ) its great refraction1 are ! great disp]sive & great reflective p[]s ( diamond2 h5ce ! extraord9>y radiance ( ! gem1 bo? z reg>ds :ite light & prismatic light4 #e4 ,velocity ( ,light4 ,ab]ration4 ,pr9ciple ( lea/ ,action4 ,9 #afgf a great impulse 0 giv5 to optics by a/ronomy4 ,9 t ye> ,olav ,roem]1 a le>n$ ,dane1 0 engag$ at ! ,obs]vatory ( ,p>is 9 obs]v+ ! eclipses ( ,jupit]'s moons4 ,! planet1 ^: di/ance f ! sun is #dge1fic1jjj miles1 has f\r satellites4 ,we are n[ only conc]n$ ) ! "o ne>e/ to ! planet4 ,roem] wat*$ ?is moon1 saw x move r\nd ! planet1 plunge into ,jupit]'s %ad[1 behav+ l a lamp sudd5ly ext+ui%$3 !n at ! o!r edge ( ! %ad[ he saw x reappe>1 l a lamp sudd5ly light$4 ,! moon ?us act$ ! "p ( a signal light to ! a/ronom]1 & enabl$ him to tell exactly its "t ( revolution4 ,! p]iod betwe5 two successive light+s up ( ! lun> lamp he f\nd to be #db h\rs1 #bh m9utes1 & #ce seconds4 ,?is measurem5t ( "t 0 s accurate1 t hav+ det]m9$ ! mom5t :5 ! moon em]g$ f ! %ad[1 ! mom5t ( its hundr$? appe>ance c\ld also be det]m9$4 ,9 fact1 x w\ld be #ajj times #db h\rs1 #bh m9utes1 #ce seconds1 aft] ! fir/ obs]vation4 ,roem]'s fir/ obs]vation 0 made :5 ! e>? 0 9 ! "p ( its orbit ne>e/ ,jupit]4 ,ab\t six mon?s aft]w>ds1 ! e>? be+ !n at ! opposite side ( its orbit1 :5 ! little moon ought to h made its hundr$? appe>ance1 x 0 f\nd unpunctual1 be+ fully #ae m9utes beh9d its calculat$ "t4 ,its appe>ance1 moreov]1 _h be5 gr[+ gradually lat]1 z ! e>? retreat$ t[>ds ! "p ( its orbit mo/ di/ant f ,jupit]4 ,roem] reason$ ?us3 ',_h ,i be5 able to rema9 at ! o!r side ( ! e>?'s orbit1 ! moon might h appe>$ always at ! prop] in/ant2 an obs]v] plac$ !re w\ld probably h se5 ! moon #ae m9utes ago1 ! ret>dation 9 my case be+ due to ! fact t ! light requires #ae m9utes to travel f ! place :]e my fir/ obs]vation 0 made to my pres5t position4' ,?is fla% ( g5ius 0 imm$iately succe$$ by ano!r4 ',if ?is surmise be correct1' ,roem] reason$1 '!n z ,i approa* ,jupit] along ! o!r side ( ! e>?'s orbit1 ! ret>dation ought to become gradually less1 & :5 ,i rea* ! place ( my fir/ obs]vation1 !re ought to be no ret>dation at all4' ,he f\nd ?is to be ! case1 & ?us n only prov$ t light requir$ "t to pass ?r\gh space1 b also det]m9$ its rate ( propagation4 ,! velocity ( light1 z det]m9$ by ,roem]1 is #aib1ejj miles 9 a second4 ,= a "t1 h[ev]1 ! obs]vations & reason+s ( ,roem] fail$ to produce conviction4 ,!y 7 d\bt$ by ,cass9i1 ,font5elle1 & ,hooke4 ,subsequ5tly came ! unexpect$ corroboration ( ,roem] by ! ,engli% a/ronom]1 ,bradley1 :o notic$ t ! fix$ />s did n really appe> to be fix$1 b t !y describe little orbits 9 ! heav5s e ye>4 ,! result p]plex$ him1 b ,bradley _h a m9d op5 to sugge/ion1 & capable ( see+1 9 ! smalle/ fact1 a picture ( ! l>ge/4 ,he 0 "o day ^u ! ,?ames 9 a boat1 & notic$ t z long z 8 c\rse rema9$ un*ang$1 ! vane ^u 8 ma/head %[$ ! w9d to be bl[+ con/antly 9 ! same direction1 b t ! w9d appe>$ to v>y ) e *ange 9 ! direction ( 8 boat4 ',"h1' z ,:ewell says1 '0 ! image ( 8 case4 ,! boat 0 ! e>?1 mov+ 9 its orbit1 & ! w9d 0 ! light ( a />4' ,we may ask1 9 pass+1 :at1 )\t ! faculty :i* =m$ ! 'image1' w\ld ,bradley's w9d & vane h be5 to him8 ,a w9d & vane1 & no?+ m4 ,y w imm$iately und]/& ! mean+ ( ,bradley's discov]y4 ,imag9e y\rself 9 a motionless railway-tra91 ) a %[] ( ra9 desc5d+ v]tically d[nw>ds4 ,! mom5t ! tra9 beg9s to move1 ! ra9-drops beg9 to slant1 & ! quick] ! motion ( ! tra9 ! great] is ! obliquity4 ,9 a precisely simil> mann] ! rays f a />1 v]tically ov]head1 are caus$ to slant by ! motion ( ! e>? ?r\gh space4 ,kn[+ ! spe$ ( ! tra91 & ! obliquity ( ! fall+ ra91 ! velocity ( ! drops may be calculat$2 & kn[+ ! spe$ ( ! e>? 9 h] orbit1 & ! obliquity ( ! rays due to ?is cause1 we c calculate j z easily ! velocity ( light4 ,bradley did ?is1 & ! 'ab]ration ( light1' z 8 discov]y is call$1 enabl$ him to assign to x a velocity almo/ id5tical ) t d$uc$ by ,roem] f a totally diff]5t me?od ( obs]vation4 ,subsequ5tly ,fizeau1 & q rec5tly ,cornu1 employ+ n planet>y or /ell> di/ances1 b simply ! bread? ( ! city ( ,p>is1 det]m9$ ! velocity ( light3 :ile ,f\cault--a man ( ! r>e/ me*anical g5ius--solv$ ! problem )\t quitt+ 8 private room4 ,ow+ to an error 9 ! det]m9ation ( ! e>?'s di/ance f ! sun1 ! velocity assign$ to light by bo? ,roem] & ,bradley is too great4 ,) a close approximation to accuracy x may be reg>d$ z #ahf1jjj miles a second4 ,by ,roem]'s discov]y1 ! notion ent]ta9$ by ,desc>tes1 & esp\s$ by ,hooke1 t light is propagat$ in/antly ?r\gh space1 0 ov]?r[n4 ,b ! e/abli%m5t ( its motion ?r\gh /ell> space l$ to speculations reg>d+ its velocity 9 transp>5t t]re/rial sub/ances4 ,! 'index ( refraction' ( a ray pass+ f air into wat] is #d_/c4 ,newton assum$ ^! numb]s to mean t ! velocity ( light 9 wat] be+ #d1 its velocity 9 air is #c2 & he d$uc$ ! ph5om5a ( refraction f ?is assumption4 ,huygh5s took ! opposite & tru] view4 ,accord+ to ?is great man1 ! velocity ( light 9 wat] be+ #c1 its velocity 9 air is #d2 b bo? 9 ,newton's "t & ours ! same great pr9ciple det]m9$1 & det]m9es1 ! c\rse ( light 9 all cases4 ,9 pass+ f po9t to po9t1 :atev] be ! m$ia 9 its pa?1 or h[ev] x may be refract$ or reflect$1 light takes ! c\rse :i* occupies lea/ "t4 ,?us 9 fig4 #d1 tak+ its velocity 9 air & 9 wat] into acc\nt1 ! light rea*es ,g f ,i m rapidly by travell+ fir/ to ,o1 & !re *ang+ its c\rse1 ?an if x proce$$ /raight f ,i to ,g4 ,?is is readily compreh5d$1 because1 9 ! latt] case1 x w\ld pursue a great] di/ance ?r\gh ! wat]1 :i* is ! m ret>d+ m$ium4 #f4 ,desc>tes' ,explanation ( ! ,ra9b[4 ,snell's law ( refraction is "o ( ! corn]-/ones ( optical sci5ce1 & its applications to-day are million-fold4 ,imm$iately aft] its discov]y ,desc>tes appli$ x to ! explanation ( ! ra9b[4 ,a beam ( sol> light fall+ obliquely ^u a ra9-drop is refract$ on ent]+ ! drop4 ,x is 9 "p reflect$ at ! back ( ! drop1 & on em]g+ x is aga9 refract$4 ,by ^! two refractions1 & ?is s+le reflection1 ! light is s5t to ! eye ( an obs]v] fac+ ! drop1 & ) 8 back to ! sun4 ,conceive a l9e drawn f ! sun1 ?r\gh ! back ( 8 head1 to ! obs]v]'s eye & prolong$ beyond x4 ,conceive a second l9e drawn f ! %[] to ! eye1 & enclos+ an angle ( #db ) ! l9e drawn f ! sun4 ,along ?is second l9e a ra9-drop :5 /ruck by a sunbeam w s5d r$ light to ! eye4 ,e o!r drop simil>ly situat$1 t is1 e drop at an angul> di/ance ( #db f ! l9e ?r\gh ! sun & eye1 w d ! same4 ,a circul> b& ( r$ light is ?us =m$1 :i* may be reg>d$ z ! b\nd>y ( ! base ( a cone1 ) its apex at ! obs]v]'s eye4 ,because ( ! magnitude ( ! sun1 ! angul> wid? ( ?is r$ b& w be half a degree4 ,f ! eye ( ! obs]v] conceive ano!r l9e to be drawn1 enclos+ an angle1 n ( #db1 b ( #dj1 ) ! prolongation ( ! l9e drawn f ! sun4 ,along ?is o!r l9e a ra9-drop1 at its remote end1 :5 /ruck by a sol> beam1 w s5d violet light to ! eye4 ,all drops at ! same angul> di/ance w d ! same1 & we %all !re=e obta9 a b& ( violet light ( ! same wid? z ! r$ b&4 ,^! two b&s con/itute ! limit+ col\rs ( ! ra9b[1 & betwe5 !m ! b&s correspond+ to ! o!r col\rs lie4 ,?us ! l9e drawn f ! eye to ! middle ( ! b[1 & ! l9e drawn ?r\gh ! eye to ! sun1 always enclose an angle ( ab\t #da4 ,to acc\nt = ?is 0 ! great difficulty1 :i* rema9$ unsolv$ up to ! "t ( ,desc>tes4 ,tak+ a p5 9 h&1 & calculat+ by means ( ,snell's law ! track ( e ray ?r\gh a ra9drop1 ,desc>tes f\nd t1 at "o p>ticul> angle1 ! rays1 reflect$ at its back1 em]g$ f ! drop almo/ p>allel to ea* o!r4 ,!y 7 ?us enabl$ to pres]ve _! int5sity ?r\gh long atmosph]ic di/ances4 ,at all o!r angles ! rays quitt$ ! drop div]g5t1 & ?r\gh ?is div]g5ce became s enfeebl$ z to be practically lo/ to ! eye4 ,! angle ( p>allelism "h ref]r$ to 0 t ( =ty-"o degrees1 :i* obs]vation _h prov$ to be inv>iably associat$ ) ! ra9b[4 ,f :at has be5 said1 x is cle> t two obs]v]s /&+ beside ea* o!r1 or "o above ! o!r1 nay1 t ev5 ! two eyes ( ! same obs]v]1 d n see exactly ! same b[4 ,! position ( ! base ( ! cone *anges ) t ( its apex4 ,& "h we h no difficulty 9 answ]+ a "q (t5 ask$--namely1 :e!r a ra9b[ is ev] se5 reflect$ 9 wat]4 ,see+ two b[s1 ! "o 9 ! heav5s1 ! o!r 9 ! wat]1 y might be dispos$ to inf] t ! "o be>s ! same relation to ! o!r t a tree ^u ! wat]'s edge be>s to its reflect$ image4 ,! rays1 h[ev]1 :i* rea* an obs]v]'s eye aft] reflection f ! wat]1 & :i* =m a b[ 9 ! wat]1 w\ld1 7 _! c\rse f ! %[] un9t]rupt$1 conv]ge to a po9t v]tically "u ! obs]v]1 & z f> bel[ ! level ( ! wat] z 8 eye is above x4 ,b "u no circum/ances c\ld an eye above ! wat]-level & "o bel[ x see ! same b[--9 o!r words1 ! self-same drops ( ra9 _c =m ! reflect$ b[ & ! b[ se5 directly 9 ! heav5s4 ,! reflect$ b[1 !re=e1 is n1 9 ! usual optical s5se ( ! t]m1 ! image ( ! b[ se5 9 ! sky4 #g4 ,analysis & ,syn!sis ( ,light4 ,doctr9e ( ,col\rs4 ,9 ! ra9b[ a new ph5om5on 0 introduc$--! ph5om5on ( col\r4 ,& "h we arrive at "o ( ^? po9ts 9 ! hi/ory ( sci5ce1 :5 great m5's lab\rs s int]m+le t x is difficult to assign to ea* work] 8 precise me$ ( hon\r4 ,desc>tes 0 at ! ?re%old ( ! discov]y ( ! composition ( sol> light2 b = ,newton 0 res]v$ ! enunciation ( ! true law4 ,he w5t to "w 9 ?is way3 ,?r\gh ! clos$ w9d[-%utt] ( a room he pi]c$ an orifice1 & all[$ a ?9 sunbeam to pass ?r\gh x4 ,! beam /amp$ a r\nd :ite image ( ! sun on ! opposite wall ( ! room4 ,9 ! pa? ( ?is beam ,newton plac$ a prism1 expect+ to see ! beam refract$1 b also expect+ to see ! image ( ! sun1 aft] refraction1 /ill r\nd4 ,to 8 a/oni%m5t1 x 0 drawn out to an image ) a l5g? five times its bread?4 ,x 01 moreov]1 no long] :ite1 b divid$ into b&s ( diff]5t col\rs4 ,newton saw imm$iately t sol> light 0 composite1 n simple4 ,8 elongat$ image reveal$ to him ! fact t "s con/itu5ts ( ! light 7 m deflect$ by ! prism ?an o!rs1 & he conclud$1 !re=e1 t :ite light 0 a mixture ( lights ( diff]5t col\rs1 possess+ diff]5t degrees ( refrangibility4 ,let u reproduce ?is celebrat$ exp]im5t4 ,on ! scre5 is n[ /amp$ a lum9\s disk1 :i* may /& = ,newton's image ( ! sun4 ,caus+ ! beam 7f ! ap]ture ,l1 fig4 #g7 :i* produces ! disk to pass ?r\gh a l5s 7,e71 we =m a %>p image ( ! ap]ture4 ,plac+ 9 ! track ( ! beam a prism 7,p71 we obta9 ,newton's col\r$ image1 ) its r$ & violet ends1 :i* he call$ a spectrum4 ,newton divid$ ! spectrum into sev5 p>ts--r$1 orange1 yell[1 gre51 blue1 indigo1 violet2 :i* are commonly call$ ! sev5 prim>y or prismatic col\rs4 ,! draw+ out ( ! :ite light into its con/itu5t col\rs is call$ disp]sion4 ,illu/ration3 ,fig4 #g4 ,?is 0 ! fir/ analysis ( sol> light by ,newton2 b ! sci5tific m9d is fond ( v]ification1 & nev] neglects x :]e x is possible4 ,newton complet$ 8 pro( by syn!sis 9 ?is way3 ,! spectrum n[ be=e y is produc$ by a glass prism4 ,caus+ ! decompos$ beam to pass ?r\gh a second simil> prism1 b s plac$ t ! col\rs are refract$ back & rebl5d$1 ! p]fectly :ite lum9\s disk is re/or$4 ,illu/ration3 ,fig4 #h4 ,9 ?is case1 refraction & disp]sion are simultane\sly aboli%$4 ,are !y always s8 ,c we h ! "o )\t ! o!r8 ,x 0 ,newton's conclusion t we c\ld n4 ,"h he err$1 & 8 error1 :i* he ma9ta9$ to ! end ( 8 life1 ret>d$ ! progress ( optical discov]y4 ,dollond subsequ5tly prov$ t by comb9+ two diff]5t k9ds ( glass1 ! col\rs c be ext+ui%$1 /ill leav+ a residue ( refraction1 & he employ$ ?is residue 9 ! con/ruction ( a*romatic l5ses--l5ses yield+ no col\r--:i* ,newton ?\ght an impossibility4 ,by sett+ a wat]-prism--wat] conta9$ 9 a w$ge-%ap$ vessel ) glass sides 7,b1 fig4 #h7--;9 opposition to a w$ge ( glass 7to ! "r ( ,b71 ?is po9t c be illu/rat$ be=e y4 ,we h fir/ ( all ! position 7dott$7 ( ! unrefract$ beam m>k$ ^u ! scre52 !n we produce ! n>r[ wat]-spectrum 7,w72 f9ally1 by introduc+ a fl9t-glass prism1 we refract ! beam back1 until ! col\r disappe>s 7at ,a74 ,! image ( ! slit is n[ :ite2 b ?\gh ! disp]sion is aboli%$1 !re rema9s a v s5sible am\nt ( refraction4 ,?is is ! place to illu/rate ano!r po9t be>+ ^u ! in/rum5tal means employ$ 9 ^! lectures4 ,bodies diff] widely f ea* o!r z to _! p[]s ( refraction & disp]sion4 ,note ! position ( ! wat]-spectrum ^u ! scre54 ,alt]+ 9 no p>ticul> ! w$ge-%ap$ vessel1 b simply sub/itut+ = ! wat] ! transp>5t bisulphide ( c>bon1 y notice h[ mu* high] ! beam is ?r[n1 & h[ mu* ri*] is ! display ( col\r4 ,to augm5t ! size ( our spectrum we "h employ 7at ,l7 a slit1 in/ead ( a circul> ap]ture4#f ,illu/ration3 ,fig4 #i4 ,! syn!sis ( :ite light may be effect$ 9 ?ree ways1 all ( :i* are wor?y ( att5tion3 ,"h1 9 ! fir/ in/ance1 we h a ri* spectrum produc$ by ! decomposition ( ! beam 7f ,l1 fig4 #i74 ,"o face ( ! prism 7,p7 is protect$ by a diaphragm 7n %[n 9 ! figure71 ) a longitud9al slit1 ?r\gh :i* ! beam passes into ! prism4 ,x em]ges decompos$ at ! o!r side4 ,i p]mit ! col\rs to pass ?r\gh a cyl9drical l5s 7,c71 :i* s squeezes !m toge!r z to produce ^u ! scre5 a %>ply def9$ rectangul> image ( ! longitud9al slit4 ,9 t image ! col\rs are rebl5d$1 & x is p]fectly :ite4 ,betwe5 ! prism & ! cyl9drical l5s may be se5 ! col\rs1 track+ !mselves ?r\gh ! du/ ( ! room4 ,cutt+ (f ! m refrangible fr+e by a c>d1 ! rectangle is se5 r$3 cutt+ (f ! less refrangible fr+e1 ! rectangle is se5 blue4 ,by means ( a ?9 glass prism 7,w71 ,i deflect "o portion ( ! col\rs1 & leave ! residual portion4 ,on ! scre5 are n[ two col\r$ rectangles produc$ 9 ?is way4 ,^! are complem5t>y col\rs--col\rs :i*1 by _! union1 produce :ite4 ,note1 t by judici\s managem5t1 "o ( ^! col\rs is r5d]$ yell[1 & ! o!r blue4 ,i )draw ! ?9 prism2 yell[ & blue imm$iately comm+le1 & we h :ite z ! result ( _! union4 ,on our way1 !n1 we remove ! fallacy1 fir/ expos$ by ,wns*1 & aft]w>ds indep5d5tly by ,helmholtz1 t ! mixture ( blue & yell[ lights produces gre54 ,re/or+ ! circul> ap]ture1 we obta9 once m a spectrum l t ( ,newton4 ,by means ( a l5s1 we c ga!r up ^! col\rs1 & build !m toge!r1 n to an image ( ! ap]ture1 b to an image ( ! c>bon-po9ts !mselves4 ,f9ally1 by means ( a rotat+ disk1 on :i* are spread 9 sectors ! col\rs ( ! spectrum1 we bl5d toge!r ! prismatic col\rs 9 ! eye itself1 & ?us produce ! impression ( :it5ess4 ,hav+ unravell$ ! int]wov5 con/itu5ts ( :ite light1 we h next to inquire1 ,:at "p ! con/itution s reveal$ enables ?is ag5t to play 9 ,nature8 ,to x we owe all ! ph5om5a ( col\r1 & yet n to x alone2 = !re mu/ be a c]ta9 relation%ip betwe5 ! ultimate p>ticles ( natural bodies & :ite light1 to enable !m to extract f x ! luxury ( col\r4 ,b ! function ( natural bodies is "h selective1 n creative4 ,!re is no col\r g5]at$ by any natural body :atev]4 ,natural bodies h %[]$ ^u !m1 9 ! :ite light ( ! sun1 ! sum total ( all possible col\rs2 & _! action is limit$ to ! sift+ ( t total--! appropriat+ or absorb+ ( "s ( its con/itu5ts1 & ! reject+ ( o!rs4 ,x w fix ?is subject 9 y\r m9ds if ,i say1 t x is ! portion ( light :i* !y reject1 & n t :i* !y appropriate or absorb1 t gives bodies _! col\rs4 ,let u beg9 our exp]im5tal inquiries "h by ask+1 ,:at is ! mean+ ( blackness8 ,pass a black ribbon ?r\gh ! col\rs ( ! spectrum2 x qu5*es all ( !m4 ,! mean+ ( blackness is ?us reveal$--x is ! result ( ! absorption ( all ! con/itu5ts ( sol> light4 ,pass a r$ ribbon ?r\gh ! spectrum4 ,9 ! r$ light ! ribbon is a vivid r$4 ,:y8 ,because ! light t ent]s ! ribbon is n qu5*$ or absorb$1 b 9 great "p s5t back to ! eye4 ,place ! same ribbon 9 ! gre5 ( ! spectrum2 x is black z jet4 ,x absorbs ! gre5 light1 & r5d]s ! space on :i* t light falls a space ( int5se d>kness4 ,place a gre5 ribbon 9 ! gre5 ( ! spectrum4 ,x %9es vividly ) its prop] col\r2 transf] x to ! r$1 x is black z jet4 ,"h x absorbs all ! light t falls ^u x1 & (f]s m]e d>kness to ! eye4 ,?us1 :5 :ite light is employ$1 ! r$ sifts x by qu5*+ ! gre51 & ! gre5 sifts x by qu5*+ ! r$1 bo? exhibit+ ! residual col\r4 ,! process ?r\gh :i* natural bodies acquire _! col\rs is !re=e a negative "o4 ,! col\rs are produc$ by subtraction1 n by addition4 ,?is r$ glass is r$ because x de/roys all ! m refrangible rays ( ! spectrum4 ,?is blue liquid is blue because x de/roys all ! less refrangible rays4 ,bo? toge!r are opaque because ! light transmitt$ by ! "o is qu5*$ by ! o!r4 ,9 ?is way1 by ! union ( two transp>5t sub/ances1 we obta9 a comb9ation z d>k z pit* to sol> light4 ,?is o!r liquid1 f9ally1 is purple because x de/roys ! gre5 & ! yell[1 & all[s ! t]m9al col\rs ( ! spectrum to pass unimp$$4 ,f ! bl5d+ ( ! blue & ! r$ ?is gorge\s purple is produc$4 ,"o /ep fur!r = ! sake ( exactness4 ,! light :i* falls ^u a body is divid$ into two portions1 "o ( :i* is reflect$ f ! surface ( ! body2 & ?is is ( ! same col\r z ! incid5t light4 ,if ! incid5t light be :ite1 ! sup]ficially reflect$ light w also be :ite4 ,sol> light1 = example1 reflect$ f ! surface ( ev5 a black body1 is :ite4 ,! blacke/ camph9e smoke 9 a d>k room1 ?r\gh :i* a sunbeam passes f an ap]ture 9 ! w9d[-%utt]1 r5d]s ! track ( ! beam :ite1 by ! light scatt]$ f ! surfaces ( ! soot p>ticles4 ,! moon appe>s to u z if ',clo!d 9 :ite samite1 my/ic1 wond]ful2' b 7 x cov]$ ) ! blacke/ velvet x w\ld /ill hang z a :ite orb 9 ! heav5s1 %9+ ^u our _w sub/antially z x does n[4 #h4 ,col\rs ( ,pigm5ts z di/+ui%$ f ,col\rs ( ,light4 ,! second portion ( ! incid5t light ent]s ! body1 & ^u its treatm5t !re ! col\r ( ! body dep5ds4 ,& "h a mom5t may prop]ly be giv5 to ! analysis ( ! action ( pigm5ts ^u light4 ,!y are compos$ ( f9e p>ticles mix$ ) a vehicle2 b h[ intimately soev] ! p>ticles may be bl5d$1 !y /ill rema9 p>ticles1 sep>at$1 x may be1 by exce$+ly m9ute di/ances1 b /ill sep>at$4 ,to use ! sci5tific phrase1 !y are n optically cont9u\s4 ,n[1 :]ev] optical cont9uity is ruptur$ we h reflection ( ! incid5t light4 ,x is ! multitude ( reflections at ! limit+ surfaces ( ! p>ticles t prev5ts light f pass+ ?r\gh sn[1 p[d]$ glass1 or common salt4 ,! light "h is exhau/$ 9 e*oes1 n ext+ui%$ by true absorption4 ,x is ! same k9d ( reflection t r5d]s ! ?und]-cl\d s imp]vi\s to light4 ,su* a cl\d is compos$ ( p>ticles ( wat]1 mix$ ) p>ticles ( air1 bo? sep>ately transp>5t1 b practically opaque :5 ?us mix$ toge!r4 ,9 ! case ( pigm5ts1 !n1 ! light is reflect$ at ! limit+ surfaces ( ! p>ticles1 b x is 9 "p absorb$ )9 ! p>ticles4 ,! reflection is necess>y to s5d ! light back to ! eye2 ! absorption is necess>y to give ! body its col\r4 ,! same rem>ks apply to fl[]s4 ,! rose is r$1 9 virtue1 n ( ! light reflect$ f its surface1 b ( light :i* has ent]$ its sub/ance1 :i* has be5 reflect$ f surfaces )91 & :i*1 9 return+ ?r\gh ! sub/ance1 has _h its gre5 ext+ui%$4 ,a simil> process 9 ! case ( h>d gre5 leaves ext+ui%es ! r$1 & s5ds gre5 light f ! body ( ! leaves to ! eye4 ,all bodies1 ev5 ! mo/ transp>5t1 are m or less absorb5t ( light4 ,take ! case ( wat]4 ,a glass cell ( cle> wat] int]pos$ 9 ! track ( our beam does n p]ceptibly *ange any "o ( ! col\rs ( ! spectrum4 ,/ill absorption1 ?\gh ins5sible1 has "h occurr$1 & to r5d] x s5sible we h only to increase ! dep? ( ! wat] ?r\gh :i* ! light passes4 ,in/ead ( a cell an in* ?ick1 let u take a lay]1 t5 or fifte5 feet ?ick3 ! col\r ( ! wat] is !n v evid5t4 ,by augm5t+ ! ?ickness we absorb m ( ! light1 & by mak+ ! ?ickness v great we absorb ! light altoge!r4 ,lampblack or pit* c d no m1 & ! only diff]5ce 9 ?is respect betwe5 !m & wat] is t a v small dep? 9 _! case suffices to ext+ui% all ! light4 ,! diff]5ce betwe5 ! highe/ kn[n transp>5cy & ! highe/ kn[n opacity is "o ( degree m]ely4 ,if1 !n1 we r5d] wat] suffici5tly deep to qu5* all ! light2 & if f ! int]ior ( ! wat] no light rea*es ! eye1 we h ! condition necess>y to produce blackness4 ,look$ prop]ly d[n ^u1 !re are portions ( ! ,atlantic ,ocean to :i* "o w\ld h>dly ascribe a trace ( col\r3 at ! mo/ a t9t ( d>k indigo rea*es ! eye4 ,! wat]1 9 fact1 is practically black1 & ?is is an indication bo? ( its dep? & purity4 ,b ! case is entirely *ang$ :5 ! ocean conta9s solid p>ticles 9 a /ate ( me*anical susp5sion1 capable ( s5d+ ! light imp++ on !m back to ! eye4 ,?r[1 = example1 a :ite pebble1 or a :ite d9n] plate1 into ! blacke/ ,atlantic wat]2 z x s9ks x becomes gre5] & gre5]1 &1 be=e x disappe>s1 x rea*es a vivid blue gre54 ,break su* a pebble1 or plate1 into fragm5ts1 ^! w behave l ! unbrok5 mass3 gr9d ! pebble to p[d]1 e p>ticle w yield its modicum ( gre52 & if ! p>ticles be s f9e z to rema9 susp5d$ 9 ! wat]1 ! scatt]$ light w be a uni=m gre54 ,h5ce ! gre5ness ( %oal wat]4 ,y g to b$ ) ! black wat] ( ! ,atlantic ar\nd y4 ,y rise 9 ! morn+1 f9d x a vivid gre51 & correctly inf] t y are cross+ ! ,bank ( ,newf\ndl&4 ,su* wat] is f\nd *>g$ ) f9e matt] 9 a /ate ( me*anical susp5sion4 ,! light f ! bottom may sometimes come into play1 b x is n necess>y4 ,! subaque\s foam1 g5]at$ by ! screw or paddle-:eels ( a /eam]1 also s5ds =? a vivid gre54 ,! foam "h furni%es a reflect+ surface1 ! wat] betwe5 ! eye & x ! absorb+ m$ium4 ,no?+ c be m sup]b ?an ! gre5 ( ! ,atlantic waves :5 ! circum/ances are fav\rable to ! exhibition ( ! col\r4 ,z long z a wave rema9s unbrok5 no col\r appe>s1 b :5 ! foam j d\bles ov] ! cre/ l an ,alp9e sn[-cornice1 "u ! cornice we (t5 see a display ( ! mo/ exquisite gre54 ,x is metallic 9 its brilliancy4 ,! foam is fir/ illum9at$1 & x scatt]s ! light 9 all directions2 ! light :i* passes ?r\gh ! high] portion ( ! wave alone rea*es ! eye1 & gives to t portion its mat*less col\r4 ,! fold+ ( ! wave1 produc+1 z x does1 a s]ies ( longitud9al protub]ances & furr[s :i* act l cyl9drical l5ses1 introduces v>iations 9 ! int5sity ( ! light1 & mat]ially enhances its beauty4 ,we are n[ prep>$ = ! fur!r consid]ation ( a po9t already adv]t$ to1 & reg>d+ :i* error long f\nd curr5cy4 ,y w f9d x /at$ 9 _m books t blue light & yell[ light mix$ toge!r1 produce gre54 ,b blue & yell[ h be5 j prov$ to be complem5t>y col\rs1 produc+ :ite by _! mixture4 ,! mixture ( blue & yell[ pigm5ts und\bt$ly produces gre51 b ! mixture ( pigm5ts is a totally diff]5t ?+ f ! mixture ( lights4 ,helmholtz has reveal$ ! cause ( ! gre5 produc$ by a mixture ( blue & yell[ pigm5ts4 ,no natural col\r is pure4 ,a blue liquid1 or a blue p[d]1 p]mits n only ! blue to pass ?r\gh x1 b a portion ( ! adjac5t gre54 ,a yell[ p[d] is transp>5t n only to ! yell[ light1 b also 9 "p to ! adjac5t gre54 ,n[1 :5 blue & yell[ are mix$ toge!r1 ! blue cuts (f ! yell[1 ! orange1 & ! r$2 ! yell[1 on ! o!r h&1 cuts (f ! violet1 ! indigo1 & ! blue4 ,gre5 is ! only col\r to :i* bo? are transp>5t1 & ! consequ5ce is t1 :5 :ite light falls ^u a mixture ( yell[ & blue p[d]s1 ! gre5 alone is s5t back to ! eye4 ,y h already se5 t ! f9e blue ammonia-sulphate ( copp] transmits a l>ge portion ( gre51 :ile cutt+ (f all ! less refrangible light4 ,a yell[ solution ( picric acid also all[s ! gre5 to pass1 b qu5*es all ! m refrangible light4 ,:at mu/ occur :5 we s5d a beam ?r\gh bo? liquids8 ,! exp]im5tal answ] to ?is "q is n[ be=e y3 ! gre5 b& ( ! spectrum alone rema9s ^u ! scre54 ,! impurity ( natural col\rs is /rik+ly illu/rat$ by an obs]vation rec5tly communicat$ to me by ,mr4 ,woodbury4 ,on look+ ?r\gh a blue glass at gre5 leaves 9 sun%9e1 he saw ! sup]ficially reflect$ light blue4 ,! light1 on ! contr>y1 :i* came f ! body ( ! leaves 0 crimson4 ,on exam9ation1 ,i f\nd t ! glass employ$ 9 ?is obs]vation transmitt$ bo? ends ( ! spectrum1 ! r$ z well z ! blue1 & t x qu5*$ ! middle4 ,?is furni%$ an easy explanation ( ! effect4 ,9 ! delicate spr+ foliage ! blue ( ! sol> light is = ! mo/ "p absorb$1 & a light1 ma9ly yell[i% gre51 b conta9+ a consid]able quantity ( r$1 escapes f ! leaf to ! eye4 ,on look+ at su* foliage ?r\gh ! violet glass1 ! gre5 & ! yell[ are /opp$1 & ! r$ alone rea*es ! eye4 ,?us reg>d$1 !re=e1 ! leaves appe> l fa9tly blu%+ roses1 & pres5t a v beautiful appe>ance4 ,) ! blue ammonia-sulphate ( copp]1 :i* transmits no r$1 ?is effect is n obta9$4 ,z ! ye> advances ! crimson gradually h>d5s to a copp]y r$2 & 9 ! d>k gre5 leaves ( old ivy x is almo/ abs5t4 ,p]mitt+ a beam ( :ite light to fall ^u fre% leaves 9 a d>k room1 ! sudd5 *ange f gre5 to r$1 & f r$ back to gre51 :5 ! violet glass is alt]nately introduc$ & )drawn1 is v surpris+4 ,look$ at ?r\gh ! same glass1 ! mead[s 9 ,may appe> ( a w>m purple4 ,) a solution ( p]manganate ( pota%1 :i*1 :ile x qu5*es ! c5tre ( ! spectrum1 p]mits its ends to pass m freely ?an ! violet glass1 excell5t effects are also obta9$4#g ,?is "q ( absorption1 consid]$ ) ref]5ce to its molecul> me*anism1 is "o ( ! mo/ subtle & difficult 9 physics4 ,we are n yet 9 a condition to grapple ) x1 b we %all be by-&-by4 ,mean:ile we may pr(itably glance back on ! web ( relations :i* ^! exp]im5ts reveal to u4 ,we h1 fir/ly1 9 sol> light an ag5t ( exce$+ complexity1 compos$ ( innum]able con/itu5ts1 refrangible 9 diff]5t degrees4 ,we f9d1 secondly1 ! atoms & molecules ( bodies gift$ ) ! p[] ( sift+ sol> light 9 ! mo/ v>i\s ways1 & produc+ by ?is sift+ ! col\rs obs]v$ 9 nature & art4 ,to d ?is !y mu/ possess a molecul> /ructure comm5surate 9 complexity ) t ( light itself4 ,?irdly1 we h ! human eye & bra91 s organiz$ z to be able to take 9 & di/+ui% ! multitude ( impressions ?us g5]at$4 ,! light1 !re=e1 at />t+ is complex2 to sift & select x z !y d1 natural bodies mu/ be complex2 :ile to take 9 ! impressions ?us g5]at$1 ! human eye & bra91 h[ev] we may simplify our conceptions ( _! action1#h mu/ be highly complex4 ,:5ce ?is triple complexity8 ,if :at are call$ mat]ial purposes 7 ! only end to be s]v$1 a mu* simpl] me*anism w\ld be suffici5t4 ,b1 in/ead ( simplicity1 we h prodigality ( relation & adaptation--& ?is1 app>5tly1 = ! sole purpose ( enabl+ u to see ?+s rob$ 9 ! spl5d\rs ( col\r4 ,w\ld x n seem t ,nature h>b\r$ ! int5tion ( educat+ u = o!r enjoym5ts ?an ^? d]ivable f meat & dr9k8 ,at all ev5ts1 :atev] ,nature meant--& x w\ld be m]e presumption to dogmatize z to :at %e meant--we f9d ourselves "h1 z ! up%ot ( h] op]ations1 end[$1 n only ) capacities to enjoy ! mat]ially useful1 b end[$ ) o!rs ( indef9ite scope & application1 :i* deal alone ) ! beautiful & ! true4 ,,lecture ,,ii4 ,,orig9 ,,( ,,physical ,,!ories ,,scope ,,( ,,! ,,imag9ation ,,newton ,,& ,,! ,,emission ,,!ory ,,v]ification ,,( ,,physical ,,!ories ,,! ,,lum9if]\s ,,e!r ,,wave ,,!ory ,,( ,,light ,,?omas ,,"y ,,fresnel ,,& ,,arago ,,conception ,,( ,,wave-,,motion ,,int]f]5ce ,,( ,,waves ,,con/itution ,,( ,,s\nd-,,waves ,,analogies ,,( ,,s\nd ,,& ,,light ,,illu/rations ,,( ,,wave-,,motion ,,int]f]5ce ,,( ,,s\nd-,,waves ,,optical ,,illu/rations ,,pit* ,,& ,,col\r ,,l5g?s ,,( ,,! ,,waves ,,( ,,light ,,& ,,rates ,,( ,,vibration ,,( ,,! ,,e!r-,,p>ticles ,,int]f]5ce ,,( ,,light ,,ph5om5a ,,:i* ,,fir/ ,,sugge/$ ,,! ,,undulatory ,,!ory ,,boyle ,,& ,,hooke ,,! ,,col\rs ,,( ,,?9 ,,plates ,,! ,,soap-,,bubble ,,newton',s ,,r+s ,,!ory ,,( ',,fits' ,,its ,,explanation ,,( ,,! ,,r+s ,,ov]-,,?r[ ,,( ,,! ,,!ory ,,diffraction ,,( ,,light ,,col\rs ,,produc$ ,,by ,,diffraction ,,col\rs ,,( ,,"m-,,(-,,pe>l4 #a4 ,orig9 & ,scope ( ,physical ,!ories4 ,we might v>y & ext5d our exp]im5ts on ,light indef9itely1 & !y c]ta9ly w\ld prove u to possess a wond]ful ma/]y ov] ! ph5om5a4 ,b ! ve/ure ( ! ag5t only w\ld ?us be reveal$1 n ! ag5t itself4 ,! human m9d1 h[ev]1 is s con/itut$ t x c nev] re/ satisfi$ ) ?is outw>d view ( natural ?+s4 ,brightness & fre%ness take possession ( ! m9d :5 x is cross$ by ! light ( pr9ciples1 %[+ ! facts ( ,nature to be organically connect$4 ,let u1 !n1 inquire :at ?is ?+ is t we h be5 g5]at+1 reflect+1 refract+ & analyz+4 ,9 do+ ?is1 we %all le>n t ! life ( ! exp]im5tal philosoph] is tw(old4 ,he lives1 9 8 vocation1 a life ( ! s5ses1 us+ 8 h&s1 eyes1 & e>s 9 8 exp]im5ts3 b su* a "q z t n[ be=e u c>ries him beyond ! m>g9 ( ! s5ses4 ,he _c consid]1 mu* less answ]1 ! "q1 ',:at is light8' )\t transport+ himself to a _w :i* und]lies ! s5sible "o1 & out ( :i* all optical ph5om5a spr+4 ,to realise ?is subs5sible _w ! m9d mu/ possess a c]ta9 pictorial p[]4 ,x mu/ be able to =m def9ite images ( ! ?+s :i* t _w conta9s2 & to say t1 if su* or su* a /ate ( ?+s exi/ 9 ! subs5sible _w1 !n ! ph5om5a ( ! s5sible "o mu/1 ( necessity1 gr[ out ( ?is /ate ( ?+s4 ,physical !ories are ?us =m$1 ! tru? ( :i* is inf]r$ f _! p[] to expla9 ! kn[n & to pr$ict ! unkn[n4 ,?is conception ( physical !ory implies1 z y p]ceive1 ! ex]cise ( ! imag9ation--a ^w :i* seems to r5d] _m respectable p1 bo? 9 ! ranks ( sci5ce & out ( !m1 uncom=table4 ,t m5 9 ! ranks ( sci5ce %\ld feel ?us is1 ,i ?9k1 a pro( t !y h suff]$ !mselves to be misl$ by ! popul> def9ition ( a great faculty1 in/ead ( obs]v+ its op]ation 9 _! own m9ds4 ,)\t imag9ation we _c take a /ep beyond ! b\rne ( ! m]e animal _w1 p]haps n ev5 to ! edge ( ?is "o4 ,b1 9 speak+ ?us ( imag9ation1 ,i d n mean a riot\s p[] :i* deals caprici\sly ) facts1 b a well-ord]$ & discipl9$ p[]1 ^: sole function is to =m su* conceptions z ! intellect imp]atively dem&s4 ,imag9ation1 ?us ex]cis$1 nev] really sev]s itself f ! _w ( fact4 ,?is is ! /oreh\se f :i* its mat]ials are d]iv$2 & ! magic ( its art consi/s1 n 9 creat+ ?+s anew1 b 9 s *ang+ ! magnitude1 position1 gr\p+1 & o!r relations ( s5sible ?+s1 z to r5d] !m fit = ! requirem5ts ( ! intellect 9 ! subs5sible _w4#i ,desc>tes imag9$ space to be fill$ ) some?+ t transmitt$ light in/antane\sly4 ,fir/ly1 because1 9 8 exp]i5ce1 no measurable int]val 0 kn[n to exi/ betwe5 ! appe>ance ( a fla% ( light1 h[ev] di/ant1 & its effect ^u consci\sness2 & secondly1 because1 z f> z 8 exp]i5ce w5t1 no physical p[] is convey$ f place to place )\t a vehicle4 ,b 8 imag9ation help$ itself f>!r by illu/rations drawn f ! _w ( fact4 ',:51' he says1' "o walks 9 d>kness ) /aff 9 h&1 ! mom5t ! di/ant end ( ! /aff /rikes an ob/acle ! h& feels x4 ,?is expla9s :at might o!rwise be ?\ght /range1 t ! light rea*es u in/antane\sly f ! sun4 ,i wi% !e to believe t light 9 ! bodies t we call lum9\s is no?+ m ?an a v brisk & viol5t motion1 :i*1 by means ( ! air & o!r transp>5t m$ia1 is convey$ to ! eye1 exactly z ! %ock ?r\gh ! walk+-/ick rea*es ! h& ( a bl9d man4 ,?is is in/antane\s1 & w\ld be s ev5 if ! int]v5+ di/ance 7 great] ?an t betwe5 e>? & heav54 ,x is !re=e no m necess>y t any?+ mat]ial %\ld rea* ! eye f ! lum9\s object1 ?an t some?+ %\ld be s5t f ! gr\nd to ! h& ( ! bl9d man :5 he is consci\s ( ! %ock ( 8 /aff4' ,! celebrat$ ,rob]t ,hooke at fir/ ?rew d\bt ^u ?is notion ( ,desc>tes1 b he aft]w>ds sub/antially esp\s$ x4 ,! belief 9 in/antane\s transmission 0 de/roy$ by ! discov]y ( ,roem] ref]r$ to 9 our la/ lecture4 #b4 ,! ,emission ,!ory ( ,light4 ,! case ( ,newton /ill m =cibly illu/rates ! position1 t 9 =m+ physical !ories we draw = our mat]ials ^u ! _w ( fact4 ,be=e he began to deal ) light1 he 0 intimately acqua9t$ ) ! laws ( ela/ic collision1 :i* all ( y h se5 m or less p]fectly illu/rat$ on a billi>d-table4 ,z reg>ds ! collision ( s5sible ela/ic masses1 ,newton knew ! angle ( incid5ce to be equal to ! angle ( reflection1 & he also knew t exp]im5t1 z %[n 9 our la/ lecture 7fig4 #c71 _h e/abli%$ ! same law ) reg>d to light4 ,he ?us f\nd 9 8 previ\s k ! mat]ial = !oretic images4 ,he _h only to *ange ! magnitude ( conceptions already 9 8 m9d to arrive at ! ,emission ,!ory ( ,light4 ,newton suppos$ light to consi/ ( ela/ic p>ticles ( inconceivable m9ut5ess1 %ot out ) inconceivable rapidity by lum9\s bodies4 ,optical reflection c]ta9ly occurr$ z if light consi/$ ( su* p>ticles1 & ?is 0 ,newton's ju/ification = introduc+ !m4 ,b ?is is n all4 ,9 ano!r important p>ticul>1 also1 ,newton's conceptions reg>d+ ! nature ( light 7 influ5c$ by 8 previ\s k4 ,he _h be5 pond]+ ov] ! ph5om5a ( gravitation1 & _h made himself at home amid ! op]ations ( ?is univ]sal p[]4 ,p]haps 8 m9d at ?is "t 0 too fre%ly & too deeply imbu$ ) ^! notions to p]mit ( 8 =m+ an unfett]$ judgm5t reg>d+ ! nature ( light4 ,be t z x may1 ,newton saw 9 ,refraction ! result ( an attractive =ce ex]t$ on ! light-p>ticles4 ,he c>ri$ 8 conception out ) ! mo/ sev]e consi/5cy4 ,dropp+ v]tically d[nw>ds t[>ds ! e>?'s surface1 ! motion ( a body is accel]at$ z x approa*es ! e>?4 ,dropp+ d[nw>ds t[>ds a horizontal surface--say f air on to glass or wat]--! velocity ( ! light-p>ticles1 :5 !y came close to ! surface1 is1 accord+ to ,newton1 also accel]at$4 ,approa*+ su* a surface obliquely1 he suppos$ ! p>ticles1 :5 close to x1 to be drawn d[n ^u x1 z a projectile is deflect$ by gravity to ! surface ( ! e>?4 ,?is deflection 01 accord+ to ,newton1 ! refraction se5 9 our la/ lecture 7fig4 #d74 ,f9ally1 x 0 suppos$ t diff]5ces ( col\r might be due to diff]5ces 9 ! 'bigness' ( ! p>ticles4 ,?is 0 ! physical !ory ( light enunciat$ & def5d$ by ,newton2 & y w obs]ve t x simply consi/s 9 ! transf]5ce ( conceptions1 born 9 ! _w ( ! s5ses1 to a subs5sible _w4 ,b1 ?\gh ! region ( physical !ory lies ?us beh9d ! _w ( s5ses1 ! v]ifications ( !ory occur 9 t _w4 ,lay+ ! !oretic conception at ! root ( matt]s1 we det]m9e by d$uction :at are ! ph5om5a :i* mu/ ( necessity gr[ out ( ?is root4 ,if ! ph5om5a ?us d$uc$ agree ) ^? ( ! actual _w1 x is a presumption 9 fav\r ( ! !ory4 ,if1 z new classes ( ph5om5a arise1 !y also are f\nd to h>monise ) !oretic d$uction1 ! presumption becomes /ill /rong]4 ,if1 f9ally1 ! !ory conf]s prophetic vision ^u ! inve/igator1 enabl+ him to pr$ict ! occurr5ce ( ph5om5a :i* h nev] yet be5 se51 & if ^? pr$ictions be f\nd on trial to be rigidly correct1 ! p]suasion ( ! tru? ( ! !ory becomes ov]p[]+4 ,?us work+ backw>ds f a limit$ numb] ( ph5om5a1 ! human m9d1 by its own expansive =ce1 rea*es a conception :i* cov]s !m all4 ,!re is no m wond]ful p]=mance ( ! intellect ?an ?is2 b we c r5d] no acc\nt ( x4 ,l ! scriptural gift ( ! ,_s1 no man c tell :5ce x come?4 ,! passage f fact to pr9ciple is sometimes sl[1 sometimes rapid1 & at all times a s\rce ( intellectual joy4 ,:5 rapid1 ! pleasure is conc5trat$1 & becomes a k9d ( ec/asy or intoxication4 ,to any "o :o has exp]i5c$ ?is pleasure1 ev5 9 a mod]ate degree1 ! action ( ,ar*im$es :5 he quitt$ ! ba?1 & ran nak$1 cry+ ',eureka6' ?r\gh ! /reets ( ,syracuse1 becomes intelligible4 ,h[1 !n1 did x f>e ) ! ,emission ,!ory :5 ! d$uctions f x 7 br\ght face to face ) natural ph5om5a8 ,te/$ by exp]im5t1 x 0 f\nd compet5t to expla9 _m facts1 & ) transc5d5t +5uity its au?or s\ght to make x acc\nt = all4 ,he s f> succe$$1 t m5 s celebrat$ z ,laplace & ,malus1 :o liv$ till #ahab1 & ,biot & ,brew/]1 :o liv$ till our own "t1 7 f\nd among 8 disciples4 #c4 ,! ,undulatory ,!ory ( ,light4 ,/ill1 ev5 at an e>ly p]iod ( ! exi/5ce ( ! ,emission ,!ory1 "o or two great m5 7 f\nd esp\s+ a diff]5t "o4 ,!y furni% ano!r illu/ration ( ! law t1 9 =m+ !ories1 ! sci5tific imag9ation mu/ draw its mat]ials f ! _w ( fact & exp]i5ce4 ,x 0 kn[n long ago t s\nd is convey$ 9 waves or pulses ?r\gh ! air2 & no soon] 0 ?is tru? well h\s$ 9 ! m9d ?an x became ! basis ( a !oretic conception4 ,x 0 suppos$ t light1 l s\nd1 might also be ! product ( wave-motion4 ,b :at1 9 ?is case1 c\ld be ! mat]ial =m+ ! waves8 ,= ! waves ( s\nd we h ! air ( our atmosph]e2 b ! /ret* ( imag9ation :i* fill$ all space ) a lum9if]\s e!r trembl+ ) ! waves ( light 0 s bold z to %ock cauti\s m9ds4 ,9 "o ( my late/ conv]sations ) ,sir ,david ,brew/]1 he said to me t 8 *ief objection to ! undulatory !ory ( light 01 t he c\ld n ?9k ! ,creator capable ( s clumsy a contrivance z ! fill+ ( space ) e!r to produce light4 ,?is1 ,i may say1 is v dang]\s gr\nd1 & ! qu>rel ( sci5ce ) ,sir ,david1 on ?is po9t z ) _m e/imable p]sons on o!r po9ts1 is1 t !y pr(ess to "k too mu* ab\t ! m9d ( ! ,creator4 ,?is conception ( an e!r 0 advocat$1 & successfully appli$ to v>i\s ph5om5a ( optics1 by ! illu/ri\s a/ronom]1 ,huygh5s4 ,he d$uc$ f x ! laws ( reflection & refraction1 & appli$ x to expla9 ! d\ble refraction ( ,icel& sp>4 ,! !ory 0 esp\s$ & def5d$ by ! celebrat$ ma!matician1 ,eul]4 ,!y 71 h[ev]1 oppos$ by ,newton1 ^: au?ority at ! "t bore !m d[n4 ,or %all we say x 0 au?ority m]ely8 ,n q s4 ,newton's prepond]ance 0 9 "s degree due to ! fact t1 ?\gh ,huygh5s & ,eul] 7 "r 9 ! ma91 !y did n possess suffici5t data to prove !mselves "r4 ,no human au?ority1 h[ev] high1 c ma9ta9 itself aga9/ ! voice ( ,nature speak+ ?r\gh exp]im5t4 ,b ! voice ( ,nature may be an unc]ta9 voice1 ?r\gh ! scant9ess ( data4 ,?is 0 ! case at ! p]iod n[ ref]r$ to1 & at su* a p]iod1 by ! au?ority ( ,newton1 all antagoni/s 7 naturally ov]borne4 ,! m>* ( m9d is rhy?mic1 n uni=m1 & ?is great ,emission ,!ory1 :i* held its gr\nd s long1 resembl$ "o ( ^? circles :i*1 accord+ to y\r c\ntryman ,em]son1 ! int]mitt5t =ce ( g5ius p]iodically draws r\nd ! op]ations ( ! intellect1 b :i* are ev5tually brok5 ?r\gh by pressure f beh9d4 ,9 ! ye> #aggc 0 born1 at ,milv]ton1 9 ,som]set%ire1 a circle-break] ( ?is k9d4 ,he 0 educat$ = ! pr(ession ( a physician1 b 0 too /rong to be ti$ d[n to pr(essional r\t9e4 ,he devot$ himself to ! /udy ( natural philosophy1 & became 9 all its dep>tm5ts a ma/]4 ,he 0 also a ma/] ( lett]s4 ,languages1 anci5t & mod]n1 7 h\s$ )9 8 bra91 &1 to use ! words ( 8 epitaph1 'he fir/ p5etrat$ ! obscurity :i* _h veil$ = ages ! hi]oglyphics ( ,egypt4' ,x fell to ! lot ( ?is man to discov] facts 9 optics :i* ,newton's !ory 0 incompet5t to expla91 & 8 m9d roam$ 9 se>* ( a suffici5t !ory4 ,he _h made himself acqua9t$ ) all ! ph5om5a ( wave-motion2 ) all ! ph5om5a ( s\nd2 work+ successfully 9 ?is doma9 z an orig9al discov]]4 ,?us in=m$ & discipl9$1 he 0 prep>$ to detect any resemblance :i* might reveal itself betwe5 ! ph5om5a ( light & ^? ( wave-motion4 ,su* resemblances he did detect2 &1 spurr$ on by ! discov]y1 he pursu$ 8 speculations & exp]im5ts1 until he f9ally succe$$ 9 plac+ on an immovable basis ! ,undulatory ,!ory ( ,light4 ,! f\nd] ( ?is great !ory 0 ,?omas ,"y1 a "n1 p]haps1 unfamili> to _m ( y1 b :i* ought to be famili> to y all4 ,p]mit me1 !re=e1 by a k9d ( geometrical con/ruction :i* ,i once v5tur$ to employ 9 ,london1 to give y a notion ( ! magnitude ( ?is man4 ,let ,newton /& erect 9 8 age1 & ,"y 9 84 ,draw a /raight l9e f ,newton to ,"y1 tang5t to ! heads ( bo?4 ,?is l9e w\ld slope d[nw>ds f ,newton to ,"y1 because ,newton 0 c]ta9ly ! tall] man ( ! two4 ,b ! slope w\ld n be /eep1 = ! diff]5ce ( /ature 0 n excessive4 ,! l9e w\ld =m :at eng9e]s call a g5tle gradi5t f ,newton to ,"y4 ,place und]nea? ?is l9e ! bigge/ man born 9 ! int]val betwe5 bo?4 ,x may be d\bt$ :e!r he w\ld rea* ! l9e2 = if he did he w\ld be tall] intellectually ?an ,"y1 & !re 0 probably none tall]4 ,b ,i d n want y to re/ on ,engli% e/imates ( ,"y2 ! ,g]man1 ,helmholtz1 a k9dr$ g5ius1 ?us speaks ( him3 ,8 0 "o ( ! mo/ pr(\nd m9ds t ! _w has ev] se52 b he _h ! mis=tune to be too mu* 9 advance ( 8 age4 ,he excit$ ! wond] ( 8 contempor>ies1 :o1 h[ev]1 7 unable to foll[ him to ! heights at :i* 8 d>+ intellect 0 accu/om$ to so>4 ,8 mo/ important ideas lay1 !re=e1 buri$ & =gott5 9 ! folios ( ! ,royal ,society1 until a new g5]ation gradually & pa9fully made ! same discov]ies1 & prov$ ! exactness ( 8 ass]tions & ! tru? ( 8 demon/rations4 ,x is q true1 z ,helmholtz says1 t ,"y 0 9 advance ( 8 age2 b some?+ is to be add$ :i* illu/rates ! responsibility ( our public writ]s4 ,= tw5ty ye>s ?is man ( g5ius 0 qu5*$--hidd5 f ! appreciative intellect ( 8 c\ntry-m5--deem$ 9 fact a dream]1 ?r\gh ! vigor\s s>casm ( a writ] :o _h !n possession ( ! public e>1 & :o 9 ! ,ed9burgh ,review p\r$ ridicule ^u ,"y & 8 speculations4 ,to ! celebrat$ ,fr5*m5 ,fresnel & ,arago he 0 fir/ indebt$ = ! re/itution ( 8 rights2 = !y1 especially ,fresnel1 indep5d5tly remade & va/ly ext5d$ 8 discov]ies4 ,to ! /ud5ts ( 8 works ,"y has long s9ce appe>$ 9 8 true light1 b ^! tw5ty blank ye>s pu%$ him f ! public m9d1 :i* became 9 "t fill$ ) ! fame ( ,"y's colleague at ! ,royal ,in/itution1 ,davy1 & aft]w>ds ) ! fame ( ,f>aday4 ,c>lyle ref]s to a rem>k ( ,novalis1 t a man's self-tru/ is enorm\sly increas$ ! mom5t he f9ds t o!rs believe 9 him4 ,if ! opposite rem>k be true--if x be a fact t public disbelief weak5s a man's =ce--!re is no calculat+ ! am\nt ( damage ^! tw5ty ye>s ( neglect may h done to ,"y's productiv5ess z an inve/igator4 ,x rema9s to be /at$ t 8 assailant 0 ,mr4 ,h5ry ,br\gham1 aft]w>ds ,"l ,*ancellor ( ,engl&4 #d4 ,wave-,motion1 ,int]f]5ce ( ,waves1 ',:irlpool ,rapids' ( ,niag>a4 ,our h>de/ "w is n[ be=e u4 ,b ! capacity = h>d "w dep5ds 9 a great measure on ! antec$5t w9d+ up ( ! w2 ,i w\ld call ^u y1 !re=e1 to gird up y\r lo9s = com+ lab\rs4 ,9 ! e>lie/ writ+s ( ! anci5ts we f9d ! notion t s\nd is convey$ by ! air4 ,ari/otle gives expression to ?is notion1 & ! great ar*itect ,vitruvius comp>es ! waves ( s\nd to waves ( wat]4 ,b ! real me*anism ( wave-motion 0 hidd5 f ! anci5ts1 & inde$ 0 n made cle> until ! "t ( ,newton4 ,! c5tral difficulty ( ! subject 01 to di/+ui% betwe5 ! motion ( ! wave itself1 & ! motion ( ! p>ticles :i* at any mom5t con/itute ! wave4 ,/& ^u ! sea%ore & obs]ve ! advanc+ roll]s be=e !y are di/ort$ by ! friction ( ! bottom4 ,e wave has a back & a front1 &1 if y cle>ly seize ! image ( ! mov+ wave1 y w see t e p>ticle ( wat] along ! front ( ! wave is 9 ! act ( ris+1 :ile e p>ticle along its back is 9 ! act ( s9k+4 ,! p>ticles 9 front rea* 9 succession ! cre/ ( ! wave1 & z soon z ! cre/ is pa/ !y beg9 to fall4 ,!y !n rea* ! furr[ or s9us ( ! wave1 & c s9k no f>!r4 ,imm$iately aft]w>ds !y become ! front ( ! succe$+ wave1 rise aga9 until !y rea* ! cre/1 & !n s9k z be=e4 ,?us1 :ile ! waves pass onw>ds horizontally1 ! individual p>ticles are simply lift$ up & d[n v]tically4 ,obs]ve a sea-f[l1 or1 if y are a swimm]1 ab&on y\rself to ! action ( ! waves2 y are n c>ri$ =w>d1 b simply rock$ up & d[n4 ,! propagation ( a wave is ! propagation ( a =m1 & n ! transf]5ce ( ! sub/ance :i* con/itutes ! wave4 ,! l5g? ( ! wave is ! di/ance f cre/ to cre/1 :ile ! di/ance ?r\gh :i* ! individual p>ticles oscillate is call$ ! amplitude ( ! oscillation4 ,y w notice t 9 ?is description ! p>ticles ( wat] are made to vibrate across ! l9e ( propagation4#aj ,& n[ we h to take a /ep =w>ds1 & x is ! mo/ important /ep ( all4 ,y c picture two s]ies ( waves proce$+ f diff]5t orig9s ?r\gh ! same wat]4 ,:51 = example1 y ?r[ two /ones into /ill wat]1 ! r+-waves proce$+ f ! two c5tres ( di/urbance int]sect ea* o!r4 ,n[1 no matt] h[ num]\s ^! waves may be1 ! law holds good t ! motion ( e p>ticle ( ! wat] is ! algebraic sum ( all ! motions imp>t$ to x4 ,if cre/ co9cide ) cre/ & furr[ ) furr[1 ! wave is lift$ to a d\ble height above its s9us2 if furr[ co9cide ) cre/1 ! motions are 9 opposition & _! sum is z]o4 ,we h !n /ill wat]4 ,?is action ( wave ^u wave is te*nically call$ int]f]5ce1 a t]m1 to be rememb]$4 ,to ! eye ( a p]son conv]sant ) ^! pr9ciples1 no?+ c be m int]e/+ ?an ! cross+ ( wat] ripples4 ,?r\gh _! int]f]5ce ! wat]-surface is sometimes %iv]$ into ! mo/ beautiful mosaic1 trembl+ rhy?mically z if ) a k9d ( visible music4 ,:5 waves are skilfully g5]at$ 9 a di% ( m]cury1 a /rong light ?r[n ^u ! %9+ surface1 & reflect$ on to a scre51 reveals ! motions ( ! liquid metal4 ,! %ape ( ! vessel det]m9es ! =ms ( ! figures produc$4 ,9 a circul> di%1 = example1 a di/urbance at ! c5tre propagates itself z a s]ies ( circul> waves1 :i*1 aft] reflection1 aga9 meet at ! c5tre4 ,if ! po9t ( di/urbance be a little way remov$ f ! c5tre1 ! int]f]5ce ( ! direct & reflect$ waves produces ! magnific5t *as+ %[n 9 ! annex$ figure4#aa ,! light reflect$ f su* a surface yields a patt]n ( extraord9>y beauty4 ,:5 ! m]cury is slightly /ruck by a ne$le-po9t 9 a direction conc5tric ) ! surface ( ! vessel1 ! l9es ( light run r\nd 9 mazy coils1 int]lac+ & unravell+ !mselves 9 a wond]ful mann]4 ,:5 ! vessel is squ>e1 a spl5did *equ]-"w is produc$ by ! cross+ ( ! direct & reflect$ waves4 ,?us1 9 ! case ( wave-motion1 ! mo/ ord9>y causes give rise to mo/ exquisite effects4 ,! words ( ,em]son are p]fectly applicable "h3-- ,illu/ration3 ,fig4 #aj4 ',?\ c'/ n wave ?y /aff 9 ! air1 ,or dip ?y paddle 9 ! lake1 ,b x c>ves ! br[ ( beauty !re4 ,& ! ripples 9 rhymes ! o>s =sake4' ,! mo/ impressive illu/ration ( ! action ( waves on waves t ,i h ev] se5 occurs ne> ,niag>a4 ,= a di/ance ( two miles1 or !reab\ts1 bel[ ! ,falls1 ! riv] ,niag>a fl[s unruffl$ ?r\gh its excavat$ gorge4 ,! b$ subsequ5tly n>r[s1 & ! wat] quick5s its motion4 ,at ! place call$ ! ',:irlpool ,rapids1' ,i e/imat$ ! wid? ( ! riv] at #cjj feet1 an e/imate confirm$ by ! dwell]s on ! spot4 ,:5 x is rememb]$ t ! dra9age ( ne>ly half a cont95t is compress$ into ?is space1 ! impetuosity ( ! riv]'s escape ?r\gh ?is gorge may be imag9$4 ,two k9ds ( motion are "h obvi\sly active1 a motion ( translation & a motion ( undulation--! race ( ! riv] ?r\gh its gorge1 & ! great waves g5]at$ by its collision ) ! ob/acles 9 its way4 ,9 ! middle ( ! /ream1 ! ru% & toss+ are mo/ viol5t2 at all ev5ts1 ! impetu\s =ce ( ! individual waves is "h mo/ /rik+ly display$4 ,va/ pyramidal heaps leap incessantly f ! riv]1 "s ( !m ) su* en]gy z to j]k _! summits into ! air1 :]e !y hang susp5d$ z bundles ( liquid pe>ls1 :i*1 :5 %one ^u by ! sun1 are ( indescribable beauty4 ,! fir/ impression1 &1 inde$1 ! curr5t explanation ( ^! ,rapids is1 t ! c5tral b$ ( ! riv] is cumb]$ ) l>ge b\ld]s1 & t ! jo/l+1 toss+1 & wild leap+ ( ! wat]s !re are due to its impact aga9/ ^! ob/acles4 ,a v diff]5t explanation occurr$ to me ^u ! spot4 ,b\ld]s d]iv$ f ! adjac5t cliffs visibly cumb] ! sides ( ! riv]4 ,aga9/ ^! ! wat] rises & s9ks rhy?mically b viol5tly1 l>ge waves be+ ?us produc$4 ,on ! g5]ation ( ea* wave !re is an imm$iate comp\nd+ ( ! wave-motion ) ! riv]-motion4 ,! ridges1 :i* 9 /ill wat] w\ld proce$ 9 circul> curves r\nd ! c5tre ( di/urbance1 cross ! riv] obliquely1 & ! result is1 t at ! c5tre waves comm+le :i* h really be5 g5]at$ at ! sides4 ,?is cross+ ( waves may be se5 on a small scale 9 any gutt] aft] ra92 x may also be se5 on simply p\r+ wat] f a wide-lipp$ jug4 ,:]e cre/ & furr[ cross ea* o!r1 ! wave is annull$2 :]e furr[ & furr[ cross1 ! riv] is pl\gh$ to a great] dep?2 & :]e cre/ & cre/ aid ea* o!r1 we h t a/oni%+ leap ( ! wat] :i* breaks ! cohesion ( ! cre/s1 & tosses !m %att]$ into ! air4 ,! ph5om5a obs]v$ at ! ,:irlpool ,rapids con/itute1 9 fact1 "o ( ! gr&e/ illu/rations ( ! pr9ciple ( int]f]5ce4 #e4 ,analogies ( ,s\nd & ,light4 ,?omas ,"y's fundam5tal discov]y 9 optics 0 t ! pr9ciple ( ,int]f]5ce 0 applicable to light4 ,long prior to 8 "t an ,italian philosoph]1 ,grimaldi1 _h /at$ t "u c]ta9 circum/ances two ?9 beams ( light1 ea* ( :i*1 act+ s+ly1 produc$ a lum9\s spot ^u a :ite wall1 :5 caus$ to act toge!r1 p>tially qu5*$ ea* o!r & d>k5$ ! spot4 ,?is 0 a /atem5t ( fundam5tal significance1 b x requir$ ! discov]ies & ! g5ius ( ,"y to give x mean+4 ,h[ he did s w gradually become cle> to y4 ,y "k t air is compressible3 t by pressure x c be r5d]$ m d5se1 & t by dilatation x c be r5d]$ m r>e4 ,prop]ly agitat$1 a tun+-=k n[ s\nds 9 a mann] audible to y all1 & mo/ ( y "k t ! air ?r\gh :i* ! s\nd is pass+ is p>cell$ out into spaces 9 :i* ! air is cond5s$1 foll[$ by o!r spaces 9 :i* ! air is r>efi$4 ,^! cond5sations & r>efactions con/itute :at we call waves ( s\nd4 ,y c imag9e ! air ( a room trav]s$ by a s]ies ( su* waves1 & y c imag9e a second s]ies s5t ?r\gh ! same air1 & s relat$ to ! fir/ t cond5sation co9cides ) cond5sation & r>efaction ) r>efaction4 ,! consequ5ce ( ?is co9cid5ce w\ld be a l\d] s\nd ?an t produc$ by ei!r sy/em ( waves tak5 s+ly4 ,b y c also imag9e a /ate ( ?+s :]e ! cond5sations ( ! "o sy/em fall ^u ! r>efactions ( ! o!r sy/em4 ,9 ?is case 7o!r ?+s be+ equal7 ! two sy/ems w\ld completely neutralize ea* o!r4 ,ea* ( !m tak5 s+ly produces s\nd2 bo? ( !m tak5 toge!r produce no s\nd4 ,?us by add+ s\nd to s\nd we produce sil5ce1 z ,grimaldi1 9 8 exp]im5t1 produc$ d>kness by add+ light to light4 ,?r\gh 8 inve/igations on s\nd1 :i* 7 fruitful & pr(\nd1 ,"y approa*$ ! /udy ( light4 ,he put mean+ into ! obs]vation ( ,grimaldi1 & imm5sely ext5d$ x4 ,) spl5did success he appli$ ! undulatory !ory to ! explanation ( ! col\rs ( ?9 plates1 & to ^? ( /riat$ surfaces4 ,he discov]$ & expla9$ classes ( col\r :i* _h be5 previ\sly unnotic$ or unkn[n4 ,on ! assumption t light 0 wave-motion1 all 8 exp]im5ts on int]f]5ce 7 acc\nt$ =2 on ! assumption t light 0 fly+ p>ticles1 no?+ 0 expla9$4 ,9 ! "t ( ,huygh5s & ,eul] a m$ium _h be5 assum$ = ! transmission ( ! waves ( light2 b ,newton rais$ ! objection t1 if light consi/$ ( ! waves ( su* a m$ium1 %ad[s c\ld n exi/4 ,! waves1 he cont5d$1 w\ld b5d r\nd opaque bodies & produce ! motion ( light beh9d !m1 z s\nd turns a corn]1 or z waves ( wat] wa% r\nd a rock4 ,x 0 prov$ t ! b5d+ r\nd ref]r$ to by ,newton actually occurs1 b t ! inflect$ waves aboli% ea* o!r by _! mutual int]f]5ce4 ,"y also disc]n$ a fundam5tal diff]5ce betwe5 ! waves ( light & ^? ( s\nd4 ,c\ld y see ! air ?r\gh :i* s\nd-waves are pass+1 y w\ld obs]ve e individual p>ticle ( air oscillat+ to & fro1 9 ! direction ( propagation4 ,c\ld y see ! lum9if]\s e!r1 y w\ld also f9d e individual p>ticle mak+ a small excursion to & fro2 b "h ! motion1 l t assign$ to ! wat]-p>ticles above ref]r$ to1 w\ld be across ! l9e ( propagation4 ,! vibrations ( ! air are longitud9al1 ^? ( ! e!r transv]sal4 ,! mo/ famili> illu/ration ( ! int]f]5ce ( s\nd-waves is furni%$ by ! beats produc$ by two musical s\nds slightly out ( unison4 ,:5 two tun+-=ks 9 p]fect unison are agitat$ toge!r ! two s\nds fl[ )\t r\ghness1 z if !y 7 b "o4 ,b1 by atta*+ ) wax to "o ( ! =ks a little weight1 we cause x to vibrate m sl[ly ?an its neighb\r4 ,suppose t "o ( !m p]=ms #aja vibrations 9 ! "t requir$ by ! o!r to p]=m #ajj1 & suppose t at />t+ ! cond5sations & r>efactions ( bo? =ks co9cide4 ,at ! #aja/ vibration ( ! quick] =k !y w aga9 co9cide1 t =k at ?is po9t hav+ ga9$ "o :ole vibration1 or "o :ole wavel5g?1 ^u ! o!r4 ,b a little reflection w make x cle> t1 at ! #ej? vibration1 ! two =ks cond5sation :]e ! o!r t5ds to produce a r>efaction2 by ! unit$ action ( ! two =ks1 !re=e1 ! s\nd is qu5*$1 & we h a pause ( sil5ce4 ,?is occurs :]e "o =k has ga9$ half a wavel5g? ^u ! o!r4 ,at ! #aja/ vibration1 z already /at$1 we h co9cid5ce1 &1 !re=e1 augm5t$ s\nd2 at ! #aej? vibration we h aga9 a qu5*+ ( ! s\nd4 ,"h ! "o =k is ?ree half-waves 9 advance ( ! o!r4 ,9 g5]al t]ms1 ! waves conspire :5 ! "o s]ies is an ev5 numb] ( half-wave l5g?s1 & !y de/roy ea* o!r :5 ! "o s]ies is an odd numb] ( half-wave l5g?s 9 advance ( ! o!r4 ,) two =ks s circum/anc$1 we obta9 ^? int]mitt5t %ocks ( s\nd sep>at$ by pauses ( sil5ce1 to :i* we give ! "n ( beats4 ,by a suitable arrangem5t1 moreov]1 x is possible to make "o s\nd :olly ext+ui% ano!r4 ,along f\r di/9ct l9es1 = example1 ! vibrations ( ! two prongs ( a tun+-=k completely blot ea* o!r out4#ab ,! pit* ( s\nd is :olly det]m9$ by ! rapidity ( ! vibration1 z ! int5sity is by ! amplitude4 ,:at pit* is to ! e> 9 ac\/ics1 col\r is to ! eye 9 ! undulatory !ory ( light4 ,?\gh nev] se51 ! l5g?s ( ! waves ( light h be5 det]m9$4 ,_! exi/5ce is prov$ by _! effects1 & f _! effects also _! l5g?s may be accurately d$uc$4 ,?is may1 moreov]1 be done 9 _m ways1 &1 :5 ! diff]5t det]m9ations are comp>$1 ! /ricte/ h>mony is f\nd to exi/ betwe5 !m4 ,?is cons5sus ( evid5ce is "o ( ! /ronge/ po9ts ( ! undulatory !ory4 ,! %orte/ waves ( ! visible spectrum are ^? ( ! extreme violet2 ! longe/1 ^? ( ! extreme r$2 :ile ! o!r col\rs are ( int]m$iate pit* or wavel5g?4 ,! l5g? ( a wave ( ! extreme r$ is su*1 t x w\ld require #ci1jjj su* waves1 plac$ end to end1 to cov] "o in*1 :ile #fd1fca ( ! extreme violet waves w\ld be requir$ to span ! same di/ance4 ,n[1 ! velocity ( light1 9 r\nd numb]s1 is #ahf1jjj miles p] second4 ,r$uc+ ?is to in*es1 & multiply+ ! numb] ?us f\nd by #ci1jjj1 we f9d ! numb] ( waves ( ! extreme r$1 9 #ahf1jjj miles1 to be f\r hundr$ & sixty millions ( millions4 ,all ^! waves ent] ! eye1 & /rike ! ret9a at ! back ( ! eye 9 "o second4 ,9 a simil> mann]1 x may be f\nd t ! numb] ( %ocks correspond+ to ! impression ( violet is six hundr$ & sev5ty-eight millions ( millions4 ,all space is fill$ ) matt] oscillat+ at su* rates4 ,f e /> waves ( ^! dim5sions move1 ) ! velocity ( light1 l sph]ical %ells 9 all directions4 ,& 9 e!r1 j z 9 wat]1 ! motion ( e p>ticle is ! algebraic sum ( all ! sep>ate motions imp>t$ to x4 ,"o motion does n blot out ! o!r2 or1 if ext9ction occur at "o po9t1 x is /rictly aton$ =1 by augm5t$ motion1 at "s o!r po9t4 ,e /> decl>es by its light its undamag$ individuality1 z if x alone _h s5t its ?rills ?r\gh space4 #f4 ,int]f]5ce ( ,light4 ,illu/ration3 ,fig4 #aa4 ,! pr9ciple ( int]f]5ce1 z j /at$1 applies to ! waves ( light z x does to ! waves ( wat] & ! waves ( s\nd4 ,& ! conditions ( int]f]5ce are ! same 9 all ?ree4 ,if two s]ies ( light-waves ( ! same l5g? />t at ! same mom5t f a common orig9 7say ,a1 fig4 #aa71 cre/ co9cides ) cre/1 s9us ) s9us1 & ! two sy/ems bl5d toge!r to a s+le sy/em 7,a m n7 ( d\ble amplitude4 ,if bo? s]ies />t at ! same mom5t1 "o ( !m be+1 at />t+1 a :ole wavel5g? 9 advance ( ! o!r1 !y also add !mselves toge!r1 & we h an augm5t$ lum9\s effect4 ,! same occurs :5 ! "o sy/em ( waves is any ev5 numb] ( semi-undulations 9 advance ( ! o!r4 ,b if ! "o sy/em be half a wave-l5g? 7z at ,a' a'1 fig4 #ab71 or any odd numb] ( half wavel5g?s1 9 advance1 !n ! cre/s ( ! "o fall ^u ! s9uses ( ! o!r2 ! "o sy/em1 9 fact1 t5ds to lift ! p>ticles ( e!r at ! precise places :]e ! o!r t5ds to depress !m2 h5ce1 ?r\gh ! jo9t action ( ^! oppos+ =ces 7indicat$ by ! arr[s7 ! light-e!r rema9s p]fectly /ill4 ,?is /illness ( ! e!r is :at we call d>kness1 :i* corresponds ) a dead level 9 ! case ( wat]4 ,illu/ration3 ,fig4 #ab4 ,x 0 said 9 our fir/ lecture1 ) ref]5ce to ! col\rs produc$ by absorption1 t ! function ( natural bodies is selective1 n creative2 t !y ext+ui% c]ta9 con/itu5ts ( ! :ite sol> light1 & appe> 9 ! col\rs ( ! unext+ui%$ light4 ,x mu/ at once occur to y t1 inasmu* z we h 9 int]f]5ce an ag5cy by :i* light may be self-ext+ui%$1 we may h 9 x ! conditions = ! production ( col\r4 ,b ?is w\ld imply t c]ta9 con/itu5ts are qu5*$ by int]f]5ce1 :ile o!rs are p]mitt$ to rema94 ,?is is ! fact2 & x is entirely due to ! diff]5ce 9 ! l5g?s ( ! waves ( light4 #g4 ,col\rs ( ?9 ,films4 ,obs]vations ( ,boyle & ,hooke4 ,?is subject may be illu/rat$ by ! ph5om5a :i* fir/ sugge/$ ! undulatory !ory to ! m9d ( ,hooke4 ,^! are ! col\rs ( ?9 transp>5t films ( all k9ds1 kn[n z ! col\rs ( ?9 plates4 ,9 ?is relation no object 9 ! _w possesses a deep] sci5tific int]e/ ?an a common soap-bubble4 ,& "h let me say em]ges "o ( ! difficulties :i* ! /ud5t ( pure sci5ce enc\nt]s 9 ! pres5ce ( 'practical' communities l ^? ( ,am]ica & ,engl&2 x is n to be expect$ t su* communities c ent]ta9 any pr(\nd sympa?y ) lab\rs :i* seem s f> remov$ f ! doma9 ( practice z are _m ( ! lab\rs ( ! man ( sci5ce4 ,imag9e ,dr4 ,drap] sp5d+ 8 days 9 bl[+ soap-bubbles & 9 /udy+ _! col\rs6 ,w\ld y %[ him ! necess>y pati5ce1 or grant him ! necess>y support8 ,& yet be x rememb]$ x 0 ?us t m9ds l ^? ( ,boyle1 ,newton & ,hooke 7 occupi$2 & t on su* exp]im5ts has be5 f\nd$ a !ory1 ! issues ( :i* are incalculable4 ,i see no o!r way = y1 laym51 ?an to tru/ ! sci5tific man ) ! *oice ( 8 inquiries2 he /&s be=e ! tribunal ( 8 pe]s1 & by _! v]dict on 8 lab\rs y ought to abide4 ,:5ce1 !n1 are d]iv$ ! col\rs ( ! soap-bubble8 ,imag9e a beam ( :ite light imp++ on ! bubble4 ,:5 x rea*es ! fir/ surface ( ! film1 a kn[n fraction ( ! light is reflect$ back4 ,b a l>ge portion ( ! beam ent]s ! film1 rea*es its second surface1 & is aga9 9 "p reflect$4 ,! waves f ! second surface ?us turn back & hotly pursue ! waves f ! fir/ surface4 ,&1 if ! ?ickness ( ! film be su* z to cause ! necess>y ret>dation1 ! two sy/ems ( waves int]f]e ) ea* o!r1 produc+ augm5t$ or dim9i%$ light1 z ! case may be4 ,b1 inasmu* z ! waves ( light are ( diff]5t l5g?s1 x is pla9 t1 to produce ext9ction 9 ! case ( ! long] waves1 a great] ?ickness ( film is necess>y ?an 9 ! case ( ! %ort] ones4 ,diff]5t col\rs1 !re=e1 mu/ appe> at diff]5t ?icknesses ( ! film4 ,take ) y a little bottle ( _s ( turp5t9e1 & p\r x into "o ( y\r c\ntry ponds4 ,y w !n see ! gl[+ ( ^? col\rs ov] ! surface ( ! wat]4 ,on a small scale we produce !m ?us3 ,a common tea-tray is fill$ ) wat]1 b5ea? ! surface ( :i* dips ! end ( a pipette4 ,a beam ( light falls ^u ! wat]1 & is reflect$ by x to ! scre54 ,_s ( turp5t9e is p\r$ into ! pipette2 x desc5ds1 issues f ! end 9 m9ute drops1 :i* rise 9 succession to ! surface4 ,on rea*+ x1 ea* drop spreads sudd5ly out z a film1 & gl[+ col\rs imm$iately fla% =? ^u ! scre54 ,! col\rs *ange z ! ?ickness ( ! film *anges by evaporation4 ,!y are also arrang$ 9 zones1 9 consequ5ce ( ! gradual dim9ution ( ?ickness f ! c5tre outw>ds4 ,any film :atev] w produce ^! col\rs4 ,! film ( air betwe5 two plates ( glass squeez$ toge!r1 exhibits1 z %[n by ,hooke1 ri* fr+es ( col\r4 ,a p>ticul>ly f9e example ( ^! fr+es is n[ be=e y4 ,nor is ev5 air necess>y2 ! rupture ( optical cont9uity suffices4 ,smite ) an axe ! black1 transp>5t ice--black1 because x is pure & ( great dep?--"u ! mora9e ( a glaci]2 y readily produce 9 ! int]ior flaws :i* no air c rea*1 & f ^! flaws ! col\rs ( ?9 plates sometimes break l fire4 ,b ! s\rce ( mo/ hi/oric int]e/ is1 z already /at$1 ! soap-bubble4 ,) "o ( ! mixtures employ$ by ! em95t bl9d philosoph]1 ,plateau1 9 8 rese>*es on ! cohesion figures ( ?9 films1 we obta9 9 /ill air a bubble t5 or twelve in*es 9 diamet]4 ,y may look at ! bubble itself1 or y may look at its projection ^u ! scre52 ri* col\rs arrang$ 9 zones are1 9 bo? cases1 exhibit$4 ,r5d]+ ! beam p>allel1 & p]mitt+ x to imp+e ^u ! sides1 bottom1 & top ( ! bubble1 gorge\s fans ( col\r1 reflect$ f ! bubble1 ov]spread ! scre51 rotat+ z ! beam is c>ri$ r\nd4 ,by ?is exp]im5t ! int]nal motions ( ! film are also /rik+ly display$4 ,n 9 a mom5t are great !ories elaborat$3 ! facts :i* dem& !m become fir/ prom95t2 !n1 to ! p]iod ( obs]vation succe$s a p]iod ( pond]+ & ( t5tative explanation4 ,by su* ef=ts ! human m9d is gradually prep>$ = ! f9al !oretic illum9ation4 ,! col\rs ( ?9 plates1 = example1 occupi$ ! att5tion ( ,rob]t ,boyle4 ,9 8 ',exp]im5tal ,hi/ory ( ,col\rs' he cont5ds aga9/ ! s*ools :i* affirm$ t col\r 0 'a p5etrative quality t rea*es to ! inn]mo/ p>ts ( ! object1' adduc+ oppos+ facts4 ',to give y a fir/ in/ance1' he says1 ',i %all ne$ b to rem9d y ( :at ,i told y a little aft] ! beg9n+ ( ?is essay1 t\*+ ! blue & r$ & yell[ t may be produc$ ^u a piece ( temp]$ /eel2 = ^! col\rs1 ?\gh !y be v vivid1 yet if y break ! /eel !y adorn1 !y w appe> to be b sup]ficial4' ,he !n describes1 9 phraseology :i* %[s ! delight he took 9 8 "w1 ! foll[+ beautiful exp]im5t3-- ',we took a quantity ( clean lead1 & melt$ x ) a /rong fire1 & !n imm$iately p\r+ x out into a clean vessel ( conv5i5t %ape & matt] 7we us$ "o ( iron1 t ! great & sudd5 heat might n injure x71 & !n c>efully & nimbly tak+ (f ! scum t float$ on ! top1 we p]ceiv$1 z we expect$1 ! smoo? & glossy surface ( ! melt$ matt] to be adorn$ ) a v glori\s col\r1 :i*1 be+ z transitory z delightful1 did almo/ imm$iately give place to ano!r vivid col\r1 & t 0 z quickly succe$$ by a ?ird1 & ?is1 z x 71 *as$ away by a f\r?2 & s ^! wond]fully vivid col\rs successively appe>$ & vani%$ till ! metal ceas+ to be hot en\gh to hold any long] ?is pleas+ spectacle1 ! col\rs t *anc$ to adorn ! surface :5 ! lead ?us began to cool rema9$ ^u x1 b 7 s sup]ficial t h[ little soev] we scrap$ (f ! surface ( ! lead1 we did1 9 su* places1 scrape (f all ! col\r4' ',^! ?+s1' he adds1 'sugge/$ to me "s ?\ghts or rav+s :i* ,i h n n[ "t to acqua9t y )4'#ac ,he ext5ds 8 obs]vations to ess5tial oils & spirits ( w9e1 ':i* be+ %ak5 till !y h good /ore ( bubbles1 ^? bubbles w 7if att5tively consid]$7 appe> adorn$ ) v>i\s & lovely col\rs1 :i* all imm$iately vani% ^u ! retrogress+ ( ! liquid :i* af=ds ^! bubbles _! sk9s into ! re/ ( ! oil4' ,he also ref]s to ! col\r ( glass films4 ',i h se5 "o t 0 skill$ 9 fa%ion+ glasses by ! help ( a lamp bl[+ "s ( !m s /rongly z to bur/ !m2 :]eupon x 0 f\nd t ! t5acity ( ! metal 0 su* t be=e x broke x suff]$ itself to be r$uc$ into films s extremely ?9 t !y con/antly %[$ ^u _! surface ! v>y+ col\rs ( ! ra9b[4'#ad ,subsequ5t to ,boyle ! col\rs ( ?9 plates occupi$ ! att5tion ( ,rob]t ,hooke1 9 ^: writ+s we f9d a dawn+ ( ! undulatory !ory ( light4 ,he describes ) great di/9ctness ! col\rs obta9$ ) ?9 flakes ( ',muscovy glass' 7talc71 also ^? surr\nd+ flaws 9 cry/als :]e optical cont9uity is de/roy$4 ,he %[s v cle>ly ! dep5d5ce ( ! col\r ^u ! ?ickness ( ! film1 & proves by microscopic obs]vation t plates ( a uni=m ?ickness yield uni=m col\rs4 ',if1' he says1 'y take any small piece ( ! ,muscovy glass1 & ) a ne$le1 or "s o!r conv5i5t in/rum5t1 cleave x (t5times into ?9n] & ?9n] lam91 y %all f9d t until y come to a det]m9ate ?9ness ( !m !y %all appe> transp>5t & col\rless2 b if y cont9ue to split & divide !m fur!r1 y %all f9d at la/ t ea* plate %all appe> mo/ lovely t+$ or imbu$ ) a det]m9ate col\r4 ,if1 fur!r1 by any means y s flaw a pretty ?ick piece t "o "p beg9s to cleave a little f ! o!r1 & betwe5 ^! two !re be gott5 "s pellucid m$ium1 ^? lam9at$ or pellucid bodies t fill t space %all exhibit sev]al ra9b[s or col\r$ l9es1 ! col\rs ( :i* w be dispos$ & rang$ accord+ to ! v>i\s ?icknesses ( ! sev]al p>ts ( ! plate4' ,he !n describes fully & cle>ly ! exp]im5t ) press$ glasses already ref]r$ to3-- ',take two small pieces ( gr\nd & poli%$ look+-glass plate1 ea* ab\t ! bigness ( a %ill+3 take ^! two dry1 & ) y\r =ef+]s & ?umbs press !m v h>d & close toge!r1 & y %all f9d t :5 !y approa* ea* o!r v ne> !re w appe> sev]al irises or col\r$ l9es1 9 ! same mann] almo/ z 9 ! ,muscovy glass2 & y may v easily *ange any ( ! col\rs ( any "p ( ! int]pos$ body by press+ ! plates clos] & h>d] toge!r1 or leav+ !m m lax--t is1 a "p :i* appe>$ col\r$ ) a r$1 may pres5tly be t+$ ) a yell[1 blue1 gre51 purple1 or ! l4 ',any sub/ance1' he says1 'provid$ x be ?9 & transp>5t1 w %[ ^! col\rs4' ,l ,boyle1 he obta9$ !m ) glass films2 he also procur$ !m ) bubbles ( pit*1 ros91 colophony1 turp5t9e1 solutions ( sev]al gums1 z gum arabic 9 wat]1 any glut9\s liquor1 z wort1 w9e1 _s ( w9e1 oyl ( turp5t9e1 gl>e ( snails1 c4 ,hooke's writ+s %[ t ev5 9 8 day ! idea t bo? light & heat are modes ( motion _h tak5 possession ( _m m9ds4 ',fir/1' he says1 't all k9d ( fi]y burn+ bodies h _! p>ts 9 motion ,i ?9k w be easily grant$ me4 ,t ! sp>k /ruck f a fl9t & /eel is 9 rapid agitation ,i h else:]e made probable2444 t heat argues a motion ( ! int]nal p>ts is 7z ,i said be=e7 g5]ally grant$2444 & t 9 all extremely hot %9+ bodies !re is a v quick motion t causes light1 z well z a m robu/ t causes heat1 may be argu$ f ! cel]ity :]e) ! bodies are dissolv$4 ,next1 x mu/ be a vibrative motion4' ,8 ref]5ce to ! quick motion ( light & ! m robu/ motion ( heat is a rem>kable /roke ( sagacity2 b ,hooke's direct insight is bett] ?an 8 reason+2 = ! pro(s he adduces t light is 'a vibrat+ motion' h no p>ticul> be>+ ^u ! "q4 ,/ill ! ,undulatory ,!ory _h und\bt$ly dawn$ ^u ! m9d ( ?is rem>kable man4 ,9 endeav\r+ to acc\nt = ! col\rs ( ?9 plates1 he aga9 ref]s to ! relation ( col\r to ?ickness3 he dwells ^u ! fact t ! film :i* %[s ^! col\rs mu/ be transp>5t1 prov+ ?is by %[+ t h[ev] ?9 an opaque body 0 r5d]$ no col\rs 7 produc$4 ',?is1' he says1 ',i h (t5 tri$ by press+ a small globule ( m]cury betwe5 two smoo? plates ( glass1 :]eby ,i h r$uc$ t body to a mu* great] ?9ness ?an 0 requisite to exhibit ! col\rs ) a transp>5t body4' ,!n foll[s ! sagaci\s rem>k t to produce ! col\rs '!re mu/ be a consid]able reflect+ body adjac5t to ! "u or fur!r side ( ! lam9a or plate3 = ?is ,i always f\nd1 t ! great] t reflection 0 ! m vivid 7 ! appe>+ col\rs4 ,f :i* obs]vation1' he cont9ues1 'x is mo/ evid5t1 t ! reflection f ! fur!r or "u side ( ! body is ! pr9cipal cause ( ! production ( ^! col\rs4' ,he draws a diagram1 correctly repres5t+ ! reflection at ! two surfaces ( ! film2 b "h 8 cle>ness ends4 ,he ascribes ! col\rs to a coalesc5ce or confusion ( ! two reflect+ pulses2 ! pr9cipal ( int]f]5ce be+ unkn[n to him1 he c\ld n g fur!r 9 ! way ( explanation4 #h4 ,newton's ,r+s4 ,relation ( ,col\r to ,?ickness ( ,film4 ,illu/ration3 ,fig4 #ac ,9 ?is way1 !n1 by ! active op]ation ( diff]5t m9ds1 facts are obs]v$1 exam9$1 & ! precise conditions ( _! appe>ance det]m9$4 ,all su* "w 9 sci5ce is ! prelude to o!r "w2 & ! ef=ts ( ,boyle & ,hooke cle>$ ! way = ! optical c>e] ( ,newton4 ,he conqu]$ ! difficulty :i* ,hooke _h f\nd insup]able1 & det]m9$ by accurate measurem5ts ! relation ( ! ?ickness ( ! film to ! col\r x displays4 ,9 do+ ?is 8 fir/ c>e 0 to obta9 a film ( v>iable & calculable dep?4 ,on a plano-convex glass l5s 7,d ,b ,e1 fig4 #ac7 ( v feeble curvature he laid a plate ( glass 7,a ,c7 ) a plane surface1 ?us obta9+ a film ( air ( gradually increas+ dep? f ! po9t ( contact 7,b7 outw>ds4 ,on look+ at ! film 9 mono*romatic light he saw1 ) ! delight att5dant on fulfill$ prevision1 surr\nd+ ! place ( contact1 a s]ies ( bright r+s sep>at$ f ea* o!r by d>k ones1 & becom+ m closely pack$ toge!r z ! di/ance f ! po9t ( contact augm5t$ 7z 9 fig4 #ad74 ,:5 he employ$ r$ light1 8 r+s _h c]ta9 diamet]s2 :5 he employ$ blue light1 ! diamet]s 7 less4 ,9 g5]al t]ms1 ! m refrangible ! light ! small] 7 ! r+s4 ,caus+ 8 glasses to pass ?r\gh ! spectrum f r$ to blue1 ! r+s gradually contract$2 :5 ! passage 0 f blue to r$1 ! r+s exp&$4 ,?is is a beautiful exp]im5t1 & appe>s to h giv5 ,newton ! mo/ lively satisfaction4 ,:5 :ite light fell ^u1 ! glasses1 inasmu* z ! col\rs 7 n sup]pos$1 a s]ies ( iris-col\r$ circles 0 obta9$4 ,a magnifi$ image ( ,newton's r+s is n[ be=e y1 &1 by employ+ 9 succession r$1 blue1 & :ite light1 we obta9 all ! effects obs]v$ by ,newton4 ,y notice t 9 mono*romatic light ! r+s run clos] & clos] toge!r z !y rec$e f ! c5tre4 ,?is is due to ! fact t at a di/ance ! film ( air ?ick5s m rapidly ?an ne> ! c5tre4 ,:5 :ite light is employ$1 ?is clos+ up ( ! r+s causes ! v>i\s col\rs to be sup]pos$1 s t aft] a c]ta9 ?ickness !y are bl5d$ toge!r to :ite light1 ! r+s !n ceas+ altoge!r4 ,x ne$s b a mom5t's reflection to und]/& t ! col\rs ( ?9 plates1 produc$ by :ite light1 are nev] unmix$ or mono*romatic4 ,illu/ration3 ,fig4 #ad ,newton comp>$ ! t9ts obta9$ 9 ?is way ) ! t9ts ( 8 soap-bubble1 & he calculat$ ! correspond+ ?ickness4 ,h[ he did ?is may be ?us made pla9 to y3 ,suppose ! wat] ( ! ocean to be absolutely smoo?2 x w\ld !n accurately repres5t ! e>?'s curv$ surface4 ,let a p]fectly horizontal plane t\* ! surface at any po9t4 ,kn[+ ! e>?'s diamet]1 any eng9e] or ma!matician 9 ?is room c\ld tell y h[ f> ! sea's surface w lie bel[ ?is plane1 at ! di/ance ( a y>d1 t5 y>ds1 a hundr$ y>ds1 or a ?\s& y>ds f ! po9t ( contact ( ! plane & ! sea4 ,x is common1 inde$1 9 levell+ op]ations1 to all[ = ! curvature ( ! e>?4 ,newton's calculation 0 precisely simil>4 ,8 plane glass 0 a tang5t to 8 curv$ "o4 ,f its refractive index & focal di/ance he det]m9$ ! diamet] ( ! sph]e ( :i* 8 curv$ glass =m$ a segm5t1 he measur$ ! di/ances ( 8 r+s f ! place ( contact1 & he calculat$ ! dep? betwe5 ! tang5t plane & ! curv$ surface1 exactly z ! eng9e] w\ld calculate ! di/ance betwe5 8 tang5t plane & ! surface ( ! sea4 ,! wond] is1 t1 :]e su* inf9itesimal di/ances are involv$1 ,newton1 ) ! means at 8 disposal1 c\ld h work$ ) su* m>vell\s exactitude4 ,to acc\nt = ^! r+s 0 ! greate/ optical difficulty t ,newton1 ev] enc\nt]$4 ,he q appreciat$ ! difficulty4 ,ov] 8 eagle eye !re 0 no film--no vagu5ess 9 8 conceptions4 ,at ! v outset 8 !ory 0 confront$ by ! "q1 ,:y1 :5 a beam ( light is incid5t on a transp>5t body1 are "s ( ! light-p>ticles reflect$ & "s transmitt$8 ,is x t !re are two k9ds ( p>ticles1 ! "o specially fitt$ = transmission & ! o!r = reflection8 ,?is _c be ! reason2 =1 if we all[ a beam ( light :i* has be5 reflect$ f "o piece ( glass to fall ^u ano!r1 x1 z a g5]al rule1 is also divid$ into a reflect$ & a transmitt$ portion4 ,! p>ticles once reflect$ are n always reflect$1 nor are ! p>ticles once transmitt$ always transmitt$4 ,newton saw all ?is2 he knew he _h to expla9 :y x is t ! self-same p>ticle is at "o mom5t reflect$ & at ! next mom5t transmitt$4 ,x c\ld only he ?r\gh "s *ange 9 ! condition ( ! p>ticle itself4 ,! self-same p>ticle1 he affirm$1 0 affect$ by 'fits' ( easy transmission & reflection4 #i4 ,!ory ( ',fits' appli$ to ,newton's ,r+s4 ,if y are will+ to foll[ me 9 an attempt to reveal ! speculative gr\ndwork ( ?is !ory ( fits1 ! intellectual discipl9e w1 ,i ?9k1 repay y = ! necess>y ef=t ( att5tion4 ,newton 0 *>y ( /at+ :at he consid]$ to be ! cause ( ! fits1 b !re c h>dly be a d\bt t 8 m9d re/$ on a physical cause4 ,nor c !re be a d\bt t "h1 z 9 all attempts at !oris+1 he 0 compell$ to fall back ^u exp]i5ce = ! mat]ials ( 8 !ory4 ,let u attempt to re/ore 8 c\rse ( ?\ght & obs]vation4 ,a magnet w\ld furni% him ) ! notion ( attract$ & repell$ poles2 & he :o habitually saw 9 ! visible an image ( ! invisible w\ld naturally end[ 8 light-p>ticles ) su* poles4 ,turn+ _! attract$ poles t[>ds a transp>5t sub/ance1 ! p>ticles w\ld be suck$ 9 & transmitt$2 turn+ _! repell$ poles1 !y w\ld be driv5 away or reflect$4 ,?us1 by ! ascription ( poles1 ! transmission & reflection ( ! self-same p>ticle at diff]5t times might be acc\nt$ =4 ,consid] ^! r+s ( ,newton z se5 9 pure r$ light3 !y are alt]nately bright & d>k4 ,! film ( air correspond+ to ! out]mo/ ( !m is n ?ick] ?an an ord9>y soap-bubble1 & x becomes ?9n] on approa*+ ! c5tre2 /ill ,newton1 z ,i h said1 measur$ ! ?ickness correspond+ to e r+1 & %[$ ! diff]5ce ( ?ickness betwe5 r+ & r+4 ,n[1 m>k ! result4 ,= ! sake ( conv5i5ce1 let u call ! ?ickness ( ! film ( air correspond+ to ! fir/ d>k r+ d2 !n ,newton f\nd ! di/ance correspond+ to ! second d>k r+ #b d2 ! ?ickness correspond+ to ! ?ird d>k r+ #c d2 ! ?ickness correspond+ to ! t5? d>k r+ #aj d1 & s on4 ,surely !re mu/ be "s hidd5 mean+ 9 ?is little di/ance1 d1 :i* turns up s con/antly8 ,"o c imag9e ! int5se int]e/ ) :i* ,newton pond]$ its mean+4 ,obs]ve ! probable outcome ( 8 ?\ght4 ,he _h end[$ 8 light-p>ticles ) poles1 b n[ he is =c$ to introduce ! notion ( p]iodic recurr5ce4 ,"h 8 p[] ( transf] f ! s5sible to ! subs5sible w\ld r5d] x easy = him to suppose ! light-p>ticles animat$1 n only ) a motion ( translation1 b also ) a motion ( rotation4 ,newton's a/ronomical k r5d]$ all su* conceptions famili> to him4 ,! e>? has su* a d\ble motion4 ,9 ! "t occupi$ 9 pass+ ov] a million & a half ( miles ( its orbit--t is1 9 tw5ty-f\r h\rs--our planet p]=ms a complete rotation2 & 9 ! "t requir$ to pass ov] ! di/ance d1 ,newton's light-p>ticle might be suppos$ to p]=m a complete rotation4 ,true1 ! light-p>ticle is small] ?an ! planet1 & ! di/ance d1 in/ead ( be+ a million & a half ( miles1 is a little ov] ! n9ety ?\s&? ( an in*4 ,b ! two conceptions are1 9 po9t ( intellectual quality1 id5tical4 ,imag9e1 !n1 a p>ticle ent]+ ! film ( air :]e x possesses ?is precise ?ickness4 ,to ent] ! film1 its attract$ end mu/ be pres5t$4 ,)9 ! film x is able to turn once completely r\nd2 at ! o!r side ( ! film its attract$ pole w be aga9 pres5t$2 x w1 !re=e1 ent] ! glass at ! opposite side ( ! film & be lo/ to ! eye4 ,all r\nd ! place ( contact1 :]ev] ! film possesses ?is precise ?ickness1 ! light w equally disappe>--we %all !re=e h a r+ ( d>kness4 ,& n[ obs]ve h[ well ?is conception falls 9 ) ! law ( proportionality discov]$ by ,newton4 ,:5 ! ?ickness ( ! film is #b d1 ! p>ticle has "t to p]=m1 two complete rotations )9 ! film2 :5 ! ?ickness is #c d1 ?ree complete rotations2 :5 #aj d1 t5 complete rotations are p]=m$4 ,x is manife/ t 9 ea* ( ^! cases1 on arriv+ at ! second surface ( ! film1 ! attract$ pole ( ! p>ticle w be pres5t$4 ,x w1 !re=e1 be transmitt$2 &1 because no light is s5t to ! eye1 we %all h a r+ ( d>kness at ea* ( ^! places4 ,! bright r+s foll[ imm$iately f ! same conception4 ,!y occur betwe5 ! d>k r+s1 ! ?icknesses to :i* !y correspond be+ also int]m$iate betwe5 ^? ( ! d>k ones4 ,take ! case ( ! fir/ bright r+4 ,! ?ickness ( ! film is d2 9 ?is int]val ! rotat+ p>ticle c p]=m only half a rotation4 ,:51 !re=e1 x rea*es ! second surface ( ! film1 its repell$ pole is pres5t$2 x is1 !re=e1 driv5 back & rea*es ! eye4 ,at all di/ances r\nd ! c5tre correspond+ to ?is ?ickness ! same effect is produc$1 & ! consequ5ce is a r+ ( brightness4 ,! o!r bright r+s are simil>ly acc\nt$ =4 ,at ! second "o1 :]e ! ?ickness is #a;d1 a rotation & a half is p]=m$2 at ! ?ird1 two rotations & a half2 & at ea* ( ^! places ! p>ticles pres5t _! repell$ poles to ! l[] surface ( ! film4 ,!y are !re=e s5t back to ! eye1 & produce !re ! impression ( brightness4 ,?is analysis1 ?\gh involv+ difficulties :5 closely scrut9is$1 enables u to see h[ ! !ory ( fits may h gr[n into consi/5cy 9 ! m9d ( ,newton4 ,x has be5 already /at$ t ! ,emission ,!ory assign$ a great] velocity to light 9 glass & wat] ?an 9 air or /ell> space2 & t on ?is po9t x 0 at direct issue ) ! !ory ( undulation1 :i* makes ! velocity 9 air or /ell> space great] ?an 9 glass or wat]4 ,by an exp]im5t propos$ by ,arago1 & execut$ ) consummate skill by ,f\cault & ,fizeau1 ?is "q 0 br\ght to a crucial te/1 & decid$ 9 fav\r ( ! !ory ( undulation4 ,9 ! pres5t in/ance also ! two !ories are at v>iance4 ,newton assum$ t ! action :i* produces ! alt]nate bright & d>k r+s took place at a s+le surface2 t is1 ! second surface ( ! film4 ,! undulatory !ory affirms t ! r+s are caus$ by ! int]f]5ce ( waves reflect$ f bo? surfaces4 ,?is also has be5 demon/rat$ by exp]im5t4 ,by a prop] arrangem5t1 z we %all aft]w>ds le>n1 we may aboli% reflection f "o ( ! surfaces ( ! film1 & :5 ?is is done ! r+s vani% altoge!r4 ,r+s ( feeble int5sity are also =m$ by transmitt$ light4 ,^! are ref]r$ by ! undulatory !ory to ! int]f]5ce ( waves :i* h pass$ directly ?r\gh ! film1 ) o!rs :i* h suff]$ two reflections )9 ! film1 & are ?us completely acc\nt$ =4 #aj4 ,! ,diffraction ( ,light4 ,newton's esp\sal ( ! ,emission ,!ory is said to h ret>d$ sci5tific discov]y4 ,x might1 h[ev]1 be que/ion$ :e!r1 9 ! long run1 ! errors ( great m5 h n really _! effect 9 r5d]+ intellectual progress rhy?mical1 in/ead ( p]mitt+ x to rema9 uni=m1 ! 'ret>dation' 9 ea* case be+ ! prelude to a m impetu\s advance4 ,x is confusion & /agnation1 r ?an error1 t we ought to avoid4 ,?us1 ?\gh ! undulatory !ory 0 held back = a "t1 x ga!r$ /r5g? 9 ! int]val1 & its developm5t )9 ! la/ half c5tury has be5 s rapid & triumphant z to leave no rival 9 ! field4 ,we h n[ to turn to ! inve/igation ( new classes ( ph5om5a1 ( :i* x alone c r5d] a satisfactory acc\nt4 ,newton1 :o 0 famili> ) ! idea ( an e!r1 & :o introduc$ x 9 "s ( 8 speculations1 object$1 z already /at$1 t if light consi/$ ( waves %ad[s c\ld n exi/2 = t ! waves w\ld b5d r\nd ! edges ( opaque bodies & agitate ! e!r beh9d !m4 ,he 0 "r 9 affirm+ t ?is b5d+ ought to occur1 b wrong 9 suppos+ t x does n occur4 ,! b5d+ is real1 ?\gh 9 all ord9>y cases x is mask$ by ! action ( int]f]5ce4 ,?is inflection ( ! light receives ! "n ( ,diffraction4 ,to /udy ! ph5om5a ( diffraction x is necess>y t our s\rce ( light %\ld be a physical po9t1 or a f9e l9e2 = :5 a lum9\s surface is employ$1 ! waves issu+ f diff]5t po9ts ( ! surface obscure & neutralize ea* o!r4 ,a po9t ( light ( high int5sity is obta9$ by admitt+ ! p>allel rays ( ! sun ?r\gh an ap]ture 9 a w9d[-%utt]1 & conc5trat+ ! beam by a l5s ( %ort focus4 ,! small sol> image at ! focus con/itutes a suitable po9t ( light4 ,! image ( ! sun =m$ on ! convex surface ( a glass bead1 or ( a wat*-glass black5$ )91 ?\gh less int5se1 w also answ]4 ,an int5se l9e ( light is obta9$ by admitt+ ! sunlight ?r\gh a slit & s5d+ x ?r\gh a /rong cyl9drical l5s4 ,! slice ( light is contract$ to a physical l9e at ! focus ( ! l5s4 ,a glass tube black5$ )9 & plac$ 9 ! light1 reflects f its surface a lum9\s l9e :i*1 ?\gh less int5se1 also answ]s ! purpose4 ,9 ! exp]im5t n[ to be describ$ a v]tical slit ( v>iable wid? is plac$ 9 front ( ! electric lamp1 & ?is slit is look$ at f a di/ance ?r\gh ano!r v]tical slit1 also ( v>iable ap]ture1 & held 9 ! h&4 ,! light ( ! lamp be+1 9 ! fir/ place1 r5d]$ mono*romatic by plac+ a pure r$ glass 9 front ( ! slit1 :5 ! eye is plac$ 9 ! /raight l9e drawn ?r\gh bo? slits an extraord9>y appe>ance 7%[n 9 fig4 #ae7 is obs]v$4 ,fir/ly1 ! slit 9 front ( ! lamp is se5 z a vivid rectangle ( light2 b "r & left ( x is a long s]ies ( rectangles1 decreas+ 9 vividness1 & sep>at$ f ea* o!r by int]vals ( absolute d>kness4 ,! bread? ( ^! b&s is se5 to v>y ) ! wid? ( ! slit held be=e ! eye4 ,:5 ! slit is wid5$ ! b&s become n>r[]1 & cr[d m losely toge!r2 :5 ! slit is n>r[$1 ! individual b&s wid5 & also retreat f ea* o!r1 leav+ betwe5 !m wid] spaces ( d>kness ?an be=e4 ,illu/ration3 ,fig4 #ae4 ,leav+ ev]y?+ else un*ang$1 let a blue glass or a solution ( ammonia-sulphate ( copp]1 :i* gives a v pure blue1 be plac$ 9 ! pa? ( ! light4 ,a s]ies ( blue b&s is ?us obta9$1 exactly l ! =m] 9 all respects save "o2 ! blue rectangles are n>r[]1 & !y are clos] toge!r ?an ! r$ ones4 ,if we employ col\rs ( int]m$iate refrangibilities1 :i* we may d by caus+ ! diff]5t col\rs ( a spectrum to %9e ?r\gh ! slit1 we obta9 b&s ( col\r int]m$iate 9 wid?1 & occupy+ int]m$iate positions1 betwe5 ^? ( ! r$ & blue4 ,! aspect ( ! b&s 9 r$1 gre51 & violet light is repres5t$ 9 fig4 #af4 ,:5 :ite light1 !re=e1 passes ?r\gh ! slit ! v>i\s col\rs are n sup]pos$1 & in/ead ( a s]ies ( mono*romatic b&s1 sep>at$ f ea* o!r by int]vals ( d>kness1 we h a s]ies ( col\r$ spectra plac$ side by side4 ,:5 ! di/ant slit is illum9at$ by a c&le flame1 in/ead ( ! m int5se electric light1 or :5 a di/ant plat9um wire rais$ to a :ite heat by an electric curr5t is employ$1 sub/antially ! same effects are obs]v$4 ,illu/ration3 ,fig4 #af4 #aa4 ,application ( ! ,wave-!ory to ! ,ph5om5a ( ,diffraction4 ,( ^! & ( a multitude ( simil> effects ! ,emission ,!ory is incompet5t to (f] any satisfactory explanation4 ,let u see h[ !y are acc\nt$ = by ! ,!ory ( ,undulation4 ,& "h1 ) ! view ( rea*+ absolute cle>ness1 ,i mu/ make an appeal to t faculty ! importance ( :i* ,i h dwelt ^u s e>ne/ly "h & else:]e--! faculty ( imag9ation4 ,figure y\rself ^u ! sea-%ore1 ) a well-=m$ wave advanc+4 ,take a l9e ( p>ticles along ! front ( ! wave1 all at ! same di/ance bel[ ! cre/2 !y are all ris+ 9 ! same mann] & at ! same rate4 ,take a simil> l9e ( p>ticles on ! back ( ! wave1 !y are all fall+ 9 ! same mann] & at ! same rate4 ,take a l9e ( p>ticles along ! cre/1 !y are all 9 ! same condition z reg>ds ! motion ( ! wave4 ,! same is true = a l9e ( p>ticles along ! furr[ ( ! wave4 ,! p>ticles ref]r$ to 9 ea* ( ^! cases respectively1 be+ 9 ! same condition z reg>ds ! motion ( ! wave1 are said to be 9 ! same phase ( vibration4 ,b if y comp>e a p>ticle on ! front ( ! wave ) "o at ! back2 or1 m g5]ally1 if y comp>e toge!r any two p>ticles n occupy+ ! same position 9 ! wave1 _! conditions ( motion n be+ ! same1 !y are said to be 9 diff]5t phases ( vibration4 ,if "o ( ! p>ticles lie ^u ! cre/1 & ! o!r on ! furr[ ( ! wave1 !n1 z "o is ab\t to rise & ! o!r ab\t to fall1 !y are said to be 9 opposite phases ( vibration4 ,!re is /ill ano!r po9t to be cle>$ up--& x is "o ( ! utmo/ importance z reg>ds our pres5t subject4 ,let ,o 7fig4 #ag7 be a spot 9 /ill wat] :i*1 :5 di/urb$1 produces a s]ies ( circul> waves3 ! di/urbance necess>y to produce ^! waves is simply an oscillation up & d[n ( ! wat] at ,o4 ,let m n be ! position ( ! ridge ( "o ( ! waves at any mom5t1 & m' n' its position a second or two aft]w>ds4 ,n[ e p>ticle ( wat]1 z ! wave passes x1 oscillates1 z we h le>n$1 up & d[n4 ,if1 !n1 ?is oscillation be a suffici5t orig9 ( wave-motion1 ea* di/9ct p>ticle ( ! wave m n ought to give bir?1 to a s]ies ( circul> waves4 ,?is is ! important po9t up to :i* ,i wi% to lead y4 ,e p>ticle ( ! wave m n does act 9 ?is way4 ,tak+ ea* p>ticle z a c5tre1 & surr\nd+ x by a circul> wave ) a radius equal to ! di/ance betwe5 m n & m' n'1 ! coalesc5ce ( all ^! little waves w\ld build up ! l>ge ridge m' n' exactly z we f9d x built up 9 nature4 ,"h1 9 fact1 we resolve ! wave-motion into its elem5ts1 & hav+ succe$$ 9 do+ ?is we %all h no great difficulty 9 apply+ our k to optical ph5om5a4 ,illu/ration3 ,fig4 #ag4 ,n[ let u return to our slit1 &1 = ! sake ( simplicity1 we w fir/ consid] ! case ( mono*romatic light4 ,conceive a s]ies ( waves ( e!r advanc+ f ! fir/ slit t[>ds ! second1 & f9ally fill+ ! second slit4 ,:5 ea* wave passes ?r\gh ! latt] x n only pursues its direct c\rse to ! ret9a1 b div]ges "r & left1 t5d+ to ?r[ into motion ! entire mass ( ! e!r beh9d ! slit4 ,9 fact1 z already expla9$1 e po9t ( ! wave :i* fills ! slit is itself a c5tre ( a new wave sy/em :i* is transmitt$ 9 all directions ?r\gh ! e!r beh9d ! slit4 ,?is is ! celebrat$ pr9ciple ( ,huygh5s3 we h n[ to exam9e h[ ^! second>y waves act ^u ea* o!r4 ,illu/ration3 ,fig4 #ah4 ,let u fir/ reg>d ! c5tral b& ( ! s]ies4 ,let ,,ap 7fig4 #ah7 be ! wid? ( ! ap]ture held be=e ! eye1 grossly exagg]at$ ( c\rse1 & let ! dots across ! ap]ture repres5t e!r p>ticles1 all 9 ! same phase ( vibration4 ,let ,e ,t repres5t a portion ( ! ret9a4 ,f ,o1 9 ! c5tre ( ! slit1 let a p]p5dicul> ,o ,r be imag9$ drawn ^u ! ret9a4 ,! motion communicat$ to ! po9t ,r w !n be ! sum ( all ! motions emanat+ 9 ?is direction f ! e!r p>ticles 9 ! slit4 ,consid]+ ! extreme n>r[ness ( ! ap]ture1 we may1 )\t s5sible error1 reg>d all po9ts ( ! wave ,a ,p z equally di/ant f ,r4 ,no "o ( ! p>tial waves lags s5sibly beh9d ! o!rs3 h5ce1 at ,r1 & 9 its imm$iate neighb\rhood1 we h no s5sible r$uction ( ! light by int]f]5ce4 ,?is undim9i%$ light produces ! brilliant c5tral b& ( ! s]ies4 ,let u n[ consid] ^? waves :i* div]ge lat]ally beh9d ! second slit4 ,9 ?is case ! waves f ! two sides ( ! slit h1 9 ord] to conv]ge ^u ! ret9a1 to pass ov] unequal di/ances4 ,let ,a ,p 7fig4 #ai7 repres5t1 z be=e1 ! wid? ( ! second slit4 ,we h n[ to consid] ! action ( ! v>i\s p>ts ( ! wave ,a ,p ^u a po9t ,r' ( ! ret9a1 n situat$ 9 ! l9e jo9+ ! two slits4 ,illu/ration3 ,fig4 #ai4 ,let u take ! p>ticul> case 9 :i* ! diff]5ce ( pa? f ! two m>g9al po9ts ,a1 ,p1 to ! ret9a is a :ole wave-l5g? ( ! r$ light2 h[ mu/ ?is diff]5ce affect ! f9al illum9ation ( ! ret9a8 ,let u fix our att5tion ^u ! p>ticul> oblique l9e t passes ?r\gh ! c5tre ,o ( ! slit to ! ret9a at ,r'4 ,! diff]5ce ( pa? betwe5 ! waves :i* pass along ?is l9e & ^? f ! two m>g9s is1 9 ! case "h suppos$1 half a wavel5g?4 ,make e ,r' equal to ,p ,r'1 jo9 ,p & e1 & draw ,o d p>allel to ,p e4 ,a e is !n ! l5g? ( a wave ( light1 :ile ,a d is half a wave-l5g?4 ,n[ ! lea/ reflection w make x cle> t n only is !re discordance betwe5 ! c5tral & m>g9al waves1 b t e l9e ( waves su* z x ,r'1 on ! "o side ( ,o ,r'1 f9ds a l9e x' ,r' ^u ! o!r side ( ,o ,r'1 f :i* its pa? diff]s by half an undulation--) :i*1 !re=e1 x is 9 complete discordance4 ,! consequ5ce is1 t ! light on ! "o side ( ! c5tral l9e w completely aboli% ! light on ! o!r side ( t l9e1 absolute d>kness be+ ! result ( _! coalesc5ce4 ,! fir/ d>k int]val ( our s]ies ( b&s is ?us acc\nt$ =4 ,x is produc$ by an obliquity ( direction :i* causes ! pa?s ( ! m>g9al waves to be a :ole wave-l5g? diff]5t f ea* o!r4 ,:5 ! diff]5ce betwe5 ! pa?s ( ! m>g9al waves is half a wave-l5g?1 a p>tial de/ruction ( ! light is effect$4 ,! lum9\s int5sity correspond+ to ?is obliquity is a little less ?an "o-half--accurately #j4d--t ( ! undiffract$ light4 ,if ! pa?s ( ! m>g9al waves be ?ree semi-undulations diff]5t f ea* o!r1 & if ! :ole beam be divid$ into ?ree equal p>ts1 two ( ^! p>ts w1 = ! reasons j giv51 completely neutralize ea* o!r1 ! ?ird only be+ effective4 ,correspond+1 !re=e1 to an obliquity :i* produces a diff]5ce ( ?ree semi-undulations 9 ! m>g9al waves1 we h a lum9\s b&1 b "o ( consid]ably less int5sity ?an ! undiffract$ c5tral b&4 ,) a m>g9al diff]5ce ( pa? ( f\r semi-undulations we h a second ext9ction ( ! entire beam1 because "h ! beam c be divid$ into f\r equal p>ts1 e two ( :i* qu5* ea* o!r4 ,a second space ( absolute d>kness w !re=e correspond to ! obliquity produc+ ?is diff]5ce4 ,9 ?is way we might proce$ fur!r1 ! g5]al result be+ t1 :5ev] ! direction ( wave-motion is su* z to produce a m>g9al diff]5ce ( pa? ( an ev5 numb] ( semi-undulations1 we h complete ext9ction2 :ile1 :5 ! m>g9al diff]5ce is an odd numb] ( semi-undulations1 we h only p>tial ext9ction1 a portion ( ! beam rema9+ z a lum9\s b&4 ,a mom5t's reflection w make x pla9 t ! wid] ! slit ! less w be ! obliquity ( direction ne$$ to produce ! necess>y diff]5ce ( pa?4 ,) a wide slit1 !re=e1 ! b&s1 z obs]v$1 w be clos] toge!r ?an ) a n>r[ "o4 ,x is also pla9 t ! %ort] ! wave1 ! less w be ! obliquity requir$ to produce ! necess>y ret>dation4 ,! maxima & m9ima ( violet light mu/ !re=e fall ne>] to ! c5tre ?an ! maxima & m9ima ( r$ light4 ,! maxima & m9ima ( ! o!r col\rs fall betwe5 ^! extremes4 ,9 ?is simple way ! undulatory !ory completely acc\nts = ! extraord9>y appe>ance above ref]r$ to4 ,:5 a slit & telescope are us$1 in/ead ( ! slit & nak$ eye1 ! effects are magnifi$ & r5d]$ m brilliant4 ,look+1 moreov]1 ?r\gh a prop]ly adju/$ telescope ) a small circul> ap]ture 9 front ( x1 at a di/ant po9t ( light1 ! po9t is se5 encircl$ by a s]ies ( col\r$ b&s4 ,if mono*romatic light be us$1 ^! b&s are simply bright & d>k1 b ) :ite light ! circles display iris-col\rs4 ,if a slit be %ort5$ s z to =m a squ>e ap]ture1 we h two s]ies ( spectra at "r angles to ea* o!r4 ,! effects1 inde$1 are capable ( endless v>iation by v>y+ ! size1 %ape1 & numb] ( ! ap]tures ?r\gh :i* ! po9t ( light is obs]v$4 ,?r\gh two squ>e ap]tures1 ) _! corn]s t\*+ ea* o!r z at ,a1 ,s*w]d obs]v$ ! appe>ance %[n 9 fig4 #bj4 ,add+ two o!rs to !m1 z at ,b1 he obs]v$ ! appe>ance repres5t$ 9 fig4 #ba4 ,! position ( e b& ( light & %ade 9 su* figures has be5 calculat$ f !ory by ,fresnel1 ,fraunh(]1 ,h]s*el1 ,s*w]d1 & o!rs1 & completely v]ifi$ by exp]im5t4 ,y\r eyes c\ld n tell y ) great] c]ta9ty ( ! exi/5ce ( ^! b&s ?an ! !oretic calculation4 ,illu/ration3 ,fig4 #bj4 ,! /reet-lamps at night1 look$ at ?r\gh ! me%es ( a h&k]*ief1 %[ diffraction ph5om5a4 ,! diffraction effects obta9$ 9 look+ ?r\gh a bird's fea!rs are1 z %[n by ,s*w]d1 v brilliant4 ,! iridesc5ce ( c]ta9 ,alp9e cl\ds is also an effect ( diffraction :i* may be imitat$ by ! spores ( ,lycopodium4 ,:5 %ak5 ov] a glass plate ^! spores cause a po9t ( light1 look$ at ?r\gh ! du/$ plate1 to be surr\nd$ by col\r$ circles1 :i* rise to actual spl5d\r :5 ! light becomes int5se4 ,%ak5 9 ! air ! spores produce ! same effect4 ,! diffraction ph5om5a obta9$ dur+ ! artificial precipitation ( cl\ds f ! vap\rs ( v>i\s liquids 9 an int5sely illum9at$ tube are1 z ,i h else:]e %ewn1 exce$+ly f9e4 ,illu/ration3 ,fig4 #ba4 ,"o ( ! mo/ int]e/+ cases ( diffraction by small p>ticles t ev] came be=e me 0 t ( an arti/ ^: vision 0 di/urb$ by vividly col\r$ circles4 ,he 0 9 great dread ( los+ 8 sight2 assign+ z a cause ( 8 increas$ fe> t ! circles 7 becom+ l>g] & ! col\rs m vivid4 ,i ascrib$ ! col\rs to m9ute p>ticles 9 ! hum\rs ( ! eye1 & v5tur$ to enc\rage him by ! assurance t ! increase ( size & vividness on ! "p ( ! circles indicat$ t ! diffract+ p>ticles 7 becom+ small]1 & t !y might f9ally be altoge!r absorb$4 ,! pr$iction 0 v]ifi$4 ,x is ne$less to say "o ^w on ! necessity ( optical k 9 ! case ( ! practical oculi/4 ,)\t break+ gr\nd on ! *romatic ph5om5a pres5t$ by cry/als1 two o!r s\rces ( col\r may be m5tion$ "h4 ,by int]f]5ce 9 ! e>?'s atmosph]e1 ! light ( a />1 z %[n by ,arago1 is self-ext+ui%$1 ! tw9kl+ ( ! /> & ! *anges ( col\r :i* x und]goes be+ due to ?is cause4 ,look+ at su* a /> ?r\gh an op]a-glass1 & %ak+ ! glass s z to cause ! image ( ! /> to pass rapidly ov] ! ret9a1 y produce a r[ ( col\r$ beads1 ! spaces betwe5 :i* correspond to ! p]iods ( ext9ction4 ,f9e scrat*es drawn ^u glass or poli%$ metal reflect ! waves ( light f _! sides2 & "s1 be+ reflect$ f ! opposite sides ( ! same scrat*1 int]f]e ) & qu5* ea* o!r4 ,b ! obliquity ( reflection :i* ext+ui%es ! %ort] waves does n ext+ui% ! long] ones1 h5ce ! ph5om5a ( col\rs4 ,^! are call$ ! col\rs ( /riat$ surfaces4 ,!y are beautifully illu/rat$ by "m-(-pe>l4 ,?is %ell is compos$ ( exce$+ly ?9 lay]s1 :i*1 :5 cut across by ! poli%+ ( ! %ell1 expose _! edges & furni% ! necess>y small & regul> grooves4 ,! mo/ conclusive pro( t ! col\rs are due to ! me*anical /ate ( ! surface is to be f\nd 9 ! fact1 e/abli%$ by ,brew/]1 t by /amp+ ! %ell c>efully ^u black seal+-wax1 we transf] ! grooves1 & produce ^u ! wax ! col\rs ( "m-(-pe>l4 ,,lecture ,,iii4 ,,relation ,,( ,,!ories ,,to ,,exp]i5ce ,,orig9 ,,( ,,! ,,notion ,,( ,,! ,,attraction ,,( ,,gravitation ,,notion ,,( ,,pol>ity1 ,,h[ ,,g5]at$ ,,atomic ,,pol>ity ,,/ructural ,,arrangem5ts ,,due ,,to ,,pol>ity ,,ar*itecture ,,( ,,cry/als ,,consid]$ ,,z ,,an ,,introduction ,,to ,,_! ,,action ,,^u ,,light ,,notion ,,( ,,atomic ,,pol>ity ,,appli$ ,,to ,,cry/all9e ,,/ructure ,,exp]im5tal ,,illu/rations ,,cry/allization ,,( ,,wat] ,,expansion ,,by ,,heat ,,& ,,by ,,cold ,,deportm5t ,,( ,,wat] ,,consid]$ ,,& ,,expla9$ ,,be>+s ,,( ,,cry/allization ,,on ,,optical ,,ph5om5a ,,refraction ,,d\ble ,,refraction ,,pol>ization ,,action ,,( ,,t\rmal9e ,,"* ,,( ,,! ,,beams ,,em]g5t ,,f ,,icel& ,,sp> ,,pol>ization ,,by ,,ord9>y ,,refraction ,,& ,,reflection ,,depol>ization #a4 ,d]ivation ( ,!oretic ,conceptions f ,exp]i5ce4 ,"o ( ! objects ( our la/ lecture1 & t n ! lea/ important1 0 to illu/rate ! mann] 9 :i* sci5tific !ories are =m$4 ,!y1 9 ! fir/ place1 take _! rise 9 ! desire ( ! m9d to p5etrate to ! s\rces ( ph5om5a4 ,f its inf9itesimal beg9n+s1 9 ages long pa/1 ?is desire has gr[n & /r5g!n$ into an imp]i\s dem& ( man's intellectual nature4 ,x long ago prompt$ ,cs> to say t he w\ld ex*ange 8 victories = a glimpse ( ! s\rces ( ! ,nile2 x wr\ght itself into ! atomic !ories ( ,lucretius2 x impell$ ,d>w9 to ^? d>+ speculations :i* ( late ye>s h s agitat$ ! public m9d4 ,b 9 no case1 :ile fram+ !ories1 does ! imag9ation create its mat]ials4 ,x exp&s1 dim9i%es1 m\lds1 & ref9es1 z ! case may be1 mat]ials d]iv$ f ! _w ( fact & obs]vation4 ,?is is m evid5tly ! case 9 a !ory l t ( light1 :]e ! motions ( a subs5sible m$ium1 ! e!r1 are pres5t$ to ! m9d4 ,b no !ory escapes ! condition4 ,newton took c>e n to encumb] ! idea ( gravitation ) unnecess>y physical conceptions2 b we "k t he indulg$ 9 !m1 ?\gh he did n connect !m ) 8 !ory4 ,b ev5 ! !ory1 z x /&s1 did n ent] ! m9d z a revelation dissev]$ f ! _w ( exp]i5ce4 ,! g]m ( ! conception t ! sun & planets are held toge!r by a =ce ( attraction is to be f\nd 9 ! fact t a magnet _h be5 previ\sly se5 to attract iron4 ,! notion ( matt] attract+ matt] came ?us f )\t1 n f )94 ,9 our pres5t lecture ! magnetic =ce mu/ s]ve z ! portal into a new doma92 b 9 ! fir/ place we mu/ ma/] its elem5t>y ph5om5a4 ,! g5]al facts ( magnetism are mo/ simply illu/rat$ by a magnetiz$ b> ( /eel1 commonly call$ a b> magnet4 ,plac+ su* a magnet upright ^u a table1 & br++ a magnetic ne$le ne> its bottom1 "o end ( ! ne$le is obs]v$ to retreat f ! magnet1 :ile ! o!r z promptly approa*es4 ,! ne$le is held quiv]+ !re by "s invisible influ5ce ex]t$ ^u x4 ,rais+ ! ne$le along ! magnet1 b /ill avoid+ contact1 ! rapidity ( its oscillations decreases1 because ! =ce act+ ^u x becomes weak]4 ,at ! c5tre ! oscillations cease4 ,above ! c5tre1 ! end ( ! ne$le :i* _h be5 previ\sly drawn t[>ds ! magnet retreats1 & ! opposite end approa*es4 ,z we asc5d high]1 ! oscillations become m viol5t1 because ! =ce becomes /rong]4 ,at ! upp] end ( ! magnet1 z at ! l[]1 ! =ce rea*es a maximum2 b all ! l[] half ( ! magnet1 f ,e to ,s 7fig4 #bb71 attracts "o end ( ! ne$le1 :ile all ! upp] half1 f ,e to ,n1 attracts ! opposite end4 ,?is d\bl5ess ( ! magnetic =ce is call$ pol>ity1 & ! po9ts ne> ! ends ( ! magnet 9 :i* ! =ces seem conc5trat$ are call$ its poles4 ,illu/ration3 ,fig4 #bb4 ,:at1 !n1 w occur if we break ?is magnet 9 two at ! c5tre ,e8 ,%all we obta9 two magnets1 ea* ) a s+le pole8 ,no2 ea* half is 9 itself a p]fect magnet1 possess+ two poles4 ,?is may be prov$ by break+ some?+ ( less value ?an ! magnet--! /eel ( a lady's /ays1 = example1 h>d5$ & magnetiz$4 ,x acts l ! magnet4 ,:5 brok51 ea* half acts l ! :ole2 & :5 ^! p>ts are aga9 brok51 we h /ill ! p]fect magnet1 possess+1 z 9 ! fir/ in/ance1 two poles4 ,pu% y\r break+ to its utmo/ s5sible limit--y _c /op !re4 ,! bias d]iv$ f obs]vation w infallibly c>ry y beyond ! b\rne ( ! s5ses1 & compel y to reg>d ?is ?+ t we call magnetic pol>ity z resid5t 9 ! ultimate p>ticles ( ! /eel4 ,y come to ! conclusion t ea* molecule ( ! magnet is end[$ ) ?is pol> =ce4 ,l all o!r =ces1 ?is =ce ( magnetism is am5able to me*anical laws2 &1 kn[+ ! direction & magnitude ( ! =ce1 we c pr$ict its action4 ,plac+ a small magnetic ne$le ne> a b> magnet1 x takes a det]m9ate position4 ,t position might be d$uc$ !oretically f ! mutual action ( ! poles4 ,mov+ ! ne$le r\nd ! magnet1 = ea* po9t ( ! surr\nd+ space !re is a def9ite direction ( ! ne$le & no o!r4 ,a ne$le ( iron w answ] z well z ! magnetic ne$le2 = ! ne$le ( iron is magnetiz$ by ! magnet1 & acts exactly l a /eel ne$le indep5d5tly magnetiz$4 ,if we place two or m ne$les ( iron ne> ! magnet1 ! action becomes m complex1 = !n ! ne$les are n only act$ on by ! magnet1 b !y act ^u ea* o!r4 ,& if we pass to small] masses ( iron--to iron fil+s1 = example--we f9d t !y act sub/antially z ! ne$les1 arrang+ !mselves 9 def9ite =ms1 9 ob$i5ce to ! magnetic action4 ,plac+ a %eet ( pap] or glass ov] a b> magnet & %[]+ iron fil+s ^u ! pap]1 ,i notice a t5d5cy ( ! fil+s to arrange !mselves 9 det]m9ate l9es4 ,!y _c freely foll[ ?is t5d5cy1 = !y are hamp]$ by ! friction aga9/ ! pap]4 ,!y are help$ by tapp+ ! pap]2 ea* tap releas+ !m = a mom5t1 & enabl+ !m to foll[ _! t5d5cies4 ,b ?is is an exp]im5t :i* c only be se5 by myself4 ,to enable y all to see x1 ,i take a pair ( small magnets & by a simple optical arrangem5t ?r[ ! magnifi$ images ( ! magnets ^u ! scre54 ,scatt]+ iron fil+s ov] ! glass plate to :i* ! small magnets are atta*$1 & tapp+ ! plate1 y see ! arrangem5t ( ! iron fil+s 9 ^? magnetic curves :i* h be5 s long famili> to sci5tific m5 7fig4 #bc74 ,illu/ration3 ,fig4 #bc4 ,n is ! nozzle ( ! lamp2 ,m a plane mirror1 reflect+ ! beam upw>ds4 ,at ,p ! magnets & iron fil+s are plac$2 ,l is a l5s :i* =ms an image ( ! magnets & fil+s2 & ,r is a totally reflect+ prism1 :i* ca/s ! image ,g ^u ! scre54 7,by a v +5i\s device1 ,pr(essor ,may]1 ( ,hobok51 has succe$$ 9 fix+ & photograph+ ! magnetic curves4 ,i am indebt$ to 8 k9dness = ! annex$ beautiful illu/ration1 fig4 #bd47 ,! aspect ( ^! curves s fasc9at$ ,f>aday t ! great] portion ( 8 intellectual life 0 devot$ to pond]+ ov] !m4 ,he inve/$ ! space ?r\gh :i* !y run ) a k9d ( mat]iality2 & ! probability is t ! progress ( sci5ce1 by connect+ ! ph5om5a ( magnetism ) ! lum9if]\s e!r1 w prove ^! 'l9es ( =ce1' z ,f>aday lov$ to call !m1 to repres5t a condition ( ?is my/]i\s sub/ratum ( all radiant action4 ,x is n1 h[ev]1 ! magnetic curves1 z su*1 b _! relation%ip to !oretic conceptions1 t we h n[ to consid]4 ,by ! action ( ! b> magnet ^u ! ne$le we obta9 ! notion ( a pol> =ce2 by ! break+ ( ! /rip ( magnetiz$ /eel we atta9 ! notion t pol>ity c atta* itself to ! ultimate p>ticles ( matt]4 ,! exp]im5t ) ! iron fil+s introduces a new idea into ! m9d2 ! idea1 namely1 ( /ructural arrangem5t4 ,e pair ( fil+s possesses f\r poles1 two ( :i* are attractive & two repulsive4 ,! attractive poles approa*1 ! repulsive poles retreat2 ! consequ5ce be+ a c]ta9 def9ite arrangem5t ( ! p>ticles ) ref]5ce to ea* o!r4 #b4 ,!ory ( ,cry/allization4 ,n[ ?is idea ( /ructure1 z produc$ by pol> =ce1 op5s a way = ! intellect into an entirely new region1 & ! reason y are ask$ to accompany me into ?is region is1 t our next inquiry relates to ! action ( cry/als ^u light4 ,prior to speak+ ( ?is action1 ,i wi% y to realise intellectually ! process ( cry/all9e ar*itecture4 ,look !n into a granite qu>ry1 & sp5d a few m9utes 9 exam9+ ! rock4 ,x is n ( p]fectly uni=m texture4 ,x is r an agglom]ation ( pieces1 :i*1 on exam9ation1 pres5t curi\sly def9$ =ms4 ,y h !re :at m9]alogi/s call qu>tz1 y h felsp>1 y h mica4 ,9 a m9]alogical cab9et1 :]e ^! sub/ances are pres]v$ sep>ately1 y w obta9 "s notion ( _! =ms4 ,y w see !re1 also1 specim5s ( b]yl1 topaz1 em]ald1 t\rmal9e1 heavy sp>1 fluor-sp>1 ,icel& sp>--possibly a full-=m$ diamond1 z x quitt$ ! h& ( ,nature1 n yet hav+ got into ! h&s ( ! lapid>y4 ,illu/ration3 ,fig4 #bd4 ,^! cry/als1 y w obs]ve1 are put toge!r accord+ to law2 !y are n *ance productions2 &1 if y c>e to exam9e !m m m9utely1 y w f9d _! ar*itecture capable ( be+ to "s ext5t reveal$4 ,!y (t5 split 9 c]ta9 directions be=e a knife-edge1 expos+ smoo? & %9+ surfaces1 :i* are call$ planes ( cleavage2 & by foll[+ ^! planes y sometimes rea* an int]nal =m1 disguis$ b5ea? ! ext]nal =m ( ! cry/al4 ,pond] ^! beautiful edifices ( a hidd5 build]4 ,y _c help ask+ y\rself h[ !y 7 built2 & famili> z y n[ are ) ! notion ( a pol> =ce1 & ! ability ( t =ce to produce /ructural arrangem5t1 y\r inevitable answ] w be1 t ^? cry/als are built by ! play ( pol> =ces ) :i* _! molecules are end[$4 ,9 virtue ( ^! =ces1 molecule lays itself to molecule 9 a p]fectly def9ite way1 ! f9al visible =m ( ! cry/al dep5d+ ^u ?is play ( its ultimate p>ticles4 ,ev]y:]e 9 ,nature we obs]ve ?is t5d5cy to run into def9ite =ms1 & no?+ is easi] ?an to give scope to ?is t5d5cy by artificial arrangem5ts4 ,dissolve nitre 9 wat]1 & all[ ! wat] sl[ly to evaporate2 ! nitre rema9s & ! solution soon becomes s conc5trat$ t ! liquid condition c no long] be pres]v$4 ,! nitre-molecules approa* ea* o!r1 & come at l5g? )9 ! range ( _! pol> =ces4 ,!y arrange !mselves 9 ob$i5ce to ^! =ces1 a m9ute cry/al ( nitre be+ at fir/ produc$4 ,on ?is cry/al ! molecules cont9ue to deposit !mselves f ! surr\nd+ liquid4 ,! cry/al gr[s1 & f9ally we h l>ge prisms ( nitre1 ea* ( a p]fectly def9ite %ape4 ,alum cry/allizes ) ! utmo/ ease 9 ?is fa%ion4 ,! resultant cry/al is1 h[ev]1 diff]5t 9 %ape f t ( nitre1 because ! poles ( ! molecules are diff]5tly dispos$4 ,:5 !y are nurs$ ) prop] c>e1 cry/als ( ^! sub/ances may be caus$ to gr[ to a great size4 ,! condition ( p]fect cry/allization is1 t ! cry/alliz+ =ce %all act ) delib]ation4 ,!re %\ld be no hurry 9 its op]ations2 b e molecule ought to be p]mitt$1 )\t di/urbance f its neighb\rs1 to ex]cise its own rights4 ,if ! cry/allization be too sudd51 ! regul>ity disappe>s4 ,wat] may be saturat$ ) sulphate ( soda1 dissolv$ :5 ! wat] is hot1 & aft]w>ds p]mitt$ to cool4 ,:5 cold ! solution is sup]saturat$2 t is to say1 m solid matt] is conta9$ 9 x ?an corresponds to its temp]ature4 ,/ill ! molecules %[ no sign ( build+ !mselves toge!r4 ,?is is a v rem>kable1 ?\gh a v common fact4 ,! molecules 9 ! c5tre ( ! liquid are s hamp]$ by ! action ( _! neighb\rs t fre$om to foll[ _! own t5d5cies is d5i$ to !m4 ,fix y\r m9d's eye ^u a molecule )9 ! mass4 ,x wi%es to unite ) its neighb\r to ! "r1 b x wi%es equally to unite ) its neighb\r to ! left2 ! "o t5d5cy neutralizes ! o!r & x unites ) nei!r4 ,b1 if a cry/al ( sulphate ( soda be dropp$ into ! solution1 ! molecul> indecision ceases4 ,on ! cry/al ! adjac5t molecules w imm$iately precipitate !mselves2 on ^! aga9 o!rs w be precipitat$1 & ?is act ( precipitation w cont9ue f ! top ( ! flask to ! bottom1 until ! solution has1 z f> z possible1 assum$ ! solid =m4 ,! cry/als "h produc$ are small1 & confus$ly arrang$4 ,! process has be5 too ha/y to admit ( ! pure & ord]ly action ( ! cry/alliz+ =ce4 ,x typifies ! /ate ( a nation 9 :i* natural & heal?y *ange is resi/$1 until society becomes1 z x 71 sup]saturat$ ) ! desire = *ange1 ! *ange be+ !n effect$ ?r\gh confusion & revolution4 ,let me illu/rate ! action ( ! cry/alliz+ =ce by two examples ( x3 ,nitre might be employ$1 b ano!r well-kn[n sub/ance enables me to make ! exp]im5t 9 a bett] =m4 ,! sub/ance is common sal-ammoniac1 or *loride ( ammonium1 dissolv$ 9 wat]4 ,cleans+ p]fectly a glass plate1 ! solution ( ! *loride is p\r$ ov] ! glass1 to :i* :5 ! plate is set on edge1 a ?9 film ( ! liquid adh]es4 ,w>m+ ! glass slightly1 evaporation is promot$1 b by evaporation ! wat] only is remov$4 ,! plate is !n plac$ 9 a sol> microscope1 & an image ( ! film is ?r[n ^u a :ite scre54 ,! w>m? ( ! illum9at+ beam adds itself to t already imp>t$ to ! glass plate1 s t aft] a mom5t or two ! dissolv$ salt c no long] exi/ 9 ! liquid condition4 ,molecule !n closes ) molecule1 & y h a mo/ impressive display ( cry/alliz+ en]gy ov]spread+ ! :ole scre54 ,y may produce some?+ simil> if y brea! ^u ! fro/ f]ns :i* ov]spread y\r w9d[-panes 9 w9t]1 & !n obs]ve ?r\gh a pocket l5s ! subsequ5t recongelation ( ! film4 ,9 ?is case ! cry/alliz+ =ce is hamp]$ by ! adhesion ( ! film to ! glass2 nev]!less1 ! play ( p[] is /rik+ly beautiful4 ,sometimes ! cry/als />t f ! edge ( ! film & run ?r\gh x f t edge2 =1 ! cry/allization be+ once />t$1 ! molecules ?r[ !mselves by pref]5ce on ! cry/als already =m$4 ,sometimes ! cry/als />t f def9ite nuclei 9 ! c5tre ( ! film1 e small cry/all9e p>ticle :i* re/s 9 ! film furni%+ a />t+-po9t4 ,?r\gh\t ! process y notice "o feature :i* is p]fectly unalt]able1 & t is1 angul> magnitude4 ,! spicul bran* f ! trunk1 & f ^! bran*es o!rs %oot2 b ! angles enclos$ by ! spicul are unalt]able4 ,9 l mann] y may f9d alum-cry/als1 qu>tz-cry/als1 & all o!r cry/als1 di/ort$ 9 %ape4 ,!y are ?us f> at ! m]cy ( ! accid5ts ( cry/allization2 b 9 "o p>ticul> !y ass]t _! sup]iority ov] all su* accid5ts--angul> magnitude is always rigidly pres]v$4 ,my second example ( ! action ( cry/alliz+ =ce is ?is3 ,by s5d+ a voltaic curr5t ?r\gh a liquid1 y "k t we decompose ! liquid1 & if x conta9s a metal1 we lib]ate ?is metal by electrolysis4 ,?is small cell conta9s a solution ( acetate ( lead1 :i* is *os5 = our pres5t purpose1 because lead l5ds itself freely to ?is cry/alliz+ p[]4 ,into ! cell are dipp$ two v ?9 plat9um wires1 & ^! are connect$ by o!r wires ) a small voltaic batt]y4 ,on s5d+ ! voltaic curr5t ?r\gh ! solution1 ! lead w be sl[ly sev]$ f ! atoms ) :i* x is n[ comb9$2 x w be lib]at$ ^u "o ( ! wires1 & at ! mom5t ( its lib]ation x w obey ! pol> =ces ( its atoms1 & produce cry/all9e =ms ( exquisite beauty4 ,!y are n[ be=e y1 spr\t+ l f]ns f ! wire1 appe>+ inde$ l vegetable gr[?s r5d]$ s rapid z to be pla9ly visible to ! nak$ eye4 ,on rev]s+ ! curr5t1 ^! wond]ful lead-fronds w dissolve1 :ile f ! o!r wire filam5ts ( lead d>t ?r\gh ! liquid4 ,9 a mom5t or two ! gr[? ( ! lead-trees recomm5ces1 b !y n[ cov] ! o!r wire4 ,9 ! process ( cry/allization1 ,nature fir/ reveals h]self z a build]4 ,:]e d h] op]ations /op8 ,does %e cont9ue by ! play ( ! same =ces to =m ! vegetable1 & aft]w>ds ! animal8 ,:atev] ! answ] to ^! que/ions may be1 tru/ me t ! notions ( ! com+ g5]ations reg>d+ ?is my/]i\s ?+1 :i* "s h call$ 'brute matt]1' w be v diff]5t f ^? ( ! g5]ations pa/4 ,!re is h>dly a m beautiful & in/ructive example ( ?is play ( molecul> =ce ?an t furni%$ by wat]4 ,y h se5 ! exquisite f]n-l =ms produc$ by ! cry/allization ( a film ( wat] on a cold w9d[-pane4#ae ,y h also probably notic$ ! beautiful rosettes ti$ toge!r by ! cry/alliz+ =ce dur+ ! desc5t ( a sn[-%[] on a v calm day4 ,! slopes & summits ( ! ,alps are load$ 9 w9t] ) ^! blossoms ( ! fro/4 ,!y v>y inf9itely 9 detail ( beauty1 b ! same angul> magnitude is pres]v$ ?r\gh\t3 an inflexible p[] b9d+ spe>s & spicul to ! angle ( #fj degrees4 ,! common ice ( our lakes is also rul$ 9 its =mation by ! same angle4 ,y may sometimes see 9 freez+ wat] small cry/als ( /ell> %apes1 ea* /> consi/+ ( six rays1 ) ?is angle ( #fj betwe5 e two ( !m4 ,?is /ructure may be reveal$ 9 ord9>y ice4 ,9 a sunbeam1 or1 fail+ t1 9 our electric beam1 we h an in/rum5t delicate en\gh to unlock ! froz5 molecules1 )\t di/urb+ ! ord] ( _! ar*itecture4 ,cutt+ f cle>1 s\nd1 regul>ly froz5 ice1 a slab p>allel to ! planes ( freez+1 & s5d+ a sunbeam ?r\gh su* a slab1 x liquefies int]nally at special po9ts1 r\nd ea* po9t a six-petall$ liquid fl[] ( exquisite beauty be+ =m$4 ,cr[ds ( su* fl[]s are ?us produc$4 ,f an ice-h\se we sometimes take blocks ( ice pres5t+ mi/y spaces 9 ! o!rwise cont9u\s mass2 & :5 we inquire into ! cause ( ?is mi/9ess1 we f9d x to be due to myriads ( small six-petall$ fl[]s1 into :i* ! ice has be5 resolv$ by ! m]e heat ( conduction4 ,a mom5t's fur!r devotion to ! cry/allization ( wat] w be well repaid2 = ! sum ( qualities :i* r5d]s ?is sub/ance fitt$ to play its "p 9 ,nature may well excite wond] & /imulate ?\ght4 ,l almo/ all o!r sub/ances1 wat] is exp&$ by heat & contract$ by cold4 ,let ?is expansion & contraction be fir/ illu/rat$3-- ,a small flask is fill$ ) col\r$ wat]1 & /opp$ ) a cork4 ,?r\gh ! cork passes a glass tube wat]-tight1 ! liquid /&+ at a c]ta9 height 9 ! tube4 ,! flask & its tube resemble ! bulb & /em ( a !rmomet]4 ,apply+ ! heat ( a _s-lamp1 ! wat] rises 9 ! tube1 & f9ally trickles ov] ! top4 ,expansion by heat is ?us illu/rat$4 ,remov+ ! lamp & pil+ a freez+ mixture r\nd ! flask1 ! liquid column falls1 ?us %[+ ! contraction ( ! wat] by ! cold4 ,b let ! freez+ mixture cont9ue to act3 ! fall+ ( ! column cont9ues to a c]ta9 po9t2 x !n ceases4 ,! top ( ! column rema9s /ation>y = "s seconds1 & aft]w>ds beg9s to rise4 ,! contraction has ceas$1 & expansion by cold sets 94 ,let ! expansion cont9ue till ! liquid trickles a second "t ov] ! top ( ! tube4 ,! freez+ mixture has "h produc$ to all appe>ance ! same effect z ! flame4 ,9 ! case ( wat]1 contraction by cold ceases1 & expansion by cold sets 9 at ! def9ite temp]ature ( #ci ,fahr4 ,cry/allization has virtually "h comm5c$1 ! molecules prep>+ !mselves = ! subsequ5t act ( solidification1 :i* occurs at #cb1 & 9 :i* ! expansion sudd5ly culm9ates4 ,9 virtue ( ?is expansion1 ice1 z y "k1 is light] ?an wat] 9 ! proportion ( #h to #i4af ,a molecul> problem ( great int]e/ is "h involv$1 & ,i wi% n[ to place be=e y1 = ! satisfaction ( y\r m9ds1 a possible solution ( ! problem3-- ,consid]1 !n1 ! ideal case ( a numb] ( magnets depriv$ ( weight1 b reta9+ _! pol> =ces4 ,if we _h a mobile liquid ( ! specific gravity ( /eel1 we might1 by mak+ ! magnets float 9 x1 realize ?is /ate ( ?+s1 = 9 su* a liquid ! magnets w\ld nei!r s9k nor swim4 ,n[1 ! pr9ciple ( gravitation enunciat$ by ,newton is t e p>ticle ( matt]1 ( e k9d1 attracts e o!r p>ticle ) a =ce v>y+ inv]sely z ! squ>e ( ! di/ance4 ,9 virtue ( ! attraction ( gravity1 !n1 ! magnets1 if p]fectly free to move1 w\ld sl[ly approa* ea* o!r4 ,b besides ! unpol> =ce ( gravity1 :i* belongs to matt] 9 g5]al1 ! magnets are end[$ ) ! pol> =ce ( magnetism4 ,= a "t1 h[ev]1 ! pol> =ces d n come s5sibly into play4 ,9 ?is condition ! magnets resemble our wat]-molecules at ! temp]ature say ( #ej4 ,b ! magnets come at l5g? suffici5tly ne> ea* o!r to enable _! poles to int]act4 ,f ?is po9t ! action ceases to be solely a g5]al attraction ( ! masses4 ,attractions ( special po9ts ( ! masses & repulsions ( o!r po9ts n[ come into play2 & x is easy to see t ! re>rangem5t ( ! magnets consequ5t ^u ! introduction ( ^! new =ces may be su* z to require a great] am\nt ( room4 ,?is1 ,i take x1 is ! case ) our wat]-molecules4 ,l our ideal magnets1 !y approa* ea* o!r = a "t z :oles4 ,previ\s to rea*+ ! temp]ature #ci ,fahr41 ! pol> =ces _h d\btless begun to act1 b x is at ?is temp]ature t _! claim to m room exactly balances ! contraction due to cold4 ,at l[] temp]atures1 z reg>ds *ange ( volume1 ! pol> =ces pr$om9ate4 ,b !y c>ry on a /ruggle ) ! =ce ( contraction until ! freez+ temp]ature is atta9$4 ,! molecules !n close up to =m solid cry/als1 a consid]able augm5tation ( volume be+ ! imm$iate consequ5ce4 #c4 ,ord9>y ,refraction ( ,light expla9$ by ! ,wave ,!ory4 ,we h n[ to exhibit ! be>+s ( ?is act ( cry/allization ^u optical ph5om5a4 ,accord+ to ! undulatory !ory1 ! velocity ( light 9 wat] & glass is less ?an 9 air4 ,consid]1 !n1 a small portion ( a wave issu+ f a po9t ( light s di/ant t ! m9ute area may be reg>d$ z practically plane4 ,mov+ v]tically d[nw>ds1 & imp++ on a horizontal surface ( glass or wat]1 ! wave w\ld g ?r\gh ! m$ium )\t *ange ( direction4 ,z1 h[ev]1 ! velocity 9 glass or wat] is less ?an ! velocity 9 air1 ! wave w\ld be ret>d$ on pass+ into ! d5s] m$ium4 ,illu/ration3 ,fig4 #be4 ,b suppose ! wave1 be=e rea*+ ! glass1 to be oblique to ! surface2 t end ( ! wave :i* fir/ rea*es ! m$ium w be ! fir/ ret>d$ by x1 ! o!r portions z !y ent] ! glass be+ ret>d$ 9 succession4 ,x is easy to see t ?is ret>dation ( ! "o end ( ! wave mu/ cause x to sw+ r\nd & *ange its front1 s t :5 ! wave has fully ent]$ ! glass its c\rse is oblique to its orig9al direction4 ,accord+ to ! undulatory !ory1 light is ?us refract$4 ,) ^! consid]ations to guide u1 let u foll[ ! c\rse ( a beam ( mono*romatic light ?r\gh our glass prism4 ,! velocity 9 air is to its velocity 9 glass z #c3 #b4 ,let ,a ,b ,c 7fig4 #be7 be ! section ( our prism1 & a b ! section ( a plane wave approa*+ x 9 ! direction ( ! arr[4 ,:5 x rea*es c d1 "o end ( ! wave is on ! po9t ( ent]+ ! glass4 ,foll[+ x /ill fur!r1 x is obvi\s t :ile ! portion ( ! wave /ill 9 ! air passes ov] ! di/ance c e1 ! wave 9 ! glass w h pass$ ov] only two-?irds ( ?is di/ance1 or d f4 ,! l9e e f n[ m>ks ! front ( ! wave4 ,imm]s$ :olly 9 ! glass x pursues its way to g h1 :]e ! end g ( ! wave is on ! po9t ( escap+ into ! air4 ,dur+ ! "t requir$ by ! end h ( ! wave to pass ov] ! di/ance h k to ! surface ( ! prism1 ! o!r end g1 mov+ m rapidly1 w h rea*$ ! po9t i4 ,! wave1 !re=e1 has aga9 *ang$ its front1 s t aft] its em]g5ce f ! prism x w pass on to l m1 & subsequ5tly 9 ! direction ( ! arr[4 ,! refraction ( ! beam is ?us completely acc\nt$ =2 & x is1 moreov]1 bas$ ^u actual exp]im5t1 :i* proves t ! ratio ( ! velocity ( light 9 glass to its velocity 9 air is t "h m5tion$4 ,x is pla9 t if ! *ange ( velocity on ent]+ ! glass 7 great]1 ! refraction also w\ld be great]4 #d4 ,d\ble ,refraction ( ,light expla9$ by ! ,wave ,!ory4 ,! two elem5ts ( rapidity ( propagation1 bo? ( s\nd & light1 9 any sub/ance :atev]1 are ela/icity & d5sity1 ! spe$ increas+ ) ! =m] & dim9i%+ ) ! latt]4 ,! enorm\s velocity ( light 9 /ell> space is atta9able because ! e!r is at ! same "t ( inf9itesimal d5sity & ( enorm\s ela/icity4 ,n[ ! e!r surr\nds ! atoms ( all bodies1 b x is n indep5d5t ( !m4 ,9 pond]able matt] x acts z if its d5sity 7 increas$ )\t a proportionate increase ( ela/icity2 & ?is acc\nts = ! dim9i%$ velocity ( light 9 refract+ bodies4 ,we "h rea* a po9t ( c>d9al importance4 ,9 virtue ( ! cry/all9e ar*itecture t we h be5 consid]+1 ! e!r 9 _m cry/als possesses diff]5t d5sities1 & diff]5t ela/icities1 9 diff]5t directions2 ! consequ5ce is1 t 9 su* cry/als light is transmitt$ ) diff]5t velocities4 ,& z refraction dep5ds :olly ^u ! *ange ( velocity on ent]+ ! refract+ m$ium1 be+ greate/ :]e ! *ange ( velocity is greate/1 we h 9 _m cry/als two diff]5t refractions4 ,by su* cry/als a beam ( light is divid$ into two4 ,?is effect is call$ d\ble refraction4 ,9 ord9>y wat]1 = example1 !re is no?+ 9 ! gr\p+ ( ! molecules to int]f]e ) ! p]fect homog5eity ( ! e!r2 b1 :5 wat] cry/allizes to ice1 ! case is diff]5t4 ,9 a plate ( ice ! ela/icity ( ! e!r 9 a direction p]p5dicul> to ! surface ( freez+ is diff]5t f :at x is p>allel to ! surface ( freez+2 ice is1 !re=e1 a d\ble refract+ sub/ance4 ,d\ble refraction is display$ 9 a p>ticul>ly impressive mann] by ,icel& sp>1 :i* is cry/alliz$ c>bonate ( lime4 ,! diff]5ce ( e!real d5sity 9 two directions 9 ?is cry/al is v great1 ! sep>ation ( ! beam into ! two halves be+1 !re=e1 p>ticul>ly /rik+4 ,i am unwill+ to quit ?is subject be=e rais+ x to unmi/akable cle>ness 9 y\r m9ds4 ,! vibrations ( light be+ transv]sal1 ! ela/icity conc]n$ 9 ! propagation ( any ray is ! ela/icity at "r angles to ! direction ( propagation4 ,9 ,icel& sp> !re is "o direction r\nd :i* ! cry/all9e molecules are symmetrically built4 ,?is direction is call$ ! axis ( ! cry/al4 ,9 consequ5ce ( ?is symmetry ! ela/icity is ! same 9 all directions p]p5dicul> to ! axis1 & h5ce a ray transmitt$ along ! axis suff]s no d\ble refraction4 ,b ! ela/icity along ! axis is great] ?an ! ela/icity at "r angles to x4 ,consid]1 !n1 a sy/em ( waves cross+ ! cry/al 9 a direction p]p5dicul> to ! axis4 ,two directions ( vibration are op5 to su* waves3 ! e!r p>ticles c vibrate p>allel to ! axis or p]p5dicul> to x4 ,!y d bo?1 & h5ce imm$iately divide !mselves into two sy/ems propagat$ ) diff]5t velocities4 ,d\ble refraction is ! necess>y consequ5ce4 ,illu/ration3 ,fig4 #bf4 ,by means ( ,icel& sp> cut 9 ! prop] direction1 d\ble refraction is capable ( easy illu/ration4 ,caus+ ! beam :i* builds ! image ( our c>bon-po9ts to pass ?r\gh ! sp>1 ! s+le image is in/antly divid$ into two4 ,project+ 7by ! l5s ,e1 fig4 #bf7 an image ( ! ap]ture 7,l7 ?r\gh :i* ! light issues f ! electric lamp1 & introduc+ ! sp> 7,p71 two lum9\s disks 7,e ,o7 appe> imm$iately ^u ! scre5 in/ead ( "o4 ,! two beams into :i* ! sp> divides ! s+le incid5t-beam h be5 subject$ to ! close/ exam9ation4 ,!y d n behave alike4 ,"o ( !m obeys ! ord9>y law ( refraction discov]$ by ,snell1 & is1 !re=e1 call$ ! ord9>y ray3 its index ( refraction is #a4fed4 ,! o!r does n obey ?is law4 ,its index ( refraction1 = example1 is n con/ant1 b v>ies f a maximum ( #a4fed to a m9imum ( #a4dhc2 nor 9 ?is case d ! incid5t & refract$ rays always lie 9 ! same plane4 ,x is1 !re=e1 call$ ! extraord9>y ray4 ,9 calc-sp>1 z j /at$1 ! ord9>y ray is ! mo/ refract$4 ,"o consequ5ce ( ?is m]its a pass+ notice4 ,p\r wat] & bisulphide ( c>bon into two cups ( ! same dep?2 ! cup t conta9s ! m /rongly refract+ liquid w appe> %all[] ?an ! o!r4 ,place a piece ( ,icel& sp> ov] a dot ( ink2 two dots are se51 ! "o appe>+ ne>] ?an ! o!r to ! eye4 ,! ne>e/ dot belongs to ! mo/ /rongly refract$ ray1 exactly z ! ne>e/ cup-bottom belongs to ! mo/ highly refract+ liquid4 ,:5 y turn ! sp> r\nd1 ! extraord9>y image ( ! dot rotates r\nd ! ord9>y "o1 :i* rema9s fix$4 ,?is is also ! deportm5t ( our two disks ^u ! scre54 #e4 ,pol>ization ( ,light expla9$ by ! ,wave ,!ory4 ,! d\ble refraction ( ,icel& sp> 0 fir/ treat$ 9 a "w publi%$ by ,erasmus ,b>?ol9us1 9 #affi4 ,huygh5s s\ght to acc\nt = ?is ph5om5on on ! pr9ciples ( ! wave !ory1 & he succe$$ 9 do+ s4 ,he1 moreov]1 made highly important obs]vations on ! di/9ctive "* ( ! two beams transmitt$ by ! sp>1 admitt+1 ) resign$ c&\r1 t he _h n solv$ ! difficulty1 & leav+ ! solution to future times4 ,newton1 reflect+ on ! obs]vations ( ,huygh5s1 came to ! conclusion t ea* ( ! beams transmitt$ by ,icel& sp> _h two sides2 & f ! analogy ( ?is two-sid$ness ) ! two-end$ness ( a magnet1 :]e9 consi/s its pol>ity1 ! two beams came subsequ5tly to be describ$ z pol>iz$4 ,we may beg9 ! /udy ( ! pol>ization ( light1 ) ease & pr(it1 by means ( a cry/al ( t\rmal9e4 ,b we mu/ />t ) a cle> conception ( an ord9>y beam ( light4 ,x has be5 already expla9$ t ! vibrations ( ! individual e!r-p>ticles are execut$ across ! l9e ( propagation4 ,9 ! case ( ord9>y light we are to figure ! e!r-p>ticles z vibrat+ 9 all directions1 or azimu?s1 z x is sometimes express$1 across ?is l9e4 ,n[1 9 ! case ( a plate ( t\rmal9e cut p>allel to ! axis ( ! cry/al1 a beam ( light incid5t ^u ! plate is divid$ into two1 ! "o vibrat+ p>allel to ! axis ( ! cry/al1 ! o!r at "r angles to ! axis4 ,! gr\p+ ( ! molecules1 & ( ! e!r associat$ ) ! molecules1 r$uces all ! vibrations incid5t ^u ! cry/al to ^! two directions4 ,"o ( ^! beams1 namely1 t ^: vibrations are p]p5dicul> to ! axis1 is qu5*$ ) exce$+ rapidity by ! t\rmal9e4 ,to su* vibrations _m specim5s ( ! cry/al are highly opaque2 s t1 aft] hav+ pass$ ?r\gh a v small ?ickness ( ! t\rmal9e1 ! light em]ges ) all its vibrations r$uc$ to a s+le plane4 ,9 ?is condition x is :at we call plane pol>iz$ light4 ,illu/ration3 ,fig4 #bg4 ,illu/ration3 ,fig4 #bh4 ,a mom5t's reflection w %[ t1 if :at is "h /at$ be correct1 on plac+ a second plate ( t\rmal9e ) its axis p>allel to ! fir/1 ! light w pass ?r\gh bo?2 b t1 if ! axes be cross$1 ! light t passes ?r\gh ! "o plate w be qu5*$ by ! o!r1 a total int]ception ( ! light be+ ! consequ5ce4 ,let u te/ ?is conclusion by exp]im5t4 ,! image ( a plate ( t\rmal9e 7t t1 fig4 #bg7 is n[ be=e y4 ,i place p>allel to x ano!r plate 7t' t'73 ! gre5 ( ! cry/al is a little deep5$1 no?+ m2 ?is agrees ) our conclusion4 ,by means ( an endless screw1 ,i n[ turn "o ( ! cry/als gradually r\nd1 & y obs]ve t z long z ! two plates are oblique to ea* o!r1 a c]ta9 portion ( light gets ?r\gh2 b t :5 !y are at "r angles to ea* o!r1 ! space common to bo? is a space ( d>kness 7fig4 #bh74 ,our conclusion1 arriv$ at prior to exp]im5t1 is ?us v]ifi$4 ,let u n[ return to a s+le plate2 & "h let me say t x is on ! gre5 light transmitt$ by ! t\rmal9e t y are to fix y\r att5tion4 ,we h to illu/rate ! two-sid$ness ( t gre5 light1 9 contra/ to ! all-sid$ness ( ord9>y light4 ,! :ite light surr\nd+ ! gre5 image1 be+ ord9>y light1 is reflect$ by a plane glass mirror 9 all directions2 ! gre5 light1 on ! contr>y1 is n s reflect$4 ,! image ( ! t\rmal9e is n[ horizontal2 reflect$ upw>ds1 x is /ill gre52 reflect$ sideways1 ! image is r$uc$ to blackness1 because ( ! incompet5cy ( ! gre5 light to be reflect$ 9 ?is direction4 ,mak+ ! plate ( t\rmal9e v]tical1 & reflect+ x z be=e1 x is ! light ( ! upp] image t is qu5*$2 ! side image n[ %[s ! gre54 ,?is is a result ( ! greate/ significance4 ,if ! vibrations ( light 7 longitud9al1 l ^? ( s\nd1 y c\ld h no action ( ?is k9d2 & ?is v action compels u to assume t ! vibrations are transv]sal4 ,picture ! ?+ cle>ly4 ,9 ! "o case ! mirror receives1 z x 71 ! impact ( ! edges ( ! waves1 ! gre5 light be+ !n qu5*$4 ,9 ! o!r case ! sides ( ! waves /rike ! mirror1 & ! gre5 light is reflect$4 ,to r5d] ! ext9ction complete1 ! light mu/ be receiv$ ^u ! mirror at a special angle4 ,:at ?is angle is we %all le>n pres5tly4 ,! quality ( two-sid$ness conf]r$ ^u light by bi-refract+ cry/als may also be conf]r$ ^u x by ord9>y reflection4 ,malus made ?is discov]y 9 #ahjh1 :ile look+ ?r\gh ,icel& sp> at ! light ( ! sun reflect$ f ! w9d[s ( ! ,luxemb\rg palace 9 ,p>is4 ,i receive ^u a plate ( w9d[-glass ! beam f our lamp2 a great portion ( ! light reflect$ f ! glass is pol>iz$4 ,! vibrations ( ?is reflect$ beam are execut$1 = ! mo/ "p1 p>allel to ! surface ( ! glass1 & :5 ! glass is held s t ! beam %all make an angle ( #eh ) ! p]p5dicul> to ! glass1 ! :ole ( ! reflect$ beam is pol>iz$4 ,x 0 at ?is angle t ! image ( ! t\rmal9e 0 completely qu5*$ 9 our =m] exp]im5t4 ,x is call$ ! pol>iz+ angle4 ,sir ,david ,brew/] prov$ ! angle ( pol>ization ( a m$ium to be t p>ticul> angle at :i* ! refract$ & reflect$ rays inclose a "r angle4#ag ,! pol>iz+ angle augm5ts ) ! index ( refraction4 ,= wat] x is #eb2 = glass1 z already /at$1 #eh2 :ile = diamond x is #fh4 ,& n[ let u try to make sub/antially ! exp]im5t ( ,malus4 ,! beam f ! lamp is receiv$ at ! prop] angle ^u a plate ( glass & reflect$ ?r\gh ! sp>4 ,in/ead ( two images1 y see b "o4 ,s t ! light1 :5 pol>iz$1 z x n[ is by reflection1 c only get ?r\gh ! sp> 9 "o direction1 & consequ5tly c produce b "o image4 ,:y is ?is8 ,9 ! ,icel& sp> z 9 ! t\rmal9e1 all ! vibrations ( ! ord9>y light are r$uc$ to two planes at "r angles to ea* o!r2 b1 unlike ! t\rmal9e1 bo? beams are transmitt$ ) equal facility by ! sp>4 ,! two beams1 9 %ort1 em]g5t f ! sp>1 are pol>iz$1 _! directions ( vibration be+ at "r angles to ea* o!r4 ,:51 !re=e1 ! light is fir/ pol>iz$ by reflection1 ! direction ( vibration 9 ! sp> :i* co9cides ) ! direction ( vibration ( ! pol>iz$ beam1 transmits ! beam1 & t direction only4 ,only "o image1 !re=e1 is possible "u ! conditions4 ,y w n[ obs]ve t su* logic z connects our exp]im5ts is simply a transcript ( ! logic ( ,nature4 ,on ! scre5 be=e y are two disks ( light produc$ by ! d\ble refraction ( ,icel& sp>4 ,!y are1 z y "k1 two images ( ! ap]ture ?r\gh :i* ! light issues f ! cam]a4 ,plac+ ! t\rmal9e 9 front ( ! ap]ture1 two images ( ! cry/al w also be obta9$2 b n[ let u reason out be=eh& :at is to be expect$ f ?is exp]im5t4 ,! light em]g5t f ! t\rmal9e is pol>iz$4 ,plac+ ! cry/al ) its axis horizontal1 ! vibrations ( its transmitt$ light w be horizontal4 ,n[ ! sp>1 z already /at$1 has two directions ( vibration1 "o ( :i* at ! pres5t mom5t is v]tical1 ! o!r horizontal4 ,:at are we to conclude8 ,t ! gre5 light w be transmitt$ along ! latt]1 :i* is p>allel to ! axis ( ! t\rmal9e1 & n along ! =m]1 :i* is p]p5dicul> to t axis4 ,h5ce we may inf] t "o image ( ! t\rmal9e w %[ ! ord9>y gre5 light ( ! cry/al1 :ile ! o!r image w be black4 ,te/$ by exp]im5t1 our reason+ is v]ifi$ to ! lett] 7fig4 #bi74 ,illu/ration3 ,fig4 #bi4 ,illu/ration2 ,fig4 #cj4 ,let u pu% our te/ /ill fur!r4 ,by means ( an endless screw1 ! cry/al c be turn$ n9ety degrees r\nd4 ,! black image1 z ,i turn1 becomes gradually bright]1 & ! bright "o gradually d>k]2 at an angle ( =ty-five degrees bo? images are equally bright 7fig4 #cj72 :ile1 :5 n9ety degrees h be5 obta9$1 ! axis ( ! cry/al be+ !n v]tical1 ! bright & black images h *ang$ places1 exactly z reason+ w\ld h l$ u to suppose 7fig4 #ca74 ,illu/ration3 ,fig4 #ca4 ,illu/ration3 ,fig4 #cb4 ,consid]+ :at has be5 already said 7p4 #aad7 reg>d+ ! reflection ( light pol>iz$ by transmission ?r\gh t\rmal9e1 y w readily =esee :at mu/ occur :5 we receive ^u a plate ( glass1 held at ! pol>iz+ angle1 ! two beams em]g5t f our prism ( ,icel& sp>4 ,i cause bo? beams to pass side by side ?r\gh ! air1 cat* !m on a glass plate1 & seek to reflect !m upw>ds4 ,at ! pol>iz+ angle "o beam only is capable ( be+ ?us reflect$4 ,:i*8 ,y\r prompt answ] w be1 ,! beam ^: vibrations are horizontal 7fig4 #cb74 ,i n[ turn ! glass plate & try to reflect bo? beams lat]ally4 ,"o ( !m only is reflect$2 t1 namely1 ! vibrations ( :i* are v]tical 7fig4 #cc74 ,x is pla9 t1 by means ei!r ( ! t\rmal9e or ! reflect+ glass1 we c det]m9e 9 a mom5t ! direction ( vibration 9 any pol>iz$ beam4 ,illu/ration3 ,fig4 #cc4 ,z already /at$1 ! :ole ( a beam ( ord9>y light reflect$ f glass at ! pol>iz+ angle is pol>iz$2 a ^w mu/ n[ be add$ reg>d+ ! f> l>g] portion ( ! light :i* is transmitt$ by ! glass4 ,! transmitt$ beam conta9s a quantity ( pol>iz$ light equal to ! reflect$ beam2 b ?is is only a fraction ( ! :ole transmitt$ light4 ,by tak+ two plates ( glass in/ead ( "o1 we augm5t ! quantity ( ! transmitt$ pol>iz$ light2 & by tak+ a bundle ( plates1 we s increase ! quantity z to r5d] ! transmitt$ beam1 = all practical purposes1 p]fectly pol>iz$4 ,inde$1 bundles ( glass plates are (t5 employ$ z a means ( furni%+ pol>iz$ light4 ,x is important to note t ! plane ( vibration ( ?is transmitt$ light is at "r angles to t ( ! reflect$ light4 ,"o ^w m4 ,:5 ! t\rmal9es are cross$1 ! space :]e !y cross ea* o!r is black4 ,b we h se5 t ! lea/ obliquity on ! "p ( ! cry/als p]mits light to get ?r\gh bo?4 ,n[ suppose1 :5 ! two plates are cross$1 t we int]pose a ?ird plate ( t\rmal9e betwe5 !m1 ) its axis oblique to bo?4 ,a portion ( ! light transmitt$ by ! fir/ plate w get ?r\gh ?is int]m$iate "o4 ,b1 aft] x has got ?r\gh1 its plane ( vibration is *ang$3 x is no long] p]p5dicul> to ! axis ( ! cry/al 9 front4 ,h5ce x w1 9 "p1 get ?r\gh t cry/al4 ,?us1 by pure reason+1 we inf] t ! int]position ( a ?ird plate ( t\rmal9e w 9 "p aboli% ! d>kness produc$ by ! p]p5dicul> cross+ ( ! o!r two plates4 ,i h n a ?ird plate ( t\rmal9e2 b ! talc or mica :i* y employ 9 y\r /oves is a m conv5i5t sub/ance1 :i* acts 9 ! same way4 ,betwe5 ! cross$ t\rmal9es1 ,i introduce a film ( ?is cry/al ) its axis oblique to !irs4 ,y see ! edge ( ! film sl[ly desc5d+1 &1 z x desc5ds1 light takes ! place ( d>kness4 ,! d>kness1 9 fact1 seems scrap$ away1 z if x 7 some?+ mat]ial4 ,?is effect has be5 call$1 naturally b improp]ly1 depol>ization4 ,its prop] mean+ w be disclos$ 9 our next lecture4 ,^! exp]im5ts & reason+s1 if only ?or\ghly /udi$ & und]/ood1 w =m a solid gr\ndwork = ! analysis ( ! spl5did optical ph5om5a next to be consid]$4 ,,lecture ,,iv4 ,,*romatic ,,ph5om5a ,,produc$ ,,by ,,cry/als ,,9 ,,pol>iz$ ,,light ,,! ,,nicol ,,prism ,,pol>iz] ,,& ,,analyz] ,,action ,,( ,,?ick ,,& ,,?9 ,,plates ,,( ,,sel5ite ,,col\rs ,,dep5d5t ,,on ,,?ickness ,,resolution ,,( ,,pol>iz$ ,,beam ,,into ,,two ,,o!rs ,,by ,,! ,,sel5ite ,,"o ,,( ,,!m ,,m ,,ret>d$ ,,?an ,,! ,,o!r ,,recomp\nd+ ,,( ,,! ,,two ,,sy/ems ,,( ,,waves ,,by ,,! ,,analyz] ,,int]f]5ce ,,?us ,,r5d]$ ,,possible ,,consequ5t ,,production ,,( ,,col\rs ,,action ,,( ,,bodies ,,me*anically ,,/ra9$ ,,or ,,press$ ,,action ,,( ,,sonor\s ,,vibrations ,,action ,,( ,,glass ,,/ra9$ ,,or ,,press$ ,,by ,,heat ,,circul> ,,pol>ization ,,*romatic ,,ph5om5a ,,produc$ ,,by ,,qu>tz ,,! ,,magnetization ,,( ,,light ,,r+s ,,surr\nd+ ,,! ,,axes ,,( ,,cry/als ,,biaxal ,,& ,,uniaxal ,,cry/als ,,grasp ,,( ,,! ,,undulatory ,,!ory ,,! ,,col\r ,,& ,,pol>ization ,,( ,,sky-,,light ,,g5]ation ,,( ,,artificial ,,skies4 #a4 ,action ( ,cry/als on ,pol>iz$ ,light3 ! ,nicol ,prism4 ,we h ?is ev5+ to exam9e & illu/rate ! *romatic ph5om5a produc$ by ! action ( cry/als1 & d\ble-refract+ bodies g5]ally1 ^u pol>iz$ light1 & to apply ! ,undulatory ,!ory to _! elucidation4 ,= a long "t inve/igators 7 compell$ to employ plates ( t\rmal9e = ?is purpose1 & ! progress !y made ) s defective a means ( inquiry is a/oni%+4 ,b ^! m5 _h _! he>ts 9 _! "w1 & 7 on ?is acc\nt enabl$ to extract great results f small in/rum5tal appliances4 ,= our pres5t purpose we ne$ f> l>g] app>atus2 &1 happily1 9 ^! lat] times ?is ne$ has be5 to a great ext5t satisfi$4 ,we h se5 & exam9$ ! two beams em]g5t f ,icel& sp>1 & h prov$ !m to be pol>iz$4 ,if1 at ! sacrifice ( half ! light1 we c\ld aboli% "o ( ^!1 ! o!r w\ld place at our disposal a beam ( pol>iz$ light1 incomp>ably /rong] ?an any atta9able f t\rmal9e4 ,! beams1 z y "k1 are refract$ diff]5tly1 & f ?is1 z made pla9 9 #d1 ,lecture ,i41 we are able to inf] t ! "o may be totally reflect$1 :5 ! o!r is n4 ,an able optician1 nam$ ,nicol1 cut a cry/al ( ,icel& sp> 9 two halves 9 a c]ta9 direction4 ,he poli%$ ! sev]$ surfaces1 & reunit$ !m by ,canada balsam1 ! surface ( union be+ s incl9$ to ! beam trav]s+ ! sp> t ! ord9>y ray1 :i* is ! mo/ highly refract$1 0 totally reflect$ by ! balsam1 :ile ! extraord9>y ray 0 p]mitt$ to pass on4 ,let b x1 c y 7fig4 #cd7 repres5t ! section ( an elongat$ rhomb ( ,icel& sp> clov5 f ! cry/al4 ,let ?is rhomb be cut along ! plane b c2 & ! two sev]$ surfaces1 aft] hav+ be5 poli%$1 reunit$ by ,canada balsam4 ,we le>n$1 9 our fir/ lecture1 t total reflection only takes place :5 a ray seeks to escape f a m refract+ to a less refract+ m$ium1 & t x always1 "u ^! circum/ances1 takes place :5 ! obliquity is suffici5t4 ,n[ ! refractive index ( ,icel& sp> is1 = ! extraord9>y ray less1 & = ! ord9>y great]1 ?an = ,canada balsam4 ,h5ce1 9 pass+ f ! sp> to ! balsam1 ! extraord9>y ray passes f a less refract+ to a m refract+ m$ium1 :]e total reflection _c occur2 :ile ! ord9>y ray passes f a m refract+ to a less refract+ m$ium1 :]e total reflection c occur4 ,! requisite obliquity is secur$ by mak+ ! rhomb ( su* a l5g? t ! plane ( :i* b c is ! section %all be p]p5dicul>1 or ne>ly s1 to ! two end surfaces ( ! rhomb b x1 c y4 ,illu/ration3 ,fig4 #cd4 ,! inv5tion ( ! ,nicol prism 0 a great /ep 9 practical optics1 & q rec5tly su* prisms h be5 con/ruct$ ( a size & purity :i* enable audi5ces l ! pres5t to witness ! *romatic ph5om5a ( pol>iz$ light to a degree altoge!r unatta9able a %ort "t ago4 7,! two prisms employ$ 9 ^! exp]im5ts 7 l5t to me by my lam5t$ fri5d ,mr4 ,william ,spottiswoode1 & !y 7 manufactur$ by ,mr4 ,ahr5s1 an optician ( consummate skill47 #b4 ,col\rs ( ,films ( ,sel5ite 9 ,pol>iz$ ,light4 ,two ,nicol prisms play ! same "p z ! two plates ( t\rmal9e4 ,plac$ ) _! directions ( vibration p>allel1 ! light passes ?r\gh bo?2 :ile :5 ^! directions are cross$ ! light is qu5*$4 ,introduc+ a film ( mica betwe5 ! prisms1 ! light1 z 9 ! case ( ! t\rmal9e1 is re/or$4 ,b notice1 :5 ! film ( mica is ?9 y h sometimes n only light1 b col\r$ light4 ,our "w = "s "t to come w consi/ ( ! exam9ation ( su* col\rs4 ,) ?is view1 ,i w take a repres5tative cry/al1 "o easily dealt )1 because x cleaves ) great facility--! cry/al gypsum1 or sel5ite1 :i* is cry/alliz$ sulphate ( lime4 ,betwe5 ! cross$ ,nicols ,i place a ?ick plate ( ?is cry/al2 l ! mica1 x re/ores ! light1 b x produces no col\r4 ,) my p5knife ,i take a ?9 spl9t] f ! cry/al & place x betwe5 ! prisms2 ! image ( ! spl9t] gl[s ) ! ri*e/ col\rs4 ,turn+ ! prism 9 front1 ^! col\rs gradually fade & disappe>1 b1 by cont9u+ ! rotation until ! vibrat+ sections ( ! prisms are p>allel to ea* o!r1 vivid col\rs aga9 arise1 b ^! col\rs are complem5t>y to ! =m] ones4 ,"s pat*es ( ! spl9t] appe> ( "o col\r1 "s ( ano!r4 ,^! diff]5ces are due to ! diff]5t ?icknesses ( ! film4 ,z 9 ! case ( ,hooke's ?9 plates1 if ! ?ickness be uni=m ! col\r is uni=m4 ,"h1 = in/ance1 is a /ell> %ape1 e loz5ge ( ! /> be+ a film ( gypsum ( uni=m ?ickness3 ea* loz5ge1 y obs]ve1 %[s a brilliant & uni=m col\r4 ,x is easy1 by %ap+ our films s z to repres5t fl[]s or o!r objects1 to exhibit su* objects 9 hues unatta9able by art4 ,"h1 = example1 is a specim5 ( he>t's-ease1 ! col\rs ( :i* y might safely defy ! arti/ to reproduce4 ,by turn+ ! front ,nicol #ij degrees r\nd1 we pass ?r\gh a col\rless phase to a s]ies ( col\rs complem5t>y to ! =m] ones4 ,?is *ange is /ill m /rik+ly repres5t$ by a rose-tree1 :i* is n[ pres5t$ 9 its natural hues--a r$ fl[] & gre5 leaves2 turn+ ! prism #ij degrees r\nd1 we obta9 a gre5 fl[] & r$ leaves4 ,all ^! wond]ful *romatic effects h def9ite me*anical causes 9 ! motions ( ! e!r4 ,! pr9ciple ( int]f]5ce duly appli$ & int]pret$ expla9s !m all4 #c4 ,col\rs ( ,cry/als 9 ,pol>iz$ ,light expla9$ by ! ,undulatory ,!ory4 ,by ?is "t y h le>n$ t ! ^w 'light' may be us$ 9 two diff]5t s5ses3 x may mean ! impression made ^u consci\sness1 or x may mean ! physical cause ( ! impression4 ,x is ) ?is cause t we h to occupy ourselves at pres5t4 ,! lum9if]\s e!r is a sub/ance :i* fills all space1 & surr\nds ! atoms & molecules ( bodies4 ,to ?is int]-/ell> & int]-atomic m$ium def9ite me*anical prop]ties are ascrib$1 & we deal ) x 9 our reason+s & calculations z a body possess$ ( ^! prop]ties4 ,9 me*anics we h ! composition & resolution ( =ces & ( motions1 ext5d+ to ! composition & resolution ( vibrations4 ,we treat ! lum9if]\s e!r on me*anical pr9ciples1 &1 f ! composition & resolution ( its vibrations we d$uce all ! ph5om5a display$ by cry/als 9 pol>iz$ light4 ,illu/ration3 ,fig4 #ce4 ,let u take1 z an example1 ! cry/al ( t\rmal9e1 ) :i* we are n[ s famili>4 ,let a vibration cross ?is cry/al oblique to its axis4 ,exp]im5t has assur$ u t a portion ( ! light w pass ?r\gh4 ,! quantity :i* passes we det]m9e 9 ?is way4 ,let ,a ,b 7fig4 #ce7 be ! axis ( ! t\rmal9e1 & let a b repres5t ! amplitude ( an oblique e!real vibration be=e x rea*es ,a ,b4 ,f a & b let ! two p]p5dicul>s a c & b d be drawn ^u ! axis3 !n c d w be ! amplitude ( ! transmitt$ vibration4 ,i %all imm$iately ask y to foll[ me :ile ,i endeav\r to expla9 ! effects obs]v$ :5 a film ( gypsum is plac$ betwe5 ! two ,nicol prisms4 ,b1 prior to ?is1 x w be desirable to e/abli% /ill fur!r ! analogy betwe5 ! action ( ! prisms & t ( ! two plates ( t\rmal9e4 ,! magnifi$ images ( ^! plates1 ) _! axes at "r-angles to ea* o!r1 are n[ be=e y4 ,introduc+ betwe5 !m a film ( sel5ite1 y obs]ve t by turn+ ! film r\nd x may be plac$ 9 a position :]e x has no p[] to aboli% ! d>kness ( ! sup]pos$ portions ( ! t\rmal9es4 ,:y is ?is8 ,! answ] is1 t 9 ! gypsum !re are two directions1 at "r angles to ea* o!r1 9 :i* alone vibrations c take place1 & t 9 our pres5t exp]im5t "o ( ^! directions is p>allel to "o ( ! axes ( ! t\rmal9e1 & ! o!r p>allel to ! o!r axis4 ,:5 ?is is ! case1 ! film ex]cises no s5sible action ^u ! light4 ,b n[ ,i turn ! film s z to r5d] its directions ( vibration oblique to ! two t\rmal9e axes2 !n1 y see x ex]cises ! p[]1 demon/rat$ 9 ! la/ lecture1 ( p>tially re/or+ ! light4 ,illu/ration3 ,fig4 #cf4 ,let u n[ m\nt our ,nicol prisms1 & cross !m z we cross$ ! t\rmal9e4 ,introduc+ our film ( gypsum betwe5 !m1 y notice t 9 "o p>ticul> position ! film has no p[] :atev] ov] ! field ( view4 ,b1 :5 ! film is turn$ a little way r\nd1 ! light passes4 ,we h n[ to und]/& ! me*anism by :i* ?is is effect$4 ,fir/1 !n1 we h a prism :i* receives ! light f ! electric lamp1 & :i* is call$ ! pol>iz]4 ,!n we h ! plate ( gypsum 7suppos$ to be plac$ at ,s1 fig4 #cf71 & !n ! prism 9 front1 :i* is call$ ! analyz]4 ,on its em]g5ce f ! fir/ prism1 ! light is pol>iz$2 &1 9 ! p>ticul> case n[ be=e u1 its vibrations are execut$ 9 a horizontal plane4 ,we h to exam9e :at occurs :5 ! two directions ( vibration 9 ! int]pos$ gypsum are oblique to ! horizon4 ,draw a rectangul> cross 7,a ,b1 ,c ,d1 fig4 #cg7 to repres5t ^! two directions4 ,draw a l9e 7a b7 to repres5t ! amplitude ( ! horizontal vibration on ! em]g5ce ( ! light f ! fir/ ,nicol4 ,let fall f ea* end ( ?is l9e two p]p5dicul>s 7a c1 a f1 b d1 b e7 on ! two arms ( ! cross2 !n ! di/ances 7c d1 e f7 betwe5 ! feet ( ^! p]p5dicul>s repres5t ! amplitudes ( two rectangul> vibrations1 :i* are ! compon5ts ( ! fir/ s+le vibration4 ,?us ! pol>iz$ ray1 :5 x ent]s ! gypsum1 is resolv$ into its two equival5ts1 :i* vibrate at "r angles to ea* o!r4 ,illu/ration2 ,fig4 #cg4 ,9 "o ( ^! two rectangul> directions ! e!r )9 ! gypsum is m sluggi% ?an 9 ! o!r2 &1 z a consequ5ce1 ! waves t foll[ ?is direction are m ret>d$ ?an ! o!rs4 ,9 bo? cases ! undulations are %ort5$ :5 !y ent] ! gypsum1 b 9 ! "o case !y are m %ort5$ ?an 9 ! o!r4 ,y c readily imag9e t 9 ?is way ! "o sy/em ( waves may get half a wave-l5g?1 or inde$ any numb] ( half wavel5g?s1 9 advance ( ! o!r4 ,! possibility ( int]f]5ce "h at once fla%es ^u ! m9d4 ,a little consid]ation1 h[ev]1 w r5d] x evid5t t1 z long z ! vibrations are execut$ at "r angles to ea* o!r1 !y _c qu5* ea* o!r1 no matt] :at ! ret>dation may be4 ,?is br+s u at once to ! "p play$ by ! analyz]4 ,its sole function is to recomp\nd ! two vibrations em]g5t f ! gypsum4 ,x r$uces !m to a s+le plane1 :]e1 if "o ( !m be ret>d$ by ! prop] am\nt1 ext9ction w occur4 ,b "h1 z 9 ! case ( ?9 films1 ! diff]5t l5g?s ( ! waves ( light come into play4 ,r$ w require a great] ?ickness to produce ! ret>dation necess>y = ext9ction ?an blue2 consequ5tly :5 ! long] waves h be5 )drawn by int]f]5ce1 ! %ort] ones rema91 ! film ( gypsum %9+ ) ! col\rs :i* ! %ort waves conf]4 ,conv]sely1 :5 ! %ort] waves h be5 )drawn1 ! ?ickness is su* t ! long] waves rema94 ,an elem5t>y consid]ation suffices to %[1 t :5 ! directions ( vibration ( ! prisms & ! gypsum enclose an angle ( =ty-five degrees1 ! col\rs are at _! maximum brilliancy4 ,:5 ! film is turn$ f ?is direction1 ! col\rs gradually fade1 until1 at ! po9t :]e ! directions ( vibration 9 plate & prisms are p>allel1 !y disappe> altoge!r4 7,! be/ way ( obta9+ a k ( ^! ph5om5a is to con/ruct a model ( ?9 wood or pa/ebo>d1 repres5t+ ! plate ( gypsum1 its planes ( vibration1 & also ^? ( ! pol>iz] & analyz]4 ,two p>allel pieces ( ! bo>d are to be sep>at$ by an int]val :i* %all repres5t ! ?ickness ( ! film ( gypsum4 ,betwe5 !m two o!r pieces1 int]sect+ ea* o!r at a "r angle1 are to repres5t ! planes ( vibration )9 ! film2 :ile atta*$ to ! two p>allel surfaces outside are two o!r pieces ( bo>d1 :i* repres5t ! planes ( vibration ( ! pol>iz] & analyz]4 ,on ! two int]sect+ planes ! waves are to be drawn1 %[+ ! resolution ( ! fir/ pol>iz$ beam into two o!rs1 & !n ! subsequ5t r$uction ( ! two sy/ems ( vibrations to a common plane by ! analyz]4 ,foll[+ out rigidly ! int]action ( ! two sy/ems ( waves1 we are taught by su* a model t all ! ph5om5a ( col\r obta9$ by ! comb9ation ( ! waves1 :5 ! planes ( vibration ( ! two ,nicols are p>allel1 are displac$ by ! complem5t>y ph5om5a1 :5 ! planes ( vibration are p]p5dicul> to ea* o!r47 ,9 consid]+ ! next po9t1 we w op]ate1 = ! sake ( simplicity1 ) mono*romatic light--) r$ light1 = example1 :i* is easily obta9$ pure by r$ glass4 ,suppos+ a c]ta9 ?ickness ( ! gypsum produces a ret>dation ( half a wave-l5g?1 twice ?is ?ickness w produce a ret>dation ( two half wave-l5g?s1 ?ree times ?is ?ickness a ret>dation ( ?ree half wave-l5g?s1 & s on4 ,n[1 :5 ! ,nicols are p>allel1 ! ret>dation ( half a wave-l5g?1 or ( any odd numb] ( half wave-l5g?s1 produces ext9ction2 at all ?icknesses1 on ! o!r h&1 :i* correspond to a ret>dation ( an ev5 numb] ( half wave-l5g?s1 ! two beams support ea* o!r1 :5 !y are br\ght to a common plane by ! analyz]4 ,suppos+1 !n1 t we take a plate ( a w$ge =m1 :i* gr[s gradually ?ick] f edge to back1 we ought to expect1 9 r$ light1 a s]ies ( recurr5t b&s ( light & d>kness2 ! d>k b&s occurr+ at ?icknesses :i* produce ret>dations ( "o1 ?ree1 five1 etc41 half wave-l5g?s1 :ile ! bright b&s occur betwe5 ! d>k ones4 ,exp]im5t proves ! w$ge-%ap$ film to %[ ^! b&s4 ,!y are also beautifully %[n by a circul> film1 s work$ z to be ?9ne/ at ! c5tre1 & gradually increas+ 9 ?ickness f ! c5tre outw>ds4 ,a spl5did s]ies ( r+s ( light & d>kness is ?us produc$4 ,:51 in/ead ( employ+ r$ light1 we employ blue1 ! r+s are also se53 b z !y occur at ?9n] portions ( ! film1 !y are small] ?an ! r+s obta9$ ) ! r$ light4 ,! consequ5ce ( employ+ :ite light may be n[ inf]r$2 inasmu* z ! r$ & ! blue fall 9 diff]5t places1 we h iris-col\r$ r+s produc$ by ! :ite light4 ,"s ( ! *romatic effects ( irregul> cry/allization are beautiful 9 ! extreme4 ,c\ld ,i introduce betwe5 our two ,nicols a pane ( glass cov]$ by ^? fro/-f]ns :i* y\r cold wea!r r5d]s n[ s frequ5t1 ri* col\rs w\ld be ! result4 ,! beautiful effects ( ! irregul> cry/allization ( t>t>ic acid & o!r sub/ances on glass plates n[ pres5t$ to y1 illu/rate :at y might expect f ! fro/$ w9d[-pane4 ,& n only d cry/all9e bodies act ?us ^u light1 b almo/ all bodies t possess a def9ite /ructure d ! same4 ,z a g5]al rule1 organic bodies act ?us ^u light2 = _! ar*itecture implies an arrangem5t ( ! molecules1 & ( ! e!r associat$ ) ! molecules1 :i* involves d\ble refraction4 ,a film ( horn1 or ! section ( a %ell1 = example1 yields v beautiful col\rs 9 pol>iz$ light4 ,9 a tree1 ! e!r c]ta9ly possesses diff]5t degrees ( ela/icity along & across ! fibre2 &1 7 wood transp>5t1 ?is peculi>ity ( molecul> /ructure w\ld infallibly reveal itself by *romatic ph5om5a l ^? t y h se54 #d4 ,col\rs produc$ by ,/ra9 & ,pressure4 ,n only d natural bodies behave 9 ?is way1 b x is possible1 z %[n by ,brew/]1 to conf]1 by artificial /ra9 or pressure1 a tempor>y d\ble refract+ /ructure ^u non-cry/all9e bodies su* z common glass4 ,?is is a po9t wor?y ( illu/ration4 ,:5 ,i place a b> ( wood across my knee & seek to break x1 :at is ! me*anical condition ( ! b>8 ,x b5ds1 & its convex surface is /ra9$ longitud9ally2 its concave surface1 t next my knee1 is longitud9ally press$4 ,bo? 9 ! /ra9$ portion & 9 ! press$ portion ( ! wood ! e!r is ?r[n into a condition :i* w\ld r5d] ! wood1 7 x transp>5t1 d\ble-refract+4 ,=1 9 cases l ! pres5t1 ! draw+ ( ! molecules asund] longitud9ally is always accompani$ by _! approa* to ea* o!r lat]ally2 :ile ! longitud9al squeez+ is accompani$ by lat]al retreat4 ,ea* half ( ! b> ( wood exhibits ?is anti!sis1 & is !re=e d\ble-refract+4 ,let u n[ repeat ?is exp]im5t ) a b> ( glass4 ,betwe5 ! cross$ ,nicols ,i introduce su* a b>4 ,by ! dim residue ( light l+]+ ^u ! scre51 y see ! image ( ! glass1 b x has no effect ^u ! light4 ,i simply b5d ! glass b> ) my f+] & ?umb1 keep+ its l5g? oblique to ! directions ( vibration 9 ! ,nicols4 ,in/antly light fla%es out ^u ! scre54 ,! two sides ( ! b> are illum9at$1 ! edges mo/1 = "h ! /ra9 & pressure are greate/4 ,9 pass+ f longitud9al /ra9 to longitud9al pressure1 we cross a portion ( ! glass :]e nei!r is ex]t$4 ,?is is ! s-call$ neutral axis ( ! b> ( glass1 & along x y see a d>k b&1 indicat+ t ! glass along ?is axis ex]cises no action ^u ! light4 ,by employ+ ! =ce ( a press1 in/ead ( ! =ce ( my f+] & ?umb1 ! brilliancy ( ! light is greatly augm5t$4 ,aga91 ,i h "h a squ>e ( glass :i* c be ins]t$ into a press ( ano!r k9d4 ,introduc+ ! uncompress$ squ>e betwe5 ! prisms1 its neutrality is decl>$2 b x c h>dly be held suffici5tly loosely 9 ! press to prev5t its action f manife/+ itself4 ,already1 ?\gh ! pressure is inf9itesimal1 y see spots ( light at ! po9ts :]e ! press is 9 contact ) ! glass4 ,on turn+ a screw1 ! image ( ! squ>e ( glass fla%es out ^u ! scre54 ,lum9\s spaces are se5 sep>at$ f ea* o!r by d>k b&s4 ,e two adjac5t spaces are 9 opposite me*anical conditions4 ,on "o side ( ! d>k b& we h /ra91 on ! o!r side pressure1 ! b& m>k+ ! neutral axis betwe5 bo?4 ,i n[ tight5 ! vice1 & y see col\r2 tight5 /ill m1 & ! col\rs appe> z ri* z ^? pres5t$ by cry/als4 ,releas+ ! vice1 ! col\rs sudd5ly vani%2 tight5+ sudd5ly1 !y reappe>4 ,f ! col\rs ( a soap-bubble ,newton 0 able to inf] ! ?ickness ( ! bubble1 ?us unit+ by ! bond ( ?\ght app>5tly incongru\s ?+s4 ,f ! col\rs "h pres5t$ to y1 ! magnitude ( ! pressure employ$ might be inf]r$4 ,inde$1 ! late ,m4 ,w]!im1 ( ,p>is1 inv5t$ an in/rum5t = ! det]m9ation ( /ra9s & pressures1 by ! col\rs ( pol>iz$ light1 :i* exce$$ 9 accuracy all previ\s in/rum5ts ( ! k9d4 ,& n[ we h to pu% ^! consid]ations to a f9al illu/ration4 ,pol>iz$ light may be turn$ to acc\nt 9 v>i\s ways z an analyz] ( molecul> condition4 ,x may1 = in/ance1 be appli$ to reveal ! condition ( a solid body :5 x becomes sonor\s4 ,a /rip ( glass six feet long1 two in*es wide & a qu>t] ( an in* ?ick1 is held at ! c5tre betwe5 ! f+] & ?umb4 ,on sweep+ a wet wooll5 rag ov] "o ( its halves1 y he> an acute s\nd due to ! vibrations ( ! glass4 ,:at is ! condition ( ! glass :ile ! s\nd is he>d8 ,?is3 its two halves l5g!n & %ort5 9 quick succession4 ,its two ends1 !re=e1 are 9 a /ate ( quick vibration2 b at ! c5tre ! pulses f ! two ends alt]nately meet & retreat f ea* o!r4 ,betwe5 _! oppos+ actions1 ! glass at ! c5tre is kept motionless3 b1 on ! o!r h&1 x is alt]nately /ra9$ & compress$4 ,9 fig4 #ch1 ,a ,b may be tak5 to repres5t ! glass rectangle ) its c5tre cond5s$2 :ile ,a' ,b' repres5ts ! same rectangle ) its c5tre r>efi$4 ,! ends ( ! /rip suff] nei!r cond5sation nor r>efaction4 ,illu/ration3 ,fig4 #ch ,if we introduce ! /rip ( glass 7s s'1 fig4 #ci7 betwe5 ! cross$ ,nicols1 tak+ c>e to keep x oblique to ! directions ( vibration ( ! ,nicols1 & sweep our wet rubb] ov] ! glass1 ?is is :at may be expect$ to occur3 ,at e mom5t ( compression ! light w fla% ?r\gh2 at e mom5t ( /ra9 ! light w also fla% ?r\gh2 & ^! /ates ( /ra9 & pressure w foll[ ea* o!r s rapidly1 t we may expect a p]man5t lum9\s impression to be made ^u ! eye4 ,by pure reason+1 !re=e1 we rea* ! conclusion t ! light w be reviv$ :5ev] ! glass is s\nd$4 ,t x is s1 exp]im5t te/ifies3 at e sweep ( ! rubb] 7h1 fig4 #ci7 a f9e lum9\s disk 7,o7 fla%es out ^u ! scre54 ,! exp]im5t may be v>i$ 9 ?is way3 ,plac+ 9 front ( ! pol>iz] a plate ( unanneal$ glass1 y h a s]ies ( beautifully col\r$ r+s1 int]sect$ by a black cross4 ,e sweep ( ! rubb] n only aboli%es ! r+s1 b introduces complem5t>y ones1 ! black cross be+1 = ! mom5t1 supplant$ by a :ite "o4 ,?is is a modification ( a beautiful exp]im5t :i* we owe to ,biot4 ,8 app>atus1 h[ev]1 conf9$ ! obs]vation ( x to a s+le p]son at a "t4 ,illu/ration3 ,fig4 #ci4 #e4 ,col\rs ( ,unanneal$ ,glass4 ,bodies are usually exp&$ by heat & contract$ by cold4 ,if ! heat be appli$ ) p]fect uni=mity1 no local /ra9s or pressures come into play2 b1 if "o portion ( a solid be heat$ & ano!r portion n1 ! expansion ( ! heat$ portion introduces /ra9s & pressures :i* reveal !mselves "u ! scrut9y ( pol>iz$ light4 ,:5 a squ>e ( common w9d[-glass is plac$ betwe5 ! ,nicols1 y see its dim outl9e1 b x ex]ts no action on ! pol>iz$ light4 ,held = a mom5t ov] ! flame ( a _s-lamp1 on re9troduc+ x betwe5 ! ,nicols1 light fla%es out ^u ! scre54 ,"h1 z 9 ! case ( me*anical action1 y h lum9\s spaces ( /ra9 divid$ by d>k neutral axes f spaces ( pressure4 ,illu/ration3 ,fig4 #dj4 ,illu/ration3 ,fig4 #da4 ,let u apply ! heat m symmetrically4 ,a small squ>e ( glass is p]=at$ at ! c5tre1 & into ! orifice a bit ( copp] wire is introduc$4 ,plac+ ! squ>e betwe5 ! prisms1 & heat+ ! wire1 ! heat passes by conduction to ! glass1 ?r\gh :i* x spreads f ! c5tre outw>ds4 ,y imm$iately see f\r lum9\s quadrants & a dim cross1 :i* becomes gradually black]1 by comp>ison ) ! adjac5t brightness4 ,& z1 9 ! case ( pressure1 we produc$ col\rs1 s "h also1 by ! prop] application ( heat1 gorge\s *romatic effects may be evok$4 ,! condition necess>y to ! production ( ^! col\rs may be r5d]$ p]man5t by fir/ heat+ ! glass suffici5tly1 & !n cool+ x1 s t ! *ill$ mass %all rema9 9 a /ate ( p]man5t /ra9 & pressure4 ,two or ?ree examples w illu/rate ?is po9t4 ,figs4 #dj & #da repres5t ! figures obta9$ ) two pieces ( glass ?us prep>$2 two rectangul> pieces ( unanneal$ glass1 cross$ & plac$ betwe5 ! pol>iz] & analyz]1 exhibit ! beautiful iris fr+es repres5t$ 9 fig4 #db4 ,illu/ration3 ,fig4 #db4 #f4 ,circul> ,pol>ization4 ,b we h to foll[ ! e!r /ill fur!r into its hid+-places4 ,susp5d$ be=e y is a p5dulum1 :i*1 :5 drawn aside & lib]at$1 oscillates to & fro4 ,if1 :5 ! p5dulum is pass+ ! middle po9t ( its excursion1 ,i imp>t a %ock to x t5d+ to drive x at "r angles to its pres5t c\rse1 :at occurs8 ,! two impulses comp\nd !mselves to a vibration oblique 9 direction to ! =m] "o1 b ! p5dulum /ill oscillates 9 a plane4 ,b1 if ! rectangul> %ock be imp>t$ to ! p5dulum :5 x is at ! limit ( its sw+1 !n ! comp\nd+ ( ! two impulses causes ! susp5d$ ball to describe1 n a /raight l9e1 b an ellipse2 &1 if ! %ock be compet5t ( itself to produce a vibration ( ! same amplitude z ! fir/ "o1 ! ellipse becomes a circle4 ,:y d ,i dwell ^u ^! ?+s8 ,simply to make kn[n to y ! resemblance ( ^! gross me*anical vibrations to ! vibrations ( light4 ,i hold 9 my h& a plate ( qu>tz cut f ! cry/al p]p5dicul> to its axis4 ,! cry/al ?us cut possesses ! extraord9>y p[] ( twi/+ ! plane ( vibration ( a pol>iz$ ray to an ext5t dep5d5t on ! ?ickness ( ! cry/al4 ,& ! m refrangible ! light ! great] is ! am\nt ( twi/+2 s t1 :5 :ite light is employ$1 its con/itu5t col\rs are ?us drawn asund]4 ,plac+ ! qu>tz plate betwe5 ! pol>iz] & analyz]1 ?is vivid r$ appe>s2 &1 turn+ ! analyz] 9 front f "r to left1 ! o!r col\rs ( ! spectrum appe> 9 succession4 ,specim5s ( qu>tz h be5 f\nd :i* require ! analyz] to be turn$ f left to "r to obta9 ! same succession ( col\rs4 ,cry/als ( ! fir/ class are !re=e call$ "r-h&$1 & ( ! second class1 left-h&$ cry/als4 ,) pr(\nd sagacity1 ,fresnel1 to ^: g5ius we ma9ly owe ! expansion & f9al triumph ( ! undulatory !ory ( light1 reproduc$ m5tally ! me*anism ( ^! cry/als1 & %[$ _! action to be due to ! circum/ance t1 9 !m1 ! waves ( e!r s act ^u ea* o!r z to produce ! condition repres5t$ by our rotat+ p5dulum4 ,in/ead ( be+ plane pol>iz$1 ! light 9 rock cry/al is circul>ly pol>iz$4 ,two su* rays1 transmitt$ along ! axis ( ! cry/al1 & rotat+ 9 opposite directions1 :5 br\ght to int]f]5ce by ! analyz]1 are demon/rably compet5t to produce all ! obs]v$ ph5om5a4 #g4 ,complem5t>y ,col\rs ( ,bi-refract+ ,sp> 9 ,circul>ly ,pol>iz$ ,light4 ,pro( t ,yell[ & ,blue are ,complem5t>y4 ,i n[ remove ! analyz]1 & put 9 its place ! piece ( ,icel& sp> ) :i* we h already illu/rat$ d\ble refraction4 ,! two images ( ! c>bon-po9ts are n[ be=e y1 produc$1 z y "k1 by two beams vibrat+ at "r angles to ea* o!r4 ,introduc+ a plate ( qu>tz betwe5 ! pol>iz] & ! sp>1 ! two images gl[ ) complem5t>y col\rs4 ,employ+ ! image ( an ap]ture in/ead ( t ( ! c>bon-po9ts1 we h two col\r$ circles4 ,z ! analyz] is caus$ to rotate1 ! col\rs pass ?r\gh v>i\s *anges3 b !y are always complem5t>y4 ,:5 ! "o is r$1 ! o!r is gre52 :5 ! "o is yell[1 ! o!r is blue4 ,"h we h x 9 our p[] to demon/rate afre% a /atem5t made 9 our fir/ lecture1 t al?\gh ! mixture ( blue & yell[ pigm5ts produces gre51 ! mixture ( blue & yell[ lights produces :ite4 ,by enl>g+ our ap]ture1 ! two images produc$ by ! sp> are caus$ to approa* ea* o!r1 & f9ally to ov]lap4 ,! "o image is n[ a vivid yell[1 ! o!r a vivid blue1 & y notice t :]e ^! col\rs are sup]pos$ we h a pure :ite4 7,see fig4 #dc1 :]e ,n is ! end ( ! pol>iz]1 ,q ! qu>tz plate1 ,l a l5s1 & ,b ! bi-refract+ sp>4 ,! two images ov]lap at ,o1 & produce :ite by _! mixture47 ,illu/ration3 ,fig4 #dc4 #h4 ,! ,magnetization ( ,light4 ,?is br+s u to a po9t ( our inquiries :i*1 ?\gh r>ely illu/rat$ 9 lectures1 is nev]!less s likely to affect pr(\ndly ! future c\rse ( sci5tific ?\ght t ,i am unwill+ to pass x ov] )\t ref]5ce4 ,i ref] to ! exp]im5t :i* ,f>aday1 its discov]]1 call$ ! 'magnetization ( light4' ,! arrangem5t = ?is celebrat$ exp]im5t is n[ be=e y4 ,we h1 fir/1 our electric lamp1 !n a ,nicol prism1 to pol>ize ! beam em]g5t f ! lamp2 !n an electro-magnet1 !n a second ,nicol1 & f9ally our scre54 ,at ! pres5t mom5t ! prisms are cross$1 & ! scre5 is d>k4 ,i place f pole to pole ( ! electro-magnet a cyl9d] ( a peculi> k9d ( glass1 fir/ made by ,f>aday1 & call$ ,f>aday's heavy glass4 ,?r\gh ?is glass ! beam f ! pol>iz] n[ passes1 be+ int]cept$ by ! ,nicol 9 front4 ,on excit+ ! magnet light in/antly appe>s ^u ! scre54 ,by ! action ( ! magnet ^u ! heavy glass ! plane ( vibration is caus$ to rotate1 ! light be+ ?us enabl$ to get ?r\gh ! analyz]4 ,! two classes into :i* qu>tz-cry/als are divid$ h be5 already m5tion$4 ,9 my h& ,i hold a comp\nd plate1 "o half ( x tak5 f a "r-h&$1 & ! o!r f a left-h&$ cry/al4 ,plac+ ! plate 9 front ( ! pol>iz]1 ,i turn "o ( ! ,nicols until ! two halves ( ! plate %[ a common puce col\r4 ,?is yields an exce$+ly s5sitive means ( r5d]+ visible ! action ( a magnet ^u light4 ,by turn+ ei!r ! pol>iz] or ! analyz] ?r\gh ! smalle/ angle1 ! uni=mity ( ! col\r disappe>s1 & ! two halves ( ! qu>tz %[ diff]5t col\rs4 ,! magnet produces an effect equival5t to ?is rotation4 ,! puce-col\r$ circle is n[ be=e y on ! scre54 7,see fig4 #dd1 :]e ,n is ! nozzle ( ! lamp1 ,h ! fir/ ,nicol1 ,q ! biqu>tz plate1 ,l a l5s1 ,m ! electro-magnet1 ) ! heavy glass across its p]=at$ poles1 & ,p ! second ,nicol47 ,excit+ ! magnet1 "o half ( ! image becomes sudd5ly r$1 ! o!r half gre54 ,int]rupt+ ! curr5t1 ! two col\rs fade away1 & ! primitive puce is re/or$4 ,! action1 moreov]1 dep5ds ^u ! pol>ity ( ! magnet1 or1 9 o!r words1 on ! direction ( ! curr5t :i* surr\nds ! magnet4 ,rev]s+ ! curr5t1 ! r$ & gre5 reappe>1 b !y h *ang$ places4 ,! r$ 0 =m]ly to ! "r1 & ! gre5 to ! left2 ! gre5 is n[ to ! "r1 & ! r$ to ! left4 ,) ! mo/ exquisite +5uity1 ,f>aday analyz$ all ^? actions & /at$ _! laws4 ,?is exp]im5t1 h[ev]1 long rema9$ a sci5tific curiosity r ?an a fruitful g]m4 ,t x w\ld be> fruit ( ! highe/ importance1 ,f>aday felt pr(\ndly conv9c$1 & pres5t rese>*es are on ! way to v]ify 8 conviction4 ,illu/ration3 ,fig4 #dd #i4 ,iris-r+s surr\nd+ ! ,axes ( ,cry/als4 ,a few m words are necess>y to complete our k ( ! wond]ful int]action betwe5 pond]able molecules & ! e!r int]fus$ among !m4 ,symmetry ( molecul> arrangem5t implies symmetry on ! "p ( ! e!r2 atomic dissymmetry1 on ! o!r h&1 involves ! dissymmetry ( ! e!r1 &1 z a consequ5ce1 d\ble refraction4 ,9 a c]ta9 class ( cry/als ! /ructure is homog5e\s1 & su* cry/als produce no d\ble refraction4 ,9 c]ta9 o!r cry/als ! molecules are rang$ symmetrically r\nd a c]ta9 l9e1 & n ar\nd o!rs4 ,along ! =m]1 !re=e1 ! ray is undivid$1 :ile along all ! o!rs we h d\ble refraction4 ,ice is a famili> example3 its molecules are built ) p]fect symmetry ar\nd ! p]p5dicul>s to ! planes ( freez+1 & a ray s5t ?r\gh ice 9 ?is direction is n d\bly refract$2 :]eas1 9 all o!r directions1 x is4 ,icel& sp> is ano!r example ( ! same k9d3 its molecules are built symmetrically r\nd ! l9e unit+ ! two blunt angles ( ! rhomb4 ,9 ?is direction a ray suff]s no d\ble refraction1 9 all o!rs x does4 ,?is direction ( no d\ble refraction is call$ ! optic axis ( ! cry/al4 ,h5ce1 if a plate be cut f a cry/al ( ,icel& sp> p]p5dicul> to ! axis1 all rays s5t across ?is plate 9 ! direction ( ! axis w produce b "o image4 ,b1 ! mom5t we deviate f ! p>allelism ) ! axis1 d\ble refraction sets 94 ,if1 !re=e1 a beam t has be5 r5d]$ conical by a conv]g+ l5s be s5t ?r\gh ! sp> s t ! c5tral ray ( ! cone passes along ! axis1 ?is ray only w escape d\ble refraction4 ,ea* ( ! o!rs w be divid$ into an ord9>y & an extraord9>y ray1 ! "o mov+ m sl[ly ?r\gh ! cry/al ?an ! o!r2 ! "o1 !re=e1 ret>d$ ) ref]5ce to ! o!r4 ,"h1 !n1 we h ! conditions = int]f]5ce1 :5 ! waves are r$uc$ by ! analyz] to a common plane4 ,plac+ ! plate ( ,icel& sp> betwe5 ! cross$ ,nicol prisms1 & employ+ ! conical beam1 we h ^u ! scre5 a beautiful sy/em ( iris-r+s surr\nd+ ! end ( ! optic axis1 ! circul> b&s ( col\r be+ int]sect$ by a black cross 7fig4 #de74 ,! arms ( ?is cross are p>allel to ! two directions ( vibration 9 ! pol>iz] & analyz]4 ,x is easy to see t ^? rays ^: planes ( vibration )9 ! sp> co9cide ) ! plane ( vibration ( ei!r prism1 _c get ?r\gh bo?4 ,?is complete int]ception produces ! arms ( ! cross4 ,illu/ration3 ,fig4 #de4 ,) mono*romatic light ! r+s w\ld be simply bright & black--! bright r+s occurr+ at ^? ?icknesses ( ! sp> :i* cause ! rays to conspire2 ! black r+s at ^? ?icknesses :i* cause !m to qu5* ea* o!r4 ,turn+ ! analyz] #ij r\nd1 we obta9 ! complem5t>y ph5om5a4 ,! black cross gives place to a bright "o1 & e d>k r+ is supplant$ also by a bright "o 7fig4 #df74 ,"h1 z else:]e1 ! diff]5t l5g?s ( ! light-waves give rise to iris-col\rs :5 :ite light is employ$4 ,illu/ration3 ,fig4 #df4 ,illu/ration3 ,fig4 #dg4 ,besides ! regul> cry/als :i* produce d\ble refraction 9 no direction1 & ! uniaxal cry/als :i* produce x 9 all directions b "o1 ,brew/] discov]$ t 9 a l>ge class ( cry/als !re are two directions 9 :i* d\ble refraction does n take place4 ,^! are call$ biaxal cry/als4 ,:5 plates ( ^! cry/als1 suitably cut1 are plac$ betwe5 ! pol>iz] & analyz]1 ! axes 7,a ,a'1 fig4 #dg7 are se5 surr\nd$1 n by circles1 b by curves ( ano!r ord] & ( a p]fectly def9ite ma!matical "*4 ,ea* b&1 z prov$ exp]im5tally by ,h]s*el1 =ms a lemniscata2 b ! exp]im5tal pro( 0 "h1 z 9 numb]less o!r cases1 prec$$ by ! d$uction :i* %[$ t1 accord+ to ! undulatory !ory1 ! b&s mu/ possess ?is special "*4 #aj4 ,p[] ( ! ,wave ,!ory4 ,i h tak5 ?is some:at wide range ov] pol>ization itself1 & ov] ! ph5om5a exhibit$ by cry/als 9 pol>iz$ light1 9 ord] to give y "s notion ( ! firmness & complet5ess ( ! !ory :i* grasps !m all4 ,/>t+ f ! s+le assumption ( transv]se undulations1 we fir/ ( all det]m9e ! wave-l5g?s1 & f9d t on !m all ! ph5om5a ( col\r are dep5d5t4 ,! wavel5g?s may be det]m9$ 9 _m indep5d5t ways4 ,newton virtually det]m9$ !m :5 he measur$ ! p]iods ( 8 ,fits3 ! l5g? ( a fit1 9 fact1 is t ( a qu>t] ( an undulation4 ,! wave-l5g?s may be det]m9$ by diffraction at ! edges ( a slit 7z 9 ! ,app5dix to ^! ,lectures72 !y may be d$uc$ f ! int]f]5ce fr+es produc$ by reflection2 f ! fr+es produc$ by refraction2 also by l9es drawn ) a diamond ^u glass at measur$ di/ances asund]4 ,& :5 ! l5g? det]m9$ by ^! indep5d5t me?ods are comp>$ toge!r1 ! /ricte/ agreem5t is f\nd to exi/ betwe5 !m4 ,) ! wave-l5g?s once at our disposal1 we foll[ ! e!r into ! mo/ complicat$ cases ( int]action betwe5 x & ord9>y matt]1 '! !ory is equal to !m all4 ,x makes n a s+le new physical hypo!sis2 b out ( its orig9al /ock ( pr9ciples x educes ! c\nt]p>ts ( all t obs]vation %[s4 ,x acc\nts =1 expla9s1 simplifies ! mo/ entangl$ cases2 corrects kn[n laws & facts2 pr$icts & discloses unkn[n ones2 becomes ! guide ( its =m] tea*] ,obs]vation2 &1 enlight5$ by me*anical conceptions1 acquires an insight :i* pi]ces ?r\gh %ape & col\r to =ce & cause4'#ah ,b1 :ile ,i h ?us endeav\r$ to illu/rate be=e y ! p[] ( ! undulatory !ory z a solv] ( all ! difficulties ( optics1 d ,i !re=e wi% y to close y\r eyes to any evid5ce t may arise aga9/ x8 ,by no means4 ,y may urge1 & ju/ly urge1 t a hundr$ ye>s ago ano!r !ory 0 held by ! mo/ em95t m51 & t1 z ! !ory !n held _h to yield1 ! undulatory !ory may h to yield also4 ,?is seems reasonable2 b let u und]/& ! precise value ( ! argum5t4 ,9 simil> language a p]son 9 ! "t ( ,newton1 or ev5 9 our "t1 might reason ?us3 ,hipp>*us & ,ptolemy1 & numb]s ( great m5 aft] !m1 believ$ t ! e>? 0 ! c5tre ( ! sol> sy/em4 ,b ?is deep-set !oretic notion _h to give way1 & ! helio-c5tric !ory may1 9 its turn1 h to give way also4 ,?is is j z reasonable z ! fir/ argum5t4 ,:]e9 consi/s ! /r5g? ( ! pres5t !ory ( gravitation8 ,solely 9 its compet5ce to acc\nt = all ! ph5om5a ( ! sol> sy/em4 ,:]e9 consi/s ! /r5g? ( ! !ory ( undulation8 ,solely 9 its compet5ce to dis5tangle & expla9 ph5om5a a hundr$-fold m complex ?an ^? ( ! sol> sy/em4 ,accept if y w ! scepticism ( ,mr4 ,mill#ai reg>d+ ! undulatory !ory2 b if y\r scepticism be philosophical1 x w wrap ! !ory ( gravitation 9 ! same or 9 great] d\bt4#bj #aa4 ,! ,blue ( ! ,sky4 ,i am unwill+ to quit ^! *romatic ph5om5a )\t ref]r+ to a s\rce ( col\r :i* has (t5 come be=e me ( late 9 ! blue ( y\r skies at noon1 & ! deep crimson ( y\r horizon aft] ! set ( sun4 ,i w "h summ>ize & ext5d :at ,i h else:]e said ^u ?is subject4 ,pro(s ( ! mo/ cog5t description c\ld be adduc$ to %[ t ! blue light ( ! firmam5t is reflect$ light4 ,t light comes to u across ! direction ( ! sol> rays1 & ev5 aga9/ ! direction ( ! sol> rays2 & ?is lat]al & oppos+ ru% ( wave-motion c only be due to ! reb\nd ( ! waves f ! air itself1 or f some?+ susp5d$ 9 ! air4 ,! sol> light1 moreov]1 is n scatt]$ by ! sky 9 ! proportions :i* produce :ite4 ,! sky is blue1 :i* indicates an excess ( ! small] waves4 ,! blu5ess ( ! air has be5 giv5 z a reason = ! blu5ess ( ! sky2 b !n ! "q arises1 ,h[1 if ! air be blue1 c ! light ( sunrise & sunset1 :i* travels ?r\gh va/ di/ances ( air1 be yell[1 orange1 or ev5 r$8 ,! passage ( ! :ite sol> light ?r\gh a blue m$ium c\ld by no possibility r$d5 ! light2 ! hypo!sis ( a blue atmosph]e is !re=e unt5able4 ,9 fact1 ! ag5t1 :atev] x be1 :i* s5ds u ! light ( ! sky1 ex]cises 9 s do+ a di*roitic action4 ,! light reflect$ is blue1 ! light transmitt$ is orange or r$1 ,a m>k$ di/9ction is ?us exhibit$ betwe5 reflection f ! sky & t f an ord9>y cl\d1 :i* ex]cises no su* di*roitic action4 ,! cl\d1 9 fact1 takes no note ( size on ! "p ( ! waves ( e!r1 b reflects !m all alike4 ,n[ ! cause ( ?is may be t ! cl\d-p>ticles are s l>ge 9 comp>ison ) ! size ( ! waves ( e!r z to scatt] !m all indiff]5tly4 ,a broad cliff reflects an ,atlantic roll] z easily z x reflects a ripple produc$ by a sea-bird's w+2 &1 9 ! pres5ce ( l>ge reflect+ surfaces1 ! exi/+ diff]5ces ( magnitude among ! waves ( e!r may also disappe>4 ,b suppos+ ! reflect+ p>ticles1 in/ead ( be+ v l>ge1 to be v small1 9 comp>ison ) ! size ( ! waves4 ,!n1 in/ead ( ! :ole wave be+ front$ & 9 great "p ?r[n back1 a small portion only is %iv]$ (f by ! ob/acle4 ,suppose1 !n1 su* m9ute =eign p>ticles to be diffus$ 9 our atmosph]e4 ,waves ( all sizes imp+e ^u !m1 & at e collision a portion ( ! imp++ wave is /ruck (f4 ,all ! waves ( ! spectrum1 f ! extreme r$ to ! extreme violet1 are ?us act$ ^u2 b 9 :at proportions w !y be scatt]$8 ,l>g5ess is a ?+ ( relation2 & ! small] ! wave1 ! great] is ! relative size ( any p>ticle on :i* ! wave imp+es1 & ! great] also ! relative reflection4 ,a small pebble1 plac$ 9 ! way ( ! r+-ripples produc$ by heavy ra9-drops on a tranquil pond1 w ?r[ back a l>ge fraction ( ea* ripple incid5t ^u x1 :ile ! fractional "p ( a l>g] wave ?r[n back by ! same pebble might be inf9itesimal4 ,n[ to pres]ve ! sol> light :ite1 its con/itu5t proportions mu/ n be alt]$2 b 9 ! scatt]+ ( ! light by ^! v small p>ticles we see t ! proportions are alt]$4 ,! small] waves are 9 excess1 &1 z a consequ5ce1 9 ! scatt]$ light blue w be ! pr$om9ant col\r4 ,! o!r col\rs ( ! spectrum mu/1 to "s ext5t1 be associat$ ) ! blue3 !y are n abs5t1 b defici5t4 ,we ought1 9 fact1 to h !m all1 b 9 dim9i%+ proportions1 f ! violet to ! r$4 ,we h ?us reason$ our way to ! conclusion1 t 7 p>ticles1 small 9 comp>ison to ! size ( ! e!r waves1 s[n 9 our atmosph]e1 ! light scatt]$ by ^? p>ticles w\ld be exactly su* z we obs]ve 9 our azure skies4 ,&1 inde$1 :5 ?is light is analyz$1 all ! col\rs ( ! spectrum are f\nd 9 ! proportions indicat$ by our conclusion4 ,by its successive collisions ) ! p>ticles ! :ite light is m & m robb$ ( its %ort] waves2 x !re=e loses m & m ( its due proportion ( blue4 ,! result may be anticipat$4 ,! transmitt$ light1 :]e mod]ate di/ances are involv$1 w appe> yell[i%4 ,b z ! sun s9ks t[>ds ! horizon ! atmosph]ic di/ance increases1 & consequ5tly ! numb] ( ! scatt]+ p>ticles4 ,!y weak5 9 succession ! violet1 ! indigo1 ! blue1 & ev5 di/urb ! proportions ( gre54 ,! transmitt$ light "u su* circum/ances mu/ pass f yell[ ?r\gh orange to r$4 ,?is also is exactly :at we f9d 9 nature4 ,?us1 :ile ! reflect$ light gives u1 at noon1 ! deep azure ( ! ,alp9e skies1 ! transmitt$ light gives u1 at sunset1 ! w>m crimson ( ! ,alp9e sn[s4 ,b c small p>ticles be really prov$ to act 9 ! mann] indicat$8 ,no d\bt ( x4 ,ea* "o ( y c submit ! "q to an exp]im5tal te/4 ,wat] w n dissolve res91 b _s w2 & :5 _s :i* holds res9 9 solution is dropp$ into wat]1 ! res9 imm$iately sep>ates 9 solid p>ticles1 :i* r5d] ! wat] milky4 ,! co>s5ess ( ?is precipitate dep5ds on ! quantity ( ! dissolv$ res94 ,pr(essor ,brcke has giv5 u ! proportions :i* produce p>ticles p>ticul>ly suit$ to our pres5t purpose4 ,"o gramme ( clean ma/ic is dissolv$ 9 eighty-sev5 grammes ( absolute alcohol1 & ! transp>5t solution is all[$ to drop into a beak] conta9+ cle> wat] briskly /irr$4 ,an exce$+ly f9e precipitate is ?us =m$1 :i* decl>es its pres5ce by its action ^u light4 ,plac+ a d>k surface beh9d ! beak]1 & p]mitt+ ! light to fall into x f ! top or front1 ! m$ium is se5 to be ( a v fair sky-blue4 ,a trace ( soap 9 wat] gives x a t9t ( blue4 ,london milk makes an approximation to ! same col\r1 ?r\gh ! op]ation ( ! same cause3 & ,helmholtz has irrev]5tly disclos$ ! fact t a blue eye is simply a turbid m$ium4 #ab4 ,artificial ,sky4 ,b we h x 9 our p[] to imitate f> m closely ! natural conditions ( ?is problem4 ,we c g5]ate 9 air artificial skies1 & prove _! p]fect id5tity ) ! natural "o1 z reg>ds ! exhibition ( a numb] ( :olly unexpect$ ph5om5a4 ,x has be5 rec5tly %[n 9 a great numb] ( in/ances by myself t waves ( e!r issu+ f a /rong s\rce1 su* z ! sun or ! electric light1 are compet5t to %ake asund] ! atoms ( gase\s molecules4 ,! app>atus us$ to illu/rate ?is consi/s ( a glass tube ab\t a y>d 9 l5g?1 & f #b to #c in*es int]nal diamet]4 ,! gas or vap\r to be exam9$ is introduc$ into ?is tube1 & ^u x ! cond5s$ beam ( ! electric lamp is p]mitt$ to act4 ,! vap\r is s *os5 t "o1 at lea/1 ( its products ( decomposition1 z soon z x is =m$1 %all be precipitat$ to a k9d ( cl\d4 ,by graduat+ ! quantity ( ! vap\r1 ?is precipitation may be r5d]$ ( any degree ( f95ess1 =m+ p>ticles di/+ui%able by ! nak$ eye1 or p>ticles :i* are probably f> beyond ! rea* ( our highe/ microscopic p[]s4 ,i h no reason to d\bt t p>ticles may be ?us obta9$ ^: diamet]s con/itute b a v small fraction ( ! l5g? ( a wave ( violet light4 ,n[1 9 all su* cases :5 suitable vap\rs are employ$ 9 a suffici5tly att5uat$ /ate1 no matt] :at ! vap\r may be1 ! visible action comm5ces ) ! =mation ( a blue cl\d4 ,let me gu>d myself at ! outset aga9/ all misconception z to ! use ( ?is t]m4 ,! blue cl\d "h ref]r$ to is totally invisible 9 ord9>y daylight4 ,to be se51 x requires to be surr\nd$ by d>kness1 x only be+ illum9at$ by a p[]ful beam ( light4 ,?is cl\d diff]s 9 _m important p>ticul>s f ! f9e/ ord9>y cl\ds1 & might ju/ly h assign$ to x an int]m$iate position betwe5 ^! cl\ds & true cl\dless vap\r4 ,x is possible to make ! p>ticles ( ?is act9ic cl\d gr[ f an inf9itesimal & altoge!r ultra-microscopic size to p>ticles ( s5sible magnitude2 & by means ( ^! 9 a c]ta9 /age ( _! gr[?1 we produce a blue :i* rivals1 if x does n transc5d1 t ( ! deepe/ & pure/ ,italian sky4 ,introduc+ into our tube a quantity ( mix$ air & nitrite ( butyl vap\r suffici5t to depress ! m]curial column ( an air-pump "o-tw5tie? ( an in*1 add+ a quantity ( air & hydro*loric acid suffici5t to depress ! m]cury half an in* fur!r1 & s5d+ ?r\gh ?is comp\nd & highly att5uat$ atmosph]e ! beam ( ! electric light1 )9 ! tube arises gradually a spl5did azure1 :i* /r5g!ns = a "t1 rea*es a maximum ( dep? & purity1 & !n1 z ! p>ticles gr[ l>g]1 passes into :iti% blue4 ,?is exp]im5t is repres5tative1 & x illu/rates a g5]al pr9ciple4 ,v>i\s o!r col\rless sub/ances ( ! mo/ div]se prop]ties1 optical & *emical1 might be employ$ = ?is exp]im5t4 ,! incipi5t cl\d1 9 e case1 w\ld exhibit ?is sup]b blue2 ?us prov+ to demon/ration t p>ticles ( inf9itesimal size1 )\t any col\r ( _! own1 & irrespective ( ^? optical prop]ties exhibit$ by ! sub/ance 9 a massive /ate1 are compet5t to produce ! blue col\r ( ! sky4 #ac4 ,pol>ization ( ,skylight4 ,b !re is ano!r subject connect$ ) our firmam5t1 ( a m subtle & recondite "* ?an ev5 its col\r4 ,i mean t 'my/]i\s & beautiful ph5om5on1' z ,sir ,john ,h]s*el calls x1 ! pol>ization ( ! light ( ! sky4 ,look+ at v>i\s po9ts ( ! blue firmam5t ?r\gh a ,nicol prism1 & turn+ ! prism r\nd its axis1 we soon notice v>iations ( brightness4 ,9 c]ta9 positions ( ! prism1 & f c]ta9 po9ts ( ! firmam5t1 ! light appe>s to be :olly transmitt$1 :ile x is only necess>y to turn ! prism r\nd its axis ?r\gh an angle ( n9ety degrees to mat]ially dim9i% ! int5sity ( ! light4 ,exp]im5ts ( ?is k9d prove t ! blue light s5t to u by ! firmam5t is pol>iz$1 & on close scrut9y x is also f\nd t ! direction ( mo/ p]fect pol>ization is p]p5dicul> to ! sol> rays4 ,7 ! heav5ly azure l ! ord9>y light ( ! sun1 ! turn+ ( ! prism w\ld h no effect ^u x2 x w\ld be transmitt$ equally dur+ ! entire rotation ( ! prism4 ,! light ( ! sky may be 9 great "p qu5*$1 because x is 9 great "p pol>iz$4 ,! same ph5om5on is exhibit$ 9 p]fection by our act9ic cl\ds1 ! only condition necess>y to its production be+ ! smallness ( ! p>ticles4 ,9 all cases1 & ) all sub/ances1 ! cl\d =m$ at ! comm5cem5t1 :5 ! precipitat$ p>ticles are suffici5tly f9e1 is blue4 ,9 all cases1 moreov]1 ?is f9e blue cl\d pol>izes p]fectly ! beam :i* illum9ates x1 ! direction ( pol>ization enclos+ an angle ( #ij ) ! axis ( ! illum9at+ beam4 ,x is exce$+ly int]e/+ to obs]ve bo? ! gr[? & ! decay ( ?is pol>ization4 ,= t5 or fifte5 m9utes aft] its fir/ appe>ance1 ! light f a vividly illum9at$ incipi5t cl\d1 look$ at horizontally1 is absolutely qu5*$ by a ,nicol prism ) its long] diagonal v]tical4 ,b z ! sky-blue is gradually r5d]$ impure by ! introduction ( p>ticles ( too l>ge a size1 9 o!r words1 z real cl\ds beg9 to be =m$1 ! pol>ization beg9s to det]iorate1 a portion ( ! light pass+ ?r\gh ! prism 9 all its positions1 z x does 9 ! case ( skylight4 ,x is wor?y ( note t = "s "t aft] ! cessation ( p]fect pol>ization ! residual light :i* passes1 :5 ! ,nicol is 9 its position ( m9imum transmission1 is ( a gorge\s blue1 ! :it] light ( ! cl\d be+ ext+ui%$4 ,:5 ! cl\d-texture has become suffici5tly co>se to approximate to t ( ord9>y cl\ds1 ! rotation ( ! ,nicol ceases to h any s5sible effect on ! light dis*>g$ at "r angles to ! beam4 ,! p]fection ( ! pol>ization 9 a direction p]p5dicul> to ! illum9at+ beam may be also illu/rat$ by ! foll[+ exp]im5t1 :i* has be5 execut$ ) _m vap\rs4 ,a ,nicol prism l>ge en\gh to embrace ! entire beam ( ! electric lamp 0 plac$ betwe5 ! lamp & ! exp]im5tal tube4 ,s5d+ ! beam pol>iz$ by ! ,nicol ?r\gh ! tube1 ,i plac$ myself 9 front ( x1 ! eyes be+ on a level ) its axis1 my assi/ant occupy+ a simil> position beh9d ! tube4 ,! %ort diagonal ( ! l>ge ,nicol 0 9 ! fir/ in/ance v]tical1 ! plane ( vibration ( ! em]g5t beam be+ !re=e also v]tical4 ,z ! light cont9u$ to act1 a sup]b blue cl\d visible to bo? my assi/ant & myself 0 sl[ly =m$4 ,b ?is cl\d1 s deep & ri* :5 look$ at f ! positions m5tion$1 utt]ly disappe>$ :5 look$ at v]tically d[nw>ds1 or v]tically upw>ds4 ,reflection f ! cl\d 0 n possible 9 ^! directions4 ,:5 ! l>ge ,nicol 0 sl[ly turn$ r\nd its axis1 ! eye ( ! obs]v] be+ on ! level ( ! beam1 & ! l9e ( vision p]p5dicul> to x1 entire ext9ction ( ! light emitt$ horizontally occurr$ :5 ! long] diagonal ( ! l>ge ,nicol 0 v]tical4 ,b a vivid blue cl\d 0 se5 :5 look$ at d[nw>ds or upw>ds4 ,?is truly f9e exp]im5t1 :i* ,i %\ld c]ta9ly h made )\t sugge/ion1 01 z a matt] ( fact1 fir/ def9itely sugge/$ by a rem>k address$ to me 9 a lett] by ,pr(essor ,/okes4 ,all ! ph5om5a ( col\r & ( pol>ization obs]vable 9 ! case ( skylight are manife/$ by ^? act9ic cl\ds2 & !y exhibit additional ph5om5a :i* x w\ld be nei!r conv5i5t to pursue1 nor p]haps possible to detect1 9 ! actual firmam5t4 ,!y enable u1 = example1 to foll[ ! pol>ization f its fir/ appe>ance on ! b>ely visible blue to its f9al ext9ction 9 ! co>s] cl\d4 ,^! *anges1 z f> z x is n[ necess>y to ref] to !m1 may be ?us summ$ up3-- #a4 ,! act9ic cl\d1 z long z x cont9ues blue1 dis*>ges pol>iz$ light 9 all directions1 b ! direction ( maximum pol>ization1 l t ( skylight1 is at "r angles to ! direction ( ! illum9at+ beam4 #b4 ,z long z ! cl\d rema9s di/9ctly blue1 ! light dis*>g$ f x at "r angles to ! illum9at+ beam is p]fectly pol>iz$4 ,x may be utt]ly qu5*$ by a ,nicol prism1 ! cl\d f :i* x issues be+ caus$ to disappe>4 ,any deviation f ! p]p5dicul> enables a portion ( ! light to get ?r\gh ! prism4 #c4 ,! direction ( vibration ( ! pol>iz$ light is at "r angles to ! illum9at+ beam4 ,h5ce a plate ( t\rmal9e1 ) its axis p>allel to ! beam1 /ops ! light1 & ) ! axis p]p5dicul> to ! beam transmits ! light4 #d4 ,a plate ( sel5ite plac$ betwe5 ! ,nicol & ! act9ic cl\d %[s ! col\rs ( pol>iz$ light2 9 fact1 ! cl\d itself plays ! "p ( a pol>iz+ ,nicol4 #e4 ,! p>ticles ( ! blue cl\d are immeasurably small1 b !y increase gradually 9 size1 & at a c]ta9 p]iod ( _! gr[? cease to dis*>ge p]fectly pol>iz$ light4 ,= "s "t aft]w>ds ! light t rea*es ! eye1 ?r\gh ! ,nicol 9 its position ( lea/ transmission1 is ( a magnific5t blue1 f> exce$+ 9 dep? & purity t ( ! pure/ sky2 ?us ! waves t fir/ feel ! influ5ce ( size1 at bo? limits ( ! pol>ization1 are ! %orte/ waves ( ! spectrum4 ,^! are ! fir/ to accept pol>ization1 & !y are ! fir/ to escape f x4 ,,lecture ,v4 ,,range ,,( ,,vision ,,n ,,comm5surate ,,) ,,range ,,( ,,radiation ,,! ,,ultra-,,violet ,,bays ,,fluoresc5ce ,,! ,,r5d]+ ,,( ,,invisible ,,rays ,,visible ,,vision ,,n ,,! ,,only ,,s5se ,,appeal$ ,,to ,,by ,,! ,,sol> ,,& ,,electric ,,beam ,,heat ,,( ,,beam ,,combu/ion ,,by ,,total ,,beam ,,at ,,! ,,foci ,,( ,,mirrors ,,& ,,l5ses ,,combu/ion ,,?r\gh ,,ice-,,l5s ,,ignition ,,( ,,diamond ,,se>* ,,= ,,! ,,rays ,,"h ,,effective ,,sir ,,william ,,h]s*el',s ,,discov]y ,,( ,,d>k ,,sol> ,,rays ,,invisible ,,rays ,,! ,,basis ,,( ,,! ,,visible ,,deta*m5t ,,by ,a ,,ray-,,filt] ,,( ,,! ,,invisible ,,rays ,,f ,,! ,,visible ,,combu/ion ,,at ,,d>k ,,foci ,,conv]sion ,,( ,,heat-,,rays ,,into ,,light-,,rays ,,caloresc5ce ,,"p ,,play$ ,,9 ,,nature ,,by ,,d>k ,,rays ,,id5tity ,,( ,,light ,,& ,,radiant ,,heat ,,invisible ,,images ,,reflection1 ,,refraction1 ,,plane ,,pol>ization1 ,,depol>ization1 ,,circul> ,,pol>ization1 ,,d\ble ,,refraction1 ,,& ,,magnetization ,,( ,,radiant ,,heat4 #a4 ,range ( ,vision & ( ,radiation4 ,! fir/ "q t we h to consid] to-night is ?is3 ,is ! eye1 z an organ ( vision1 comm5surate ) ! :ole range ( sol> radiation--is x capable ( receiv+ visual impressions f all ! rays emitt$ by ! sun8 ,! answ] is negative4 ,if we all[$ ourselves to accept = a mom5t t notion ( gradual gr[?1 amelioration1 & asc5sion1 impli$ by ! t]m evolution1 we might fairly conclude t !re are /ores ( visual impressions await+ man1 f> great] ?an ^? n[ 9 8 possession4 ,ritt] discov]$ 9 #ahja t beyond ! extreme violet ( ! spectrum !re is a va/ efflux ( rays :i* are totally useless z reg>ds our pres5t p[]s ( vision4 ,^! ultra-violet waves1 h[ev]1 ?\gh incompet5t to awak5 ! optic n]ve1 c %ake asund] ! molecules ( c]ta9 comp\nd sub/ances on :i* !y imp+e1 ?us produc+ *emical decomposition4 ,b ?\gh ! blue1 violet1 & ultra-violet rays c act ?us ^u c]ta9 sub/ances1 ! fact is h>dly suffici5t to entitle !m to ! "n ( '*emical rays1' :i* is usually appli$ to di/+ui% !m f ! o!r con/itu5ts ( ! spectrum4 ,z reg>ds _! action ^u ! salts ( silv]1 & _m o!r sub/ances1 !y may p]haps m]it ?is title2 b 9 ! case ( ! gr&e/ example ( ! *emical action ( light--! decomposition ( c>bonic acid 9 ! leaves ( plants1 ) :i* my em95t fri5d ,dr4 ,drap] 7n[ no m7 has s indissolubly associat$ 8 "n--! yell[ rays are f\nd to be ! mo/ active4 ,!re are sub/ances1 h[ev]1 on :i* ! violet & ultra-violet waves ex]t a special decompos+ p[]2 &1 by p]mitt+ ! invisible spectrum to fall ^u surfaces prep>$ ) su* sub/ances1 we reveal bo? ! exi/5ce & ! ext5t ( ! ultraviolet spectrum4 #b4 ,ultra-violet ,rays3 ,fluoresc5ce4 ,! me?od ( exhibit+ ! action ( ! ultraviolet rays by _! *emical action has be5 long kn[n2 inde$1 ,?omas ,"y photograph$ ! ultra-violet r+s ( ,newton4 ,we h n[ to demon/rate _! pres5ce 9 ano!r way4 ,z a g5]al rule1 bodies ei!r transmit light or absorb x2 b !re is a ?ird case 9 :i* ! light fall+ ^u ! body is nei!r transmitt$ nor absorb$1 b conv]t$ into light ( ano!r k9d4 ,pr(essor ,/okes1 ! occupant ( ! *air ( ,newton 9 ! ,univ]sity ( ,cambridge1 has demon/rat$ ?is *ange ( "o k9d ( light into ano!r1 & has pu%$ 8 exp]im5ts s f> z to r5d] ! invisible rays visible4 ,a l>ge numb] ( sub/ances exam9$ by ,/okes1 :5 excit$ by ! invisible ultra-violet waves1 h be5 prov$ to emit light4 ,y "k ! rate ( vibration correspond+ to ! extreme violet ( ! spectrum2 y are aw>e t to produce ! impression ( ?is col\r1 ! ret9a is /ruck #ghi millions ( millions ( times 9 a second4 ,at ?is po9t1 ! ret9a ceases to be useful z an organ ( vision2 =1 ?\gh /ruck by waves ( m rapid recurr5ce1 !y are incompet5t to awak5 ! s5sation ( light4 ,b :5 su* non-visual waves are caus$ to imp+e ^u ! molecules ( c]ta9 sub/ances--on ^? ( sulphate ( qu99e1 = example--!y compel ^? molecules1 or _! con/itu5t atoms1 to vibrate2 & ! peculi>ity is1 t ! vibrations ?us set up are ( sl[] p]iod ?an ^? ( ! excit+ waves4 ,by ?is l[]+ ( ! rate ( vibration ?r\gh ! int]m$iation ( ! sulphate ( qu99e1 ! invisible rays are br\ght )9 ! range ( vision4 ,we %all subsequ5tly h abundant opportunity = le>n+ t transp>5cy to ! visible by no means involves transp>5cy to ! invisible rays4 ,our bisulphide ( c>bon1 = example1 :i*1 employ$ 9 prisms1 is s em95tly suitable = exp]im5ts on ! visual rays1 is by no means s suitable = ^! ultra-violet rays4 ,fl9t glass is bett]1 & rock cry/al is bett] ?an fl9t glass4 ,a glass prism1 h[ev]1 w suit our pres5t purpose4 ,ca/+ by means ( su* a prism a spectrum1 n ^u ! :ite surface ( our scre51 b ^u a %eet ( pap] :i* has be5 wett$ ) a saturat$ solution ( ! sulphate ( qu99e & aft]w>ds dri$1 an obvi\s ext5sion ( ! spectrum is reveal$4 ,we h1 9 ! fir/ in/ance1 a portion ( ! violet r5d]$ :it] & m brilliant2 b1 besides ?is1 we h ! gleam+ ( ! col\r :]e1 9 ! case ( unprep>$ pap]1 no?+ is se54 ,o!r sub/ances produce a simil> effect4 ,a sub/ance1 = example1 rec5tly discov]$ by ,presid5t ,morton1 & nam$ by him ,?all5e1 produces a v /rik+ elongation ( ! spectrum1 ! new light g5]at$ be+ ( peculi> brilliancy4 ,fluor sp>1 & "s o!r sub/ances1 :5 rais$ to a temp]ature /ill "u r$ness1 emit light4 ,dur+ ! ages :i* h elaps$ s9ce _! =mation1 ?is capacity ( %ak+ ! e!r into visual tremors appe>s to h be5 enjoy$ by ^! sub/ances4 ,light has be5 pot5tial )9 !m all ?is "t2 &1 z well expla9$ by ,drap]1 ! heat1 ?\gh n itself ( visual int5sity1 c unlock ! molecules s z to enable !m to ex]t _! long-lat5t p[] ( vibration4 ,?is deportm5t ( fluor sp> det]m9$ ,/okes 9 8 *oice ( a "n = 8 great discov]y3 he call$ ?is r5d]+ visible ( ! ultra-violet rays ,fluoresc5ce4 ,by means ( a deeply col\r$ violet glass1 we cut (f almo/ ! :ole ( ! light ( our electric beam2 b ?is glass is peculi>ly transp>5t to ! violet & ultra-violet rays4 ,! violet beam n[ crosses a l>ge j> fill$ ) wat]1 into :i* ,i p\r a solution ( sulphate ( qu99e4 ,cl\ds1 to all appe>ance opaque1 in/antly tumble d[nw>ds4 ,fragm5ts ( horse-*e/nut b>k ?r[n ^u ! wat] also s5d d[n beautiful cl\d-l /rife4 ,b ^! are n cl\ds3 !re is no?+ precipitat$ "h3 ! obs]v$ action is an action ( molecules1 n ( p>ticles4 ,! m$ium be=e y is n a turbid m$ium1 = :5 y look ?r\gh x at a lum9\s surface x is p]fectly cle>4 ,if we pa9t ^u a piece ( pap] a fl[] or a b\quet ) ! sulphate ( qu99e1 & expose x to ! full beam1 sc>cely any?+ is se54 ,b on int]pos+ ! violet glass1 ! design in/antly fla%es =? 9 /rong contra/ ) ! deep surr\nd+ violet4 ,presid5t ,morton has prep>$ = me a mo/ beautiful example ( su* a design :i*1 :5 plac$ 9 ! violet light1 exhibits a peculi>ly brilliant fluoresc5ce4 ,f ! exp]im5ts ( ,drs4 ,b5ce ,jones & ,dupr1 x w\ld seem t !re is "s sub/ance 9 ! human body resembl+ ! sulphate ( qu99e1 :i* causes all ! tissues ( ! body to be m or less fluoresc5t4 ,all animal infusions %[ ?is fluoresc5ce4 ,! cry/all9e l5s ( ! eye exhibits ! effect 9 a v /rik+ mann]4 ,:51 = example1 ,i plunge my eye into ?is violet beam1 ,i am consci\s ( a :iti%-blue %imm] fill+ ! space be=e me4 ,?is is caus$ by fluoresc5t light g5]at$ 9 ! eye itself4 ,look$ at f )\t1 ! cry/all9e l5s at ! same "t is se5 to gleam vividly4 ,long be=e its physical orig9 0 und]/ood ?is fluoresc5t light attract$ att5tion4 ,boyle describes x ) great fulness & exactness4 ',we h sometimes1' he says1 'f\nd 9 ! %ops ( our druggi/s c]ta9 wood :i* is !re call$ ,lignum ,nephriticum1 because ! inhabitants ( ! c\ntry :]e x gr[s are wont to use ! infusion ( x1 made 9 fair wat]1 aga9/ ! /one 9 ! kidneys4 ,?is wood may af=d u an exp]im5t :i*1 besides ! s+ul>ity ( x1 may give no small assi/ance to an att5tive consid]] t[>ds ! detection ( ! nature ( col\rs4 ,take ,lignum1 ,nephriticum1 & ) a knife cut x into ?9 slices3 put ab\t a h&ful ( ^! slices into two or ?ree or f\r p\nds ( ! pure/ spr+ wat]4 ,decant ?is impregnat$ wat] into a glass phial2 & if y hold x directly betwe5 ! light & y\r eye1 y %all see x :olly t9t$ ) an almo/ gold5 col\r4 ,b if y hold ?is phial f ! light1 s t y\r eye be plac$ betwixt ! w9d[ & ! phial1 ! liquid w appe> ( a deep & lovely c]ule\s col\r4' ',^!1' he cont9ues1 '& o!r ph5om5a :i* ,i h obs]v$ 9 ?is delightful exp]im5t1 div]s ( my fri5ds h look$ ^u1 n )\t "s wond]2 & ,i rememb] an excell5t oculi/1 f9d+ by accid5t 9 a fri5d's *amb] a phial full ( ?is liquor1 :i* ,i _h giv5 t fri5d1 & hav+ nev] he>d any?+ ( ! exp]im5t1 nor hav+ anybody ne> him :o c\ld tell him :at ?is /range liquor might be1 0 a great :ile appreh5sive1 z he pres5tly aft]w>ds told me1 t "s /range new di/emp] 0 invad+ 8 eyes4 ,& ,i confess t ! unusualness ( ! ph5om5on made me v solicit\s to f9d out ! cause ( ?is exp]im5t2 & ?\gh ,i am f> f pret5d+ to h f\nd x1 yet my enquiries h1 ,i suppose1 enabl$ me to give su* h9ts z may lead y\r great] sagacity to ! discov]y ( ! cause ( ?is wond]4'#ba ,goe! 9 8 ',f>b5lehre' ?us describes ! fluoresc5ce ( horse-*e/nut b>k3--',let a /rip ( fre% horse-*e/nut b>k be tak5 & clipp$ into a glass ( wat]2 ! mo/ p]fect sky-blue w be imm$iately produc$4'#bb ,sir ,john ,h]s*el fir/ notic$ & describ$ ! fluoresc5ce ( ! sulphate ( qu99e1 & %[$ t ! light proce$$ f a ?9 /ratum ( ! solution adjac5t to ! surface :]e ! light ent]s x4 ,he %[$1 moreov]1 t ! incid5t beam1 al?\gh n s5sibly weak5$ 9 lum9\s int5sity1 lo/1 9 its transmission ?r\gh ! solution ( sulphate ( qu99e1 ! p[] ( produc+ ! blue fluoresc5t light4 ,sir ,david ,brew/] also work$ at ! subject2 b to ,pr(essor ,/okes we are indebt$ n only = its expansion1 b = its full & f9al explanation4 #c4 ,! ,heat ( ! ,electric ,beam4 ,ignition ?r\gh a ,l5s ( ,ice4 ,possible ,comet>y ,temp]ature4 ,b ! waves f our inc&esc5t c>bon-po9ts appeal to ano!r s5se ?an t ( vision4 ,!y n only produce light1 b heat1 z a s5sation4 ,! magnifi$ image ( ! c>bon-po9ts is n[ ^u ! scre52 & ) a suitable in/rum5t ! heat+ p[] ( ! rays :i* =m t image might be readily demon/rat$4 ,9 ?is case1 h[ev]1 ! heat is spread ov] too l>ge an area to be v int5se4 ,draw+ out ! cam]a l5s1 & caus+ a movable scre5 to approa* ! lamp1 ! image is se5 to become small] & small]2 ! rays at ! same "t becom+ m & m conc5trat$1 until f9ally !y are able to pi]ce black pap] ) a burn+ r+4 ,pu%+ back ! l5s s z to r5d] ! rays p>allel1 & receiv+ !m ^u a concave mirror1 !y are br\ght to a focus2 pap] plac$ at t focus is caus$ to smoke & burn4 ,heat ( ?is int5sity may be obta9$ ) our ord9>y cam]a & l5s1 & a concave mirror ( v mod]ate p[]4 ,illu/ration3 ,fig4 #dh4 ,we w n[ adopt /rong] measures ) ! radiation4 ,9 ?is l>g] cam]a ( black5$ t9 is plac$ a lamp1 9 all p>ticul>s simil> to ^? already employ$4 ,b in/ead ( ga!r+ up ! rays f ! c>bon-po9ts by a cond5s+ l5s1 we ga!r !m up by a concave mirror 7m m'1 fig4 #dh71 silv]$ 9 front & plac$ beh9d ! c>bons 7,p74 ,by ?is mirror we c cause ! rays to issue ?r\gh ! orifice 9 front ( ! cam]a1 ei!r p>allel or conv]g5t4 ,!y are n[ p>allel1 & !re=e to a c]ta9 ext5t diffus$4 ,we place a convex l5s 7,l7 9 ! pa? ( ! beam2 ! light is conv]g$ to a focus 7,c71 & at t focus pap] is n only pi]c$1 b x is in/antly set ablaze4 ,_m metals may be burn$ up 9 ! same way4 ,9 our fir/ lecture ! combu/ibility ( z9c 0 m5tion$4 ,plac+ a /rip ( %eet-z9c at ?is focus1 x is in/antly ignit$1 burn+ ) its *>act]i/ic purple flame4 ,& n[ ,i w sub/itute = our glass l5s 7,l7 "o ( a m novel "*4 ,9 a smoo? iron m\ld a l5s ( pellucid ice has be5 =m$4 ,plac+ x 9 ! position occupi$ a mom5t ago by ! glass l5s1 ,i c see ! beam br\ght to a %>p focus4 ,at ! focus ,i place1 a bit ( black pap]1 ) a little gun-cotton fold$ up )9 x4 ,! pap] imm$iately ignites & ! cotton explodes4 ,/range1 is x n1 t ! beam %\ld possess su* heat+ p[] aft] hav+ pass$ ?r\gh s cold a sub/ance8 ,9 8 arctic exp$itions ,dr4 ,scoresby succe$$ 9 explod+ gunp[d] by ! sun's rays1 conv]g$ by l>ge l5ses ( ice2 "h we h succe$$ 9 produc+ ! effect ) a small l5s1 & ) a t]re/rial s\rce ( heat4 ,9 ?is exp]im5t1 y obs]ve t1 be=e ! beam rea*es ! ice-l5s1 x has pass$ ?r\gh a glass cell conta9+ wat]4 ,! beam is ?us sift$ ( con/itu5ts1 :i*1 if p]mitt$ to fall ^u ! l5s1 w\ld injure its surface1 & blur ! focus4 ,& ?is leads me to say an anticipatory ^w reg>d+ transp>5cy4 ,9 our fir/ lecture we ent]$ fully into ! production ( col\rs by absorption1 & we spoke repeat$ly ( ! qu5*+ ( ! rays ( light4 ,did ?is mean t ! light 0 altoge!r annihilat$8 ,by no means4 ,x 0 simply s l[]$ 9 refrangibility z to escape ! visual range4 ,x 0 conv]t$ into heat4 ,our r$ ribbon 9 ! gre5 ( ! spectrum qu5*$ ! gre51 b if suitably exam9$ its temp]ature w\ld h be5 f\nd rais$4 ,our gre5 ribbon 9 ! r$ ( ! spectrum qu5*$ ! r$1 b its temp]ature at ! same "t 0 augm5t$ to a degree exactly equival5t to ! light ext+ui%$4 ,our black ribbon1 :5 pass$ ?r\gh ! spectrum1 0 f\nd compet5t to qu5* all its col\rs2 b at e /age ( its progress an am\nt ( heat 0 g5]at$ 9 ! ribbon exactly equival5t to ! light lo/4 ,x is only :5 absorption takes place t heat is ?us produc$3 & heat is always a result ( absorption4 ,exam9e ! wat]1 !n1 9 front ( ! lamp aft] ! beam has pass$ ?r\gh x3 x is s5sibly w>m1 &1 if p]mitt$ to rema9 !re long en\gh1 x might be made to boil4 ,?is is due to ! absorption1 by ! wat]1 ( a c]ta9 portion ( ! electric beam4 ,b a portion passes ?r\gh unabsorb$1 & does n at all contribute to ! heat+ ( ! wat]4 ,n[1 ice is also 9 great "p transp>5t to ^! latt] rays1 & !re=e is b little melt$ by !m4 ,h5ce1 by employ+ ! portion ( ! beam transmitt$ by wat]1 we are able to keep our l5s intact1 & to produce by means ( x a %>ply def9$ focus4 ,plac$ at t focus1 :ite pap] is n ignit$1 because x fails to absorb ! rays em]g5t f ! ice-l5s4 ,at ! same place1 h[ev]1 black pap] in/antly burns1 because x absorbs ! transmitt$ light4 ,& "h x may be useful to ref] to an e/imate by ,newton1 bas$ ^u d\btful data1 b repeat$ by v>i\s a/ronom]s ( em95ce s9ce 8 "t4 ,! comet ( #afhj1 :5 ne>e/ to ! sun1 0 only a six? ( ! sun's diamet] f 8 surface4 ,newton e/imat$ its temp]ature1 9 ?is position1 to be m ?an two ?\s& times t ( molt$ iron4 ,n[ x is cle> f ! =ego+ exp]im5ts t ! temp]ature ( ! comet c\ld n be inf]r$ f its ne>ness to ! sun4 ,if its p[] ( absorption 7 suffici5tly l[1 ! comet might c>ry into ! sun's neighb\rhood ! *ill ( /ell> space4 #d4 ,combu/ion ( a ,diamond by ,radiant ,heat4 ,! exp]im5t ( burn+ a diamond 9 oxyg5 by ! conc5trat$ rays ( ! sun 0 repeat$ at ,flor5ce1 9 pres5ce ( ,sir ,humphry ,davy1 on ,tuesday1 ! #bg? ( ,m>*1 #ahad4 ,x is ?us describ$ by ,f>aday3--',to-day we made ! gr& exp]im5t ( burn+ ! diamond1 & c]ta9ly ! ph5om5a pres5t$ 7 extremely beautiful & int]e/+4 ,a glass globe conta9+ ab\t #bb cubical in*es 0 exhau/$ ( air1 & fill$ ) pure oxyg54 ,! diamond 0 support$ 9 ! c5tre ( ?is globe4 ,! ,duke's burn+-glass 0 ! in/rum5t us$ to apply heat to ! diamond4 ,x consi/s ( two d\ble convex l5ses1 di/ant f ea* o!r ab\t #c feet2 ! l>ge l5s is ab\t #ad or #ae in*es 9 diamet]1 ! small] "o ab\t #c in*es 9 diamet]4 ,by means ( ! second l5s ! focus is v mu* r$uc$1 & ! heat1 :5 ! sun %9es brightly1 r5d]$ v int5se4 ,! diamond 0 plac$ 9 ! focus & anxi\sly wat*$4 ,on a sudd5 ,sir ,h4 ,davy obs]v$ ! diamond to burn visibly1 & :5 remov$ f ! focus x 0 f\nd to be 9 a /ate ( active & rapid combu/ion4' ,! combu/ion ( ! diamond _h nev] be5 effect$ by radiant heat f a t]re/rial s\rce4 ,i tri$ to accompli% ?is be=e cross+ ! ,atlantic1 & succe$$ 9 do+ s4 ,! small diamond n[ 9 my h& is held by a loop ( plat9um wire4 ,to protect x z f> z possible f air curr5ts1 & also to conc5trate ! heat ^u x1 x is surr\nd$ by a hood ( %eet plat9um4 ,br++ a j> ( oxyg5 und]nea?1 ,i cause ! focus ( ! electric beam to fall ^u ! diamond4 ,a small fraction ( ! "t exp5d$ 9 ! exp]im5t describ$ by ,f>aday suffices to raise ! diamond to a brilliant r$4 ,plung+ x !n into ! oxyg51 x gl[s l a little :ite />2 & x w\ld cont9ue to burn & gl[ until :olly consum$4 ,! focus c also be made to fall ^u ! diamond 9 oxyg51 z 9 ! ,flor5t9e exp]im5t3 ! result is ! same4 ,x 0 simply to secure m complete ma/]y ov] ! position ( ! focus1 s z to cause x to fall accurately ^u ! diamond1 t ! mode ( exp]im5t "h describ$ 0 resort$ to4 #e4 ,ultra-r$ ,rays3 ,caloresc5ce4 ,9 ! pa? ( ! beam issu+ f our lamp ,i n[ place a cell ) glass sides conta9+ a solution ( alum4 ,all ! light ( ! beam passes ?r\gh ?is solution4 ,?is light is receiv$ on a p[]fully conv]g+ mirror silv]$ 9 front1 & br\ght to a focus by ! mirror4 ,y c see ! conical beam ( reflect$ light track+ itself ?r\gh ! du/ ( ! room4 ,a scrap ( :ite pap] plac$ at ! focus %9es !re ) dazzl+ brightness1 b x is n ev5 *>r$4 ,on remov+ ! alum cell1 h[ev]1 ! pap] in/antly inflames4 ,!re mu/1 !re=e1 be some?+ 9 ?is beam besides its light4 ,! light is n absorb$ by ! :ite pap]1 & !re=e does n burn ! pap]2 b !re is some?+ ov] & above ! light :i* is absorb$1 & :i* provokes combu/ion4 ,:at is ?is some?+8 ,9 ! ye> #ahjj ,sir ,william ,h]s*el pass$ a !rmomet] ?r\gh ! v>i\s col\rs ( ! sol> spectrum1 & m>k$ ! rise ( temp]ature correspond+ to ea* col\r4 ,he f\nd ! heat+ effect to augm5t f ! violet to ! r$2 he did n1 h[ev]1 /op at ! r$1 b pu%$ 8 !rmomet] into ! d>k space beyond x4 ,"h he f\nd ! temp]ature actually high] ?an 9 any "p ( ! visible spectrum4 ,by ?is important obs]vation1 he prov$ t ! sun emitt$ heat-rays :i* are entirely unfit = ! purposes ( vision4 ,! subject 0 subsequ5tly tak5 up by ,seebeck1 ,melloni1 ,mll]1 & o!rs1 & )9 ! la/ few ye>s x has be5 f\nd capable ( unexpect$ expansions & applications4 ,i h devis$ a me?od :]eby ! sol> or electric beam c be s filt]$ z to deta* f x1 & pres]ve intact1 ?is invisible ultra-r$ emission1 :ile ! visible & ultra-violet emissions are :olly int]cept$4 ,we are ?us enabl$ to op]ate at w ^u ! purely ultra-r$ waves4 ,9 ! heat+ ( solid bodies to inc&esc5ce1 ?is non-visual emission is ! necess>y basis ( ! visual4 ,a plat9um wire is /ret*$ 9 front ( ! table1 & ?r\gh x an electric curr5t fl[s4 ,x is w>m$ by ! curr5t1 & may be felt to be w>m by ! h&4 ,x emits waves ( heat1 b no light4 ,augm5t+ ! /r5g? ( ! curr5t1 ! wire becomes hott]2 x f9ally gl[s ) a sob] r$ light4 ,at ?is po9t ,dr4 ,drap] _m ye>s ago began an int]e/+ inve/igation4 ,he employ$ a voltaic curr5t to heat 8 plat9um1 & he /udi$1 by means ( a prism1 ! successive introduction ( ! col\rs ( ! spectrum4 ,8 fir/ col\r1 z "h1 0 r$2 !n came orange1 !n yell[1 !n gre51 & la/ly all ! %ades ( blue4 ,z ! temp]ature ( ! plat9um 0 gradually augm5t$1 ! atoms 7 caus$ to vibrate m rapidly2 %ort] waves 7 ?us introduc$1 until f9ally waves 7 obta9$ correspond+ to ! entire spectrum4 ,z ea* successive col\r 0 introduc$1 ! col\rs prec$+ x became m vivid4 ,n[ ! vividness or int5sity ( light1 l t ( s\nd1 dep5ds n ^u ! l5g? ( ! wave1 b on ! amplitude ( ! vibration4 ,h5ce1 z ! less refrangible col\rs grew m int5se :5 ! m refrangible ones 7 introduc$1 we are =c$ to conclude t side by side ) ! introduction ( ! %ort] waves we _h an augm5tation ( ! amplitude ( ! long] ones4 ,^! rem>ks apply n only to ! visible emission exam9$ by ,dr4 ,drap]1 b to ! invisible emission :i* prec$es ! appe>ance ( any light4 ,9 ! emission f ! :ite-hot plat9um wire n[ be=e y1 ! lightless waves exi/ ) :i* we />t$1 only _! int5sity has be5 increas$ a ?\s&-fold by ! augm5tation ( temp]ature necess>y to ! production ( ?is :ite light4 ,bo? effects are b\nd up toge!r3 9 an inc&esc5t solid1 or 9 a molt5 solid1 y _c h ! %ort] waves )\t ?is int5sification ( ! long] ones4 ,a sun is possible only on ^! conditions2 h5ce ,sir ,william ,h]s*el's discov]y ( ! invisible ultra-r$ sol> emission4 ,! invisible heat1 emitt$ bo? by d>k bodies & by lum9\s ones1 flies ?r\gh space ) ! velosity ( light1 & is call$ radiant heat4 ,n[1 radiant heat may be made a subtle & p[]ful explor] ( molecul> condition1 &1 ( late ye>s1 x has giv5 a new significance to ! act ( *emical comb9ation4 ,take1 = example1 ! air we brea!4 ,x is a mixture ( oxyg5 & nitrog52 & x behaves t[>ds radiant heat l a vacuum1 be+ incompet5t to absorb x 9 any s5sible degree4 ,b p]mit ! same two gases to unite *emically2 !n1 )\t any augm5tation ( ! quantity ( matt]1 )\t alt]+ ! gase\s condition1 )\t int]f]+ 9 any way ) ! transp>5cy ( ! gas1 ! act ( *emical union is accompani$ by an enorm\s dim9ution ( its dia!rmancy1 or p]vi\sness to radiant heat4 ,! rese>*es :i* e/abli%$ ?is result also prov$ ! elem5t>y gases1 g5]ally1 to be highly transp>5t to radiant heat4 ,?is1 aga91 l$ to ! pro( ( ! dia!rmancy ( elem5t>y liquids1 l brom9e1 & ( solutions ( ! solid elem5ts sulphur1 phosphorus1 & iod9e4 ,a spectrum is n[ be=e y1 & y notice t ! transp>5t bisulphide ( c>bon has no effect ^u ! col\rs4 ,dropp+ into ! liquid a few flakes ( iod9e1 y see ! middle ( ! spectrum cut away4 ,by augm5t+ ! quantity ( iod9e1 we invade ! entire spectrum1 & f9ally cut x (f altoge!r4 ,n[1 ! iod9e1 :i* proves itself ?us ho/ile to ! light1 is p]fectly transp>5t to ! ultra-r$ emission ) :i* we h n[ to deal4 ,x1 !re=e1 is to be our ray-filt]4 ,plac+ ! alum-cell aga9 9 front ( ! electric lamp1 we assure ourselves1 z be=e1 ( ! utt] inability ( ! conc5trat$ light to fire :ite pap]-,introduc+ a cell conta9+ ! solution ( iod9e1 ! light is entirely cut (f2 & !n1 on remov+ ! alum-cell1 ! :ite pap] at ! d>k focus is in/antly set on fire4 ,black pap] is m absorb5t ?an :ite = ^! rays2 & ! consequ5ce is1 t ) x ! sudd5ness & vig\r ( ! combu/ion are augm5t$4 ,z9c is burnt up at ! same place1 magnesium bur/s into vivid combu/ion1 :ile a %eet ( plat9iz$ plat9um1 plac$ at ! focus1 is heat$ to :it5ess4 ,look$ at ?r\gh a prism1 ! :ite-hot plat9um yields all ! col\rs ( ! spectrum4 ,be=e imp++ ^u ! plat9um1 ! waves 7 ( too sl[ recurr5ce to awak5 vision2 by ! atoms ( ! plat9um1 ^! long & sluggi% waves are brok5 up into %ort] ones1 be+ ?us br\ght )9 ! visual range4 ,at ! o!r end ( ! spectrum1 by ! int]position ( suitable sub/ances1 ,pr(essor ,/okes l[]$ ! refrangibility1 s z to r5d] ! non-visual rays visual1 & to ?is *ange he gave ! "n ( ,fluoresc5ce4 ,"h1 by ! int]v5tion ( ! plat9um1 ! refrangibility is rais$1 s z to r5d] ! non-visual visual1 & to ?is *ange ,i h giv5 ! "n ( ,caloresc5ce4 ,at ! p]fectly invisible focus :]e ^! effects are produc$1 ! air may be z cold z ice4 ,air1 z already /at$1 does n absorb radiant heat1 & is !re=e n w>m$ by x4 ,no?+ c\ld m =cibly illu/rate ! isolation1 if ,i may use ! t]m1 ( ! lum9if]\s e!r f ! air4 ,! wave-motion ( ! "o is heap$ up to an extraord9>y degree ( int5sity1 )\t produc+ any s5sible effect ^u ! o!r4 ,i may add t1 ) suitable precautions1 ! eye may be plac$ 9 a focus compet5t to heat plat9um to vivid r$ness1 )\t exp]i5c+ any damage1 or ! slighte/ s5sation ei!r ( light or heat4 ,! important "p play$ by ^! ultra-r$ rays 9 ,nature may be ?us illu/rat$3 ,i remove ! iod9e filt]1 & conc5trate ! total beam ^u a te/ tube conta9+ wat]4 ,x imm$iately beg9s to splutt]1 & 9 a m9ute or two x boils4 ,:at boils x8 ,plac+ ! alum solution 9 front ( ! lamp1 ! boil+ in/antly ceases4 ,n[1 ! alum is p]vi\s to all ! lum9\s rays2 h5ce x _c be ^! rays t caus$ ! boil+4 ,i n[ introduce ! iod9e1 & remove ! alum3 vigor\s ebullition imm$iately recomm5ces at ! invisible focus4 ,s t we "h fix ^u ! invisible ultra-r$ rays ! heat+ ( ! wat]4 ,we are ?us enabl$ to und]/& ! mom5t\s "p play$ by ^! rays 9 ,nature4 ,x is to !m t we owe ! w>m+ & ! consequ5t evaporation ( ! tropical ocean2 x is to !m1 !re=e1 t we owe our ra9s & sn[s4 ,!y are absorb$ close to ! surface ( ! ocean1 & w>m ! sup]ficial wat]1 :ile ! lum9\s rays plunge to great dep?s )\t produc+ any s5sible effect4 ,b we c proce$ fur!r ?an ?is4 ,"h is a l>ge flask conta9+ a freez+ mixture1 :i* has s *ill$ ! flask1 t ! aque\s vap\r ( ! air ( ?is room has be5 cond5s$ & froz5 ^u x to a :ite fur4 ,introduc+ ! alum-cell1 & plac+ ! coat+ ( ho>-fro/ at ! int5sely lum9\s focus ( ! electric lamp1 n a spicula ( ! dazzl+ fro/ is melt$4 ,introduc+ ! iod9e-cell1 & remov+ ! alum1 a broad space ( ! froz5 coat+ is in/antly melt$ away4 ,h5ce we inf] t ! sn[ & ice1 :i* fe$ ! ,rhone1 ! ,rh9e1 & o!r riv]s ) glaci]s = _! s\rces1 are releas$ f _! imprisonm5t ^u ! m\nta9s by ! invisible ultra-r$ rays ( ! sun4 #f4 ,id5tity ( ,light & ,radiant ,heat4 ,reflection f ,plane & ,curv$ ,surfaces4 ,total ,reflection ( ,heat4 ,! gr[? ( sci5ce is organic4 ,t :i* today is an end becomes to-morr[ a means to a remot] end4 ,e new discov]y 9 sci5ce is imm$iately made ! basis ( o!r discov]ies1 or ( new me?ods ( inve/igation4 ,?us ab\t fifty ye>s ago ,o,ersted1 ( ,cop5hag51 discov]$ ! deflection ( a magnetic ne$le by an electric curr5t2 & ab\t ! same "t ,?omas ,seebeck1 ( ,b]l91 discov]$ !rmoelectricity4 ,^! great discov]ies 7 soon aft]w>ds turn$ to acc\nt1 by ,nobili & ,melloni1 9 ! con/ruction ( an in/rum5t :i* has va/ly augm5t$ our k ( radiant heat4 ,?is in/rum5t1 :i* is call$ a !rmo-electric pile1 or m briefly a !rmo-pile1 consi/s ( ?9 b>s ( bismu? & antimony1 sold]$ alt]nately toge!r at _! ends1 b sep>at$ f ea* o!r else:]e4 ,f ! ends ( ?is '!rmo-pile' wires pass to a galvanomet]1 :i* consi/s ( a coil ( cov]$ wire1 )9 & above :i* are susp5d$ two magnetic ne$les1 jo9$ to a rigid sy/em1 & c>efully def5d$ f curr5ts ( air4 ,! action ( ! arrangem5t is ?is3 ! heat1 fall+ on ! pile1 produces an electric curr5t2 ! curr5t1 pass+ ?r\gh ! coil1 deflects ! ne$les1 & ! magnitude ( ! deflection may be made a measure ( ! heat4 ,! upp] ne$le moves ov] a graduat$ dial f> too small to be directly se54 ,x is n[1 h[ev]1 /rongly illum9at$2 & above x is a l5s :i*1 if p]mitt$1 w\ld =m an image ( ! ne$le & dial ^u ! ceil+4 ,!re1 h[ev]1 x c\ld n be conv5i5tly view$4 ,! beam is !re=e receiv$ ^u a look+-glass1 plac$ at ! prop] angle1 :i* ?r[s ! image ^u a scre54 ,9 ?is way ! motions ( ?is small ne$le may be made visible to y all4 ,! delicacy ( ?is app>atus is su* t 9 a room fill$1 z ?is room n[ is1 ) an audi5ce physically w>m1 x is exce$+ly difficult to "w ) x4 ,my assi/ant /&s sev]al feet (f4 ,i turn ! pile t[>ds him3 ! heat radiat$ f 8 face1 ev5 at ?is di/ance1 produces a deflection ( #ij4 ,i turn ! in/rum5t t[>ds a di/ant wall1 a little bel[ ! av]age temp]ature ( ! room4 ,! ne$le desc5ds & passes to ! o!r side ( z]o1 decl>+ by ?is negative deflection t ! pile has lo/ its w>m? by radiation aga9/ ! cold wall4 ,possess$ ( ?is in/rum5t1 ( our ray-filt]1 & ( our l>ge ,nicol prisms1 we are 9 a condition to inve/igate a subject ( great philosophical int]e/2 "o :i* long engag$ ! att5tion ( "s ( our =emo/ sci5tific work]s--! sub/antial id5tity ( light & radiant heat4 ,t !y are id5tical 9 all respects _c ( c\rse be ! case1 = if !y 7 !y w\ld act 9 ! same mann] ^u all in/rum5ts1 ! eye includ$4 ,! id5tity meant is su* z subsi/s betwe5 "o col\r & ano!r1 caus+ !m to behave alike z reg>ds reflection1 refraction1 d\ble refraction1 & pol>ization4 ,let u "h run rapidly ov] ! resemblances ( light & heat4 ,z reg>ds reflection f plane surfaces1 we may employ a look+-glass to reflect ! light4 ,m>k+ any po9t 9 ! track ( ! reflect$ beam1 cutt+ (f ! light by ! dissolv$ iod9e1 & plac+ ! pile at ! m>k$ po9t1 ! ne$le imm$iately />ts aside1 %[+ t ! heat is reflect$ 9 ! same direction z ! light4 ,?is is true = e position ( ! mirror4 ,recurr+1 = example1 to ! simple app>atus employ$ 9 our fir/ lecture 7fig4 #c1 p4 #aa72 mov+ ! index atta*$ to ! mirror along ! divisions ( our graduat$ arc 7m n71 & det]m9+ by ! pile ! positions ( ! invisible reflect$ beam1 we prove t ! angul> velocity ( ! heat-beam1 l t ( ! light-beam1 is twice t ( ! mirror4 ,illu/ration3 ,fig4 #di4 ,z reg>ds reflection f curv$ surfaces1 ! id5tity also holds good4 ,receiv+ ! beam f our electric lamp on a concave mirror 7m m1 fig4 #di71 x is ga!r$ up into a cone ( reflect$ light r5d]$ visible by ! float+ du/ ( ! air2 m>k+ ! apex ( ! cone by a po9t]1 & cutt+ (f ! light by ! iod9e solution 7,t71 a mom5t's exposure ( ! pile 7,p7 at ! m>k$ po9t produces a viol5t deflection ( ! ne$le4 ,! common reflection & ! total reflection ( a beam ( radiant heat may be simultane\sly demon/rat$4 ,f ! nozzle ( ! lamp 7,l1 fig4 #ej7 a beam imp+es ^u a plane mirror 7,m ,n71 is reflect$ upw>ds1 & ent]s a "r-angl$ prism1 ( :i* a b c is ! section4 ,x meets ! hypo!nuse at an obliquity great] ?an ! limit+ angle1#bc & is !re=e totally reflect$4 ,qu5*+ ! light by ! ray-filt] at ,f1 & plac+ ! pile at ,p1 ! totally reflect$ heat-beam is imm$iately felt by ! pile1 & decl>$ by ! galvanometric deflection4 ,illu/ration3 ,fig4 #ej4 #g4 ,invisible ,images =m$ by ,radiant ,heat4 ,p]haps no exp]im5t proves m conclusively ! sub/antial id5tity ( light & radiant heat1 ?an ! =mation ( invisible heat-images4 ,employ+ ! mirror already us$ to raise ! beam to its highe/ /ate ( conc5tration1 we obta91 z is well kn[n1 an inv]t$ image ( ! c>bon po9ts1 =m$ by ! light rays at ! focus4 ,cutt+ (f ! light by ! ray-filt]1 & plac+ at ! focus a ?9 %eet ( plat9iz$ plat9um1 ! invisible rays decl>e _! pres5ce & di/ribution1 by /amp+ ^u ! plat9um a :ite-hot image ( ! c>bons4 7,see fig4 #ea47 ,illu/ration3 ,fig4 #ea4 #h4 ,pol>ization ( ,heat4 ,:e!r radiant heat be capable ( pol>ization or n 0 = a long "t a subject ( discussion4 ,br>d _h ann\nc$ affirmative results1 b ,p[ell & ,lloyd fail$ to v]ify !m4 ,! d\bts ?us ?r[n ^u ! "q 7 remov$ by ! exp]im5ts ( ,=bes1 :o fir/ e/abli%$ ! pol>ization & 'depol>ization' ( heat4 ,! subject 0 subsequ5tly foll[$ up by ,melloni1 an inve/igator ( consummate ability1 :o sagaci\sly turn$ to acc\nt 8 own discov]y1 t ! obscure rays ( lum9\s s\rces are 9 "p transmitt$ by black glass4 ,int]cept+ by a plate ( ?is glass ! light f an oil flame1 & op]at+ ^u ! transmitt$ invisible heat1 he obta9$ effects ( pol>ization1 f> exce$+ 9 magnitude ^? :i* c\ld be obta9$ ) non-lum9\s s\rces4 ,at pres5t ! possession ( our m p]fect ray-filt]1 & m p[]ful s\rce ( heat1 enables u to pursue ?is id5tity "q to its utmo/ practical limits4 ,illu/ration3 ,fig4 #eb4 ,m\nt+ our two ,nicols 7,b & ,c1 fig4 #eb7 9 front ( ! electric lamp1 ) _! pr9cipal sections cross$1 no light rea*es ! scre54 ,plac+ our !rmo-electric pile 7,d7 beh9d ! prisms1 ) its face turn$ t[>ds ! s\rce1 no deflection ( ! galvanomet] is obs]v$4 ,int]pos+ betwe5 ! lamp 7,a7 & ! fir/ prism 7,b7 our ray-filt]1 ! light previ\sly transmitt$ ?r\gh ! fir/ ,nicol is qu5*$2 & n[ ! slighte/ turn+ ( ei!r ,nicol op5s a way = ! transmission ( ! heat1 a v small rotation suffic+ to s5d ! ne$le up to #ij4 ,:5 ! ,nicol is turn$ back to its fir/ position1 ! ne$le aga9 s9ks to z]o1 ?us demon/rat+1 9 ! pla9e/ mann]1 ! pol>ization ( ! heat4 ,:5 ! ,nicols are cross$ & ! field is d>k1 y h se51 9 ! case ( light1 ! effect ( introduc+ a plate ( mica betwe5 ! pol>iz] & analyz]4 ,9 two positions ! mica ex]ts no s5sible influ5ce2 9 all o!rs x does4 ,a precisely analog\s deportm5t is obs]v$ z reg>ds radiant heat4 ,introduc+ our ray-filt]1 ! !rmo-pile1 play+ ! "p ( an eye z reg>ds ! invisible radiation1 receives no heat :5 ! eye receives no light2 b :5 ! mica is s turn$ z to make its planes ( vibration oblique to ^? ( ! pol>iz] & analyz]1 ! heat imm$iately passes ?r\gh4 ,s /rong does ! action become1 t ! mom5t>y plung+ ( ! film ( mica into ! d>k space betwe5 ! ,nicols suffices to s5d ! ne$le up to #ij4 ,?is is ! effect to :i* ! t]m 'depol>ization' has be5 appli$2 ! exp]im5t really prov+ t ) bo? light & heat we h ! same resolution by ! plate ( mica1 & recomp\nd+ by ! analyz]1 ( ! e!real vibrations4 ,remov+ ! mica & re/or+ ! ne$le once m to #j1 ,i introduce betwe5 ! ,nicols a plate ( qu>tz cut p]p5dicul> to ! axis2 ! imm$iate deflection ( ! ne$le decl>es ! transmission ( ! heat1 & :5 ! transmitt$ beam is prop]ly exam9$1 x is f\nd to be circul>ly pol>iz$1 exactly z a beam ( light is pol>iz$ "u ! same conditions4 #i4 ,d\ble ,refraction ( ,heat4 ,i w n[ ab&on ! ,nicols1 & s5d ?r\gh ! piece ( ,icel& sp> 7,b1 fig4 #ec71 already employ$ 79 ,lecture ,,iii47 to illu/rate ! d\ble refraction ( light1 our sift$ beam ( invisible heat4 ,to det]m9e ! positions ( ! two images1 let u fir/ op]ate ^u ! lum9\s beam4 ,m>k+ ! places ( ! light-images1 we introduce betwe5 ,n & ,l our ray-filt] 7n 9 ! figure7 & qu5* ! light4 ,caus+ ! pile to approa* "o ( ! m>k$ places1 ! ne$le rema9s unmov$ until ! place has be5 atta9$2 "h ! pile at once detects ! heat4 ,pu%+ ! pile across ! int]val sep>at+ ! two m>ks1 ! ne$le fir/ falls to #j1 & !n rises aga9 to #ij 9 ! second position4 ,?is proves ! d\ble refraction ( ! heat4 ,illu/ration3 ,fig4 #ec4 ,i n[ turn ! ,icel& sp>3 ! ne$le rema9s fix$2 !re is no alt]ation ( ! deflection4 ,pass+ ! pile rapidly across to ! o!r m>k1 ! deflection is ma9ta9$4 ,once m ,i turn ! sp>1 b n[ ! ne$le falls to #j1 ris+1 h[ev]1 aga9 to #ij aft] a rotation ( #cfj4 ,we "k t 9 ! case ( light ! extraord9>y beam rotates r\nd ! ord9>y "o2 & we h "h be5 op]at+ on ! extraord9>y heat-beam1 :i*1 z reg>ds d\ble refraction1 behaves exactly l a beam ( light4 #aj4 ,magnetization ( ,heat4 ,to r5d] our s]ies ( comp>isons complete1 we mu/ demon/rate ! magnetization ( heat4 ,b "h a slight modification ( our arrangem5t w be necess>y4 ,9 repeat+ ,f>aday's exp]im5t on ! magnetization ( light1 we _h1 9 ! fir/ in/ance1 our ,nicols cross$ & ! field r5d]$ d>k1 a fla% ( light appe>+ ^u ! scre5 :5 ! magnet 0 excit$4 ,n[ ! quantity ( light transmitt$ 9 ?is case is really v small1 its effect be+ r5d]$ /rik+ ?r\gh contra/ ) ! prec$+ d>kness4 ,:5 we s place ! ,nicols t _! pr9cipal sections enclose an angle ( #de1 ! excitem5t ( ! magnet causes a f> great] positive augm5tation ( ! light1 ?\gh ! augm5tation is n s well se5 ?r\gh lack ( contra/1 because "h1 at />t+1 ! field is illum9at$4 ,9 try+ to magnetize our beam ( heat1 we w adopt ?is arrangem5t4 ,"h1 h[ev]1 at ! outset1 a consid]able am\nt ( heat falls ^u "o face ( ! pile4 ,?is x is necess>y to neutralize1 by p]mitt+ rays f ano!r s\rce to fall ^u ! opposite face ( ! pile4 ,! ne$le is ?us br\ght to z]o4 ,cutt+ (f ! light by our ray-filt]1 & excit+ ! magnet1 ! ne$le is in/antly deflect$1 prov+ t ! magnet has op5$ a door = ! heat1 exactly z 9 ,f>aday's exp]im5t x op5$ a door = ! light4 ,?us1 9 e case br\ght "u our notice1 ! sub/antial id5tity ( light & radiant heat has be5 demon/rat$4 ,by ! ref9$ exp]im5ts ( ,knoblau*1 :o work$ long & successfully at ?is "q1 ! d\ble refraction ( heat1 by ,icel& sp>1 0 fir/ demon/rat$2 b1 ?\gh he employ$ ! lum9\s heat ( ! sun1 ! obs]v$ deflections 7 exce$+ly small4 ,s1 likewise1 ^? em95t inve/igators ,de la ,povo/aye & ,desa9s succe$$ 9 magnetiz+ a beam ( heat2 b ?\gh1 9 _! case also1 ! lum9\s sol> heat 0 employ$1 ! deflection obta9$ did n am\nt to m ?an two or ?ree degrees4 ,) obscure radiant heat ! effect1 prior to ! exp]im5ts n[ br\ght be=e y1 _h n be5 obta9$2 b1 ) ! arrangem5t "h describ$1 we obta9 deflections f purely invisible heat1 equal to #aej ( ! l[] degrees ( ! galvanomet]4 #aa4 ,di/ribution ( ,heat 9 ! ,electric ,spectrum4 ,we h f9ally to det]m9e ! position & magnitude ( ! invisible radiation :i* produces ^! results4 ,= ?is purpose we employ a p>ticul> =m ( ! !rmo-pile4 ,its face is a rectangle1 :i* by movable side-pieces c be r5d]$ z n>r[ z desirable4 ,?r[+ a small & conc5trat$ spectrum ^u a scre51 by means ( an endless screw we move ! rectangul> pile ?r\gh ! entire spectrum1 & det]m9e 9 succession ! !rmal p[] ( all its col\rs4 ,illu/ration3 ,,spectrum ,,( ,,electric ,,light4 ,:5 ?is in/rum5t is br\ght to ! violet end ( ! spectrum1 ! heat is f\nd to be almo/ ins5sible4 ,z ! pile gradually moves f ! violet t[>ds ! r$1 x enc\nt]s a gradually augm5t+ heat4 ,! r$ itself possesses ! highe/ heat+ p[] ( all ! col\rs ( ! spectrum4 ,pu%+ ! pile into ! d>k space beyond ! r$1 ! heat rises sudd5ly 9 int5sity1 & at "s di/ance beyond ! r$ x atta9s a maximum4 ,f ?is po9t ! heat falls some:at m rapidly ?an x rose1 & aft]w>ds gradually fades away4 ,draw+ a horizontal l9e to repres5t ! l5g? ( ! spectrum1 & erect+ along x1 at v>i\s po9ts1 p]p5dicul>s proportional 9 l5g? to ! heat exi/+ at ^? po9ts1 we obta9 a curve :i* exhibits ! di/ribution ( heat 9 ! prismatic spectrum4 ,x is repres5t$ 9 ! adjac5t figure4 ,beg9n+ at ! blue1 ! curve rises1 at fir/ v gradually2 t[>ds ! r$ x rises m rapidly1 ! l9e ,c ,d 7fig4 #ed1 opposite page7 repres5t+ ! /r5g? ( ! extreme r$ radiation4 ,beyond ! r$ x %oots upw>ds 9 a /eep & massive peak to ,b2 :5ce x falls1 rapidly = a "t1 & aft]w>ds gradually fades f ! p]ception ( ! pile4 ,?is figure is ! result ( m ?an twelve c>eful s]ies ( measurem5ts1 f ea* ( :i* ! curve 0 con/ruct$4 ,on sup]pos+ all ^! curves1 a satisfactory agreem5t 0 f\nd to exi/ betwe5 !m4 ,s t x may safely be conclud$ t ! areas ( ! d>k & :ite spaces1 respectively1 repres5t ! relative en]gies ( ! visible & invisible radiation4 ,! "o is #g4g times ! o!r4 ,b 9 v]ification1 z already /at$1 consi/s ! /r5g? ( sci5ce4 ,det]m9+ 9 ! fir/ place ! total emission f ! electric lamp1 & !n1 by means ( ! iod9e filt]1 det]m9+ ! ultra-r$ emission2 ! diff]5ce betwe5 bo? gives ! lum9\s emission4 ,9 ?is way1 x is f\nd t ! en]gy ( ! invisible emission is eight times t ( ! visible4 ,no two me?ods c\ld be m oppos$ to ea* o!r1 & h>dly any two results c\ld bett] h>monize4 ,i ?9k1 !re=e1 y may rely ^u ! accuracy ( ! di/ribution ( heat "h assign$ to ! prismatic spectrum ( ! electric light4 ,!re is no?+ vague 9 ! mode ( inve/igation1 or d\btful 9 its conclusions4 ,spectra are1 h[ev]1 =m$ by diffraction1 :]e9 ! di/ribution ( bo? heat & light is diff]5t f t produc$ by ! prism4 ,^! diffractive spectra h be5 exam9$ ) great skill by ,drap] & ,langley4 ,9 ! prismatic spectrum ! less refrangible rays are compress$ into a mu* small] space ?an 9 ! diffraction spectrum4 ,,lecture ,,vi4 ,,pr9ciples ,,( ,,spectrum ,,analysis ,,prismatic ,,analysis ,,( ,,! ,,light ,,( ,,inc&esc5t ,,vap\rs ,,discont9u\s ,,spectra ,,spectrum ,,b&s ,,prov$ ,,by ,,buns5 ,,& ,,kir*h(f ,,to ,,be ,,*>act]i/ic ,,( ,,! ,,vap\r ,,discov]y ,,( ,,rubidium1 ,c,,sium1 ,,& ,,?allium ,,relation ,,( ,,emission ,,to ,,absorption ,,! ,,l9es ,,( ,,fraunh(] ,,_! ,,explanation ,,by ,,kir*h(f ,,sol> ,,*emi/ry ,,involv$ ,,9 ,,?is ,,explanation ,,f\cault',s ,,exp]im5t ,,pr9ciples ,,( ,,absorption ,,analogy ,,( ,,s\nd ,,& ,,light ,,exp]im5tal ,,demon/ration ,,( ,,?is ,,analogy ,,rec5t ,,applications ,,( ,,! ,,spectroscope ,,summ>y ,,& ,,conclusion4 ,we h employ$ z our s\rce ( light 9 ^! lectures ! ends ( two rods ( coke r5d]$ inc&esc5t by electricity4 ,coke is p>ticul>ly suitable = ?is purpose1 because x c be> int5se heat )\t fusion or vaporization4 ,x is also black1 :i* helps ! light2 =1 o!r circum/ances be+ equal1 z %[n exp]im5tally by ,pr(essor ,balf\r ,/ew>t1 ! black] ! body ! bright] w be its light :5 inc&esc5t4 ,/ill1 refractory z c>bon is1 if we closely exam9$ our voltaic arc1 or /ream ( light betwe5 ! c>bon-po9ts1 we %\ld f9d !re inc&esc5t c>bon-vap\r4 ,& if we c\ld deta* ! light ( ?is vap\r f ! m dazzl+ light ( ! solid po9ts1 we %\ld f9d its spectrum n only less brilliant1 b ( a totally diff]5t "* f ! spectra t we h already se54 ,in/ead ( be+ an unbrok5 succession ( col\rs f r$ to violet1 ! c>bon-vap\r w\ld yield a few b&s ( col\r ) spaces ( d>kness betwe5 !m4 ,:at is true ( ! c>bon is true 9 a /ill m /rik+ degree ( ! metals1 ! mo/ refractory ( :i* c be fus$1 boil$1 & r$uc$ to vap\r by ! electric curr5t4 ,f ! inc&esc5t vap\r ! light1 z a g5]al rule1 fla%es 9 gr\ps ( rays ( def9ite degrees ( refrangibility1 spaces exi/+ betwe5 gr\p & gr\p1 :i* are unfill$ by rays ( any k9d4 ,b ! contemplation ( ! facts w r5d] ?is subject m intelligible ?an words c make x4 ,)9 ! cam]a is n[ plac$ a cyl9d] ( c>bon holl[$ out at ! top2 9 ! holl[ is plac$ a fragm5t ( ! metal ?allium4 ,d[n ^u ?is we br+ ! upp] c>bon-po9t1 & !n sep>ate ! "o f ! o!r4 ,a /ream ( inc&esc5t ?allium-vap\r passes betwe5 !m1 ! magnifi$ image ( :i* is n[ se5 ^u ! scre54 ,x is ( a beautiful gre5 col\r4 ,:at is ! mean+ ( t gre58 ,we answ] ! "q by subject+ ! light to prismatic analysis4 ,s5t ?r\gh ! prism1 its spectrum is se5 to consi/ ( a s+le refract$ b&4 ,light ( "o degree ( refrangibility--t correspond+ to ?is p>ticul> gre5--is emitt$ by ! ?allium-vap\r4 ,we w n[ remove ! ?allium & put a bit ( silv] 9 its place4 ,! are ( silv] is n to be di/+ui%$ f t ( ?allium2 x is n only gre51 b ! same %ade ( gre54 ,are !y !n alike8 ,prismatic analysis enables u to answ] ! "q4 ,h[ev] impossible x is to di/+ui% ! "o col\r f ! o!r1 x is equally impossible to conf\nd ! spectrum ( inc&esc5t silv]-vap\r ) t ( ?allium4 ,9 ! case ( silv]1 we h two gre5 b&s in/ead ( "o4 ,if we add to ! silv] 9 our cam]a a bit ( ?allium1 we %all obta9 ! light ( bo? metals4 ,aft] wait+ a little1 we see t ! gre5 ( ! ?allium lies midway betwe5 ! two gre5s ( ! silv]4 ,h5ce ?is simil>ity ( col\r4 ,b :y h we to 'wait a little' be=e we see ?is effect8 ,! ?allium b& at fir/ almo/ masks ! silv] b&s by its sup]ior brightness4 ,inde$1 ! silv] b&s h wond]fully deg5]at$ s9ce ! bit ( ?allium 0 put 91 & = a reason wor? kn[+4 ,x is ! resi/ance (f]$ to ! passage ( ! electric curr5t f c>bon to c>bon1 t calls =? ! p[] ( ! curr5t to produce heat4 ,if ! resi/ance 7 mat]ially less5$1 ! heat w\ld be mat]ially less5$2 & if all resi/ance 7 aboli%$1 !re w\ld be no heat at all4 ,n[1 ?allium is a mu* m fusible & vaporizable metal ?an silv]2 & its vap\r facilitates ! passage ( ! electricity to su* a degree1 z to r5d] ! curr5t almo/ incompet5t to vaporize ! m refractory silv]4 ,b ! ?allium is gradually consum$2 its vap\r dim9i%es1 ! resi/ance rises1 until f9ally y see ! two silv] b&s z brilliant z !y 7 at fir/4#bd ,we h 9 ^! b&s a p]fectly unalt]able *>act]i/ic ( ! two metals4 ,y nev] get o!r b&s ?an ^! two gre5 ones f ! silv]1 nev] o!r ?an ! s+le gre5 b& f ! ?allium1 nev] o!r ?an ! ?ree gre5 b&s f ! mixture ( bo? metals4 ,e kn[n metal has its own p>ticul> b&s1 & 9 no kn[n case are ! b&s ( two diff]5t metals alike 9 refrangibility4 ,x foll[s1 !re=e1 t ^! spectra may be made a sure te/ = ! pres5ce or abs5ce ( any p>ticul> metal4 ,if we pass f ! metals to _! alloys1 we f9d no confusion4 ,copp] gives gre5 b&s2 z9c gives blue & r$ b&s2 brass--an alloy ( copp] & z9c--gives ! b&s ( bo? metals1 p]fectly unalt]$ 9 position or "*4 ,b we are n conf9$ to ! metals !mselves2 ! salts ( ^! metals yield ! b&s ( ! metals4 ,*emical union is ruptur$ by a suffici5tly high heat2 ! vap\r ( ! metal is set free1 & x yields its *>act]i/ic b&s4 ,! *lorides ( ! metals are p>ticul>ly suitable = exp]im5ts ( ?is "*4 ,common salt1 = example1 is a comp\nd ( *lor9e & sodium2 9 ! electric lamp x yields ! spectrum ( ! metal sodium4 ,! *lorides ( copp]1 li?ium1 & /rontium yield1 9 l mann]1 ! b&s ( ^! metals4 ,:51 !re=e1 ,buns5 & ,kir*h(f1 ! illu/ri\s f\nd]s ( spectrum analysis1 aft] hav+ e/abli%$ by an exhau/ive exam9ation ! spectra ( all kn[n sub/ances1 discov]$ a spectrum conta9+ b&s diff]5t f any kn[n b&s1 !y imm$iately inf]r$ ! exi/5ce ( a new metal4 ,!y 7 op]at+ at ! "t ^u a residue1 obta9$ by evaporat+ "o ( ! m9]al wat]s ( ,g]many4 ,9 t wat] !y knew ! unkn[n metal 0 conceal$1 b va/ quantities ( x _h to be evaporat$ be=e a residue c\ld be obta9$ suffici5tly l>ge to enable ord9>y *emi/ry to grapple ) ! metal4 ,!y1 h[ev]1 hunt$ x d[n1 & x n[ /&s among *emical sub/ances z ! metal ,rubidium4 ,!y subsequ5tly discov]$ a second metal1 :i* !y call$ ,csium4 ,?us1 hav+ fir/ plac$ spectrum analysis on a sure f\ndation1 !y demon/rat$ its capacity z an ag5t ( discov]y4 ,soon aft]w>ds ,mr4 ,crookes1 pursu+ ! same me?od1 discov]$ ! bright gre5 b& ( ,?allium1 & obta9$ ! salts ( ! metal :i* yield$ x4 ,! metal itself 0 fir/ isolat$ 9 +ots by ,m4 ,lamy1 a ,fr5* *emi/4 ,all ?is relates to *emical discov]y ^u e>?1 :]e ! mat]ials are 9 our own h&s4 ,b x 0 soon %[n h[ spectrum analysis might be appli$ to ! inve/igation ( ! sun & />s2 & ?is result 0 rea*$ ?r\gh ! solution ( a problem :i* _h be5 long an enigma to natural philosoph]s4 ,! scope & conque/ ( ?is problem we mu/ n[ endeav\r to compreh5d4 ,a spectrum is pure 9 :i* ! col\rs d n ov]lap ea* o!r4 ,we purify ! spectrum by mak+ our beam n>r[1 & by augm5t+ ! numb] ( our prisms4 ,:5 a pure spectrum ( ! sun has be5 obta9$ 9 ?is way1 x is f\nd to be furr[$ by innum]able d>k l9es4 ,f\r ( !m 7 fir/ se5 by ,dr4 ,wolla/on1 b !y 7 aft]w>ds multipli$ & measur$ by ,fraunh(] ) su* ma/]ly skill1 t !y are n[ univ]sally kn[n z ,fraunh(]'s l9es4 ,to give an explanation ( ^! l9es 01 z ,i h said1 a problem :i* long *all5g$ ! att5tion ( philosoph]s1 & to ,pr(essor ,kir*h(f belongs ! hon\r ( hav+ fir/ conqu]$ ?is problem4 7,! positions ( ! pr9cipal l9es1 lett]$ accord+ to ,fraunh(]1 are %[n 9 ! annex$ sket* 7fig4 #ee7 ( ! sol> spectrum4 ,a is suppos$ to /& ne> ! extreme r$1 & ,j ne> ! extreme violet47 ,illu/ration3 ,fig4 #ee4 ,! brief memoir ( two pages1 9 :i* ?is immortal discov]y is record$1 0 communicat$ to ! ,b]l9 ,academy on ,octob] #bg1 #ahei4 ,fraunh(] _h rem>k$ 9 ! spectrum ( a c&le flame two bright l9es1 :i* co9cide accurately1 z to position1 ) ! d\ble d>k l9e ,d ( ! sol> spectrum4 ,^! bright l9es are produc$ ) p>ticul> int5sity by ! yell[ flame d]iv$ f a mixture ( salt & alcohol4 ,!y are 9 fact ! l9es ( sodium vap\r4 ,kir*h(f produc$ a spectrum by p]mitt+ ! sunlight to ent] 8 telescope by a slit & prism1 & 9 front ( ! slit he plac$ ! yell[ sodium flame4 ,z long z ! spectrum rema9$ feeble1 !re always appe>$ two bright l9es1 d]iv$ f ! flame1 9 ! place ( ! two d>k l9es ,d ( ! spectrum4 ,9 ?is case1 su* absorption z ! flame ex]t$ ^u ! sunlight 0 m ?an aton$ = by ! radiation f ! flame4 ,:51 h[ev]1 ! sol> spectrum 0 r5d]$ suffici5tly int5se1 ! bright b&s vani%$1 & ! two d>k ,fraunh(] l9es appe>$ ) mu* great] %>pness & di/9ctness ?an :5 ! flame 0 n employ$4 ,?is result1 be x not$1 0 n due to any real qu5*+ ( ! bright l9es ( ! flame1 b to ! augm5tation ( ! int5sity ( ! adjac5t spectrum4 ,! exp]im5t prov$ to demon/ration1 t :5 ! :ite light s5t ?r\gh ! flame 0 suffici5tly int5se1 ! quantity :i* ! flame absorb$ 0 f> 9 excess ( t :i* x radiat$4 ,"h !n is a result ( ! utmo/ significance4 ,kir*h(f imm$iately inf]r$ f x t ! salt flame1 :i* c\ld int5sify s rem>kably ! d>k l9es ( ,fraunh(]1 ought also to be able to produce !m4 ,! spectrum ( ! ,drummond light is kn[n to exhibit ! two bright l9es ( sodium1 :i*1 h[ev]1 gradually disappe> z ! modicum ( sodium1 conta9$ z an impurity 9 ! inc&esc5t lime1 is exhau/$4 ,kir*h(f =m$ a spectrum ( ! limelight1 & aft] ! two bright l9es _h vani%$1 he plac$ 8 salt flame 9 front ( ! slit4 ,! two d>k l9es imm$iately />t$ =?4 ,?us1 9 ! cont9u\s spectrum ( ! lime-light1 he evok$1 artificially1 ! l9es ,d ( ,fraunh(]4 ,kir*h(f knew t ?is 0 an action n peculi> to ! sodium flame1 & he imm$iately ext5d$ 8 g5]alisation to all col\r$ flames :i* yield %>ply def9$ bright b&s 9 _! spectra4 ,:ite light1 ) all its con/itu5ts complete1 s5t ?r\gh su* flames1 w\ld1 he inf]r$1 h ^? precise con/itu5ts absorb$1 ^: refrangibilities are ! same z ^? ( ! bright b&s2 s t aft] pass+ ?r\gh su* flames1 ! :ite light1 if suffici5tly int5se1 w\ld h its spectrum furr[$ by b&s ( d>kness4 ,on ! occasion "h ref]r$ to ,kir*h(f also succe$$ 9 rev]s+ a bright b& ( li?ium4 ,! long-/&+ difficulty ( ,fraunh(]'s l9es fell to pieces 9 ! pres5ce ( facts & reflections l ^!1 :i* also c>ri$ ) !m an immeasurable ext5sion ( ! *emi/'s p[]4 ,kir*h(f saw t f ! agreem5t ( ! l9es 9 ! spectra ( t]re/rial sub/ances ) ,fraunh(]'s l9es1 ! pres5ce ( ^! sub/ances 9 ! sun & fix$ />s might be imm$iately inf]r$4 ,?us ! d>k l9es ,d 9 ! sol> spectrum prov$ ! exi/5ce ( sodium 9 ! sol> atmosph]e2 :ile ! bright l9es discov]$ by ,brew/] 9 a nitre flame1 :i* _h be5 prov$ to co9cide exactly ) c]ta9 d>k l9es betwe5 ,a & ,b 9 ! sol> spectrum1 prov$ ! exi/5ce ( potassium 9 ! sun4 ,all subsequ5t rese>* v]ifi$ ! accuracy ( ^! fir/ d>+ conclusions4 ,9 8 second pap]1 communicat$ to ! ,b]l9 ,academy be=e ! close ( #ahei1 ,kir*h(f prov$ ! exi/5ce ( iron 9 ! sun4 ,! bright l9es ( ! spectrum ( iron vap\r are exce$+ly num]\s1 & #fe ( !m 7 subsequ5tly prov$ by ,kir*h(f to be absolutely id5tical 9 position ) #fe d>k ,fraunh(]'s l9es4 ng/rm & ,?aln pu%$ ! co9cid5ces to #dej = iron1 :ile1 accord+ to ! same excell5t inve/igators1 ! foll[+ numb]s express ! co9cid5ces1 9 ! case ( ! respective metals to :i* !y are atta*$3-- ,calcium #ge ,b>ium #aa ,magnesium #d ,manganese #eg ,titanium #aah ,*romium #ah ,nickel #cc ,cobalt #ai ,hydrog5 #d ,alum9ium #b ,z9c #b ,copp] #g ,! probability is ov]:elm+ t all ^! sub/ances exi/ 9 ! atmosph]e ( ! sun4 ,kir*h(f's discov]y pr(\ndly modifi$ ! conceptions previ\sly ent]ta9$ reg>d+ ! con/itution ( ! sun1 lead+ him to views :i*1 ?\gh !y may be modifi$ 9 detail1 w1 ,i believe1 rema9 sub/antially valid to ! end ( "t4 ,! sun1 accord+ to ,kir*h(f1 consi/s ( a molt5 nucleus :i* is surr\nd$ by a flam+ atmosph]e ( l[] temp]ature4 ,! nucleus may1 9 "p1 be cl\ds1 mix$ )1 or und]ly+ true vap\r4 ,! light ( ! nucleus w\ld give u a cont9u\s spectrum1 l t ( ! ,drummond light2 b hav+ to pass ?r\gh ! photosph]e1 z ,kir*h(f's beam pass$ ?r\gh ! sodium flame1 ^? rays ( ! nucleus :i* ! photosph]e emit are absorb$1 & %ad$ l9es1 correspond+ to ! rays absorb$1 occur 9 ! spectrum4 ,aboli% ! sol> nucleus1 & we %\ld h a spectrum %[+ a bright l9e 9 ! place ( e d>k l9e ( ,fraunh(]1 j z1 9 ! case ( ,kir*h(f's second exp]im5t1 we %\ld h ! bright sodium l9es ( ! flame if ! lime-light 7 )drawn4 ,^! l9es ( ,fraunh(] are !re=e n absolutely d>k1 b d>k by an am\nt correspond+ to ! diff]5ce betwe5 ! light int]cept$ & ! light emitt$ by ! photosph]e4 ,almo/ e great sci5tific discov]y is approa*$ contemporane\sly by _m m9ds1 ! fact t "o m9d usually conf]s ^u x ! di/9ctness ( demon/ration be+ an illu/ration1 n ( g5ius isolat$1 b ( g5ius 9 advance4 ,?us ,f\cault1 9 #ahdi1 came to ! v]ge ( ,kir*h(f's discov]y4 ,by conv]g+ an image ( ! sun ^u a voltaic arc1 & ?us obta9+ ! spectra ( bo? sun & arc sup]pos$1 he f\nd t ! two bright l9es :i*1 ow+ to ! pres5ce ( a little sodium 9 ! c>bons or 9 ! air1 are se5 9 ! spectrum ( ! arc1 co9cide ) ! d>k l9es ,d ( ! sol> spectrum4 ,! l9es ,d he f\nd to he consid]ably /r5g!n$ by ! passage ( ! sol> light ?r\gh ! voltaic arc4 ,in/ead ( ! image ( ! sun1 ,f\cault !n project$ ^u ! arc ! image ( "o ( ! solid inc&esc5t c>bon po9ts1 :i* ( itself w\ld give a cont9u\s spectrum2 & he f\nd t ! l9es ,d 7 ?us g5]at$ 9 t spectrum4 ,f\cault's conclusion f ?is admirable exp]im5t 0 't ! arc is a m$ium :i* emits ! rays ,d on its own acc\nt1 & at ! same "t absorbs !m :5 !y come f ano!r qu>t]4' ,"h he /opp$4 ,he did n ext5d 8 obs]vations beyond ! voltaic arc2 he did n (f] any explanation ( ! l9es ( ,fraunh(]2 he did n arrive at any conception ( sol> *emi/ry1 or ( ! con/itution ( ! sun4 ,8 beautiful exp]im5t rema9$ a g]m )\t fruit1 until ! disc]nm5t1 t5 ye>s subsequ5tly1 ( ! :ole class ( ph5om5a to :i* x belongs1 enabl$ ,kir*h(f to solve ^! great problems4 ,soon aft] ! publication ( ,kir*h(f's discov]y1 ,pr(essor ,/okes1 :o also1 t5 ye>s prior to ! discov]y1 _h ne>ly anticipat$ x1 borr[$ an illu/ration f s\nd1 to expla9 ! reciprocity ( radiation & absorption4 ,a /ret*$ /r+ responds to arial vibrations :i* syn*ronize ) its own4 ,a great numb] ( su* /r+s /ret*$ 9 space w\ld r\ghly repres5t a m$ium2 & if ! note common to !m all 7 s\nd$ at a di/ance !y w\ld take up or absorb its vibrations4 ,:5 a viol9-b[ is drawn across ?is tun+-=k1 ! room is imm$iately fill$ ) a musical s\nd1 :i* may be reg>d$ z ! radiation or emission ( s\nd f ! =k4 ,a few days ago1 on s\nd+ ?is =k1 ,i notic$ t :5 its vibrations 7 qu5*$1 ! s\nd seem$ to be cont9u$1 ?\gh m feebly4 ,x appe>$1 moreov]1 to come f "u a di/ant table1 :]e /ood a numb] ( tun+-=ks ( diff]5t sizes & rates ( vibration4 ,"o ( ^!1 & "o only1 _h be5 />t$ by ! s\nd+ =k1 & x 0 ! "o ^: rate ( vibration 0 ! same z t ( ! =k :i* />t$ x4 ,?is is an in/ance ( ! absorption ( ! s\nd ( "o =k by ano!r4 ,plac+ two unisonant =ks ne> ea* o!r1 sweep+ ! b[ ov] "o ( !m1 & !n qu5*+ ! agitat$ =k1 ! o!r cont9ues to s\nd2 ?is o!r c re-excite ! =m]1 & sev]al transf]s ( s\nd betwe5 ! two =ks c be ?us effect$4 ,plac+ a c5t-piece on ea* prong ( "o ( ! =ks1 we de/roy its p]fect syn*ronism ) ! o!r1 & no su* communication ( s\nd f ! "o to ! o!r is !n possible4 ,i h n[ to br+ be=e y1 on a suitable scale1 ! demon/ration t we c d ) light :at has be5 "h done ) s\nd4 ,= sev]al days 9 #ahfa ,i endeav\r$ to accompli% ?is1 ) only p>tial success4 ,9 iron di%es a mixture ( dilute alcohol & salt 0 plac$1 & w>m$ s z to promote vaporization4 ,! vap\r 0 ignit$1 & ?r\gh ! yell[ flame ?us produc$ ! beam f ! electric lamp 0 s5t2 b a fa9t d>k5+ only ( ! yell[ b& ( a project$ spectrum c\ld be obta9$4 ,a tr\gh 0 !n made :i*1 :5 f$ ) ! salt & alcohol1 yield$ a flame t5 feet ?ick2 b ! result ( s5d+ ! light ?r\gh ?is dep? ( flame 0 /ill unsatisfactory4 ,rememb]+ t ! direct combu/ion ( sodium 9 a ,buns5's flame produces a yell[ f> m int5se ?an t ( ! salt flame1 & inf]r+ t ! int5sity ( ! col\r indicat$ ! copi\sness ( ! inc&esc5t vap\r1 ,i s5t ?r\gh ! flame f metallic sodium ! beam ( ! electric lamp4 ,! success 0 complete2 & ?is exp]im5t ,i wi% n[ to repeat 9 y\r pres5ce4#be ,fir/ly !n y notice1 :5 a fragm5t ( sodium is plac$ 9 a plat9um spoon & introduc$ into a ,buns5's flame1 an int5sely yell[ light is produc$4 ,x corresponds 9 refrangibility ) ! yell[ b& ( ! spectrum4 ,l our tun+-=k1 x emits waves ( a special p]iod4 ,:5 ! :ite light f ! electric lamp is s5t ?r\gh t flame1 y w h ocul> pro( t ! yell[ flame int]cepts ! yell[ ( ! spectrum2 9 o!r words1 t x absorbs waves ( ! same p]iod z its own1 ?us produc+1 to all int5ts & purposes1 a d>k ,fraunh(]'s b& 9 ! place ( ! yell[4 ,9 front ( ! slit 7at ,l1 fig4 #ef7 ?r\gh :i* ! beam issues is plac$ a ,buns5's burn] 7b7 protect$ by a *imney 7,c74 ,?is beam1 aft] pass+ ?r\gh a l5s1 trav]ses ! prism 7,p7 79 ! real exp]im5t !re 0 a pair ( prisms71 is !re decompos$1 & =ms a vivid cont9u\s spectrum 7,s ,s7 ^u ! scre54 ,introduc+ a plat9um spoon ) its pellet ( sodium into ! ,buns5's flame1 ! pellet fir/ fuses1 col\rs ! flame int5sely yell[1 & at l5g? bur/s into viol5t combu/ion4 ,at ! same mom5t ! spectrum is furr[$ by an int5sely d>k b& 7,d71 two in*es wide & two feet long4 ,introduc+ & )draw+ ! sodium flame 9 rapid succession1 ! sudd5 appe>ance & disappe>ance ( ! b& ( d>kness is %[n 9 a mo/ /rik+ mann]4 ,9 contra/ ) ! adjac5t brightness ?is b& appe>s absolutely black1 s vigor\s is ! absorption4 ,! blackness1 h[ev]1 is b relative1 = ^u ! d>k space falls a portion ( ! light ( ! sodium flame4 ,illu/ration3 ,fig4 #ef4 ,i h already ref]r$ to ! exp]im5t ( ,f\cault2 b o!r work]s also _h be5 engag$ on ! bord]s ( ?is subject be=e x 0 tak5 up by ,buns5 & ,kir*h(f4 ,) "s modification ,i h on a =m] occasion us$ ! foll[+ words reg>d+ ! precursors ( ! discov]y ( spectrum analysis1 & sol> *emi/ry3--',mr4 ,talbot _h obs]v$ ! bright l9es 9 ! spectra ( col\r$ flames1 & bo? he & ,sir ,john ,h]s*el po9t$ out ! possibility ( mak+ prismatic analysis a *emical te/ ( exce$+ delicacy1 ?\gh n ( entire c]ta9ty4 ,m ?an a qu>t] ( a c5tury ago ,dr4 ,mill] gave draw+s & descriptions ( ! spectra ( v>i\s col\r$ flames4 ,:eat/one1 ) 8 accu/om$ acut5ess1 analyz$ ! light ( ! electric sp>k1 & prov$ t ! metals betwe5 :i* ! sp>k pass$ det]m9$ ! bright b&s 9 its spectrum4 ,9 an inve/igation describ$ by ,kir*h(f z classical1 ,swan _h %[n t #a_/b1ejj1jjj ( a gra9 ( sodium 9 a ,buns5's flame c\ld be detect$ by its spectrum4 ,he also prov$ ! con/ancy ( ! bright l9es 9 ! spectra ( hydroc>bon flames4 ,masson publi%$ a prize essay on ! b&s ( ! induction sp>k2 :ile ,van d] ,willig51 & m rec5tly ,plck]1 h also giv5 u beautiful draw+s ( spectra obta9$ f ! same s\rce4 ',b none ( ^! di/+ui%$ m5 betray$ ! lea/ k ( ! connexion betwe5 ! bright b&s ( ! metals & ! d>k l9es ( ! sol> spectrum2 nor c\ld spectrum analysis be said to be plac$ ^u any?+ l a safe f\ndation prior to ! rese>*es ( ,buns5 & ,kir*h(f4 ,! man :o1 9 a publi%$ pap]1 came ne>e/ to ! philosophy ( ! subject 0 ng/rm4 ,9 t pap]1 translat$ by myself1 & publi%$ 9 ! ,philosophical ,magaz9e = #ahee1 he indicates t ! rays :i* a body absorbs are precisely ^? :i*1 :5 lum9\s1 x c emit4 ,9 ano!r place1 he speaks ( "o ( 8 spectra giv+ ! g5]al impression ( ! rev]sal ( ! sol> spectrum4 ,b 8 memoir1 philosophical z x is1 is di/9ctly m>k$ by ! unc]ta9ty ( 8 "t4 ,f\cault1 ,?omson1 & ,balf\r ,/ew>t h all be5 ne> ! discov]y1 :ile1 z already /at$1 x 0 almo/ hit by ! acute b unpubli%$ conjecture ( ,/okes4' ,m5tally1 z well z physically1 e ye> ( ! _w's age is ! outgr[? & (fspr+ ( all prec$+ ye>s4 ,sci5ce proves itself to be a g5u9e product ( ,nature by gr[+ accord+ to ?is law4 ,we h no solution ( cont9uity "h4 ,all great discov]ies are duly prep>$ = 9 two ways2 fir/1 by o!r discov]ies :i* =m _! prelude2 &1 secondly1 by ! %>p5+ ( ! inquir+ intellect4 ,?us ,ptolemy grew out ( ,hipp>*us1 ,cop]nicus out ( bo?1 ,kepl] out ( all ?ree1 & ,newton out ( all ! f\r4 ,newton did n rise sudd5ly f ! sea-level ( ! intellect to 8 amaz+ elevation4 ,at ! "t t he appe>$1 ! table-l& ( k 0 already high4 ,he juts1 x is true1 above ! table-l&1 z a massive peak2 /ill he is support$ by ! plateau1 & a great "p ( 8 absolute height is ! height ( humanity 9 8 "t4 ,x is ?us ) ! discov]ies ( ,kir*h(f4 ,mu* _h be5 previ\sly accompli%$2 ?is he ma/]$1 & !n by ! =ce ( individual g5ius w5t beyond x4 ,he replac$ unc]ta9ty by c]ta9ty1 vagu5ess by def9it5ess1 confusion by ord]2 & ,i d n ?9k t ,newton has a sur] claim to ! discov]ies t h made 8 "n immortal1 ?an ,kir*h(f has to ! cr$it ( ga!r+ up ! fragm5t>y k ( 8 "t1 ( va/ly ext5d+ x1 & ( infus+ into x ! life ( great pr9ciples4 ,) "o additional po9t we w w9d up our illu/rations ( ! pr9ciples ( sol> *emi/ry4 ,ow+ to ! scatt]+ ( light by matt] float+ me*anically 9 ! e>?'s atmosph]e1 ! sun is se5 n %>ply def9$1 b surr\nd$ by a lum9\s gl>e4 ,n[1 a l\d noise w dr[n a :isp]1 an int5se light w ov]p[] a feeble "o1 & s ?is circumsol> gl>e prev5ts u f see+ _m /rik+ appe>ances r\nd ! bord] ( ! sun4 ,! gl>e is aboli%$ 9 total eclipses1 :5 ! moon comes betwe5 ! e>? & ! sun1 & !re are !n se5 a s]ies ( rose-col\r$ protub]ances1 /ret*+ sometimes t5s ( ?\s&s ( miles beyond ! d>k edge ( ! moon4 ,!y are describ$ by ,vass5ius 9 ! ',philosophical ,transactions' = #agcc2 & 7 probably obs]v$ ev5 e>li] ?an ?is4 ,9 #ahdb !y attract$ great att5tion1 & 7 !n comp>$ to ,alp9e sn[-peaks r$d5$ by ! ev5+ sun4 ,t ^! prom95ces are flam+ gas1 & pr9cipally hydrog5 gas1 0 fir/ prov$ by ,m4 ,janss5 dur+ an eclipse obs]v$ 9 ,india1 on ! #ah? ( ,augu/1 #ahfh4 ,b ! prom95ces may be r5d]$ visible 9 sun%9e2 & = a reason easily und]/ood4 ,y h se5 9 ^! lectures a s+le prism employ$ to produce a spectrum1 & y h se5 a pair ( prisms employ$4 ,9 ! latt] case1 ! disp]s$ :ite light1 be+ diffus$ ov] ab\t twice ! area1 _h all its col\rs proportionately dilut$4 ,y h also se5 "o prism & a pair ( prisms employ$ to produce ! b&s ( inc&esc5t vap\rs2 b "h ! light ( ea* b&1 be+ absolutely mono*romatic1 0 incapable ( fur!r disp]sion by ! second prism1 & c\ld n !re=e be weak5$ by su* disp]sion4 ,apply ^! consid]ations to ! circumsol> region4 ,! gl>e ( :ite light r\nd ! sun c be disp]s$ & weak5$ to any ext5t1 by augm5t+ ! numb] ( prisms2 :ile a mono*romatic light1 mix$ ) ?is gl>e1 & mask$ by x1 w\ld reta9 its int5sity un5feebl$ by disp]sion4 ,^u ?is consid]ation has be5 f\nd$ a me?od ( obs]vation1 appli$ indep5d5tly by ,m4 ,janss5 9 ,india & by ,mr4 ,locky] 9 ,engl&1 by :i* ! mono*romatic b&s ( ! prom95ces are caus$ to obta9 ! ma/]y1 & to appe> 9 broad daylight4 ,by se>*+ c>efully & skilfully r\nd ! sun's rim1 ,mr4 ,locky] has prov$ ^! prom95ces to be m]e local jutt+s f a fi]y envelope :i* entirely clasps ! sun1 & :i* he has call$ ! ,*romosph]e4 ,x w\ld lead u f> beyond ! object ( ^! lectures to dwell ^u ! num]\s int]e/+ & important results obta9$ by ,sec*i1 ,respighi1 ,"y1 & o!r di/+ui%$ m5 :o h work$ at ! *emi/ry ( ! sun & its app5dages4 ,nor c ,i d m at pres5t ?an make a pass+ ref]5ce to ! excell5t lab\rs ( ,dr4 ,hugg9s 9 connexion ) ! fix$ />s1 nebulae1 & comets4 ,!y1 m ?an any o!rs1 illu/rate ! lit]al tru? ( ! /atem5t1 t ! e/abli%m5t ( spectrum analysis1 & ! explanation ( ,fraunh(]'s l9es1 c>ri$ ) !m an immeasurable ext5sion ( ! *emi/'s range4 ,! truly p[]ful exp]im5ts ( ,pr(essor ,dew> are daily add+ to our k1 :ile ! ref9$ rese>*es ( ,capt4 ,abney & o!rs are op5+ new fields ( inquiry4 ,b my object "h is to make pr9ciples pla91 r ?an to foll[ out ! details ( _! illu/ration4 ,,summ>y ,,& ,,conclusion4 ,my desire 9 ^! lectures has be5 to %[ y1 ) z little brea* ( cont9uity z possible1 some?+ ( ! pa/ gr[? & pres5t aspect ( a dep>tm5t ( sci5ce1 9 :i* h lab\r$ "s ( ! greate/ intellects ! _w has ev] se54 ,i h s\ght to conf] ^u ea* exp]im5t a di/9ct intellectual value1 = exp]im5ts ought to be ! repres5tatives & expositors ( ?\ght--a language address$ to ! eye z spok5 words are to ! e>4 ,9 association ) its context1 no?+ is m impressive or in/ructive ?an a fit exp]im5t2 b1 ap>t f its context1 x r suits ! conjur]'s purpose ( surprise1 ?an ! purpose ( education :i* ought to be ! rul+ motive ( ! sci5tific man4 ,& n[ a brief summ>y ( our "w w n be out ( place4 ,our pres5t ma/]y ov] ! laws & ph5om5a ( light has its orig9 9 ! desire ( man to "k4 ,we h se5 ! anci5ts busy ) ?is problem1 b1 l a *ild :o uses 8 arms aimlessly1 = want ( ! necess>y muscul> tra9+1 s ^! e>ly m5 speculat$ vaguely & confus$ly reg>d+ natural ph5om5a1 n hav+ _h ! discipl9e ne$$ to give cle>ness to _! insight1 & firmness to _! grasp ( pr9ciples4 ,!y assur$ !mselves ( ! rectil9eal propagation ( light1 & t ! angle ( incid5ce 0 equal to ! angle ( reflection4 ,= m ?an a ?\s& ye>s--,i might say1 inde$1 = m ?an fifte5 hundr$ ye>s--! sci5tific intellect appe>s z if smitt5 ) p>alysis1 ! fact be+ t1 dur+ ?is "t1 ! m5tal =ce1 :i* might h run 9 ! direction ( sci5ce1 0 div]t$ into o!r directions4 ,! c\rse ( inve/igation1 z reg>ds light1 0 resum$ 9 #aajj by an ,arabian philosoph] nam$ ,alhaz54 ,!n x 0 tak5 up 9 succession by ,rog] ,bacon1 ,vitellio1 & ,kepl]4 ,^! m51 ?\gh fail+ to detect ! pr9ciples :i* rul$ ! facts1 kept ! fire ( inve/igation con/antly burn+4 ,!n came ! fundam5tal discov]y ( ,snell1 t corn]/one ( optics1 z ,i h already call$ x1 & imm$iately aft]w>ds we h ! application1 by ,desc>tes1 ( ,snell's discov]y to ! explanation ( ! ra9b[4 ,foll[+ ?is we h ! ov]?r[1 by ,roem]1 ( ! notion ( ,desc>tes1 t light 0 transmitt$ in/antane\sly ?r\gh space4 ,!n came ,newton's cr[n+ exp]im5ts on ! analysis & syn!sis ( :ite light1 by :i* x 0 prov$ to be comp\nd$ ( v>i\s k9ds ( light ( diff]5t degrees ( refrangibility4 ,up to 8 demon/ration ( ! composition ( :ite light1 ,newton _h be5 ev]y:]e triumphant--triumphant 9 ! heav5s1 triumphant on ! e>?1 & 8 subsequ5t exp]im5tal "w is1 = ! mo/ "p1 ( immortal value4 ,b infallibility is n an attribute ( man1 &1 soon aft] 8 discov]y ( ! nature ( :ite light1 ,newton prov$ himself human4 ,he suppos$ t refraction & *romatic disp]sion w5t h& 9 h&1 & t y c\ld n aboli% ! "o )\t at ! same "t aboli%+ ! o!r4 ,"h ,dollond correct$ him4 ,b ,newton committ$ a grav] error ?an ?is4 ,sci5ce1 z ,i s\ght to make cle> to y 9 our second lecture1 is only 9 "p a ?+ ( ! s5ses4 ,! roots ( ph5om5a are emb$d$ 9 a region beyond ! rea* ( ! s5ses1 & less ?an ! root ( ! matt] w nev] satisfy ! sci5tific m9d4 ,we f9d1 accord+ly1 9 ?is c>e] ( optics ! greate/ m9ds con/antly ye>n+ to break ! b\nds ( ! s5ses1 & to trace ph5om5a to _! subs5sible f\ndation4 ,?us impell$1 !y ent]$ ! region ( !ory1 & "h ,newton1 ?\gh drawn f "t to "t t[>ds tru?1 0 drawn /ill m /rongly t[>ds error2 & he made error 8 sub/antial *oice4 ,8 exp]im5ts are imp]i%able1 b 8 !ory has pass$ away4 ,= a c5tury x /ood l a dam across ! c\rse ( discov]y2 b1 z ) all b>ri]s t re/ ^u au?ority1 & n ^u tru?1 ! pressure f beh9d increas$1 & ev5tually swept ! b>ri] away4 ,9 #ahjh ,malus1 look+ ?r\gh ,icel& sp> at ! sun1 reflect$ f ! w9d[ ( ! ,luxemb\rg ,palace 9 ,p>is1 discov]$ ! pol>ization ( light by reflection4 ,z /at$ at ! "t1 ?is discov]y u%]$ 9 ! d>ke/ h\r 9 ! =tunes ( ! wave !ory4 ,b ! d>kness did n cont9ue4 ,9 #ahaa ,arago discov]$ ! spl5did *romatic ph5om5a :i* we h _h illu/rat$ by ! deportm5t ( plates ( gypsum 9 pol>iz$ light2 he also discov]$ ! rotation ( ! plane ( pol>ization by qu>tz-cry/als4 ,9 #ahac ,seebeck discov]$ ! pol>ization ( light by t\rmal9e4 ,t same ye> ,brew/] discov]$ ^? magnific5t b&s ( col\r t surr\nd ! axes ( biaxal cry/als4 ,9 #ahad ,wolla/on discov]$ ! r+s ( ,icel& sp>4 ,all ^! effects1 :i*1 )\t a !oretic clue1 w\ld leave ! human m9d 9 a jungle ( ph5om5a )\t h>mony or relation1 7 organically connect$ by ! !ory ( undulation4 ,! wave !ory 0 appli$ & v]ifi$ 9 all directions1 ,airy be+ especially conspicu\s = ! sev]ity & conclusiv5ess ( 8 pro(s4 ,a mo/ rem>kable v]ification fell to ! lot ( ! late ,sir ,william ,hamilton1 ( ,dubl91 :o1 tak+ up ! !ory :]e ,fresnel _h left x1 arriv$ at ! conclusion t at f\r special po9ts ( ! 'wave-surface' 9 d\ble-refract+ cry/als1 ! ray 0 divid$1 n into two p>ts b into an inf9ite numb] ( p>ts2 =m+ at ^! po9ts a cont9u\s conical envelope in/ead ( two images4 ,no human eye _h ev] se5 ?is envelope :5 ,sir ,william ,hamilton inf]r$ its exi/5ce4 ,he ask$ ,dr4 ,lloyd to te/ exp]im5tally ! tru? ( 8 !oretic conclusion4 ,lloyd1 tak+ a cry/al ( arragonite1 & foll[+ ) ! mo/ scrupul\s exactness ! indications ( !ory1 cutt+ ! cry/al :]e !ory said x ought to be cut1 obs]v+ x :]e !ory said x ought to be obs]v$1 discov]$ ! lum9\s envelope :i* _h previ\sly be5 a m]e idea 9 ! m9d ( ! ma!matician4 ,nev]!less ?is great !ory ( undulation1 l _m ano!r tru?1 :i* 9 ! long run has prov$ a bless+ to humanity1 _h to e/abli%1 by hot conflict1 its "r to exi/5ce4 ,illu/ri\s names 7 array$ aga9/ x4 ,x _h be5 enunciat$ by ,hooke1 x _h be5 exp\nd$ & appli$ by ,huygh5s1 x _h be5 def5d$ by ,eul]4 ,b !y made no impression4 ,&1 inde$1 ! !ory 9 _! h&s lack$ ! /r5g? ( a demon/ration4 ,x fir/ took ! =m ( a demon/rat$ v]ity 9 ! h&s ( ,?omas ,"y4 ,he br\ght ! waves ( light to be> ^u ea* o!r1 caus+ !m to support ea* o!r1 & to ext+ui% ea* o!r at w4 ,f _! mutual actions he det]m9$ _! l5g?s1 & appli$ 8 k 9 all directions4 ,he f9ally %[$ t ! difficulty ( pol>ization yield$ to ! grasp ( !ory4 ,aft] him came ,fresnel1 ^: transc5d5t ma!matical abilities enabl$ him to give ! !ory a g5]ality unatta9$ by ,"y4 ,he seiz$ x 9 its entirety2 foll[$ ! e!r into ! he>ts ( cry/als ( ! mo/ complicat$ /ructure1 & into bodies subject$ to /ra9 & pressure4 ,he %[$ t ! facts discov]$ by ,malus1 ,arago1 ,brew/]1 & ,biot 7 s _m ganglia1 s to speak1 ( 8 !oretic organism1 d]iv+ f x su/5ance & explanation4 ,) a m9d too /rong = ! body ) :i* x 0 associat$1 t body became a wreck long be=e x _h become old1 & ,fresnel di$1 leav+1 h[ev]1 beh9d him a "n immortal 9 ! annals ( sci5ce4 ,"o ^w m ,i %\ld l to say reg>d+ ,fresnel4 ,!re are ?+s bett] ev5 ?an sci5ce4 ,"* is high] ?an ,intellect1 b x is especially pleasant to ^? :o wi% to ?9k well ( human nature :5 high intellect & upright "* are f\nd comb9$4 ,!y 7 comb9$ 9 ?is "y ,fr5*man4 ,9 ^? hot conflicts ( ! undulatory !ory1 he /ood =? z a man ( integrity1 claim+ no m ?an 8 "r1 & ready to conc$e _! rights to o!rs4 ,he at once recogniz$ & ackn[l$g$ ! m]its ( ,?omas ,"y4 ,inde$1 x 0 he1 & 8 fell[-c\ntryman ,arago1 :o fir/ />tl$ ,engl& into ! consci\sness ( ! inju/ice done to ,"y 9 ! ',ed9burgh ,review4' ,i %\ld l to read to y a brief extract f a lett] writt5 by ,fresnel to ,"y 9 #ahbd1 z x ?r[s a pleasant light ^u ! "* ( ! ,fr5* philosoph]4 ',= a long "t1' says ,fresnel1 't s5sibility1 or t vanity1 :i* p call love ( glory has be5 mu* blunt$ 9 me4 ,i lab\r mu* less to cat* ! suffrages ( ! public1 ?an to obta9 t inw>d approval :i* has always be5 ! sweete/ rew>d ( my ef=ts4 ,)\t d\bt1 9 mom5ts ( disgu/ & disc\ragem5t1 ,i h (t5 ne$$ ! spur ( vanity to excite me to pursue my rese>*es4 ,b all ! complim5ts ,i h receiv$ f ,arago1 ,de la ,place1 & ,biot nev] gave me s mu* pleasure z ! discov]y ( a !oretic tru? or ! confirmation ( a calculation by exp]im5t4' 99 99 99 99 99 ,?is1 !n1 is ! core ( ! :ole matt] z reg>ds sci5ce4 ,x mu/ be cultivat$ = its own sake1 = ! pure love ( tru?1 r ?an = ! applause or pr(it t x br+s4 ,& n[ my occupation 9 ,am]ica is well-nigh gone4 ,/ill ,i w bespeak y\r tol]ance = a few conclud+ rem>ks1 9 ref]5ce to ! m5 :o h bequea!d to u ! va/ body ( k ( :i* ,i h s\ght to give y "s fa9t idea 9 ^! lectures4 ,:at 0 ! motive t spurr$ !m on8 ,:at urg$ !m to ^? battles & ^? victories ov] retic5t ,nature1 :i* h become ! h]itage ( ! human race8 ,x is nev] to be =gott5 t n "o ( ^? great inve/igators1 f ,ari/otle d[n to ,/okes & ,kir*h(f1 _h any practical end 9 view1 accord+ to ! ord9>y def9ition ( ! ^w 'practical4' ,!y did n propose to !mselves money z an end1 & k z a means ( obta9+ x4 ,= ! mo/ "p1 !y nobly rev]s$ ?is process1 made k _! end1 & su* money z !y possess$ ! means ( obta9+ x4 ,we see to-day ! issues ( _! "w 9 a ?\s& practical =ms1 & ?is may be ?\ght suffici5t to ju/ify1 if n ennoble1 _! ef=ts4 ,b !y did n "w = su* issues2 _! rew>d 0 ( a totally diff]5t k9d4 ,9 :at way diff]5t8 ,we love clo!s1 we love luxuries1 we love f9e equipages1 we love money1 & any man :o c po9t to ^! z ! result ( 8 ef=ts 9 life1 ju/ifies ^! results be=e all ! _w4 ,9 ,am]ica & ,engl&1 m especially1 he is a 'practical' man4 ,b ,i w\ld appeal confid5tly to ?is assembly :e!r su* ?+s exhau/ ! dem&s ( human nature8 ,! v pres5ce "h = six inclem5t nights ( ?is great audi5ce1 embody+ s mu* ( ! m5tal =ce & ref9em5t ( ?is va/ city1#bf is an answ] to my "q4 ,i ne$ n tell su* an assembly t !re are joys ( ! intellect z well z joys ( ! body1 or t ^! pleasures ( ! _s con/itut$ ! rew>d ( our great inve/igators4 ,l$ on by ! :isp]+s ( natural tru?1 ?r\gh pa9 & self-d5ial1 !y (t5 pursu$ _! "w4 ,) ! rul+ passion /rong 9 dea?1 "s ( !m1 :5 no long] able to hold a p51 dictat$ to _! fri5ds ! la/ results ( _! lab\rs1 & !n re/$ f !m = ev]4 ,c\ld we h se5 ^! m5 at "w1 )\t any k ( ! consequ5ces ( _! "w1 :at %\ld we h ?\ght ( !m8 ,to ! un9itiat$1 9 _! day1 !y might (t5 appe> z big *ildr5 play+ ) soap-bubbles & o!r trifles4 ,x is s to ?is h\r4 ,c\ld y wat* ! true inve/igator--y\r ,h5ry or y\r ,drap]1 = example--9 8 laboratory1 unless animat$ by 8 _s1 y c\ld h>dly und]/& :at keeps him !re4 ,_m ( ! objects :i* rivet 8 att5tion might appe> to y utt]ly trivial2 & if y 7 to ask him :at is ! use ( 8 "w1 ! *ances are t y w\ld conf\nd him4 ,he might n be able to express ! use ( x 9 intelligible t]ms4 ,he might n be able to assure y t x w put a doll> into ! pocket ( any human be+ pres5t or to come4 ,t sci5tific discov]y may put n only doll>s into ! pockets ( individuals1 b millions into ! ex*equ]s ( nations1 ! hi/ory ( sci5ce amply proves2 b ! hope ( its do+ s nev] 01 & x nev] c be1 ! motive p[] ( ! inve/igator4 ,i "k t "s risk is run 9 speak+ ?us be=e practical m54 ,i "k :at ,de ,tocqueville says ( y4 ',! man ( ! ,nor?1' he says1 'has n only exp]i5ce1 b k4 ,he1 h[ev]1 does n c>e = sci5ce z a pleasure1 & only embraces x ) avidity :5 x leads to useful applications4' ,b :at1 ,i w\ld ask1 are ! hopes ( useful applications :i* h caus$ y s _m times to fill ?is place1 9 spite ( sn[-drifts & bit+ cold8 ,:at1 ,i may ask1 is ! orig9 ( t k9dness :i* drew me f my "w 9 ,london to address y "h1 & :i*1 if ,i p]mitt$ x1 w\ld s5d me home a millionaire8 ,n because ,i _h taught y to make a s+le c5t by sci5ce am ,i "h to-night1 b because ,i tri$ to ! be/ ( my ability to pres5t sci5ce to ! _w z an intellectual good4 ,surely no two t]ms 7 ev] s di/ort$ & misappli$ ) ref]5ce to man1 9 8 high] relations1 z ^! t]ms useful & practical4 ,let u exp& our def9itions until !y embrace all ! ne$s ( man1 8 highe/ intellectual ne$s inclusive4 ,x is specially on ?is gr\nd ( its adm9i/]+ to ! high] ne$s ( ! intellect2 x is ma9ly because ,i believe x to be :olesome1 n only z a s\rce ( k b z a means ( discipl9e1 t ,i urge ! claims ( sci5ce ^u y\r att5tion4 ,b ) ref]5ce to mat]ial ne$s & joys1 surely pure sci5ce has also a ^w to say4 ,p sometimes speak z if /eam _h n be5 /udi$ be=e ,james ,watt1 or electricity be=e ,:eat/one & ,morse2 :]eas1 9 po9t ( fact1 ,watt & ,:eat/one & ,morse1 ) all _! practicality1 7 ! m]e outcome ( antec$5t =ces1 :i* act$ )\t ref]5ce to practical ends4 ,?is also1 ,i ?9k1 m]its a mom5t's att5tion4 ,y are delight$1 & ) good reason1 ) y\r electric telegraphs1 pr\d ( y\r /eam-eng9es & y\r factories1 & *>m$ ) ! productions ( photography4 ,y see daily1 ) j elation1 ! creation ( new =ms ( indu/ry--new p[]s ( add+ to ! weal? & com=t ( society4 ,indu/rial ,engl& is heav+ ) =ces t5d+ to ?is end2 & ! pulse ( indu/ry beats /ill /rong] 9 ! ,unit$ ,/ates4 ,& yet1 :5 analyz$1 :at are indu/rial ,am]ica & indu/rial ,engl&8 ,if y c tol]ate fre$om ( spee* on my "p1 ,i w answ] ?is "q by an illu/ration4 ,/rip a /rong arm1 & reg>d ! knott$ muscles :5 ! h& is cl5*$ & ! arm b5t4 ,is ?is exhibition ( en]gy ! "w ( ! muscle alone8 ,by no means4 ,! muscle is ! *annel ( an influ5ce1 )\t :i* x w\ld be z p[]less z a lump ( pla/ic d\gh4 ,x is ! delicate unse5 n]ve t unlocks ! p[] ( ! muscle4 ,& )\t ^? filam5ts ( g5ius1 :i* h be5 %ot l n]ves ?r\gh ! body ( society by ! orig9al discov]]1 indu/rial ,am]ica1 & indu/rial ,engl&1 w\ld be v mu* 9 ! condition ( t pla/ic d\gh4 ,at ! pres5t "t !re is a cry 9 ,engl& = te*nical education1 & x is a cry 9 :i* ! mo/ commonplace intellect c jo91 its necessity is s obvi\s4 ,b !re is no su* cry = orig9al inve/igation4 ,/ill1 )\t ?is1 z surely z ! /ream dw9dles :5 ! spr+ dies1 s surely w 'te*nical education' lose all =ce ( gr[?1 all p[] ( reproduction4 ,our great inve/igators h giv5 u suffici5t "w = a "t2 b if _! _s die out1 we %all f9d ourselves ev5tually 9 ! condition ( ^? ,*9ese m5tion$ by ,de ,tocqueville1 :o1 hav+ =gott5 ! sci5tific orig9 ( :at !y did1 7 at l5g? compell$ to copy )\t v>iation ! inv5tions ( an ance/ry wis] ?an !mselves1 :o _h drawn _! inspiration direct f ,nature4 ,bo? ,engl& & ,am]ica h reason to be> ^? ?+s 9 m9d1 = ! l>g5ess & ne>ness ( mat]ial results are only too likely to cause bo? c\ntries to =get ! small spiritual beg9n+s ( su* results1 9 ! m9d ( ! sci5tific discov]]4 ,y multiply1 b he creates4 ,& if y />ve him1 or o!rwise kill him--nay1 if y fail to secure = him free scope & enc\ragem5t--y n only lose ! motive p[] ( intellectual progress1 b infallibly sev] y\rselves f ! spr+s ( indu/rial life4 ,:at has be5 said ( te*nical op]ations holds equally good = education1 = "h also ! orig9al inve/igator con/itutes ! f\nta9-head ( k4 ,x belongs to ! tea*] to give ?is k ! requisite =m2 an hon\rable & (t5 a difficult task4 ,b x is a task :i* receives its f9al sanctification1 :5 ! tea*] himself hone/ly tries to add a rill to ! great /ream ( sci5tific discov]y4 ,inde$1 x may be d\bt$ :e!r ! real life ( sci5ce c be fully felt & communicat$ by ! man :o has n himself be5 taught by direct communion ) ,nature4 ,we may1 x is true1 h good & in/ructive lectures f m5 ( ability1 ! :ole ( ^: k is second-h&1 j z we may h good & in/ructive s]mons f intellectually able & unreg5]ate m54 ,b = t p[] ( sci5ce1 :i* corresponds to :at ! ,puritan fa!rs w\ld call exp]im5tal religion 9 ! he>t1 y mu/ asc5d to ! orig9al inve/igator4 ,to keep society z reg>ds sci5ce 9 heal?y play1 ?ree classes ( work]s are necess>y3 ,fir/ly1 ! inve/igator ( natural tru?1 ^: vocation x is to pursue t tru?1 & ext5d ! field ( discov]y = ! tru?'s own sake & )\t ref]5ce to practical ends4 ,secondly1 ! tea*] ( natural tru?1 ^: vocation x is to give public diffusion to ! k already won by ! discov]]4 ,?irdly1 ! appli] ( natural tru?1 ^: vocation x is to make sci5tific k available = ! ne$s1 com=ts1 & luxuries ( civiliz$ life4 ,^! ?ree classes ought to co-exi/ & int]act4 ,n[1 ! popul> notion ( sci5ce1 bo? 9 ?is c\ntry & 9 ,engl&1 (t5 relates n to sci5ce /rictly s call$1 b to ! applications ( sci5ce4 ,su* applications1 especially on ?is cont95t1 are s a/\nd+--!y spread !mselves s l>gely & umbrage\sly be=e ! public eye--t !y (t5 %ut out f view ^? work]s :o are engag$ 9 ! quiet] & pr(\nd] bus9ess ( orig9al inve/igation4 ,take ! electric telegraph z an example1 :i* has be5 repeat$ly =c$ ^u my att5tion ( late4 ,i am n "h to att5uate 9 ! slighte/ degree ! s]vices ( ^? :o1 9 ,engl& & ,am]ica1 h giv5 ! telegraph a =m s wond]fully fitt$ = public use4 ,!y e>n$ a great rew>d1 & !y h receiv$ x4 ,b ,i %\ld be untrue to y & to myself if ,i fail$ to tell y t1 h[ev] high 9 p>ticul> respects _! claims & qualities may be1 y\r practical m5 did n discov] ! electric telegraph4 ,! discov]y ( ! electric telegraph implies ! discov]y ( electricity itself1 & ! developm5t ( its laws & ph5om5a4 ,su* discov]ies are n made by practical m51 & !y nev] w be made by !m1 because _! m9ds are beset by ideas :i*1 ?\gh ( ! highe/ value f "o po9t ( view1 are n ^? :i* /imulate ! orig9al discov]]4 ,! anci5ts discov]$ ! electricity ( amb]2 & ,gilb]t1 9 ! ye> #afjj1 ext5d$ ! discov]y to o!r bodies4 ,!n foll[$ ,boyle1 ,von ,gu]icke1 ,gray1 ,canton1 ,du ,fay1 ,klei/1 ,cunu1 & y\r own ,frankl94 ,b _! =m ( electricity1 ?\gh tri$1 did n come into use = telegraphic purposes4 ,!n appe>$ ! great ,italian ,volta1 :o discov]$ ! s\rce ( electricity :i* be>s 8 "n1 & appli$ ! mo/ pr(\nd insight1 & ! mo/ delicate exp]im5tal skill to its developm5t4 ,!n arose ! man :o add$ to ! p[]s ( 8 intellect all ! graces ( ! human he>t1 ,mi*ael ,f>aday1 ! discov]] ( ! great doma9 ( magneto-electricity4 ,o,ersted discov]$ ! deflection ( ! magnetic ne$le1 & ,arago & ,/urgeon ! magnetization ( iron by ! electric curr5t4 ,! voltaic circuit f9ally f\nd its !oretic ,newton 9 ,ohm2 :ile ,h5ry1 ( ,pr9ceton1 :o _h ! sagacity to recognize ! m]its ( ,ohm :ile !y 7 /ill decri$ 9 8 own c\ntry1 0 at ?is "t 9 ! van ( exp]im5tal inquiry4 ,9 ! works ( ^! m5 y h all ! mat]ials employ$ at ?is h\r1 9 all ! =ms ( ! electric telegraph4 ,nay1 m2 ,gauss1 ! illu/ri\s a/ronom]1 & ,web]1 ! illu/ri\s natural philosoph]1 bo? pr(essors 9 ! ,univ]sity ( ,gtt+51 wi%+ to e/abli% a rapid mode ( communication betwe5 ! obs]vatory & ! physical cab9et ( ! univ]sity1 did ?is by means ( an electric telegraph4 ,?us1 be=e y\r practical m5 appe>$ ^u ! sc5e1 ! =ce _h be5 discov]$1 its laws inve/igat$ & made sure1 ! mo/ complete ma/]y ( its ph5om5a _h be5 atta9$--nay1 its applicability to telegraphic purposes demon/rat$--by m5 ^: sole rew>d = _! lab\rs 0 ! noble excitem5t ( rese>*1 & ! joy att5dant on ! discov]y ( natural tru?4 ,are we to ignore all ?is8 ,we d s at our p]il4 ,= ,i say aga9 t1 beh9d all our practical applications1 !re is a region ( intellectual action to :i* practical m5 h r>ely contribut$1 b f :i* !y draw all _! supplies4 ,cut !m (f f ?is region1 & !y become ev5tually helpless4 ,9 no case is ! adage tru]1 ',o!r m5 lab\r$1 b ye are ent]$ into _! lab\rs1' ?an 9 ! case ( ! discov]] & appli] ( natural tru?4 ,b n[ a ^w on ! o!r side4 ,:ile practical m5 are n ! m5 to make ! necess>y antec$5t discov]ies1 ! cases are r>e1 ?\gh1 9 our day1 n abs5t1 9 :i* ! discov]] kn[s h[ to turn 8 lab\rs to practical acc\nt4 ,diff]5t qualities ( m9d & habits ( ?\ght are usually ne$$ 9 ! two cases2 & :ile ,i wi% to give emphatic utt]ance to ! claims ( ^? ^: position1 ow+ to ! simple fact ( _! intellectual elevation1 is (t5 misund]/ood1 ,i am n "h to exalt ! "o class ( work]s at ! exp5se ( ! o!r4 ,!y are ! necess>y complem5ts ( ea* o!r4 ,b rememb] t "o class is sure to be tak5 c>e (4 ,all ! mat]ial rew>ds ( society are already )9 _! rea*1 :ile t same society habitually ascribes to !m intellectual a*ievem5ts :i* 7 nev] !irs4 ,?is _c b act to ! detrim5t ( ^? /udies out ( :i*1 n only our k ( nature1 b our pres5t indu/rial arts !mselves1 h sprung1 & f :i* ! ris+ g5ius ( ! c\ntry is incessantly tempt$ away4 ,pa/eur1 "o ( ! mo/ illu/ri\s memb]s ( ! ,in/itute ( ,france1 9 acc\nt+ = ! disa/r\s ov]?r[ ( 8 c\ntry1 & ! pr$om9ance ( ,g]many 9 ! late w>1 expresses himself ?us3 ',few p]sons compreh5d ! real orig9 ( ! m>vels ( indu/ry & ! weal? ( nations4 ,i ne$ no fur!r pro( ( ?is ?an ! employm5t1 m & m frequ5t1 9 (ficial language1 & 9 writ+s ( all sorts1 ( ! errone\s expression appli$ sci5ce4 ,! ab&onm5t ( sci5tific c>e]s by m5 capable ( pursu+ !m ) di/9ction1 0 rec5tly deplor$ 9 ! pres5ce ( a m9i/] ( ! greate/ tal5t4 ,! /atesman endeav\r$ to %[ t we ought n to be surpris$ at ?is result1 because 9 our day ! reign ( !oretic sci5ce yield$ place to t ( appli$ sci5ce4 ,no?+ c\ld be m errone\s ?an ?is op9ion1 no?+1 ,i v5ture to say1 m dang]\s1 ev5 to practical life1 ?an ! consequ5ces :i* might fl[ f ^! words4 ,!y h re/$ 9 my m9d z a pro( ( ! imp]i\s necessity ( re=m 9 our sup]ior education4 ,!re exi/s no category ( ! sci5ces1 to :i* ! "n ( appli$ sci5ce c\ld be rightly giv54 ,we h sci5ce1 & ! applications ( sci5ce1 :i* are unit$ toge!r z ! tree & its fruit4' ,& ,cuvi]1 ! great comp>ative anatomi/1 writes ?us ^u ! same !me3 ',^! gr& practical innovations are ! m]e applications ( tru?s ( a high] ord]1 n s\ght ) a practical int5t1 b pursu$ = _! own sake1 & solely ?r\gh an ard\r = k4 ,^? :o appli$ !m c\ld n h discov]$ !m2 b ^? :o discov]$ !m _h no incl9ation to pursue !m to a practical end4 ,engag$ 9 ! high regions :i!r _! ?\ghts _h c>ri$ !m1 !y h>dly p]ceiv$ ^! practical issues ?\gh born ( _! own de$s4 ,^! ris+ work%ops1 ^! peopl$ colonies1 ^? %ips :i* furr[ ! seas--?is abundance1 ?is luxury1 ?is tumult--all ?is comes f discov]ies 9 sci5ce1 & x all rema9s /range to ! discov]]s4 ,at ! po9t :]e sci5ce m]ges into practice !y ab&on x2 x conc]ns !m no m4' ,:5 ! ,pilgrim ,fa!rs l&$ at ,plym\? ,rock1 & :5 ,p5n made 8 treaty ) ! ,indians1 ! new-com]s _h to build _! h\ses1 to cultivate ! e>?1 & to take c>e ( _! s\ls4 ,9 su* a community sci5ce1 9 its m ab/ract =ms1 0 n to be ?\ght (4 ,& at ! pres5t h\r1 :5 y\r h>dy ,we/]n pione]s /& face to face ) /ubborn ,nature1 pi]c+ ! m\nta9s & subdu+ ! =e/ & ! prairie1 ! pursuit ( sci5ce1 = its own sake1 is n to be expect$4 ,! fir/ ne$ ( man is food & %elt]2 b a va/ portion ( ?is cont95t is already rais$ f> beyond ?is ne$4 ,! g5tlem5 ( ,new ,york1 ,brooklyn1 ,bo/on1 ,philadelphia1 ,baltimore1 & ,wa%+ton h already built _! h\ses1 & v beautiful !y are2 !y h also secur$ _! d9n]s1 to ! excell5ce ( :i* ,i c also be> te/imony4 ,!y h1 9 fact1 rea*$ t precise condition ( well-be+ & indep5d5ce :5 a culture1 z high z humanity has yet rea*$1 may be ju/ly dem&$ at _! h&s4 ,!y h rea*$ t maturity1 z possessors ( weal? & leisure1 :5 ! inve/igator ( natural tru?1 = ! tru?'s own sake1 ought to f9d among !m promot]s & protectors4 ,among ! _m problems be=e !m !y h ?is to solve1 :e!r a republic is able to fo/] ! highe/ =ms ( g5ius4 ,y are famili> ) ! writ+s ( ,de ,tocqueville1 & mu/ be aw>e ( ! int5se sympa?y :i* he felt = y\r in/itutions2 & ?is sympa?y is all ! m valuable f ! philosophic c&\r ) :i* he po9ts out n only y\r m]its1 b y\r defects & dang]s4 ,n[ if ,i come "h to speak ( sci5ce 9 ,am]ica 9 a critical & capti\s _s1 an invisible radiation f my words & mann] w enable y to f9d me out1 & w guide y\r treatm5t ( me to-night4 ,b if ,i 9 no unfri5dly _s--9 a _s1 inde$1 ! rev]se ( unfri5dly--v5ture to repeat be=e y :at ?is great hi/orian & analy/ ( democratic in/itutions said ( ,am]ica1 ,i am p]suad$ t y w he> me out4 ,he wrote "s ?ree & tw5ty ye>s ago1 &1 p]haps1 w\ld n write ! same to-day2 b x w d nobody any h>m to h 8 words repeat$1 &1 if necess>y1 laid to he>t4 ,9 a "w publi%$ 9 #ahej1 ,de ,tocqueville says3 ',x mu/ be confess$ t1 among ! civiliz$ peoples ( our age1 !re are few 9 :i* ! highe/ sci5ces h made s little progress z 9 ! ,unit$ ,/ates4'#bg ,he decl>es 8 conviction t1 _h y be5 alone 9 ! univ]se1 y w\ld soon h discov]$ t y _c long make progress 9 practical sci5ce )\t cultivat+ !oretic sci5ce at ! same "t4 ,b1 accord+ to ,de ,tocqueville1 y are n ?us alone4 ,he refuses to sep>ate ,am]ica f its ance/ral home2 & x is !re1 he cont5ds1 t y collect ! treasures ( ! intellect1 )\t tak+ ! tr\ble to create !m4 ,de ,tocqueville evid5tly d\bts ! capacity ( a democracy to fo/] g5ius z x 0 fo/]$ 9 ! anci5t ari/ocracies4 ',! future1' he says1 'w prove :e!r ! passion = pr(\nd k1 s r>e & s fruitful1 c be born & develop$ z readily 9 democratic societies z 9 ari/ocracies4 ,= my "p1' he cont9ues1 ',i c h>dly believe x4' ,he speaks ( ! unquiet fev]i%ness ( democratic communities1 n 9 times ( great excitem5t1 = su* times may give an extraord9>y impetus to ideas1 b 9 times ( peace4 ,!re is !n1 he says1 'a small & uncom=table agitation1 a sort ( incessant attrition ( man aga9/ man1 :i* tr\bles & di/racts ! m9d )\t imp>t+ to x ei!r l(t9ess or animation4' ,x re/s ) y to prove :e!r ^! ?+s are necess>ily s--:e!r sci5tific g5ius _c f9d1 9 ! mid/ ( y1 a tranquil home4 ,i %\ld be lo? to ga9say s ke5 an obs]v] & s pr(\nd a political writ]1 b1 s9ce my arrival 9 ?is c\ntry1 ,i h be5 unable to see any?+ 9 ! con/itution ( society1 to prev5t a /ud5t1 ) ! root ( ! matt] 9 him1 f be/[+ ! mo/ /eadfa/ devotion on pure sci5ce4 ,if great sci5tific results are n a*iev$ 9 ,am]ica1 x is n to ! small agitations ( society t ,i %\ld be dispos$ to ascribe ! defect1 b to ! fact t ! m5 among y :o possess ! end[m5ts necess>y = pr(\nd sci5tific inquiry1 are lad5 ) duties ( adm9i/ration1 or tuition1 s heavy z to be utt]ly incompatible ) ! cont9u\s & tranquil m$itation :i* orig9al inve/igation dem&s4 ,x may well be ask$ :e!r ,h5ry w\ld h be5 trans=m$ into an adm9i/rator1 or :e!r ,drap] w\ld h =sak5 sci5ce to write hi/ory1 if ! orig9al inve/igator _h be5 hon\r$ z he ought to be 9 ?is l&4 ,i h>dly ?9k !y w\ld4 ,/ill ,i d n imag9e ?is /ate ( ?+s likely to la/4 ,9 ,am]ica !re is a will+ness on ! "p ( individuals to devote _! =tunes1 9 ! matt] ( education1 to ! s]vice ( ! commonweal?1 :i* is probably )\t a p>allel else:]e2 & ?is will+ness requires b wise direction to enable y effectually to wipe away ! reproa* ( ,de ,tocqueville4 ,y\r mo/ difficult problem w be1 n to build in/itutions1 b to discov] m54 ,y may erect laboratories & end[ !m2 y may furni% !m ) all ! appliances ne$$ = inquiry2 9 s do+ y are b creat+ opportunity = ! ex]cise ( p[]s :i* come f s\rces entirely beyond y\r rea*4 ,y _c create g5ius by bidd+ = x4 ,9 biblical language1 x is ! gift ( ,god2 & ! mo/ y c\ld d1 7 y\r weal?1 & y\r will+ness to apply x1 a million-fold :at !y are1 w\ld be to make sure t ?is glori\s plant %all h ! fre$om1 light1 & w>m? necess>y = its developm5t4 ,we see f "t to "t a noble tree dragg$ d[n by p>asitic runn]s4 ,^! ! g>d5] c remove1 ?\gh ! vital =ce ( ! tree itself may lie beyond him3 & s1 9 _m a case y m5 ( weal? c lib]ate g5ius f ! hamp]+ toils :i* ! /ruggle = exi/5ce (t5 ca/s ar\nd x4 ,drawn by y\r k9dness1 ,i h come "h to give ^! lectures1 & n[ t my visit to ,am]ica has become almo/ a ?+ ( ! pa/1 ,i look back ^u x z a memory )\t a s+le /a94 ,no lectur] 0 ev] rew>d$ z ,i h be54 ,f ?is vantage-gr\nd1 h[ev]1 let me rem9d y t ! "w ( ! lectur] is n ! highe/ "w2 t 9 sci5ce1 ! lectur] is usually ! di/ributor ( intellectual weal? amass$ by bett] m54 ,& ?\gh lectur+ & tea*+1 9 mod]ation1 w 9 g5]al promote _! moral heal?1 x is n solely or ev5 *iefly1 z lectur]s1 b z inve/igators1 t y\r highe/ m5 ought to be employ$4 ,y h sci5tific g5ius among/ y--n s[n broadca/1 believe me1 x is s[n ?us n[h]e--b /ill scatt]$ "h & !re4 ,take all unnecess>y imp$im5ts out ( its way4 ,keep y\r sympa!tic eye ^u ! orig9ator ( k4 ,give him ! fre$om necess>y = 8 rese>*es1 n ov]load+ him1 ei!r ) ! duties ( tuition or ( adm9i/ration1 nor dem&+ f him s-call$ practical results--above all ?+s1 avoid+ t "q :i* ignorance s (t5 addresses to g5ius3 ',:at is ! use ( y\r "w8' ,let him make tru? 8 object1 h[ev] unpractical = ! "t be+ x may appe>4 ,if y ca/ y\r bread ?us ^u ! wat]s1 be assur$ x w return to y1 ?\gh x be aft] _m days4 ,,app5dix4 ,,on ,,! ,,spectra ,,( ,,pol>iz$ ,,light4 ,mr4 ,william ,spottiswoode introduc$ "s ye>s ago to ! memb]s ( ! ,royal ,in/itution1 9 a v /rik+ =m1 a s]ies ( exp]im5ts on ! spectra ( pol>iz$ light4 ,) 8 l>ge ,nicol prisms he 9 ! fir/ place repeat$ & expla9$ ! exp]im5ts ( ,f\cault & ,fizeau1 & subsequ5tly enri*$ ! subject by v beautiful additions ( 8 own4 ,i "h app5d a portion ( ! ab/ract ( 8 disc\rse3-- ',x is well kn[n t if a plate ( sel5ite suffici5tly ?9 be plac$ betwe5 two ,nicol's prisms1 or1 m te*nically speak+1 betwe5 a pol>iz] & analyz]1 col\r w be produc$4 ,& ! "q propos$ is1 ,:at is ! nature ( t col\r8 is x simply a pure col\r ( ! spectrum1 or is x a comp\nd1 & if s1 :at are its compon5t p>ts8 ,! answ] giv5 by ! wave !ory is 9 brief ?is3 ,9 its passage ?r\gh ! sel5ite plate ! rays h be5 s sep>at$ 9 ! direction ( _! vibrations & 9 ! velocity ( _! transmission1 t1 :5 re-comp\nd$ by means ( ! analyz]1 !y h 9 "s in/ances neutraliz$ "o ano!r4 ,if ?is be ! case1 ! fact ought to be visible :5 ! beam em]g+ f ! analyz] is disp]s$ by ! prism2 = !n we h ! rays ( all ! diff]5t col\rs rang$ side by side1 &1 if any be want+1 _! abs5ce w be %[n by ! appe>ance ( a d>k b& 9 _! place 9 ! spectrum4 ,b n only s2 ! spectrum ought also to give an acc\nt ( ! o!r ph5om5a exhibit$ by ! sel5ite :5 ! analyz] is turn$ r\nd1 viz4 t :5 ! angle ( turn+ am\nts to #de1 all trace ( col\r disappe>s2 & also t :5 ! angle am\nts to #ij1 col\r reappe>s1 n1 h[ev]1 ! orig9al col\r1 b "o complem5t>y to x4 ',y see 9 ! spectrum ( ! r$di% light produc$ by ! sel5ite a broad b d>k b& 9 ! blue2 :5 ! analyz] is turn$ r\nd ! b& becomes less & less d>k1 until :5 ! angle ( turn+ am\nts to #de x has entirely disappe>$4 ,at ?is /age ea* "p ( ! spectrum has its own proportional int5sity1 & ! :ole produces ! col\rless image se5 )\t ! spectroscope4 ,la/ly1 z ! turn+ ( ! analyz] is cont9u$1 a d>k b& appe>s 9 ! r$1 ! "p ( ! spectrum complem5t>y to t occupi$ by ! fir/ b&2 & ! d>kness is mo/ complete :5 ! turn+ am\nts to #ij4 ,?us we h f ! spectroscope a complete acc\nt ( :at has tak5 place to produce ! orig9al col\r & its *anges4 ',x is fur!r well kn[n t ! col\r produc$ by a sel5ite1 or o!r cry/al plate1 is dep5d5t ^u ! ?ickness ( ! plate4 ,&1 9 fact1 if a s]ies ( plates be tak51 giv+ diff]5t col\rs1 _! spectra are f\nd to %[ b&s arrang$ 9 diff]5t positions4 ,! ?9n] plates %[ b&s 9 ! p>ts ( ! spectrum ne>e/ to ! violet1 :]e ! waves are %ort]1 & consequ5tly give rise to r$d] col\rs2 :ile ! ?ick] %[ b&s ne>] to ! r$1 :]e ! waves are long] & consequ5tly supply blu] t9ts4 ',:5 ! ?ickness ( ! plate is cont9ually increas$1 s t ! col\r produc$ has gone ?r\gh ! complete cycle ( ! spectrum1 a fur!r increase ( ?ickness causes a reproduction ( ! col\rs 9 ! same ord]2 b x w be notic$ t at ea* recurr5ce ( ! cycle ! t9ts become pal]1 until :5 a numb] ( cycles h be5 p]=m$1 & ! ?ickness ( ! plate is consid]able1 all trace ( col\r is lo/4 ,let u n[ take a s]ies ( plates1 ! fir/ two ( :i*1 z y see1 give col\rs2 ) ! o!rs :i* are successively ( great] ?ickness ! t9ts are s feeble t !y c sc>cely be di/+ui%$4 ,! spectrum ( ! fir/ %[s a s+le b&2 t ( ! second1 two2 %[+ t ! second s]ies ( t9ts is n id5tical ) ! fir/1 b t x is produc$ by ! ext9ction ( two col\rs f ! compon5ts ( :ite light4 ,! spectra ( ! o!rs %[ s]ies ( b&s m & m num]\s 9 proportion to ! ?ickness ( ! plate1 an array :i* may be increas$ indef9itely4 ,! total light1 !n1 ( :i* ! spectrum is depriv$ by ! ?ick] plates is tak5 f a great] numb] ( its p>ts2 or1 9 o!r words1 ! light :i* /ill rema9s is di/ribut$ m & m ev5ly ov] ! spectrum2 & 9 ! same proportion ! sum total ( x approa*es m & m ne>ly to :ite light4 ',^! exp]im5ts 7 made m ?an ?irty ye>s ago by ! ,fr5* philosoph]s1 ,,mm4 ,f\cault & ,fizeau4 ',if in/ead ( sel5ite1 ,icel& sp>1 or o!r ord9>y cry/als1 we use plates ( qu>tz cut p]p5dicul>ly to ! axis1 & turn ! analyz] r\nd z be=e1 ! light1 in/ead ( exhibit+ only "o col\r & its complem5t>y ) an int]m$iate /age 9 :i* col\r is abs5t1 *anges cont9u\sly 9 t9t2 & ! ord] ( ! col\r dep5ds p>tly ^u ! direction 9 :i* ! analyz] is turn$1 & p>tly ^u ! "* ( ! cry/al1 i4e4 :e!r x is "r-h&$ or left-h&$4 ,if we exam9e ! spectrum 9 ?is case we f9d t ! d>k b& nev] disappe>s1 b m>*es f "o end ( ! spectrum to ano!r1 or vice v]s1 precisely 9 su* a direction z to give rise to ! t9ts se5 by direct projection4 ',! k9d ( pol>ization effect$ by ! qu>tz plates is call$ circul>1 :ile t effect$ by ! o!r class ( cry/als is call$ plane1 on acc\nt ( ! =m ( ! vibrations execut$ by ! molecules ( !r2 & ?is leads u to exam9e a little m closely ! nature ( ! pol>ization ( diff]5t p>ts ( ^! spectra ( pol>iz$ light4 ',n[1 two ?+s are cle>3 fir/1 t if ! light be plane-pol>iz$--t is1 if all ! vibrations ?r\gh\t ! entire ray are rectil9e> & 9 "o plane--!y mu/ 9 all _! be>+s h ref]5ce to a p>ticul> direction 9 space1 s t !y w be diff]5tly affect$ by diff]5t positions ( ! analyz]4 ,secondly1 t if ! vibrations be circul>1 !y w be affect$ 9 precisely ! same way 7:atev] t may be7 9 all positions ( ! analyz]4 ,?is /atem5t m]ely recapitulates a fundam5tal po9t 9 pol>ization4 ,9 fact1 plane-pol>iz$ light is alt]nately transmitt$ & ext+ui%$ by ! analyz] z x is turn$ ?r\gh #ij2 :ile circul>ly pol>iz$ light if we c\ld get a s+le ray rema9s to all appe>ance un*ang$4 ,& if we exam9e c>efully ! spectrum ( light :i* has pass$ ?r\gh a sel5ite1 or o!r ord9>y cry/al1 we %all f9d t1 comm5c+ ) two consecutive b&s 9 position1 ! p>ts occupi$ by ! b&s & ^? midway betwe5 !m are plane-pol>iz$1 = !y become alt]nately d>k & bright2 :ile ! int]m$iate p>ts1 i4e4 ! p>ts at "o-f\r? ( ! di/ance f "o b& to ! next1 rema9 p]man5tly bright4 ,^! are1 9 fact1 circul>ly pol>iz$4 ,b x w\ld be incorrect to conclude f ?is exp]im5t alone t su* is really ! case1 because ! same appe>ance w\ld be se5 if ^? p>ts 7 unpol>iz$1 i4e4 9 ! condition ( ord9>y lights4 ,& on su* a supposition we %\ld conclude ) equal ju/ice t ! p>ts on ei!r side ( ! p>ts la/ m5tion$ 7e4g4 ! p>ts sep>at$ by eigh? p>ts ( ! int]val betwe5 two b&s7 7 p>tially pol>iz$4 ,b !re is an in/rum5t ( v simple con/ruction1 call$ a qu>t]-undulation plate1 a plate usually ( mica1 ^: ?ickness is an odd multiple ( a qu>t] ( a wave-l5g?1 :i* enables u to discrim9ate betwe5 light unpol>iz$ & circul>ly pol>iz$4 ,! exact me*anical effect produc$ ^u ! ray c\ld h>dly be expla9$ 9 detail )9 our pres5t limits ( "t2 b suffice x = ! pres5t to say t1 :5 plac$ 9 a prop] position1 ! plate trans=ms plane into circul> & circul> into plane pol>ization4 ,t be+ s1 ! p>ts :i* 7 orig9ally b&$ ought to rema9 bright1 & ^? :i* orig9ally rema9$ bright ought to become b&$ dur+ ! rotation ( ! analyz]4 ,! g5]al effect to ! eye w consequ5tly be a g5]al %ift+ ( ! b&s ?r\gh "o-f\r? ( ! space :i* sep>ates ea* pair4 ',circul> pol>ization1 l circul> motion g5]ally1 may ( c\rse be ( two k9ds1 :i* diff] only 9 ! direction ( ! motion4 ,&1 9 fact1 to conv]t ! circul> pol>ization produc$ by ?is plate f "o ( ^! k9ds to ! o!r 7say f "r-h&$ to left-h&$1 or vice v]s71 we h only to turn ! plate r\nd ?r\gh #ij4 ,conv]sely1 "r-h&$ circul> pol>ization w be *ang$ by ! plate into plane-pol>ization 9 "o direction1 :ile left-h&$ w be *ang$ into plane at "r angles to ! fir/4 ,h5ce if ! plate be turn$ r\nd ?r\gh #ij we %all see t ! b&s are %ift$ 9 a direction opposite to t 9 :i* !y 7 mov$ at fir/4 ,9 ?is !re=e we h evid5ce n only t ! pol>ization imm$iately on ei!r side ( a b& is circul>2 b also t t imm$iately on ! "o side is "r-h&$1 :ile t imm$iately on ! o!r is left-h&$#bh4 ',if "t p]mitt$1 ,i might ent] /ill fur!r into detail1 & %[ t ! pol>ization betwe5 ! plane & ! circul> is elliptical1 & ev5 ! positions ( ! long] & %ort] axes & ! direction ( motion 9 ea* case4 ,b suffici5t has1 p]haps1 be5 said = our pres5t purpose4 ',be=e proce$+ to ! m v>i$ =ms ( spectral b&s1 :i* ,i hope pres5tly to br+ "u y\r notice1 ,i %\ld l to ask y\r att5tion = a few m9utes to ! peculi> ph5om5a exhibit$ :5 two plates ( sel5ite giv+ complem5t>y col\rs are us$4 ,! appe>ance ( ! spectrum v>ies ) ! relative position ( ! plates4 ,if !y are simil>ly plac$--t is1 z if !y 7 "o plate ( cry/al--!y w behave z a s+le plate1 ^: ?ickness is ! sum ( ! ?icknesses ( ea*1 & w produce d\ble ! numb] ( b&s :i* "o alone w\ld give2 & :5 ! analyz] is turn$1 ! b&s w disappe> & re-appe> 9 _! complem5t>y positions1 z usual 9 ! case ( plane-pol>ization4 ,if "o ( !m be turn$ r\nd ?r\gh #de1 a s+le b& w be se5 at a p>ticul> position 9 ! spectrum4 ,?is breaks into two1 :i* rec$e f "o ano!r t[>ds ! r$ & violet ends respectively1 or advance t[>ds "o ano!r accord+ to ! direction 9 :i* ! analyz] is turn$4 ,if ! plate be turn$ ?r\gh #de 9 ! opposite direction1 ! effects w be rev]s$4 ,! d>kness ( ! b&s is1 h[ev]1 n equally complete dur+ _! :ole passage4 ,la/ly1 if "o ( ! plates be turn$ ?r\gh #ij1 no b&s w be se51 & ! spectrum w be alt]nately bright & d>k1 z if no plates 7 us$1 except only t ! pol>ization is itself turn$ ?r\gh #ij4 ',if a w$ge-%ap$ cry/al be us$1 ! b&s1 in/ead ( be+ /raight1 w cross ! spectrum diagonally1 ! direction ( ! diagonal 7dext] or s9i/]7 be+ det]m9$ by ! position ( ! ?ick] end ( ! w$ge4 ,if two simil> w$ges be us$ ) _! ?icke/ ends toge!r1 !y w act z a w$ge ^: angle & ^: ?ickness is d\ble ( ! fir/4 ,if !y be plac$ 9 ! rev]se position !y w act z a flat plate1 & ! b&s w aga9 cross ! spectrum 9 /raight l9es at "r angles to its l5g?4 ',if a concave plate be us$ ! b&s w dispose !mselves 9 a fanlike arrangem5t1 _! div]g5ce dep5d+ ^u ! di/ance ( ! slit f ! c5tre ( concavity4 ',if two qu>tz w$ges1 "o ( :i* has ! optic axis p>allel to ! edge ( ! refractory angle1 & ! o!r p]p5dicul> to x1 b 9 "o ( ! planes conta9+ ! angle 7,bab9et's ,comp5sator71 ! appe>ances ( ! b&s are v v>i\s4 ',! diagonal b&s1 besides sometimes d\bl+ !mselves z ) ord9>y w$ges1 sometimes comb9e s z to =m longitud9al 7in/ead ( transv]se7 b&s2 & sometimes cross "o ano!r s z to =m a diap] patt]n ) bright comp>tm5ts 9 a d>k framework1 & vice v]s1 accord+ to ! position ( ! plates4 ',! effects ( diff]5t dispositions ( ! int]pos$ cry/als might be v>i$ indef9itely2 b en\gh has p]haps be5 said to %[ ! delicacy ( ! me?od ( spectrum analysis z appli$ to ! exam9ation ( pol>iz$ light4' 99 99 99 99 99 ,! s+ul> & beautiful effect obta9$ ) a circul> plate ( sel5ite1 ?9 at ! c5tre1 & gradually ?ick5+ t[>ds ! circumf]5ce1 is easily connect$ ) a simil> effect obta9$ ) ,newton's r+s4 ,let a ?9 slice ( light fall ^u ! glasses :i* %[ ! r+s1 s z to cov] a n>r[ c5tral v]tical zone pass+ ?r\gh !m all4 ,! image ( ?is zone ^u ! scre5 is cross$ by portions ( ! iris-r+s4 ,subject+ ! reflect$ beam to prismatic analysis1 ! resultant spectrum may be reg>d$ z an indef9ite numb] ( images ( ! zone plac$ side by side4 ,9 ! image be=e disp]sion we h iris-r+s1 ! ext9ction ( ! light be+ n[h]e complete2 b :5 ! diff]5t col\rs are sep>at$ by disp]sion1 ea* col\r is cross$ transv]sely by its own sy/em ( d>k int]f]5ce b&s1 :i* become gradually clos] ) ! increas+ refrangibility ( ! light4 ,! complete spectrum1 !re=e1 appe>s furr[$ by a sy/em ( cont9u\s d>k b&s1 cross+ ! col\rs transv]sely1 & approa*+ ea* o!r z !y pass f r$ to blue4 ,9 ! case ( ! plate ( sel5ite1 a slit is plac$ 9 front ( ! pol>iz]1 & ! film ( sel5ite is held close to ! slit1 s t ! light passes ?r\gh ! c5tral zone ( ! film4 ,z 9 ! case ( ,newton's r+s1 ! image ( ! zone is cross$ by iris-col\r$ b&s2 b :5 subject$ to prismatic disp]sion1 ! light ( ! zone yields a spectrum furr[$ by b&s ( complete d>kness exactly z 9 ! case ( ,newton's r+s & = a simil> reason4 ,?is is ! beautiful effect describ$ by ,mr4 ,spottiswoode z ! fanlike arrangem5t ( ! b&s--! fan op5+ out at ! r$ end ( ! spectrum4 99 99 99 99 99 ,,measurem5t ,,( ,,! ,,waves ,,( ,,light4 ,! diffraction fr+es describ$ 9 ,lecture ,,ii41 in/ead ( be+ =m$ on ! ret9a1 may be =m$ on a scre51 or ^u gr\nd glass1 :5 !y c be look$ at ?r\gh a magnify+ l5s f beh9d1 or !y c be obs]v$ 9 ! air :5 ! gr\nd glass is remov$4 ,in/ead ( p]mitt+ !m to =m on ! ret9a1 we w suppose !m =m$ on a scre54 ,?is places u 9 a condition to und]/&1 ev5 )\t trigonometry1 ! solution ( ! important problem ( measur+ ! l5g? ( a wave ( light4 ,we w suppose ! scre5 s di/ant t ! rays fall+ ^u x f ! two m>g9s ( ! slit are s5sibly p>allel4 ,we h le>n$ 9 ,lecture ,,ii4 t ! fir/ ( ! d>k b&s corresponds to a diff]5ce ( m>g9al pa? ( "o undulation2 ! second d>k b& to a diff]5ce ( pa? ( two undulations2 ! ?ird d>k b& to a diff]5ce ( ?ree undulations1 & s on4 ,n[ ! angul> di/ance ( ! b&s f ! c5tre is capable ( exact measurem5t2 ?is di/ance dep5d+1 z already /at$1 on ! wid? ( ! slit4 ,) a slit #a4ce millimet] wide1#bi ,s*w]d f\nd ! angul> di/ance ( ! fir/ d>k b& f ! c5tre ( ! field to be #a'ch2 ! angul> di/ances ( ! second1 ?ird1 f\r? d>k b&s be+ twice1 ?ree times1 f\r times ?is quantity4 ,illu/ration3 ,fig4 #eg4 ,let ,a ,b1 fig4 #eg1 be ! plate 9 :i* ! slit is cut1 & ,c ,d ! grossly exagg]at$ wid? ( ! slit1 ) ! beam ( r$ light proce$+ f x at ! obliquity correspond+ to ! fir/ d>k b&4 ,let fall a p]p5dicul> f "o edge1 ,d1 ( ! slit on ! m>g9al ray ( ! o!r edge at d4 ,! di/ance1 ,c d1 betwe5 ! foot ( ?is p]p5dicul> & ! o!r edge is ! l5g? ( a wave ( ! light4 ,! angle ,c ,d d1 moreov]1 be+ equal to ,r ,c ,r'1 is1 9 ! case n[ "u consid]ation1 #a'ch4 ,f ! c5tre ,d1 ) ! wid? ,d ,c z radius1 describe a semicircle2 its radius ,d ,c be+ #a4ce millimet]1 ! l5g? ( ?is semicircle is f\nd by an easy calculation to be #d4bdh millimet]s4 ,! l5g? ,c d is s small t x s5sibly co9cides ) ! arc ( ! circle4 ,h5ce ! l5g? ( ! semicircle is to ! l5g? ,c d ( ! wave z #ahj to #a'ch1 or1 r$uc+ all to seconds1 z #fdh1jjj to #ih4 ,?us1 we h ! proportion-- #fdh1jjj 3 #ih 33 #d4bdh to ! wave-l5g? ,c d4 ,mak+ ! calculation1 we f9d ! wave-l5g? = ?is p>ticul> k9d ( light to be #j4jjjfdc ( a millimet]1 or #j4jjjjbf ( an in*4 ,,footnotes3 ,footnote #a3 ,among :om may be especially m5tion$ ! late ,sir ,edmund ,head1 ,b>t41 ) :om ,i _h _m conv]sations on ?is subject4 ,footnote #b3 ,at ^: h&s x gives me pleasure to /ate ,i h always exp]i5c$ hon\rable & lib]al treatm5t4 ,footnote #c3 ,"o ( ! e>lie/ ( ^! came f ,mr4 ,john ,amory ,l[ell ( ,bo/on4 ,footnote #d3 ,x w be subsequ5tly %[n h[ ?is simple app>atus may be employ$ to det]m9e ! 'pol>iz+ angle' ( a liquid4 ,footnote #e3 ,f ?is pr9ciple ,sir ,john ,h]s*el d$uces 9 a simple & elegant mann] ! fundam5tal law ( reflection4--,see ,famili> ,lectures1 p4 #bcf4 ,footnote #f3 ,! l[ disp]sive p[] ( wat] masks1 z ,helmholtz has rem>k$1 ! imp]fect a*romatism ( ! eye4 ,) ! nak$ eye ,i c see a di/ant blue disk %>ply def9$1 b n a r$ "o4 ,i c also see ! l9es :i* m>k ! upp] & l[] b\nd>ies ( a horizontally refract$ spectrum %>p at ! blue end1 b ill-def9$ at ! r$ end4 ,project+ a lum9\s disk ^u a scre51 & cov]+ "o semicircle ( ! ap]ture ) a r$ & ! o!r ) a blue or gre5 glass1 ! diff]5ce betwe5 ! app>5t sizes ( ! two semicircles is 9 my case1 & 9 num]\s o!r cases1 extraord9>y4 ,_m p]sons1 h[ev]1 see ! app>5t sizes ( ! two semicircles rev]s$4 ,if ) a spectacle glass ,i correct ! disp]sion ( ! r$ light ov] ! ret9a1 !n ! blue ceases to give a %>ply def9$ image4 ,?us exam9$1 ! dep>ture ( ! eye f a*romatism appe>s v gross inde$4 ,footnote #g3 ,bo? 9 foliage & 9 fl[]s !re are /rik+ diff]5ces ( absorption4 ,! copp] bee* & ! gre5 bee*1 = example1 take 9 diff]5t rays4 ,b ! v gr[? ( ! tree is due to "s ( ! rays ?us tak5 94 ,are ! *emical rays1 !n1 ! same 9 ! copp] & ! gre5 bee*8 ,9 two su* fl[]s z ! primrose & ! violet1 :]e ! absorptions1 to judge by ! col\rs1 are almo/ complem5t>y1 are ! *emically active rays ! same8 ,! g5]al relation ( col\r to *emical action is wor?y ( ! application ( ! me?od by :i* ,dr4 ,drap] prov$ s conclusively ! *emical pot5cy ( ! yell[ rays ( ! sun4 ,footnote #h3 ,"y1 ,helmholtz1 & ,maxwell r$uce all diff]5ces ( hue to comb9ations 9 diff]5t proportions ( ?ree prim>y col\rs4 ,x is demon/rable by exp]im5t t f ! r$1 gre51 & violet all ! o!r col\rs ( ! spectrum may be obta9$4 ,"s ye>s ago ,sir ,*>les ,:eat/one drew my att5tion to a "w by ,*ri/ian ,ern/ ,wns*1 ,leipzig #agib1 9 :i* ! au?or ann\nces ! proposition t !re are nei!r five nor sev51 b only ?ree simple col\rs 9 :ite light4 ,wns* produc$ five spectra1 ) five prisms & five small ap]tures1 & he mix$ ! col\rs fir/ 9 pairs1 & aft]w>ds 9 o!r ways & proportions4 ,8 result is t r$ is a simple col\r incapable ( be+ decompos$2 t orange is comp\nd$ ( int5se r$ & weak gre52 t yell[ is a mixture ( int5se r$ & int5se gre52 t gre5 is a simple col\r2 t blue is comp\nd$ ( saturat$ gre5 & saturat$ violet2 t indigo is a mixture ( saturat$ violet & weak gre52 :ile violet is a pure simple col\r4 ,he also f9ds t yell[ & indigo blue produce :ite by _! mixture4 ,yell[ mix$ ) bright blue 7,ho*blau7 also produces :ite1 :i* seems1 h[ev]1 to h a t+e ( gre51 :ile ! pigm5ts ( ^! two col\rs :5 mix$ always give a m or less beautiful gre51 ,wns* v emphatically di/+ui%es ! mixture ( pigm5ts f t ( lights4 ,speak+ ( ! g5]ation ( yell[1 he says1 ',i say expressly r$ & gre5 light1 because ,i am speak+ ab\t light-col\rs 7,li*tf>b571 & n ab\t pigm5ts4' ,h[ev] faulty 8 !ories may be1 ,wns*'s exp]im5ts appe> 9 ! ma9 to be precise & conclusive4 ,ne>ly t5 ye>s subsequ5tly1 ,"y adopt$ r$1 gre51 & violet z ! ?ree prim>y col\rs1 ea* ( !m capable ( produc+ ?ree s5sations1 "o ( :i*1 h[ev]1 pr$om9ates ov] ! two o!rs4 ,helmholtz adopts1 elucidates1 & enri*es ?is notion4 7,popul> ,lectures1 p4 #bdi4 ,! pap] ( ,helmholtz on ! mixture ( col\rs1 translat$ by myself1 is publi%$ 9 ! ,philosophical ,magaz9e = #aheb4 ,maxwell's memoir on ! ,!ory ( ,comp\nd ,col\rs is publi%$ 9 ! ,philosophical ,transactions1 vol4 #aej1 p4 #fg47 ,footnote #i3 ,! foll[+ *>m+ extract1 be>+ ^u ?is po9t1 0 discov]$ & writt5 out = me by my deeply lam5t$ fri5d ,dr4 ,b5ce ,jones1 :5 ,hon4 ,secret>y to ! ,royal ,in/itution3-- ',9 e k9d ( magnitude !re is a degree or sort to :i* our s5se is proportion$1 ! p]ception & k ( :i* is ( ! greate/ use to mank9d4 ,! same is ! gr\ndwork ( philosophy2 =1 ?\gh all sorts & degrees are equally ! object ( philosophical speculation1 yet x is f ^? :i* are proportion$ to s5se t a philosoph] mu/ set out 9 8 inquiries1 asc5d+ or desc5d+ aft]w>ds z 8 pursuits may require4 ,he does well inde$ to take 8 views f _m po9ts ( sight1 & supply ! defects ( s5se by a well-regulat$ imag9ation2 nor is he to be conf9$ by any limit 9 space or "t2 b1 z 8 k ( ,nature is f\nd$ on ! obs]vation ( s5sible ?+s1 he mu/ beg9 ) ^!1 & mu/ (t5 return to !m to exam9e 8 progress by !m4 ,"h is 8 secure hold3 & z he sets out f !nce1 s if he likewise trace n (t5 8 /eps backw>ds ) caution1 he w be 9 haz>d ( los+ 8 way 9 ! labyr9?s ( ,nature4'--7,maclaur93 ,an ,acc\nt ( ,sir ,i4 ,newton's ,philosophical ,discov]ies4 ,writt5 #agbh2 second edition1 #agej2 pp4 #ah1 #ai47 ,footnote #aj3 ,i d n wi% to encumb] ! conception "h ) ! details ( ! motion1 b ,i may draw att5tion to ! beautiful model ( ,pr(4 ,lyman1 :]e9 waves are %[n to be produc$ by ! circul> motion ( ! p>ticles4 ,?is1 z prov$ by ! bro!rs ,web]1 is ! real motion 9 ! case ( wat]-waves4 ,footnote #aa3 ,copi$ f ,web]'s ,well5lehre4 ,footnote #ab3 ,see ,lectures on ,s\nd1 #a/ & #bnd ed41 ,lecture ,,vii42 & #crd ed41 ,*ap4 ,,viii4 ,longmans4 ,footnote #ac3 ,boyle's ,works1 ,bir*'s edition1 p4 #fge4 ,footnote #ad3 ,page #gdc4 ,footnote #ae3 ,! beautiful plumes produc$ by wat]-cry/allization h be5 successfully photograph$ by ,pr(essor ,lockett4 ,footnote #af3 ,9 a little volume entitl$ ',=ms ( ,wat]1' ,i h m5tion$ t cold iron floats ^u molt5 iron4 ,9 company ) my fri5d ,sir ,william ,arm/rong1 ,i _h repeat$ opportunities ( witness+ ?is fact 9 8 works at ,elswick1 #ahfc4 ,f>aday1 ,i rememb]1 spoke to me subsequ5tly ( ! p]fection ( iron ca/+s z probably due to ! swell+ ( ! metal on solidification4 ,beyond ?is1 ,i h giv5 ! subject no special att5tion2 & ,i "k t _m intellig5t iron-f\nd]s d\bt ! fact ( expansion4 ,x is q possible t ! solid floats because x is n wett$ by ! molt5 iron1 its volume be+ virtually augm5t$ by capill>y repulsion4 ,c]ta9 flies walk freely ^u wat] 9 virtue ( an action ( ?is k9d4 ,) bismu?1 h[ev]1 x is easy to bur/ iron bottles by ! =ce ( solidification4 ,footnote #ag3 ,?is beautiful law is usually ?us express$3 ,! index ( refraction ( any sub/ance is ! tang5t ( its pol>iz+ angle4 ,) ! aid ( ?is law & an app>atus simil> to t figur$ at page #ae1 we c readily det]m9e ! index ( refraction ( any liquid4 ,! refract$ & reflect$ beams be+ visible1 !y c readily be caus$ to inclose a "r angle4 ,! pol>iz+ angle ( ! liquid may be ?us f\nd ) ! %>pe/ precision4 ,x is !n only necess>y to seek out its natural tang5t to obta9 ! index ( refraction4 ,footnote #ah3 ,:ewell4 ,footnote #ai3 ,remov$ f u s9ce ^! words 7 writt54 ,footnote #bj3 ,! only essay kn[n to me on ! ,undulatory ,!ory1 f ! p5 ( an ,am]ican writ]1 is an excell5t "o by ,presid5t ,b>n>d1 publi%$ 9 ! ,smi?sonian ,report = #ahfb4 ,footnote #ba3 ,boyle's ,works1 ,bir*'s edition1 vol4 i4 pp1 #gbi & #gcj4 ,footnote #bb3 ,w]ke1 ,b4 xxix4 p4 #bd4 ,footnote #bc3 ,def9$ 9 ,lecture ,i4 ,footnote #bd3 ,?is circum/ance ought n to be lo/ sight ( 9 ! exam9ation ( comp\nd spectra4 ,o!r simil> in/ances might be cit$4 ,footnote #be3 ,! d>k b& produc$ :5 ! sodium is plac$ )9 ! lamp 0 obs]v$ on ! same occasion4 ,!n 0 also obs]v$ = ! fir/ "t ! magnific5t blue b& ( li?ium :i* ! ,buns5's flame fails to br+ out4 ,footnote #bf3 ,new ,york3 = m ?an a decade no su* wea!r _h be5 exp]i5c$4 ,! sn[ 0 s deep t ! ord9>y means ( locomotion 7 = a "t susp5d$4 ,footnote #bg3 ',il faut reconnatre que p>mi les peuples civiliss de nos j\rs il en e/ p5 *ez qui les hautes sci5ces ai5t fait mo9s de progrs qu'aux tats-,unis1 ou qui ai5t f\rni mo9s de gr&s arti/es1 de potes illu/res et de clbres criva9s4' 7,de la ,dmocratie en ,amrique1 etc4 tome ii4 p4 #cf47 ,footnote #bh3 ,at ^! po9ts ! two rectangul> vibrations into :i* ! orig9al pol>iz$ ray is resolv$ by ! plates ( gypsum1 act ^u ea* o!r l ! two rectangul> impulses imp>t$ to our p5dulum 9 ,lecture ,,iv41 "o be+ giv5 :5 ! p5dulum is at ! limit ( its sw+4 ,vibration is ?us conv]t$ into rotation4 ,footnote #bi3 ,! millimet] is ab\t #a_/be? ( an in*4 ,,index4 ,absorption1 pr9ciples (1 #aii ,airy1 ,sir ,george1 sev]ity & conclusiv5ess ( 8 pro(s1 #bji ,alhaz51 8 inquiry respect+ light1 #ad1 #bjg ,analyz]1 pol>iz] &1 #abg ----recomp\nd+ ( ! two sy/ems ( waves by ! analyz]1 #abi ng/rm1 8 pap] on spectrum analysis1 #bjb ,arago1 ,franois1 & ,dr4 ,"y1 #ej ----8 discov]ies respect+ light1 #bjh ,atomic pol>ity1 #ic-if ,bacon1 ,rog]1 8 inquiry respect+ light1 #ad1 #bjg ,b>?ol9us1 ,erasmus1 on ,icel& sp>1 #aab ,br>d on pol>ization ( heat1 #ahj ,blackness1 mean+ (1 #cb ,boyle1 ,rob]t1 8 obs]vations on col\rs1 #fe1 #ff ----8 rem>ks on fluoresc5ce1 #afc1 #afd ,bradley1 ,james1 discov]s ! ab]ration ( light1 #ba1 #bb ,brew/]1 ,sir ,david1 8 *ief objection to ! undulatory !ory ( light1 #dg ,brew/]1 ,sir ,david1 8 discov]y 9 biaxal cry/als1 #bji ,br\gham1 ,mr4 7aft]w>ds ,"l71 ridicules ,dr4 ,t4 ,"y's speculations1 #ej1 #ea ,csium1 discov]y (1 #aic ,caloresc5ce1 #agd ,cl\ds1 act9ic1 #aeb-aed ----pol>ization (1 #aee ,col\rs ( ?9 plates1 #fd ----,boyle's obs]vations on1 #fe1 #ff ----,hooke on ! col\rs ( ?9 plates1 #fg ----( /riat$ surfaces1 #hi1 #ij ,comet ( #afhj1 ,newton's e/imate ( ! temp]ature (1 #afh ,crookes1 ,mr41 8 discov]y ( ?allium1 #aic ,cry/als1 action (1 ^u light1 #ih ----built by pol> =ce1 #ih ----illu/rations ( cry/allization1 #ii ----ar*itecture (1 consid]$ z an introduction to _! action ^u light1 #ih ----be>+s ( cry/allization ^u optical ph5om5a1 #ajf ,cry/als1 r+s surr\nd+ ! axes (1 uniaxal & biaxal1 #ade ,cuvi] on ard\r = k1 #bbj ,de ,tocqueville1 writ+s (1 #bae1 #bbb1 #bbc ,desc>tes1 8 explanation ( ! ra9b[1 #bd1 #be ----8 ideas respect+ ! transmission ( light1 #dc ----8 notion ( light1 #bjg ,diamond1 ignition ( a1 9 oxyg51 #afi ,dia!rmancy1 #agc ,diffraction ( light1 ph5om5a (1 #gh ----b&s1 #gh1 #gi ----explanation (1 #hj ----col\rs produc$ by1 #hi ,dollond1 8 exp]im5ts on a*romatism1 #bh ,drap]1 ,dr41 8 inve/igation on heat1 #agb ,drummond light1 spectrum (1 #aie ,e>?1 daily orbit (1 #gd ,electric beam1 heat ( !1 #afh ,electricity1 discov]ies 91 #bag1 #bah ,emission !ory ( light1 bases ( !1 #de ----,newton esp\ses ! !ory1 & ! results ( ?is esp\sal1 #gg ,e!r1 ,huygh5s & ,eul] advocate & def5d ! conception ( an1 #dh1 #eh ----object$ to by ,newton1 #eh ,eul] esp\ses & def5ds ! conception ( an e!r1 #dh1 #eh ,eusebius on ! natural philosoph]s ( 8 "t1 #ac ,expansion by cold1 #ajd ,exp]im5t1 uses (1 #c ,eye1 !1 its imp]fections1 gr[n = ages t[>ds p]fection1 #h ----imp]fect a*romatism ( !1 #bi1 note ,f>aday1 ,mi*ael1 8 discov]y ( magneto-electricity1 #bah ',fits1' !ory (1 #gc ----its explanation ( ,newton's r+s1 #gd ----ov]?r[ ( ! !ory1 #gg ,fizeau det]m9es ! velocity ( light1 #bb ,fluoresc5ce1 ,/okes's discov]y (1 #afa ----! "n1 #agd ,=bes1 ,pr(essor1 pol>izes & depol>izes heat1 #ahj ,f\cault1 det]m9es ! velocity ( light1 #bb ----8 exp]im5ts on absorption1 #aig1 #aih ,fraunh(]1 8 !oretical calculations respect+ diffraction1 #hg ----8 l9es1 #aic ------_! explanation by ,kir*h(f1 #aic ,fresnel1 & ,dr4 ,"y1 #ej ----8 !oretical calculations respect+ diffraction1 #hg ----8 ma!matical abilities & immortal "n1 #baj ,goe! on fluoresc5ce1 #afe ,gravitation1 orig9 ( ! notion ( ! attraction (1 #ib ----/r5g? ( ! !ory (1 #adh ,grimaldi1 8 discov]y ) respect to light1 #ef ----,"y's g5]alizations (1 #ef ,hamilton1 ,sir ,william1 ( ,dubl91 8 discov]y ( conical refraction1 #bji ,heat1 g5]ation (1 #f ----,dr4 ,drap]'s inve/igation respect+1 #aga ,helmholtz1 8 e/imate ( ! g5ius ( ,"y1 #ej ----on ! imp]fect a*romatism ( ! eye1 #bi note1 #ca ----reveals ! cause ( gre5 9 ! case ( pigm5ts1 #cg ,h5ry1 ,pr(essor ,joseph1 8 invitation1 #b ,h]s*el1 ,sir ,john1 8 !oretical calculations respect+ diffraction1 #hg ----fir/ notices & describes ! fluoresc5ce ( sulphate ( qu99e1 #afe ----8 exp]im5ts on spectra1 #bja ,h]s*el1 ,sir ,william1 8 exp]im5ts on ! heat ( ! v>i\s col\rs ( ! sol> spectrum1 #aga ,hooke1 ,rob]t1 on ! col\rs ( ?9 plates1 #fg ----8 rem>ks on ! idea t light & heat are modes ( motion1 #fh ,horse-*e/nut b>k1 fluoresc5ce (1 #afe ,hugg9s1 ,dr41 8 lab\rs1 #bje ,huygh5s advocates ! conception ( e!r1 #dh1 #eh ----8 celebrat$ pr9ciple1 #hc ,huygh5s on ! d\ble refraction ( ,icel& sp>1 #aab ,icel& sp>1 #aji ----d\ble refraction caus$ by1 #aaj ----?is d\ble refraction fir/ treat$ by ,erasmus ,b>?ol9us1 #aab ----"* ( ! beams em]g5t f1 #aad ----te/$ by t\rmal9e1 #aaf ----,knoblau*'s demon/ration ( ! d\ble refraction (1 #ahe ,ice-l5s1 combu/ion ?r\gh1 #afg ,imag9ation1 scope ( !1 #db ----note by ,maclaur9 on ?is po9t1 #dc note ,janss51 ,m41 on ! rose-col\r$ sol> prom95ces1 #bjd ,jupit]1 ,roem]'s obs]vations ( ! moons (1 #bj ,jupit]'s di/ance f ! sun1 #bj ,kepl]1 8 inve/igations on ! refraction ( light1 #ad1 #bjg ,kir*h(f1 ,pr(essor1 8 explanation ( ,fraunh(]'s l9es1 #aic ----8 precursors1 #bja ----8 claims1 #bjc ,knoblau*1 8 demon/ration ( ! d\ble refraction ( heat ( ,icel& sp>1 #ahe ,lactantius1 on ! natural philosoph]s ( 8 "t1 #ac ,lamy1 ,m41 isolates ?allium 9 +ots1 #aic ,lesley1 ,pr(essor1 8 invitation1 #b ,light famili> to ! anci5ts1 #e ----g5]ation (1 #f1 #g ----sph]ical ab]ration (1 #h ----! rectil9eal propagation (1 & mode ( produc+ x1 #i ----illu/ration %[+ t ! angle ( incid5ce is equal to ! angle ( reflection1 #aj1 #aa ----/]ility ( ! ,middle ,ages1 #ac ----hi/ory ( refraction1 #ad ----demon/ration ( ! fact ( refraction1 #ad ----p>tial & total reflection (1 #af-bj ----velocity (1 #bj ----,bradley's discov]y ( ! ab]ration ( light1 #ba1 #bb ----pr9ciple ( lea/ "t1 #bc ----,desc>tes & ! ra9b[1 #bd ----,newton's analysis (1 #bf1 #bg ----syn!sis ( :ite light1 #cj ----complem5t>y col\rs1 #ca ----yell[ & blue lights produce :ite by _! mixture1 #ca ----:at is ! mean+ ( blackness8 #cb ----analysis ( ! action ( pigm5ts ^u1 #cc ----absorption1 #cd ----mixture ( pigm5ts contra/$ ) mixture ( lights1 #cg ----,wns* on ?ree simple col\rs 9 :ite light1 #ci note ----,newton arrives at ! emission !ory1 #de ----,"y's discov]y ( ! undulatory !ory1 #di ----illu/rations ( wave-motion1 #eh ----int]f]5ce ( s\nd-waves1 #eh ----velocity (1 #fj ----pr9ciple ( int]f]5ce ( waves (1 #fa ----ph5om5a :i* fir/ sugge/$ ! undulatory !ory #fb-fi ----soap-bubbles & _! col\rs1 #fb-fe ----,newton's r+s1 #fi-gg ----8 esp\sal ( ! emission !ory1 & ! results ( ?is esp\sal1 #gg ----transmitt$ light1 #gg ----diffraction1 #gg1 #hi ----orig9 ( ! notion ( ! attraction ( gravitation1 #ib ----pol>ity1 h[ g5]at$1 #ic ----action ( cry/als ^u1 #ih ----refraction (1 #ajf ----ela/icity & d5sity1 #ajh ----d\ble refraction1 #aji ----*romatic ph5om5a produc$ by cry/als 9 pol>iz$1 #aba ----! ,nicol prism1 #abb ----me*anism (1 #abe ----vibrations1 #abe ----composition & resolution ( vibrations1 #abh ----pol>iz] & analyz]1 #abg ----recomp\nd+ ! two sy/ems ( waves by ! analyz]1 #abi ----int]f]5ce ?us r5d]$ possible1 #aca ----*romatic ph5om5a produc$ by qu>tz1 #aci ----magnetization1 (1 #ada ----r+s surr\nd+ ! axes ( cry/als1 #adc ----col\r & pol>ization ( sky1 #adi1 #aed ----range ( vision incomm5surate ) range ( radiation1 #aei ----effect ( ?all5e on ! spectrum1 #afb ----fluoresc5ce1 #afb ----transp>5cy1 #afg ----! ultra-r$ rays1 #agj ----"p play$ 9 ,nature by ^! rays1 #age ----conv]sion ( heat-rays into light-rays1 #agf ----id5tity ( radiant heat &1 #agg ----pol>ization ( heat1 #ahj ----pr9ciples ( spectrum analysis1 #ahi ----spectra ( inc&esc5t vap\rs1 #aij ----,fraunh(]'s l9es1 & ,kir*h(f's explanation ( !m1 #aic ----sol> *emi/ry1 #aie-aig ----demon/ration ( analogy betwe5 s\nd &1 #aih1 #aii ----,kir*h(f & 8 precursors1 #bja ----rose-col\r$ sol> prom95ces1 #bjd ----results obta9$ by v>i\s work]s1 #bje ----summ>y & conclusion1 #bjf ----pol>iz$1 ! spectra (1 #bbg ----measurem5t ( ! waves (1 #bcd ,lignum ,nephriticum1 fluoresc5ce (1 #afd ,lloyd1 ,dr41 on pol>ization ( heat1 #ahj1 #bji ,locky]1 ,mr41 on ! rose-col\r$ sol> prom95ces1 #bje ,lycopodium1 diffraction effects caus$ by ! spores (1 #hh ,magnetization ( light1 #ada ,malus1 8 discov]y respect+ reflect$ light ?r\gh ,icel& sp>1 #aae ----discov]s ! pol>ization ( light by reflection1 #bjh ,masson1 8 essay on ! b&s ( ! induction sp>k1 #bjb ,melloni1 on ! pol>ization ( heat1 #ahj ,metals1 combu/ion (1 #e1 #f ----spectrum analysis (1 #aij ----spectrum b&s prov$ by ,buns5 & ,kir*h(f to be *>act]i/ic ( ! vap\r (1 #aib ,mill1 ,john ,/u>t1 8 scepticism reg>d+ ! undulatory !ory1 #adi ,mill]1 ,dr41 8 draw+s & descriptions ( ! spectra ( v>i\s col\r$ flames1 #bja ,morton1 ,pr(essor1 8 discov]y ( ?all5e1 #afb ,"m-(-pe>l1 col\rs (1 #ij ,nature1 a savage's int]pretation (1 #d ,newton1 ,sir ,isaac1 8 exp]im5ts on ! composition ( sol> light1 #bf ----8 spectrum1 #bg ----disp]sion1 #bg ----arrives at ! emission !ory ( light1 #de ----8 objection to ! conception ( an e!r esp\s$ & def5d$ by ,huygh5s & ,eul]1 #eh ----8 optical c>e]1 #gj ----8 r+s1 #fi-gg ----8 r+s expla9$ by ! !ory ( 'fits1' #gc ----esp\ses ! emission !ory1 #gg ----effects ( ?is esp\sal1 #gg ----8 idea ( gravitation1 #ib ----8 errors1 #bjh ,nicol prism1 !1 #abb ,ocean1 col\r ( !1 #ce ,o,ersted1 discov]s ! deflection ( a magnetic ne$le by an electric curr5t1 #agf ,optics1 sci5ce (1 #d ,pa/eur ref]r$ to1 #bai ,physical !ories1 orig9 (1 #da-dd ,pigm5ts1 analysis ( ! action (1 ^u light1 #cc ----mixture (1 contra/$ ) mixture ( lights1 #cg ----,helmholtz reveals ! cause ( ! gre5 9 ! case ( mix$ blue & yell[ pigm5ts1 #cg ----impurity ( natural col\rs1 #cg ,pit* ( s\nd1 #ei ,plck]1 8 draw+s ( spectra1 #bjb ,pol>iscope1 /a9$ glass 9 !1 #acj1aca ----unanneal$ glass 9 !1 #acf ,pol>ity1 notion (1 h[ g5]at$1 #ic ----atomic1 #ic-if ----/ructural arrangem5ts due to1 #if ----pol>ization ( light1 #aab ----te/$ by t\rmal9e1 #aaf ----& by reflection & refraction1 #aai ----depol>ization1 #abj ,pol>ization ( light1 #aab ----circul>1 #adj ----sky-light1 #adi1 #aeg ----( artificial sky1 #aef ----( radiant heat1 #ahj ,pol>iz] & analyz]1 #abg ,poles ( a magnet1 #ic ,p[ell1 ,pr(essor1 on pol>ization ( heat1 #ahj ,prism1 ! ,nicol1 #abb ,qu>tz1 *romatic ph5om5a produc$ by1 #aci ,radiant heat1 #agb ----dia!rmancy1 or p]vi\sness to radiant heat1 #agc ----conv]sion ( heat-rays into light rays1 #agd ----=mation ( invisible heat-images1 #agi ----pol>ization (1 #ahj ----d\ble refraction1 #ahb ----magnetization (1 #ahd ,ra9b[1 ,desc>tes' explanation ( !1 #bd ,refraction1 demon/ration (1 #ad ,refraction ( light1 #ajf ----d\ble1 #aji ,reflection1 p>tial & total1 #af-bj ,respighi1 results obta9$ by1 #bje ,ritt]1 8 discov]y ( ! ultraviolet rays ( ! sun1 #aei ,roem]1 ,olav1 8 obs]vations ( ,jupit]'s moons1 #bj ----8 det]m9ation ( ! velocity ( light1 #ba ,rubidium1 discov]y (1 #aic ,ru/+ ( iron1 :at x is1 #e ,s*w]d1 8 obs]vations respect+ diffraction1 #hg ,sci5ce1 gr[? (1 #agf1 #bjc ,scoresby1 ,dr41 succe$s 9 explod+ gunp[d] by ! sun's rays convey$ by l>ge l5ses ( ice1 #afg ,sec*i1 results obta9$ by1 #bje ,seebeck1 ,?omas1 discov]s !rmo-electricity1 #agf ----discov]s ! pol>ization ( light by t\rmal9e1 #bjh ,sel5ite1 exp]im5ts ) ?ick & ?9 plates (1 #abd ,silv] spectrum1 analysis (1 #aij1 #aia ,sky-light1 col\r & pol>ization (1 #adi1 #aed ----g5]ation ( artificial skies1 #aeb ,snell1 ,willebrord1 8 discov]y1 #ad ----8 law1 #ae1 #bd ,soap-bubbles & _! col\rs1 #fc1 #fe ,s\nd1 e>ly notions ( ! anci5ts respect+1 #ea ----int]f]5ce ( waves (1 #eh ----pit* (1 #ei ----analogies ( light &1 #ef ----demon/ration ( analogy betwe51 & light1 #aih1 #aii ,sonor\s vibrations1 action (1 #acd ,spectrum analysis1 pr9ciples (1 #ahi ,spectra ( inc&esc5t vap\rs1 #aij ----discont9u\s1 #aia1 #aib ----( pol>iz$ light1 #bbg ,spectrum b&s prov$ by ,buns5 & ,kir*h(f to be *>act]i/ic ( ! vap\r1 #aib ----its capacity z an ag5t ( discov]y1 #aic ----analysis ( ! sun & />s1 #aic ,spottiswoode1 ,mr4 ,william1 #abc1 #bbg ,/ew>t1 ,pr(essor ,balf\r1 #bjb ,/okes1 ,pr(essor1 results ( 8 exam9ation ( sub/ances excit$ by ! ultra-violet waves1 #afa ----8 discov]y ( fluoresc5ce1 #afb ----on fluoresc5ce1 #afe ----ne>ly anticipates ,kir*h(f's discov]y1 #aih1 #bjb ,/riat$ surfaces1 col\rs (1 #hi ,sulphate ( qu99e fir/ notic$ & describ$ by ,sir ,john ,h]s*el1 #afe ,sun1 *emi/ry ( !1 #aie ,sun1 rose-col\r$ sol> prom95ces1 #bjd ,talbot1 ,mr41 8 exp]im5ts1 #bja ,t>t>ic acid1 irregul> cry/allization (1 & its effects1 #aca ,?all5e1 its effect on ! spectrum1 #afb ,?allium1 spectrum analysis (1 #aij1 #aia ----discov]y (1 #aic ----isolat$ 9 +ots by ,m4 ,lamy1 #aic ,!ory1 relation (1 to exp]i5ce1 #ia ,!rmo-electric pile1 #agf ,!rmo-electricity1 discov]y (1 #agf ,tombel9e1 ,mont1 inv]t$ image (1 #ai ,t\rmal9e1 pol>ization ( light by means (1 #aab ,transmitt$ light1 reason =1 #gg ,transp>5cy1 rem>ks on1 #afg ,ultra-violet sun-rays1 discov]$ by ,ritt]1 #aei ----effects (1 #afj ,ultra-r$ rays ( ! sol> spectrum1 #aga ----"p play$ by !1 #agc ,undulatory !ory ( light1 bases ( !1 #dg ----,sir ,david ,brew/]'s *ief objection to !1 #dg ,undulatory !ory ( light1 ,"y's f\ndation ( !1 #di ----ph5om5a :i* fir/ sugge/$ !1 #fb1 #fi ----,mr4 ,mill's scepticism reg>d+ !1 #adc ----a demon/rat$ v]ity 9 ! h&s ( ,"y1 #baj ,vass5ius describes ! rose-col\r$ sol> prom95ces 9 #agcc1 #bjd ,vitellio1 8 skill & consci5ti\sness1 #ad ----8 inve/igations respect+ light1 #bjg ,voltaic batt]y1 use (1 & its production ( heat1 #f1 #g ,wat]1 deportm5t (1 consid]$ & expla9$1 #aje1 #ajf ,waves ( wat]1 #ea ----l5g? ( a wave1 #eb ----int]f]5ce ( waves1 #ec-ee ,w]!im1 ,m41 8 in/rum5t = ! det]m9ation ( /ra9s & pressures by ! col\rs ( pol>iz$ light1 #acd ,:eat/one1 ,sir ,*>les1 8 analysis ( ! light ( ! electric sp>k1 #bjb ,:irlpool ,rapids1 illu/ration ( ! pr9ciple ( ! int]f]5ce ( waves at !1 #ee ,willig51 ,van d]1 8 draw+s ( spectra1 #bjb ,wolla/on1 ,dr41 fir/ obs]ves l9es 9 sol> spectrum1 #aic ----discov]s ! r+s ( ,icel& sp>1 #bji ,woodbury1 ,mr41 on ! impurity ( natural col\rs1 #cg ,wns*1 ,*ri/ian ,ern/1 on ! ?ree simple col\rs 9 :ite lights1 #ci note ----8 exp]im5ts1 #ci note ,"y1 ,dr4 ,?omas1 8 discov]y ( ,egyptian hi]oglyphics1 #di2 ----& ! undulatory !ory ( light1 #di ----,helmholtz's e/imate ( him1 #ej ----ridicul$ by ,br\gham 9 ! ',ed9burgh ,review1' #ej ----g5]alizes ,grimaldi's obs]vation on light1 #ef1 #eg ----photographs ! ultra-violet r+s ( ,newton1 #afj