,illu/ration3 ,,col\r-,,pat* ,,app>atus4 ,,! ,,romance ,,( ,,sci5ce4 ,,col\r ,,measurem5t ,,& ,,mixture4 ,) ,num]\s ,illu/rations4 ,,by ,,capta9 ,w4 de ,w4 ,,abney1 ,c4,b41 ,r4,e41 ,d4,c4,l41 ,f4,r4,s4 ,,publi%$ ,,"u ,,! ,,direction ,,( ,,! ,,committee ,,( ,,g5]al ,,lit]ature ,,& ,,education ,,appo9t$ ,,by ,,! ,,society ,,= ,,promot+ ,,*ri/ian ,,k4 ,,society ,,= ,,promot+ ,,*ri/ian ,,k4 ,,london3 ,,nor?umb]l& ,,av5ue1 ,w4,c42 #dc1 ,,que5 ,,victoria ,,/reet1 ,e4,c4 ,,brighton3 #ace1 ,,nor? ,,/reet4 ,,new ,,york3 ,e4 ,j4 ,b4 ,,"y ,,co4 #ahia4 ,,preface4 ,"s t5 ye>s ago !re 7 ?ree measurem5ts ( ! spectrum :i* ,i set myself to c>ry out2 ! la/ two1 at all ev5ts1 involv+ new me?ods ( exp]im5t+4 ,! ?ree measurem5ts 73 7#a/7 ,! heat+ effect2 7#bnd7 ! lum9osity2 & 7#crd7 ! *emical effect on v>i\s salts1 ( ! diff]5t rays ( ! spectrum4 ,! task is n[ complet$1 & x 0 9 c>ry+ out ! second "p ( x t ,g5]al ,fe/+1 :o jo9$ me 9 ! rese>*1 & myself 7 l$ into a wid] /udy ( col\r ?an at fir/ int5d$1 z ! app>atus we devis$ enabl$ u to c>ry out exp]im5ts :i*1 :il/ difficult "u ord9>y circum/ances1 became easy to make4 ,on two occasions1 at ! invitation ( ! ,society ( ,arts1 ,i h deliv]$ a %ort c\rse ( lectures on ! subject ( ,col\r1 & naturally ,i *ose to treat x f ! po9t ( view ( our own me?ods ( exp]im5t+2 & ^! lectures1 exp&$ & modifi$1 =m ! basis ( ! pres5t volume4 ,z a treatise x mu/ necess>ily be incomplete1 z x sc>cely t\*es on ! hi/ory ( ! subject--a "p :i* mu/ always be ( deep int]e/4 ,! solely physiological aspect ( col\r has also be5 sc>cely dealt )2 t "p :i* ! physici/ c submit to measurem5t be+ t :i* alone 0 practicable "u ! circum/ances4 ,w4 ,de ,w4 ,abney4 ,s\? ,k5s+ton1 #a/ ,may1 #ahia4 ,,cont5ts4 ,,*apt] ,i4 ,s\rces ( ,light--,reflect$ ,light--,reflection f ,r\gh5$ ,surfaces--,col\r ,con/ants p4 #aa ,,*apt] ,,ii4 ,a ,/&>d ( ,light--,=mation ( ! ,spectrum by ,prisms & by ! ,diffraction ,grat+--,wave-l5g?s ( ! pr9cipal ,fraunh(] ,l9e--,position ( ,col\rs 9 ! ,spectrum p4 #ag ,,*apt] ,,iii4 ,! ,visible & ,invisible ,p>ts ( ! ,spectrum--,me?ods = %[+ ! ,exi/5ce ( ! ,invisible ,portions--,phosphoresc5ce--,photography ( ! ,d>k ,rays--,!rmo-,electric ,curr5ts p4 #cj ,,*apt] ,,iv4 ,description ( ,col\r ,pat* ,app>atus--,rotat+ ,sectors--,me?od ( mak+ a ,scale = ! ,spectrum p4 #da ,,*apt] ,v4 ,absorption ( ! ,spectrum--,analysis ( ,col\r--,vibrations ( ,rays--,absorption by ,pigm5ts--,phosphoresc5ce--,int]f]5ce p4 #ea ,,*apt] ,,vi4 ,scatt]$ ,light--,sunset ,col\rs--,law ( ! ,scatt]+ by ,f9e ,p>ticles--,sunset ,cl\ds--,lum9osities ( ,sunlight at diff]5t ,altitudes ( ! ,sun p4 #fb ,,*apt] ,,vii4 ,lum9osity ( ! ,spectrum to ,normal-ey$ & ,col\r-bl9d ,p]sons--,me?od ( det]m9+ ! ,lum9osity ( ,pigm5ts--,addition ( "o ,lum9osity to ano!r p4 #gf ,,*apt] ,,viii4 ,me?ods ( ,measur+ ! ,int5sity ( ! ,diff]5t ,col\rs ( ! ,spectrum1 reflect$ f ,pigm5t$ ,surfaces--,templates = ! ,spectrum p4 #hh ,,*apt] ,,ix4 ,col\r ,mixtures--,yell[ ,spot 9 ! ,eye--,comp>ison ( ,diff]5t ,lights--,simple ,col\rs by ,mix+ ,simple ,col\rs--,yell[ & ,blue f ,:ite p4 #aab ,,*apt] ,x4 ,ext9ction ( ,col\r by ,:ite ,light--,ext9ction ( ,:ite ,light by ,col\r p4 #abf ,,*apt] ,,xi4 ,prim>y ,col\rs--,molecul> ,sw+s--,col\r ,s5sations--,s5sations abs5t 9 ! ,col\r-bl9d p4 #acc ,,*apt] ,,xii4 ,=mation ( ,col\r ,equations--,koenig's ,curves--,maxwell's ,app>atus & ,curves p4 #adg ,,*apt] ,,xiii4 ,mat* ( ,comp\nd ,col\rs ) ,simple ,col\rs--,all ,col\rs r$uc$ to ,numb]s--,me?od ( ,mat*+ a ,col\r ) a ,spectrum ,col\r & ,:ite ,light p4 #aef ,,*apt] ,,xiv4 ,complem5t>y ,col\rs--,complem5t>y ,pigm5t ,col\rs--,measurem5t ( ,complem5t>y ,col\rs p4 #afg ,,*apt] ,,xv4 ,p]si/5ce ( ,images on ! ,ret9a--,! ,use ( ,col\r$ ,discs p4 #agi ,,*apt] ,,xvi4 ,contra/ ,col\rs--,measurem5t ( ,contra/ ,col\rs--,fatigue ( ! ,eye--,aft]-,images p4 #aif ,,li/ ,,( ,,illu/rations4 ,,fig4 ,,page ,col\r-pat* app>atus ,frontispiece #a4 ,spectrum ( sunlight #ah #b4 ,c>bon poles ( an electric light #bj #c4 ,curve = conv]t+ prismatic spectrum into wave-l5g?s #bh #d4 ,! !rmopile #ce #e4 ,heat+ effect ( diff]5t s\rces ( radiation #ch #f4 ,col\r-pat* app>atus #db #g4 ,rotat+ sectors #de #h4 ,spectrum ( ,c>bon ,sodium & ,li?ium #dh #i4 ,int]f]5ce b&s #fj #aj4 ,absorption ( rays by ! atmosph]e #fh #aa4 ,lum9osity curve ( spectrum ( ! positive pole ( ! electric light #gi #ab4 ,rectangles ( :ite & v]milion #hb #ac4 ,arrangem5t = measur+ ! lum9osities ( pigm5ts #hc #ad4 ,measurem5t ( ! int5sity ( rays reflect$ f :ite & col\r$ surfaces #hh #ae4 ,int5sity ( rays reflect$ f v]milion1 em]ald gre51 & ,fr5* ultram>9e #ib #af4 ,me?od ( obta9+ two pat*es ( id5tical col\r #ie #ag4 ,absorption by r$1 blue1 & gre5 glasses #ii #ah4 ,light reflect$ f metallic surfaces #ajj #ai4 ,int5sities ( v]milion1 c>m9e1 m]curic iodide1 & ,indian r$ #aja #bj4 ,int5sities ( gamboge1 ,indian yell[1 cadmium yell[1 & yell[ o*re #aja #ba4 ,int5sities ( em]ald gre51 *rom\s oxide1 & t]re v]te #ajc #bb4 ,int5sities ( indigo1 ,antw]p blue1 cobalt1 & ,fr5* ultram>9e #ajd #bc4 ,me?od ( obta9+ a col\r template #ajd #bd4 ,template ( c>m9e #ajf #be4 ,template ( lum9osity ( :ite light #ajh #bf4 ,absorption ( transmitt$ & reflect$ light by ,prussian blue & c>m9e #ajg #bg4 ,collimator = comp>+ ! int5sity ( two s\rces ( light #aji #bh4 ,spectrum int5sities ( sunlight1 gaslight1 & blue sky #aji #bi4 ,comp>ison ( sun & sky lights #aaa #cj4 ,slide ) slits to be us$ 9 ! spectrum #aac #ca4 ,scre5 on :i* to mat* gamboge #aaf #cb4 ,diaphragm 9 front ( prism #abh #cc4 ,curve ( s5sitiv5ess ( silv] bromo-iodide #acf #cd4 ,curves ( col\r s5sations #aci #ce4 ,koenig's curves ( col\r s5sations #aea #cf4 ,maxwell's col\r-box #aeb #cg4 ,maxwell's curves ( col\r s5sations #aed #ch4 ,*romatic circle #afh #ci4 ,disc to cause alt]nate op5+ & clos+ ( two slits #agi #dj4 ,disc pa9t$ blue & r$ #aha #da4 ,electro-motor ) discs atta*$ #ahc #db4 ,me?od ( cutt+ disc to all[ an ov]lap ( a second disc #ahd #dc4 ,arrangem5t to f9d value ( gamboge 9 t]ms ( em]ald gre5 & v]milion #ahh #dd4 ,disc arrang$ to give approximately all ! spectrum col\rs #aib #de4 ,me?od ( %[+ contra/ col\rs #aif ,,col\r ,,measurem5t ,,& ,,mixture4 ,,*apt] ,i4 ,s\rces ( ,light--,reflect$ ,light--,reflection f ,r\gh5$ ,surfaces--,col\r ,con/ants4 ,!re is no?+1 p]haps1 9 our ev]yday life :i* appeals m to ! m9d ?an col\r1 yet s accu/om$ are ! g5]ality ( mank9d to its influ5ce t b few /op to inquire ! :y & :]e=e ( its exi/5ce1 or its cause4 ,to ^? few1 h[ev]1 !re is a s\rce ( endless & b\ndless enjoym5t 9 its /udy2 = 9 ! realms ( physical & physiological sci5ce !re is p]haps no o!r subject 9 :i* exp]im5ts give results s fasc9at+ & (t5 s beautiful4 ,al?\gh its s]i\s /udy mu/ be und]tak5 ) a cle> m9d1 a good eye1 & a fair supply ( pati5ce1 yet a g5]al idea ( ! subject may be grasp$ by ^? :o are possess$ ( b ord9>y intellig5ce4 ,col\r ph5om5a are enc\nt]$ ne>ly e day ( "o's life1 & ! fact t !y are s frequ5tly met )1 prev5ts t att5tion to !m1 or ev5 _! rem>k4 ,:o among/ u1 = in/ance1 has notic$ ! exi/5ce ( :at are call$ positive & negative aft] images1 aft] look+ at "s /rongly illum9at$ object1 or w\ld h gaug$ ! fact t a c]ta9 portion ( ! n]v\s sy/em c be fatigu$ by a col\r1 & give rise to images ( its complem5t>y1 _h n an ent]pris+ adv]tis]1 :o manufactures a h\sehold necess>y1 drawn att5tion to x 9 a mann] t c\ld n be misund]/ood4 ,if on an autumn aft]noon we pass ?r\gh a g>d5 :il/ x is /ill p]fectly light1 we c notice ! gorge\s col\r+ ( ! fl[]s1 & appreciate ) ! eyes ! beauty ( ea* t9t4 ,z ev5+ comes on ! t9ts d>k51 ! d>ke/-col\r$ fl[]s beg9 to lose _! col\r1 & only ! brighte/ /rike ! eye4 ,:5 night /ill fur!r closes 9 e col\r goes1 ?\gh ! outl9es ( ! fl[]s may /ill be di/+ui%$2 & x w\ld n be impossible1 9 "s p>ts1 to see a t9y speck ( pale light ^u ! gr\nd among/ !m4 ,?is speck ( light we %\ld "k f exp]i5ce to be ! light f a gl[-worm4 ,:y is x t we lose ! col\r ( ! fl[]s & recognize ! t9y light f ?is small worm8 ,! reason = ! "o is t 9 ord] = objects :i* are n self-lum9\s to be se5 at all1 light mu/ fall on !m & illum9ate !m1 & ! light :i* !y reflect may be col\r$ if !y possess ! qualities to reflect col\r$ light4 ,! gl[-worm's light is se51 n because x does n emit light 9 ! day-"t1 b because ! eye1 be+ limit$ 9 s5sitiv5ess1 is unable to di/+ui% x :5 x is flood$ ) ! light ( day4 ,! gl[-worm1 h[ev]1 is self-lum9\s1 z is %[n by ! fact t x emits light 9 ! d>k1 ! light itself be+ slightly col\r$ if comp>$ ) t ( day4 ,t a c&le-flame or ! sun is self-lum9\s is an axiom1 & ne$ n be philosophis$ ^u2 b :at mu/ be impress$ on ! read] is1 t ?\gh an object :i* requires to be illum9at$ to be se51 is n self-lum9\s1 yet :5 illum9at$ x does 9 fact become a s\rce ( illum9ation to ! eye1 al?\gh ! light is only light reflect$ f its surface4 ,x is a po9t wor? rememb]+ t ! r\gh] ! surface ( an object1 ! bright] to ! eye x w be4 ,t is1 a col\r$ object :5 poli%$ w be a bad second>y s\rce ( illum9ation1 z ! light incid5t ^u x w be v ne>ly reflect$ f ! surface1 accord+ to ! ord9>y laws ( reflection2 b if x be r\gh5$ x w become a mu* bett] s\rce1 z ! r\ghnesses1 ?\gh obey+ ! laws ( reflection1 w reflect light 9 e direction4 ,a good example ( ?is is an ord9>y %eet ( glass4 ,light f a s\rce fall+ on its surface is sc>cely reflect$ 9 any direction except 9 t det]m9$ by ! ord9>y laws ( reflection1 & x w be sc>cely visible to ! eye4 ,gr9d its surface1 h[ev]1 & ! innum]able facets caus$ by ! gr9d+ w reflect light back to ! eye 9 :atev] position x be plac$1 & w ?us be di/9ctly se54 ,we may "h premise t ev5 ! r\ghe/ surface w reflect a great] p]c5tage--v>y+ greatly accord+ to ! nature ( ! surface--( light 9 ! direction :i* x w\ld d if x 7 a smoo? surface ?an 9 any o!r2 & 9 tak+ measurem5ts ( ! light irregul>ly reflect$ f a r\gh surface1 ?is fact mu/ be borne 9 m9d4 ,n only mu/ we "k h[ col\r is produc$1 b we mu/ also be able to ref] x to "s /&>d :i* %all be readily reproduc$1 & :i* %all be unalt]able4 ,!re are two v>iable factors :i* h to be tak5 into acc\nt 9 col\r exp]im5ts3 ! fir/ is ! quality ( light :i* illum9ates ! object1 & ! second is ! s5sitiv5ess ( ! eye :i* p]ceives x1 z light is only a s5sation :i* is recogniz$ by ! bra9 ?r\gh ! m$ium ( ! eye4 ,we %all1 z we g on1 see t diff]5t qualities ( light may cause objects to appe> ( diff]5t hues1 & fur!r t eyes may v>y 9 p]ceptive p[]1 to an ext5t ( :i* ! l>ge majority ( p are n aw>e4 ,h5ce x becomes necess>y z f> z possible to elim9ate ^! v>iables4 ,! task :i* we h set ourselves to p]=m !n1 is fir/ to f9d a suitable light = exp]im5tal "w1 & next to endeav\r to ref] col\r to an eye :i* has no abnormal defects4 ,?is be+ accompli%$1 we h !n to f9d means to measure ! diff]5t con/ants :i* are involv$ 9 col\r1 & to ref] ! measurem5ts to "s /&>d4 ,col\r con/ants are ?ree1 viz4 hue1 lum9osity1 & purity2 & x w be se5 t if ^! ?ree are det]m9$1 ! measurem5t ( ! col\r is complete4 ,p]haps ! mean+ ( ^! t]ms may require to be expla9$4 ,! hue ( a col\r is :at 9 common p>lance is (t5 call$ ! col\r4 ,?us we talk ( rose1 violet1 mag5ta1 em]ald gre51 & s on1 b = measur+ purposes ! hue _h be/ be ref]r$ to ! spectrum col\rs z a /&>d 7! means ( do+ s w be %ortly expla9$71 = !y are simple col\rs1 :i* c be express$ by numb]s4 ,comp\nd col\rs1 :i* x may be said are inv>iably to be f\nd 9 nature1 be+ mixtures ( simple col\rs1 c be j z readily ref]r$ to ! spectrum4 ,by ! lum9osity ( a col\r we mean its brightness1 ! /&>d ( ref]5ce be+ ! brightness ( a :ite surface :5 illum9at$ by ! same :ite light4 ,by ! purity ( a col\r we mean its fre$om f admixture ) :ite light4 ,an example ( diff]5t degrees ( purity w be f\nd 9 wa%es ( wat]-col\rs ( diff]5t t5uity4 ,?us if we wa% a %eet ( pap] ) a light t9t ( c>m9e1 ! :it5ess ( ! pap] is n oblit]at$2 if we pass ano!r wa% ov] x ! :it5ess ( ! pap] is less5$1 & s on4 ,! lighte/ t9t is t :i* is mo/ lack+ 9 purity4 ,,*apt] ,,ii4 ,a ,/&>d ,light--,=mation ( ! ,spectrum by ,prisms & by ! ,diffraction ,grat+--,wave-l5g?s ( ! pr9cipal ,fraunh(] ,l9e--,position ( ,col\rs 9 ! ,spectrum4 ,z we h to turn to ! spectrum = pure & simple col\rs1 f :i* we may produce any comp\nd col\r we may wi% to deal )1 we w fir/ consid] ! light ) :i* we %all =m x4 ,a spectrum may be produc$ f any s\rce ( light1 su* z sunlight1 limelight1 ! electric light1 gaslight1 or inc&esc5ce electric light1 z also f inc&esc5t vap\rs1 or gases2 b x is only a solid :i* is1 or is r5d]$ inc&esc5t1 t w give u a cont9u\s spectrum1 z x is call$1 t is1 a spectrum :i* is unbrok5 by gaps ( non-lum9osity1 or sudd5 *ange ( brightness1 ?r\gh\t its l5g?4 ,fig4 #a4--,spectrum ( ,sunlight4 ,! great desid]atum = ! /udy ( col\r is a light :i* n only gives a practically cont9u\s spectrum1 b "o :i* is produc$ by ! radiation ( matt] :i* is black :5 cold1 & :i* c be kept at a con/antly high temp]ature4 ,we h purposely said black 9 ! s5t5ce above1 s9ce x is believ$ t diff]5tly col\r$ bodies1 :5 heat$ to equal temp]atures1 might n give ! same relative int5sities to ! diff]5t p>ts ( ! spectrum1 ! v>iation be+ dep5d5t on ! col\r ( ! heat$ body4 ,a black body mu/ always give ! same visible spectrum :5 heat$ to ! same temp]ature4 ,! spectrum ( sunlight 7,fig4 #a7 is n cont9u\s1 z we f9d x cross$ by an innum]able numb] ( f9e l9es ( v>y+ bread? & blackness4 ,?is want ( cont9uity w\ld n be fatal to its adoption 7 x possible to use x outside ! limits ( our atmosph]e1 z !n1 unless ! temp]ature ( ! sun itself *ang$1 ! spectrum produc$ w\ld be inv>iable2 b un=tunately ! relative brightness or lum9osity ( ! diff]5t p>ts ( ! spectrum v>ies f day to day1 & h\r to h\r1 accord+ to ! height ( ! sun above ! horizon 7see ,*ap4 ,,vi472 & its integral brightness v>ies accord+ to ! cle>ness ( ! sky4 ,x is evid5t !n1 t1 z a ref]5ce light1 sunlight is mo/ unsuitable1 s we may dismiss x f our possible /&>ds4 ,fig4 #b4--,! ,c>bon ,poles ( an ,electric ,light4 ,by ! process ( elim9ation we may arrive at ! light ^u :i* we c rely1 = ! purpose we h 9 view1 viz4 ! production ( a spectrum ( mod]ate size1 & suffici5tly bright to be well view$ :5 project$ ^u a scre54 ,= "s purposes1 z = in/ance 9 becom+ acqua9t$ ) ! g5]al "* ( ! spectrum1 a feebl] light1 su* z gaslight1 or light f electrical gl[ lamps1 may be employ$1 s9ce ! spectrum may be view$ directly by ! eye )\t ! int]v5tion ( a scre54 ,!y h two drawbacks = our object3 "o be+ ! want ( g5]al int5sity1 & ! o!r ! feeble lum9osity ( blue & violet rays 9 _! spectrum 7see page #aaj74 ,! limelight we c also dismiss = want ( /ead9ess4 ,its :it5ess & lum9osity v>ies accord+ to ! oxyg5 play+ on ! lime cyl9d]1 r5d]+ ! relative int5sities ( ! diff]5t p>ts ( ! spectrum s erratic z to make x unreliable4 ,?is leaves ! 7electric7 arc-light z ! only "o :i* is really available4 ,rememb] h[ ! arc-light is produc$4 ,a curr5t ( electricity passes betwe5 ! ends ( two ?ick black c>bon rods1 or poles z !y are call$1 ?r\gh an air space ( small int]val1 & ! passage ( ! curr5t r5d]s ! tips ( ^! rods :ite-hot 7,fig4 #b74 ,! c5tre ( ! end ( "o pole1 call$ ! positive pole1 :]e a crat]-l depression is =m$1 is ! "p :i* atta9s ! :ite/ heat1 & its temp]ature seems to be con/ant1 & to be t ( ! volatilization ( c>bon4 ,num]\s exp]im5ts h be5 made by ! writ]1 & he has f\nd t ! light emitt$ by ?is crat] 9 ! positive pole is1 )9 ! limits ( ! error ( obs]vation1 always ( ! same :it5ess1 & consequ5tly gives a spectrum :i* is unv>y+ 9 ! proportionate int5sities ( ! diff]5t col\rs4 ,:5 ! exp]im5ts made to det]m9e ! lum9osity ( ! spectrum are describ$1 ! me?od ( asc]ta9+ ?is w be readily und]/ood4 ,9 ! spectrum produc$ by ?is light !re are two places 9 ! violet :]e !re are b&s ( violet l9es slightly bright] ?an ! g5]al spectrum4 ,!y are pr9cipally due to ! light emitt$ f ! inc&esc5t vap\r ( c>bon1 :i* is volatiliz$ & plays betwe5 ! two poles 7see ,fig4 #b72 b z ^! b&s are ( b small visual int5sity1 & situat$ t[>ds ! limit ( ! visible spectrum1 !y d n int]f]e ) eye-measures ( col\rs1 ?\gh !y d1 to a c]ta9 ext5t1 to ! analysis ( radiation by photography4 ,if we ?r[ ! positive pole a little beh9d ! negative pole we c1 h[ev]1 consid]ably mitigate ?is evil4 ,we c sep>ate ! c>bon rods to su* a degree t ! :ite-hot crat] faces ! obs]v]1 & a good deal ( ! arc is hidd54 ,?is is well se5 9 ! figure4 ,we h n[ describ$ ! light we h adopt$1 & ! reasons = adopt+ x2 & hav+ obta9$ our light1 we c n[ consid] by :at plan we %all =m our spectrum4 ,!re are two ways op5 to u--"o by glass prisms1 & ! o!r by a diffraction grat+4 ,glass prisms sep>ate :ite light1 or inde$ any light1 into its compon5ts1 f ! fact t ! refraction ( ea* col\r$ ray diff]s f e o!r4 ,?us ! r$ rays are lea/ refract$1 & ! violet ! mo/1 & ! yell[1 gre5 & blue are int]m$iate betwe5 !m1 be+ plac$ 9 ! ord] ( lea/ refrangibility4 ,betwe5 ^! !re is ( c\rse e %ade ( simple col\r1 "o melt+ into ! o!r4 ,9 ord] to =m a pure & bright spectrum ) prisms1 9 a room ( limit$ dim5sions1 we h to use c]ta9 auxili>y app>atus :i* are n positively ess5tial1 ?\gh conv5i5t4 ,! real ess5tials to =m a spectrum are a n>r[ slit1 a glass prism1 ) p]fectly plane faces1 & a l5s4 ,if ?is be ! only app>atus available1 ! slit mu/ be plac$ at a long di/ance f ! prism1 ! beam ( light mu/ pass ?r\gh ! slit on to ! prism1 & ! l5s mu/ be plac$ at su* a di/ance f ! slit t x =ms a %>p image on a scre54 ,:5 ! light passes ?r\gh ! prism1 ! scre5 w h to be rotat$ 9 ! arc ( a circle1 s t its di/ance f ! slit measur$ along ! l9e ( ! ray to ! prism1 & f ! prism to ! scre51 is ! same z x w\ld be )\t ! int]v5+ prism4 ,an app>atus ( ?is description is n conv5i5t1 h[ev]1 z x requires mu* m space ?an is (t5 available4 ,if a l5s be plac$ betwe5 ! slit & ! prism1 at exactly its focal l5g? f ! =m]1 ! light ent]+ ! slit w1 aft] passage ?r\gh ! l5s1 em]ge z p>allel rays1 t is1 !y w em]ge z !y w\ld d if ! slit 7 plac$ at an inf9ite di/ance f ! obs]v]4 ,! focal l5g? ( ?is collimat+ l5s ne$ n be great] ?an twelve to eighte5 in*es1 s t ! great space requir$ by ! crud] app>atus is v mu* curtail$4 ,! l5s & slit are m\nt$ "o at ea* end ( a tube ( ! necess>y l5g?1 & are ?us h&y to use4 ,in/ead ( "o prism two or ?ree may be us$1 giv+ an angul> disp]sion ( ! spectrum two or ?ree times respectively great] ?an t :i* w\ld be giv5 by only "o prism2 consequ5tly to obta9 a giv5 l5g? ( spectrum ) ! increas$ disp]sion1 ! focal l5g? ( ! l5s us$ to focus ! image on ! scre5 may be dim9i%$4 ,! drawback to ! use ( prisms is t ! disp]sion ( ! r$ end ( ! spectrum is mu* less ?an t ( ! blue end1 & is apt to give a false impression z to ! relative lum9osities (1 & l5g? ( spectrum occupi$ by1 ! diff]5t col\rs4 ,9 "s text-books x is told u t ! diffraction grat+ gives u a disp]sion :i* is 9 exact relation to ! wave-l5g?4 ,?is is n true1 h[ev]1 z x c only give "o small portion 9 su* relation%ip1 & t only :5 x is specially set = ! purpose4 ,! subject ( diffraction is "o into :i* x w\ld be =eign to our purpose to w&]4 ,we may say t = measures su* z we %all make1 x is h&i] to employ prisms1 z ! prismatic spectrum is m int5se ?an ! diffraction spectrum4 ,?is c be readily und]/ood :5 we consid] ! subject ev5 sup]ficially4 ,if we ?r[ a beam ( light on a grat+ :i* conta9s p]haps "s #ad1jjj p>allel l9es 9 ! space ( "o in* 9 wid?1 ! l9es be+ rul$ on a plane & bright metallic surface1 & receive ! reflect$ beam on a scre51 ! appe>ance t is pres5t$ is a :ite c5tral spot1 toge!r ) six or sev5 spectra ( gradually dim9i%+ brightness on ea* side ( x1 all except ! fir/ pair ov]lapp+ "o ano!r4 ,t ^! diff]5t spectra d exi/ c be readily %[n by plac+ 9 ! beam a piece ( r$ glass1 :5 symmetrical pairs ( ! r$ "p ( ! spectrum w be f\nd1 "o ( ea* pair be+ on opposite sides ( :at w n[ be ! c5tral r$ spot4 ,half ! light fall+ on ! grat+ is conc5trat$ 9 ?is c5tral spot1 & ! rema9+ half goes to =m ! spectra2 ! pair ne>e/ ! c5tral spot be+ ! brighte/4 ,we ?us are drawn to ! conclusion t at ! outside we c only h less ?an "o-qu>t] ( ! incid5t light to =m ! brighte/ spectrum we c use4 ,) two good prisms we use at la/ ?ree-f\r?s ( ! incid5t light1 s t = ! same l5g? ( spectrum we c get at lea/ ?ree times ! av]age brightness t we %\ld get 7 we to employ a diffraction grat+4 ,we mu/ n[ refre% ! read]'s memory ) a few simple facts ab\t light1 9 ord] t our mean+ may be cle> :5 we speak ( rays ( diff]5t wave-l5g?s4 ,e col\r 9 ! spectrum has a diff]5t wave-l5g?1 & x is ow+ to ?is diff]5ce 9 wave-l5g? t we are able to sep>ate !m by refraction1 or diffraction1 & to isolate !m4 ,light1 or inde$ any radiation1 is caus$ by a rhy?mic oscillation ( ! impalpable m$ium :i* we1 = want ( a bett] t]m1 call e!r1 & ! di/ance betwe5 two ( ^! waves :i* are 9 ! same phase is call$ ! wave-l5g? ( ! p>ticul> radiation4 ,! ext5t ( ! oscillation is call$ ! amplitude1 :i* :5 squ>$ is 9 effect a measure ( ! int5sity ( ! radiation4 ,?us at sea ! di/ance betwe5 ! cre/s ( two waves is ! wave-l5g?1 & ! height f tr\gh to cre/ ! amplitude2 & ! int5sity1 or p[] ( do+ "w1 ( two waves ( ! same wave-l5g?s b ( diff]5t heights1 is z ! squ>e ( _! heights4 ,?us1 if ! height ( "o 7 "o unit1 & ( ! o!r two units1 ! latt] c\ld d f\r times m "w ?an ! =m]4 ,! waves ( radiation :i* give ! s5sation ( col\r 9 ! spectrum v>y 9 l5g?1 n p]haps to ! ext5t t might be imag9$1 consid]+ ! great diff]5ce t is p]ceiv$ by ! eye1 b /ill !y are m>k$ly diff]5t4 ,! fact t ! spectrum ( sunlight is n cont9u\s1 b is brok5 up by innum]able f9e l9es1 has already be5 allud$ to4 ,! position ( ^! l9es is always ! same1 z reg>ds ! col\r 9 :i* !y are situat$1 & is absolutely fix$ directly we "k _! wave-l5g?2 h5ce if we "k ! wave-l5g?s ( ^! l9es1 we c ref] ! col\r 9 :i* !y lie to !m4 ,n[ "s l9es ( ! sol>-spectrum are black] & consequ5tly m m>k$ ?an o!rs1 & in/ead ( ref]r+ ! col\rs to ! f9] l9es1 we c ref] !m to ! di/ance !y are f "o or m ( ^! d>k] l9es1 :]e ^! latt] are absolutely fix$2 9 fact !y act z mile-/ones on a road4 ,9 ! r$ we h ?ree l9es 9 ! sol> spectrum1 :i* = sake ( easy ref]5ce are call$ ,a1 ,b & ,c2 9 ! orange we h a l9e call$ ,d1 9 ! gre5 a l9e call$ ,e1 9 ! blue ,f1 9 ! violet ,g1 & 9 ! extreme violet ,h4 ,^! l9es are our fiducial l9es1 & all col\rs c be ref]r$ to !m4 ,! foll[+ are ! wave-l5g?s ( ^! l9es1 on ! scale ( #a_/aj1jjj1jjj ( a millimetre z a unit ,a #geid ,b #fhfg ,c #fefb ,d #ehib ,e #ebfi ,f #dhfa ,g #dcjg ,h #cifh ,:5 ! spectrum is produc$ by prisms ! int]vals betwe5 ^! l9es are n proportional to ! wave-l5g?s1 & consequ5tly if we measure ! di/ance ( a ray 9 ! spectrum f two ( ^! l9es1 we h to resort to calculation1 or to a graphically drawn curve1 to asc]ta9 its wave-l5g?4 ,= ! purpose ( exp]im5ts 9 col\r ! graphic curve f :i* ! wave-l5g? c imm$iately be read (f is suffici5t4 ,! foll[+ diagram 7,fig4 #c7 %[s h[ ?is c be done4 ,! names & range ( ! pr9cipal col\rs :i* are se5 9 ! spectrum has be5 a matt] ( "s controv]sy4 ,pr(essor ,rood has1 h[ev]1 made obs]vations :i* may be accept$ z correct ) a mod]ately bright spectrum4 ,if ! spectrum be divid$ into #ajjj p>ts betwe5 ,a 9 ! r$1 & ,h1 ! limit ( ! violet1 he makes ! foll[+ table ( col\rs4 ---------------------------------------- ------- ,scale4 ,col\r4 ---------------------------------------- ------- #j to #adi ,r$4 #adi to #aid ,orange r$4 #aid to #baj ,orange4 #baj to #bcj ,orange yell[4 #bcj to #bdj ,yell[4 #bdj to #cdd ,yell[ gre5 & gre5 yell[4 #cdd to #ddg ,gre5 & blue gre54 #ddg to #die ,azure blue4 #die to #hjf ,blue & blue violet4 #hjf to #ajjj ,violet4 ---------------------------------------- ------- ,fig4 #c4--;,curve = conv]t+ ! ,prismatic ,spectrum into ,wave-l5g?s4 ,9 ! above scale 7,fig4 #c7 ,a #j1 ,b #gdj1 ,c #aabg1 ,d #bbjc1 ,e #cfca1 ,f #dicb1 ,g #gecf1 ,h #ajjj4 ,^! are ! ma9 subdivisions ( col\r1 b x mu/ be recollect$ t "o melts into ! o!r4 ,:5 ! spectrum is v bright ! col\rs t5d to alt] 9 hue2 ?us ! orange becomes pal]1 & ! yell[ :it]1 & ! blue pal]4 ,on ! o!r h&1 if ! spectrum be dim9i%$ 9 brightness ! t5d5cy is = ! col\rs to *ange 9 ! opposite direction4 ,?us ! yell[ almo/ disappe>s & becomes ( a gre5 hue1 :il/ ! orange becomes r$d]1 & ! spectrum itself becomes %ort] to ! eye ?an be=e4 ,let u /rictly gu>d ourselves1 h[ev]1 f ! criticism t all eyes see n alike4 ,suffice x to say t ! above table is correct = ! ord9>y or normal eye1 & does n necess>ily apply to ^? :o h defective vision z reg>ds col\r s5sation4 ,,*apt] ,,iii4 ,! ,visible & ,invisible ,p>ts ( ! ,spectrum--,me?ods = %[+ ! ,exi/5ce ( ! ,invisible ,portions--,phosphoresc5ce--,photography ( ! ,d>k ,rays--,!rmo-,electric ,curr5ts4 ,we are apt to =get1 :5 look+ at ! spectrum1 t :at ! eye sees is n all t is to be f\nd 9 ! prismatic analysis ( light4 ,! spectrum1 x mu/ be recollect$1 is n limit$ to ^? rays :i* ! eye p]ceives4 ,!re are rays bo? beyond ! extreme violet & bel[ ! extreme r$1 :i* exi/ & :i* ex]cise a m>k$ effect on ! _w's economy4 ,?us1 rays beyond ! violet are ^? :i* ) ! violet & ! blue rays pr9cipally affect vegetation1 enabl+ c]ta9 *emical *anges to take place :i* are necess>y = its gr[? & heal?2 :il/ ! rays bel[ ! r$ are ^? possess+ ! greate/ am\nt ( en]gy1 & if !y fall ^u bodies :i* absorb !m1 z v ne>ly all bodies d to a c]ta9 ext5t1 !y heat !m4 ,! w>m? we feel f sunlight is pr9cipally due to ! d>k rays :i* lie bel[ ! r$ ( ! spectrum4 ,! exi/5ce ( bo? k9ds ( ^! d>k rays may be demon/rat$ 9 a v simple mann] by ! effect t !y produce on c]ta9 bodies4 ,= in/ance1 !re is a yell[ dye ) :i* *eap ribbon is dy$1 :i* if plac$ 9 ! spectrum & beyond ! violet causes a visible prolongation ( ! spectrum4 ,! light 9 ! newly-se5 & once invisible "p ( ! spectrum is yell[1 ! col\r ( ! ribbon itself4 ,9 fact1 ! :ole ( t "p ( ! spectrum1 :i* on ! :ite scre5 is se5 z blue & violet1 becomes yell[1 ! r$ & gre5 rema9+ un*ang$4 ,?is *ange 9 col\r is due to fluoresc5ce1 a ph5om5on ( light :i* ,sir ,g4 ,/okes f\nd 0 caus$ by an alt]ation 9 ! l5g?s ( ! waves ( light :5 reflect$ f c]ta9 bodies4 ,x is n meant to imply by ?is t ! wave-l5g? ( any ray fall+ on a body c be alt]$ by reflection1 b only t ! body itself on :i* ! rays fall emits rays ( light :i* are n ( ! same wave-l5g? z ^? :i* fall ^u x4 ,n[ x is a fact t ! rays t lie beyond ! violet1 & :i* are ord9>ily invisible1 are %ort] ?an ! violet rays1 & t ^! are %ort] ?an ! yell[ rays4 ,x foll[s !re=e t :51 :at we may n[ call1 ! ultra-violet rays fall on ! yell[ dy$ ribbon1 ! waves emitt$ by x are s l5g!n$ t !y appe> yell[ to ! eye in/ead ( d>k1 violet1 or blue4 ,we c also bru% a solution ( qu99e on ! scre51 & imm$iately ! place :]e ! ultra-violet rays fall is illum9at$ by a violet light4 ,we d n see ! ultra-violet rays !mselves1 b only ! rays ( increas$ wave-l5g?1 :i* are emitt$ by _! effect on ! sulphate ( qu99e4 ,common ma*9e oil z us$ = eng9es also emits gre5i% rays :5 excit$ by ! ultra-violet rays1 & a v beautiful col\r x is4 ,fluoresc5ce !n is "o means ( demon/rat+ ! exi/5ce ( ! ultra-violet rays--or ,ritt]'s rays z !y 7 =m]ly call$1 aft] _! discov]]--9 a v simple mann]4 ,! me?od ( r5d]+ ! effects ( ! infra-r$ rays visible to ! eye is also int]e/+4 ,all1 or at all ev5ts mo/1 ( our read]s h se5 ,balma9's lum9\s pa9t4 ,a glass or c>d coat$ ) ?is sub/ance1 :i* is ess5tially a sulphide ( calcium1 :5 expos$ to ! light ( ! sun1 or ( ! electric arc1 & !n tak5 into comp>ative d>kness1 is se5 to %9e ) a peculi> violet-col\r$ light4 ,if :5 ?us excit$ we place x 9 a bright spectrum = "s little "t1 we %all f9d on %utt+ (f ! light t :]e ! ultra-violet & blue fell on x1 ! violet light is int5s] ?an ! light ( ! ma9 "p ( ! scre52 :]e ! yell[ fell !re is nei!r increase or dim9ution 9 brightness2 b t 9 ! r$ x becomes d>k]1 & also beyond ! limit ( ! visible spectrum1 indicat+ ! exi/5ce ( rays beyond1 :i* ?r\gh _! great] l5g? h n ! p[] ( affect+ ! eye4 ,if ! spectrum be %ut (f1 h[ev]1 v soon aft] x falls on ! plate1 x has be5 ass]t$ t ! r$ & infra-r$ rays h increas$ ! brightness ( t p>ticul> "p ( ! plate on :i* !y fell4 ,at fir/ ^! two obs]vations seem to contradict "o ano!r2 !y d n 9 reality4 ,we may expose a tablet ( ,balma9's pa9t to light1 & place a heat$ iron 9 contact ) ! back ( ! plate2 we %all !n f9d t ! iron produces a bright image ( its surface on a less bright backgr\nd4 ,?is bright image w gradually fade away1 & ! same space w ev5tually become d>k comp>$ ) ! re/ ( ! plate4 ,! reason ( ?is is cle>4 ,:5 light excites ! pa9t a c]ta9 am\nt ( en]gy is p\r$ into x1 :i* x radiates out sl[ly z light4 ,:5 ! hot iron is plac$ 9 contact ) x1 ! heat causes ! light to radiate m rapidly1 & consequ5tly ) great] int5sity1 at ! "p :]e its surface t\*es1 & ! en]gy ( t p>ticul> portion becomes us$ up4 ,:5 ! en]gy ( radiation ( ?is "p becomes less ?an t ( ! re/ ( ! tablet1 its light mu/ ( necessity be ( less brightness ?an t ( ! backgr\nd1 ) :i* ! heat$ iron has _h no contact4 ,= ?is reason ! image ( ! iron subsequ5tly appe>s d>k4 ,we %all see pres5tly1 & z be=e /at$1 t ! pr9cipal heat+ effect ( ! spectrum lies 9 ! r$ & infra-r$1 & x is ow+ to ! heat+ ( ! pa9t by ^! rays t ! image might be at fir/ slightly bright] ?an ! backgr\nd1 & subsequ5tly d>k]4 ,!re is ano!r way 9 :i* ! exi/5ce ( bo? ! ultra-violet & infra-r$ rays c be demon/rat$1 & t is by means ( photography4 ,if we place an ord9>y photographic plate 9 ! spectrum & develop x1 we %all f9d t besides be+ affect$ by ! blue & violet rays1 x is also affect$ by ! rays beyond ! violet1 ! en]gy ( ^! rays be+ capable ( caus+ a decomposition ( ! s5sitive silv] salt4 ,if qu>tz prisms & l5ses be us$1 & ! electric light be ! s\rce ( illum9ation1 ! ultra-violet spectrum w ext5d to an enorm\s ext5t4 ,a m difficult1 b p]haps ev5 m int]e/+ means ( illu/rat+ ! exi/5ce ( ! infra-r$ rays1 & fir/ due to ! writ]1 c be made by means ( photography4 ,x is possible to prep>e a photographic plate ) bromide ( silv]1 :i* is s molecul>ly arrang$ t x becomes capable ( be+ decompos$ n only by ! violet & blue rays1 b also by ! r$ rays1 & by ^? rays :i* h wave-l5g?s ( ne>ly ?ree times t ( ! r$ rays4 ,x w\ld be inappropriate to ent] into a description ( ! me?od ( ! prep>ation ( ^! plates4 ,^? :o are curi\s z to x w f9d a description 9 ! ,bak]ian lecture publi%$ 9 ! ,philosophical ,transactions ( ! ,royal ,society = #ahha4 ,) plates s prep>$ x has be5 f\nd possible to obta9 impressions 9 ! d>k ) ! rays com+ f a black object1 heat$ to only a black heat4 ,t ^! d>k rays possess great] en]gy or capacity = do+ "w ( "s k9d ?an any o!r rays ( ! spectrum1 c be %[n by means ( a l9e> !rmopile 7,fig4 #d71 if x be s arrang$ z to all[ only a n>r[ v]tical slice ( light to rea* its face4 ,fig4 #d4--,! ,!rmopile4 ,! pr9ciple ( ! !rmopile we ne$ n describe 9 detail4 ,suffice x to say t ! heat+ ( ! sold]$ junctions ( two dissimil> metals 7!re are t5 pairs ( antimony & bismu? 9 ! above in/rum5t7 produces a feeble curr5t ( electricity1 :i*1 h[ev]1 is suffici5t to cause a deflection to ! susp5d$ ne$le ( a delicate galvanomet]4 ,to ! ne$le is atta*$ a mirror weigh+ a fraction ( a gra91 & ! deflections are made visible by ! reflection f x ( a beam ( light issu+ f a fix$ po9t along a scale4 ,! great] ! heat+ ( ! junctions ( ! !rmopile1 )9 limits :i* 9 ^! cases are nev] exce$$1 ! great] is ! curr5t produc$1 & consequ5tly ! great] is ! deflection ( ! mirror-be>+ ne$le1 & ( ! beam ( light along ! scale4 ,9 ord] to get a comp>ative measure ( ! en]gies ( ! diff]5t rays1 x is necess>y t !y %\ld be completely absorb$4 ,n[ ! junctions !mselves ( ! pile be+ metal1 & !re=e m or less bright1 w n absorb completely1 b if !y be coat$ ) a f9e lay] ( lamp-black1 ! rays fall+ on ! pile w be absorb$ by ?is sub/ance1 & _! absorption w cause a rise 9 temp]ature 9 x1 & ! heat w be communicat$ to ! !rmopile4 ,if we make a bright spectrum1 & "o n too long1 say ?ree in*es 9 l5g?1 & pass ! l9e> !rmopile ?r\gh its l5g?1 we %all f9d t :5 ! galvanomet] is atta*$1 ! galvanomet] ne$le w be diff]5tly deflect$ 9 its v>i\s p>ts4 ,! deflection w be almo/ ins5sible 9 ! violet1 b s5sible 9 ! blue1 r m 9 ! gre51 /ill m 9 ! yell[1 & x w fur!r increase 9 ! r$4 ,:51 h[ev]1 ! slit ( ! !rmopile is plac$ beyond ! limit ( ! visible spectrum1 ! deflection enorm\sly increases1 & w increase till a position is rea*$ z f> bel[ ! r$ z ! yell[ is above x4 ,aft] ?is maximum is rea*$1 by mov+ ! pile /ill fur!r f ! r$1 ! galvanomet] ne$le w travel t[>ds its z]o1 & f9ally all deflection w cease4 ,at ?is po9t we may suppose we h rea*$ ! limit ( ! spectrum1 b if rock-salt prisms & l5ses be us$1 ! limit w be increas$4 ,:at ! real limit ( ! spectrum is1 is at pres5t unkn[n2 ,mr4 ,langley ) 8 bolomet]1 & rock-salt prisms1 an in/rum5t m s5sitive ?an ! !rmopile1 mu/ h ne>ly rea*$ x4 ,fig4 #e4--;,heat+ effect ( diff]5t ,s\rces ( ,radiation4 ,! above figure is a graphic repres5tation ( ! heat+ effect ( ! spectrum ( ! electric light1 sunlight1 & ! inc&esc5ce electric light1 on ! lamp-black coat+ ( ! !rmopile1 z %[n by ! galvanomet]4 ,! va/ diff]5ce betwe5 ! heat+ effect ( ! visible rays ( ! fir/ two s\rces comp>$ ) ! la/ is cle>ly indicat$4 ,s9ce e ray may be tak5 z totally absorb$1 ! heat+ ( ! lamp-black is a measure ( ! en]gy or ! capacity ( p]=m+ "w ( "s description1 :i* !y possess4 ,waves ( ! sea d "w :5 !y beat aga9/ ! %ore1 & !y d "w :5 !y lift a vessel4 ,if we notice a %ip at an*or we %all f9d t beh9d ! vessel & t[>ds ! %ore ! waves are l[]$ 9 height or amplitude2 ! en]gy :i* !y h exp5d$ 9 rais+ ! vessel ( necessity causes ?is l[]+4 ,9 ! same way ! waves ( light1 aft] fall+ on matt] ^: molecules or atoms are sw++ 9 unison ) !m1 are de/roy$1 & ! en]gy is sp5t 9 ei!r decompos+ ! matt] into a simpl] =m at fir/--?\gh ! subsequ5t =m may be m complex--or 9 rais+ its temp]ature4 ,z lamp-black or c>bon is 9 its simple/ =m1 ! only "w done ^u x by ! en]gy ( radiation is ! rais+ ( its temp]ature1 & x is = ?is reason t ?is mat]ial is s excell5t = cov]+ ! junctions ( ! pile4 ,! eye evid5tly does n absorb all rays1 s9ce only a limit$ "p ( ! spectrum is visible1 & x w\ld be useless to take a measure ( ! heat+ effect ( lamp-black = ! visible "p ( ! spectrum z a measure ( its lum9osity1 s9ce ! latt] fades (f 9 ! r$--! v place 9 :i* ! heat curve rises rapidly4 ,,*apt] ,,iv4 ,description ( ,col\r ,pat* ,app>atus--,rotat+ ,sectors--,me?od ( mak+ a ,scale = ! ,spectrum4 ,be=e proce$+ fur!r we mu/ describe some:at 9 detail two or ?ree pieces ( app>atus to be us$ 9 ! exp]im5ts we %all make4 ,! fir/ piece 0 devis$ by ! writ] a few ye>s ago1 & has got rid ( sev]al objections :i* exi/$ 9 old] pieces ( app>atus4 ,x is n only useful = lecture purposes1 b also = c>eful laboratory "w4 ,! ord9>y lecture app>atus = ?r[+ a spectrum on ! scre5 is ( too crude a =m to be effective = ! purpose we h 9 view2 ! purity ( ! col\rs se5 on ! scre5 is m ?an d\btful1 & ?is alone unfits x = our exp]im5ts4 ,if we want to =m a pure spectrum we mu/ h a n>r[ slit1 prisms ) true1 flat surfaces1 & l5ses ( prop] curvature4 ,z a rule ! ord9>y lecture app>atus = =m+ ! spectrum lacks all ( ^! requisites4 ,fig4 #f4--;,col\r ,pat* ,app>atus4 ,! accompany+ diagram 7,fig4 #f7 w give an idea ( ! app>atus we %all employ4 ,on ! usual slit ,s#a ( a collimator ,c is ?r[n1 by means ( a cond5s+ l5s ,l#a1 a beam ( light1 :i* emanates f ! int5sely :ite-hot c>bon positive pole ( ! electric light4 ,! focus is s adju/$ t an image ( ! crat] is =m$ on ! slit4 ,! collimat+ l5s ,l#b is fill$ by ?is beam1 & ! rays issue p>allel to "o ano!r & fall on ! prisms ,p#a & ,p#b1 :i* disp]se !m4 ,! disp]s$ beam falls on a correct$ photographic l5s ,l#c1 atta*$ to a cam]a 9 ! ord9>y way4 ,x is ( slightly l>g] diamet] ?an ! height ( ! prisms1 & a spectrum is =m$ on ! focus+-scre5 ,d1 :i* is slew$ at a slight angle ) ! p]p5dicul> to ! axis ( ! l5s ,l#c4 ,?is is necess>y1 because ! focus ( ! lea/ refrangible or r$ rays is long] ?an t ( ! m refrangible or blue rays4 ,by slew+ ! focus+-scre5 z %[n1 a v good g5]al focus = e ray may be obta9$4 ,:5 ! focus+-scre5 is remov$1 ! rays =m a confus$ pat* ( p>ti-col\r$ light on a :ite scre5 ,f1 plac$ "s f\r feet (f ! cam]a4 ,! rays1 h[ev]1 c be collect$ by a l5s ,l#d1 ( ab\t two feet focus1 plac$ ne> ! position ( ! focus+-scre51 & slightly askew4 ,?is =ms an image on ! scre5 ( ! ne> surface ( ! la/ prism ,p#b2 & if correctly adju/$1 ! rectangul> pat* ( light %\ld be pure & )\t any fr+es ( col\r4 ,! c>d ,d slides into ! grooves :i* ord9>ily take ! d>k slide4 ,9 x w be se5 a slit ,s#b1 ! utility ( :i* w be expla9$ lat] on4 ,we %all usually require a second pat* ( :ite light1 ) :i* to comp>e ! fir/ pat*4 ,n[1 al?\gh ! light f ! positive pole ( ! c>bons is uni=m 9 quality1 x sometimes v>ies 9 quantity1 z x is difficult to keep its image always 9 exactly ! c5tre ( ! slit4 ,if we c take "o "p ( ! light com+ ?r\gh ! slit to =m ! spectrum1 & ano!r "p to =m ! second pat* ( :ite light1 !n ! brightness ( ! two w v>y toge!r4 ,at fir/ sight ?is might appe> difficult to atta92 b advantage is tak5 ( ! fact t f ! fir/ surface ( ! fir/ prism ,p#a a c]ta9 am\nt ( light is reflect$4 ,plac+ a l5s ,l#e1 & a mirror ,g1 9 ! pa? ( ?is reflect$ beam1 ano!r squ>e pat* ( light c be ?r[n on ! same scre5 z t on :i* ! fir/ is ?r[n1 & ?is second pat* may be made ( ! same size z ! fir/ pat*1 if ! l5s ,l#e be ( suitable focus1 & x c be sup]pos$ ov] ! fir/ pat* if requir$2 or1 z is useful 9 "s cases1 ! two pat*es may be plac$ side by side1 j t\*+ ea* o!r4 ,we are ?us able to secure two squ>e :ite pat*es ^u ! scre5 ,f1 "o f ! re-comb9ation ( ! spectrum1 & "o f ! reflect$ beam4 ,if a rod be plac$ 9 ! pa? ( ^! two beams :5 !y are sup]pos$1 ea* beam w ?r[ a %ad[ ( ! rod ^u ! scre54 ,! %ad[ ca/ by ! integrat$ spectrum w be illum9at$ by ! reflect$ beam1 & ! %ad[ ca/ by ! latt] w be illum9at$ by ! =m]4 ,9 fact we h an ord9>y ,rum=d photomet]1 & ! two %ad[s may be caus$ to t\* "o ano!r by mov+ ! rod t[>ds or f ! scre54 ,:5 ! illum9ation ( ! two %ad[s by ! :ite light is equal1 ! :ole %\ld appe> z "o unbrok5 gray pat*4 ,to prev5t confusion to ! eye a black mask is plac$ on ! scre5 ,f ) a squ>e ap]ture cut out ( x1 on :i* ! two %ad[s are caus$ to fall4 ,if x be desir$ to dim9i% ! brightness ( ei!r pat*1 x c be accompli%$ by ! introduction ( rotat+ sectors ,m1 :i* c be op5$ & clos$ at pleasure dur+ rotation1 9 ! pa? ( "o or o!r ( ! beams4 ,fig4 #g4--,rotat+ ,sectors4 ,! annex$ figure 7,fig4 #g7 is a bird's-eye view ( ! in/rum5t4 ,a ,a are two sectors1 "o ( :i* is capable ( clos+ ! op5 ap]ture by means ( a lev] arrangem5t ,c1 :i* moves a sleeve 9 :i* is fix$ a p9 work+ 9 a screw groove1 :i* all[s ! ap]ture 9 ! sectors to be op5$ & clos$ at pleasure dur+ _! revolution2 ,d is an electro-motor caus+ ! sectors to rotate4 ,to %[ its effici5cy1 if two /rips ( pap]1 "o coat$ ) lamp-black & ! o!r :ite1 are plac$ side by side on ! scre51 & if "o %ad[ f ! rod falls on ! :ite /rip1 & ! o!r %ad[ on ! black /rip ( pap]1 & ! rotat+ sectors are int]pos$ 9 ! pa? ( ! light illum9at+ ! %ad[ ca/ on ! :ite /rip1 ! ap]ture ( ! sectors c be clos$ till ! :ite pap] appe>s absolutely black] ?an ! black pap]4 ,:ite ?us becomes d>k] ?an lamp-black1 ow+ to ! want ( illum9ation4 ,?is is an int]e/+ exp]im5t1 & we %all see its be>+s z we proce$1 z x indicates t ev5 lamp-black reflects a c]ta9 am\nt ( :ite or o!r light4 ,hav+ ?us expla9$ ! ma9 "p ( ! app>atus ) :i* we %all "w1 we c g on & %[ h[ mono*romatic light ( any degree ( purity c be produc$ on ! scre54 ,if ! slit 9 ! c>dbo>d slide ,d be pass$ ?r\gh ! spectrum :5 x has be5 focus$ on ! focus+-scre51 only "o small /rip ( practically mono*romatic light w rea* ! scre51 & in/ead ( ! :ite pat* on ! scre5 we %all h a succession ( col\r$ pat*es1 ! col\r v>y+ accord+ to ! position ! slit occupies 9 ! spectrum4 ,x %\ld be not$ t ! purity ( ! col\r dep5ds on two ?+s--! n>r[ness ( ! slit ,s#a ( ! collimator1 & ( ! slit ,s#b 9 ! c>d4 ,if two slits be cut 9 ! c>d ,d1 we %all h two col\r$ pat*es ov]lapp+ "o ano!r1 & if ! reflect$ beam falls on ! same space we %all h a mixture ( col\r$ light ) :ite light1 & ei!r ! col\r$ light or ! :ite light c be r$uc$ 9 brightness by ! introduction ( ! rotat+ sectors4 ,if ! rod be introduc$ 9 ! pa? ( ! rays we %all h two %ad[s ca/1 "o illum9at$ ) col\r$ light1 mono*romatic or comp\nd1 & ! o!r ) :ite light1 & ^! c be plac$ side by side1 & surr\nd$ by ! black mask z be=e describ$4 ,fig4 #h4--,spectrum ( ,sodium ,li?ium & ,c>bon4 ,!re is "o o!r "p ( ! app>atus :i* may be m5tion$1 & t is ! indicator1 :i* tells u :at "p ( ! spectrum is pass+ ?r\gh ! slit4 ,j outside ! cam]a1 & 9 a l9e ) ! focus+-scre51 is a clip c>ry+ a v]tical ne$le4 ,a small beam ( light passes outside ! prism ,p#a2 ?is is caught by a mirror atta*$ to ! side ( ! app>atus1 & is reflect$ s z to ca/ a %ad[ ( ! ne$le on to ! back ( ! c>d ,d1 on :i* a c>efully divid$ scale ( tw5tie?s ( an in* is drawn4 ,to fix ! position ( ! slit ! poles ( ! electric light are bru%$ ov] ) a solution ( ! c>bonates ( sodium & li?ium 9 hydro*loric acid1 & ! image ( ! arc is ?r[n on ! slit4 ,?is gets rid ( ! cont9u\s spectrum1 & only ! bright l9es due to ! inc&esc5t vap\rs appe> on ! focus+-scre5 7,fig4 #h74 ,among/ o!r l9es we h ! r$ & blue l9es due to ! vap\r ( li?ium2 ! orange1 yell[ 7,d71 & gre5 l9es ( sodium1 toge!r ) ! violet l9es ( calcium 7^! la/ due to ! impurities ( ! c>bons =m+ ! poles74 ,^! l9es are caus$ successively to fall on ! c5tre ( ! slit by mov+ ! c>d ,d1 :i* = ! nonce is cov]$ ) a piece ( gr\nd glass1 & ! position ( ! %ad[ ( ! ne$le-po9t on ! scale is regi/]$ = ea*4 ,a fur!r *eck c be made by tak+ a photograph ( ^! l9es1 or ( ! sol> spectrum1 & hav+ fix$ accurately on ! scale any "o ( ^! l9es already nam$1 ! position ( ! o!rs on ! scale may be asc]ta9$ by measurem5t f ! photograph4 ,n[ ! wave-l5g?s ( ^! bright l9es h be5 mo/ accurately asc]ta9$1 9 fact z accurately z ! d>k l9es 9 ! sol> spectrum4 ,?us ! scale on ! c>d is a means ( localiz+ ! col\r pass+ ?r\gh ! slit or slits4 ,%\ld m ?an "o slit be us$ 9 ! spectrum ! positions ( ea* c be det]m9$ 9 exactly ! same way4 ,! mo/ t$i\s "p ( ! :ole exp]im5tal arrangem5t ) ?is app>atus is :at may be call$ ! scal+ ( ! spectrum4 ,a fairly l>ge spectrum may be =m$ ^u ! scre5 )\t alt]+ any arrangem5t ( ! app>atus1 :5 x has be5 adju/$ to =m col\r pat*es4 ,if a l5s ,l#f 7see ,fig4 #f7 ( %ort focus be plac$ 9 front ( ,l#d 7! big comb9+ l5s71 an enl>g$ spectrum w be ?r[n ^u ! scre5 ,f1 & if slits be plac$ 9 ! spectrum ! images ( _! ap]tures are =m$ by ! respective col\r$ rays pass+ ?r\gh !m1 s t ! col\rs :i* are comb9$ 9 ! pat* c be imm$iately se54 ,,*apt] ,v4 ,absorption ( ! ,spectrum--,analysis ( ,col\r--,vibrations ( ,rays--,absorption by ,pigm5ts--,phosphoresc5ce--,int]f]5ce4 ,we mu/ n[ briefly consid] :at is ! orig91 or at all ev5ts ! cause1 ( ! col\r :i* we see 9 objects4 ,x is n propos$ to ent] into ?is by any means m9utely1 b only suffici5tly to enable u to und]/& ! subject :i* is to be br\ght be=e y4 ,:at = in/ance is ! cause ( ! col\r ( ?is gre5 solution ( *lorophyll1 :i* is an extract ( cabbage leaves8 ,if we place x 9 ! front ( ! spectrum app>atus & ?r[ ! spectrum on ! scre51 we f9d t :ile !re is a c]ta9 am\nt ( blue transmitt$1 ! gre5 is /rong1 & !re are r$ b&s left1 b a good deal ( ! spectrum is totally absorb$4 ,=m+ a col\r pat* ( ?is absorption spectrum on ! scre51 we see t x is ! same col\r z ! *lorophyll solution1 & ( ?is we c judge m accurately by us+ ! reflect$ beam1 & plac+ ! rod 9 position to ca/ %ad[s4 7,! light ( ! reflect$ beam is t ( ! light ent]+ ! slit47 ,! col\r !n ( ! *lorophyll is due to ! abs5ce ( c]ta9 col\rs f ! spectrum ( :ite light4 ,:5 :ite light passes ?r\gh x1 ! mat]ial absorbs1 or filt]s out1 "s ( ! col\r$ rays1 & all[s o!rs to pass m or less unaffect$1 & x is ! re-comb9ation ( ^! la/ :i* makes up ! col\r ( ! *lorophyll4 ,we h a gre5 dye :i* to ! eye is v simil> 9 col\r to *lorophyll1 b putt+ a solution ( x 9 front ( ! spectrum1 we see t x cuts (f diff]5t rays to ! latt]4 ,x w\ld be q possible to mi/ake "o gre5 = ! o!r1 b directly we analyze ! :ite light :i* has filt]$ ?r\gh ea* by means ( ! spectrum1 we at once see t !y diff]4 ,h5ce ! spectrum enables ! eye to discrim9ate by analysis :at x w\ld o!rwise be unable to d4 ,any col\r$ solution or transp>5t body may be analyz$ 9 ! same way1 &1 z we %all see subsequ5tly1 ! int5sity ( e ray aft] pass+ ?r\gh x c be accurately comp>$ ) ! orig9al incid5t light4 ,!re are "s cases1 inde$ ! majority ( cases1 9 :i* ! col\r transmitt$ ?r\gh a small ?ickness ( ! mat]ial is diff]5t to t transmitt$ ?r\gh a great] ?ickness4 ,= in/ance1 a weak solution ( litmus 9 wat] is blue :5 a ?9 lay] is exam9$1 & r$ :5 x is a ?ick] or m conc5trat$ lay]4 ,bi*romate ( pota% is m ruddy z ! ?ickness increases4 ,?is c be readily und]/ood by a ref]5ce to ! law ( absorption4 ,suppose we h a ?9 lay] ( a liquid :i* gives a purple col\r :5 two simple col\rs1 r$ & blue1 pass ?r\gh x1 & t ?is ?9 lay] cuts (f "o-qu>t] ( ! r$ & "o-half ( ! blue incid5t on x1 ano!r lay] ( equal ?ickness w cut (f ano!r qu>t] ( ! ?ree-qu>t]s ( r$ pass+ ?r\gh ! fir/ lay]1 & half ( ! "o-half left ( ! blue2 we %all ?us h n9e-sixte5?s ( ! r$ pass+ & only a qu>t] ( ! blue4 ,) a ?ird lay] we %all h tw5ty-sev5 sixty-f\r?s ( r$ & only "o-eigh? ( blue left1 %[+ t z ! ?ickness ( ! liquid is increas$ ! blue rapidly disappe>s1 leav+ ! r$ ! dom9ant col\r4 ,n[ :at is true ( two simple col\rs is equally true ( any numb] ( !m1 :]e ! rates ( absorption diff] f "o ano!r1 & :at is true = a solution is true = a transp>5t solid4 ,9 "s opaque bodies1 su* z rocks1 ! reflect$ col\r (t5 diff]s slightly f t ( ! same :5 !y are cut into ?9 & poli%$ slices1 ?r\gh :i* ! light c pass4 ,! reason is t :5 opaque1 light p5etrates to a v small di/ance ?r\gh ! surface1 & is reflect$ back1 :il/ 9 ^! lay]s ! col\r has to /ruggle ?r\gh m col\r$ matt]1 & em]ges ( a diff]5t hue4 ,! "q :y sub/ances transmit "s rays & qu5* o!rs1 br+s u into ! doma9 ( molecul> physics4 ,( all bran*es ( physical sci5ce ?is is p]haps ! mo/ fasc9at+ & ! mo/ speculative1 yet x is "o :i* is be+ built up on ! solid f\ndations ( exp]im5t & ma!matics1 till x has atta9$ an importance :i* ! que/ions dep5d+ on x fully w>rants4 ,we h to picture to ourselves1 9 ! case 9 po9t1 molecules1 & ! atoms compos+ !m1 ( a size :i* no microscope c br+ to view1 vibrat+ 9 c]ta9 def9ite p]iods :i* are simil> to ! p]iods ( oscillation ( ! waves ( light4 ,at page #bf we h giv5 ! l5g?s ( "s ( ! waves :i* give ! s5sation ( col\r$ light4 ,n[ z light1 ( :atev] col\r x may be1 is practically transmitt$ ) ! same velocity ?r\gh air :i* has ! same d5sity ?r\gh\t1 x foll[s t ! numb] ( vibrations p] second ( ea* ray c be obta9$ by divid+ ! velocity ( light 9 any m$ium by ! wave-l5g?4 ,! foll[+ table gives r\ghly ! numb] ( vibrations p] second ( ! e!r giv+ rise to ! col\rs fix$ by ! d>k sol> l9es4 ---------------------------------------- ,"n ( ,l9e4 ,millions ( ,millions ( ,vibrations p] ,second4 ---------------------------------------- ,a 9 ! ,r$ #cie ,b #dcg ,c #deh ,d ,orange #eaj ,e ,gre5 #egj ,f ,blue #fah ,g ,violet #fig ,h ,ultra-,violet #geg ---------------------------------------- ,if we endeav\r to gauge :at ?is rate ( oscillation means we %all sc>cely be able to realize x1 ev5 by a comp>ison ) "s physically measurable rate ( vibration4 ,a tun+-=k1 = in/ance1 giv+ ! middle ,c1 vibrates #ebh times p] second4 ,comp>e ?is ) ! numb] ( vibrations ( ! waves ( light1 & we /ill are z f> z ev] f realiz+ x1 yet ! velocity ( light1 & ! l5g?s ( ! diff]5t waves h be5 accurately det]m9$2 ! latt]1 al?\gh ! mu* small] quantity1 ) ev5 great] accuracy ?an ! fir/4 ,^! rates ( vibration mu/ !re=e be--_c help be+--at all ev5ts approximately true4 ,?is be+ s1 we "k t "s ( ! atoms ( ! molecules at lea/1 & p]haps 9 "s cases ! molecules !mselves1 are vibrat+ at ! same rate z ^? waves ( light1 :i* !y refuse to all[ to pass4 ,if we h a *ild's sw+ beg9n+ to oscillate1 we "k t x is only by well-tim$ bl[s t ! ext5t ( ! sw+ is p]man5tly increas$1 & ! en]gy ex]t$ by ! p]son :o gives ! well-tim$ bl[ is exp5d$ on produc+ ! increas$ amplitude4 ,9 ! same way if ! rate ( vibration ( a wave ( light is 9 accord ) t ( a molecule or atom1 ! amplitude or sw+ ( ! atom or molecule is increas$1 & ! en]gy ( ! wave & !re=e its amplitude is totally or p>tially de/roy$2 & z ! amplitude is a function ( ! int5sity ( ! light1 ! ray fails to be se5 at all1 or else is dim9i%$ 9 brightness4 ,9 :at way ! atoms vibrate :]e m ?an "o ray is absorb$ is /ill a matt] ( speculation1 b no d\bt z exp]im5tal me?ods are m fully develop$1 & ma!maticians inve/igate ! results ( su* exp]im5ts1 we %all be able to =m a picture ( ! vibrations !mselves4 ,at page #acg a speculation z to ! reason :y solids or liquids c absorb m waves ( light ?an "o :i* are adjac5t to ea* o!r is put =w>d1 b x does n deal ) ! absorptions :i* occupy v>i\s p>ts ( ! spectrum4 ,aga91 too1 we h ! fact t ! en]gy absorb$ by ^! atoms & molecules f ! waves ( light1 mu/ %[ itself z "w done on !m--x may be z heat or z *emical action4 ,we %all see by & by t 9 "s cases1 no d\bt1 at lea/ a "p is exp5d$ 9 ! latt] =m ( "w4 ,p]haps ?is mode ( look+ at ! "q ( col\r 9 objects may make ! subject m int]e/+ to ! read] ?an x at fir/ appe>s to be des]v+4 ,! :ole subject is "o :i* enl>ges ! faculty ( mak+ m5tal pictures1 & ?is is "o ( ! mo/ useful =ms ( sci5tific education4 ,b h[ c we di/+ui% betwe5 pigm5ts :i* to ! eye are app>5tly ! same8 ,if we dye pap] ) ! gre5 dye ref]r$ to1 we c place x 9 ! spectrum1 & we %all see t ! dye reflects diff]5tly to ! :ite pap]4 ,9 fact we %all f9d t x refuses to reflect 9 ^? p>ts ( ! spectrum :i* ! transp>5t solution refus$ to transmit4 ,s long z ! light passes ?r\gh ! dye-/uff1 x is indiff]5t1 z reg>ds ! col\r produc$1 :e!r ! col\r+ matt] be at a di/ance f ! pap] or :e!r ! latt] be dy$ ) x1 z we c see at once4 ,if we place ! solution ( ! dye 9 ! reflect$ beam ( ! app>atus & =m a pat* on ! scre51 & alongside ?r[ ! pat* ( :ite light f ! integrat$ or recomb9$ spectrum ^u ! dy$ pap]1 x w be f\nd t ! two col\rs are alike2 t is1 ! gre5-col\r$ light on ! :ite pap]1 or ! :ite light on ! gre5 pap] are ! same4 ,simil>ly we may exp]im5t on o!r dyes1 su* z mag5ta1 log-wood1 c41 & we %all see t l results are obta9$4 ,x %\ld be said1 h[ev]1 t :5 ! pap] is dy$ ) ! col\r+ matt] a small quantity ( :ite light w be reflect$ f ! surface ( ! pap] itself4 ,we may n[ say t ! g5]al col\r is giv5 to a body by its refusal to transmit or reflect1 m or less completely1 c]ta9 rays ( ! spectrum4 ,%\ld ! solv5t =m a comp\nd ) ! dye1 p]haps ?is w\ld n be absolutely true1 b 9 ! l>ge majority ( cases ! /atem5t is correct4 ,:5 we h bodies :i* are also fluoresc5t1 ?is /atem5t w\ld also h to be modifi$1 b we ne$ n consid] ^! = ! pres5t4 ,ano!r s\rce ( col\r 9 objects1 ?\gh v r>ely met )1 & :i* = our object we ne$ n /ay to expla9 9 detail1 is ! int]f]5ce ( light4 ,su* is se5 9 soap-bubbles4 ,briefly x may be said t ! col\rs are due to rays ( light reflect$ f ! inn] surface ( ! film1 :i* qu5* o!r rays ( light ( ! same wave-l5g? reflect$ f ! out] surface4 ,if two s]ies ( waves ( ! same wave-l5g? are go+ 9 ! same direction & f ! same s\rce1 ea* ( :i* has ! same int5sity z ! o!r1 t is1 hav+ ! same amplitude1 & x happ5s t ! "o s]ies is exactly half a wave-l5g? beh9d ! o!r1 !n ! cre/ ( "o wave 9 ! fir/ s]ies w fill up ! tr\gh ( ! o!r 9 ! second s]ies1 & no motion w\ld result1 & ?is lack ( motion means d>kness1 s9ce x is ! wave motion :i* gives ! s5sation ( light4 ,if !n we h :ite light fall+ on two reflect+ surfaces1 su* z ! front & back ( a soap-film1 "p ( ! light w be reflect$ f ea*1 & if ! film be ( su* a ?ickness t ! latt] reflects light exactly #a_/b wave-l5g?1 #c_/b or #e_/b wave-l5g?1 c41 ( "s col\r beh9d ! =m]1 ! col\r due to t p>ticul> wave-l5g? w be abs5t f ! reflect$ :ite light1 & in/ead ( :ite light we %all h col\r$ light1 due to ! comb9ation ( all ! col\rs less ?is col\r1 :i* is qu5*$4 ,a v pretty exp]im5t to make is to ?r[ ! image ( a soap film on ! scre51 & to wat* ! *ange 9 ! col\rs ( ! film4 ,_! brilliancy increases z ! film becomes ?9n]1 & ! b&s1 :i* fir/ appe> close to ea* o!r1 sep>ate1 & !n we see a l>ge expanse ( *ang+ col\r4 ,a soap solution %\ld be made accord+ to almo/ any ( ! publi%$ =mul1 & a piece ( flat c>d be dipp$ 9 x1 & be drawn across a r+ ( wire "s in* 9 diamet]1 or--:at ! writ] pref]s be/--! /op ( a photographic l5s4 ,a film w =m & fill ! ap]ture4 ,! r+ or /op may be plac$ v]tically 9 a clamp1 & a beam ( light caus$ to fall at an angle ( ab\t #de degrees on to ! film4 ,if a l5s be plac$ 9 ! pa? ( ! reflect$ beam to =m an image ( ! ap]ture1 ! col\rs :i* ! film %[s c be exhibit$ to an audi5ce1 if ! diamet] ( ! image be made f\r or five feet4 ,in/ead ( ?is l>ge image1 a small image may be ?r[n on ! slit ( ! spectroscope1 by us+ a l5s ( a great] focal l5g?1 & if ! beam be s direct$ t x falls on ! axis ( ! collimator1 a v fairly bright spectrum may be also ?r[n on ! scre54 ,! appe>ance ( ! spectrum is some:at l t %[n 9 ! above diagram 7,fig4 #i74 ,fig4 #i4--;,int]f]5ce ,b&s4 ,if we take a horizontal l9e across ! spectrum1 we %all see :at p>ticul> col\rs are miss+ f ! reflect$ light :i* falls on ! "p ( ! slit correspond+ to t l9e4 ,! col\rs ( "s objects1 su* z ( ! opal1 & ! lovely col\r+ ( "s fea!rs are due to int]f]5ce ( light4 ,! p>tial scatt]+ ( diff]5t rays by small p>ticles w also cause light to be col\r$1 z we %all see 9 ! exp]im5ts we %all make to imitate ! col\r ( sunlight at v>i\s altitudes ( ! sun4 ,we may1 h[ev]1 take x z a rule t ! col\r ( objects is produc$ by ! great] or less absorption ( "s rays1 & ! reflection 9 ! case ( opaque bodies1 or ! transmission1 9 ! case ( transp>5t bodies1 ( ! rema9d]4 ,,*apt] ,,vi4 ,scatt]$ ,light--,sunset ,col\rs--,law ( ! ,scatt]+ by ,f9e ,p>ticles--,sunset ,cl\ds--,lum9osities ( ,sunlight at diff]5t ,altitudes ( ! ,sun4 ,x is probable t we %\ld be able to asc]ta9 approximately ! true col\r ( sunlight 7if we may talk ( ! col\r ( :ite light7 if we c\ld collect all ! light f a cl\dless sky1 & cond5se x on a pat* ( sunlight ?r[n on a scre54 ,= skylight is1 aft] all1 only a portion ( ! light ( ! sun1 scatt]$ f small p>ticles 9 ! atmosph]e1 "p ( ! light be+ scatt]$ into space1 & "p to our e>?4 ,! small p>ticles ( wat] & du/--& :5 we say small we mean small :5 measur$ on ! same scale z we measure ! l5g?s ( waves ( light--diff]5tiate betwe5 waves ( diff]5t l5g?s1 & scatt] ! blue rays m ?an ! gre51 & ! gre5 ?an ! r$2 consequ5tly :at ! sun lacks 9 blue & gre5 is to be f\nd 9 ! light ( ! sky4 ,! effect t small wat] p>ticles h ^u light pass+ ?r\gh !m c be v well se5 9 ! /reets ( ,london at night1 :5 ! atmosph]e is at all foggy4 ,gaslights at ! f> end ( a /reet appe> to become ruby r$ & dim1 & half-way d[n only orange1 b bright]1 :il/ close to !y are ( ! ord9>y yell[ col\r1 & ( normal brightness4 ,:5 no fog is pres5t ! gas-lights 9 ! di/ance & close to are ( ! same col\r & brightness1 %[+ t _! *ange 9 appe>ance is simply due to ! mi/y atmosph]e int]v5+ betwe5 !m & ! obs]v]4 ,we c imitate ! light f ! sun1 aft] its passage ?r\gh v>i\s ?icknesses ( atmosph]e1 9 a v p]fect mann] 9 ! lecture-room1 us+ ! electric light z a s\rce4 ,a cond5s+ l5s is put 9 front ( ! lamp1 & 9 front ( t a circul> ap]ture 9 a plate4 ,beyond t aga9 is a l5s :i* ?r[s an enl>g$ image ( ! ap]ture on ! scre51 :i* we may call our mock sun4 ,if we place a tr\gh ( glass1 9 :i* is a dilute solution ( hyposulphite ( soda1 c>efully filt]$ f motes z f> z possible1 9 front ( ! ap]ture1 we h an image ( ! ap]ture unaffect$ by ! ins]tion ( ! solution4 ,! :ite disc on ! scre5 w1 z we h said be=e1 be a close approximation to sunlight on a ,may-day ab\t noon1 :5 ! sky is cle>4 ,by dropp+ into ! tr\gh a little dilute hydro*loric acid1 a *ange w be f\nd to come ov] ! light ( ! mock sun2 a pale yell[ col\r w spread ov] its surface1 & ?is w give way to an orange t9t1 & at ! same "t its brightness w dim9i%4 ,gradually ! orange w give place to r$1 ! lum9osity w be v small1 be+ ( ! same hue z t se5 9 ! sun :5 view$ ?r\gh a ,london fog4 ,f9ally ! la/ trace ( r$ w s m+le ) ! scatt]$ :ite light t ! image w disappe>1 & !n ! exp]im5t is ov]4 ,if we track ! cause ( ?is *ange ( col\r 9 our artificial sun1 we %all f9d t x is due to m9ute p>ticles ( sulphur sep>at+ out f ! solution ( hyposulphite1 & ! long] ! "t t elapses ! m turbid ! dilute solution w become4 ,?is exp]im5t exemplifies ! action ( small p>ticles on light4 ,exam9+ ! tr\gh x w be f\nd t :il/ ! light :i* passes ?r\gh ! solution pr9cipally loses blue rays1 ! light :i* is scatt]$ f ! sides is almo/ c]ulean 9 blue1 & c well be comp>$ ) ! light f ! sky4 ,we c analyze ! transmitt$ light v readily by focus+ ! beam f ! positive pole ( ! electric light on to ! slit ( our col\r app>atus1 & plac+ ! l5s ,l#f7;,fig4 #f7 9 position to =m ! l>ge spectrum on ! scre54 ,we c also %[ ! col\r ( ! light :i* goes to =m ! spectrum1 by s5d+ ! pat* ( light reflect$ f ! fir/ surface ( ! fir/ prism j above x4 ,we ?us h ! spectrum & ! light =m+ ! spectrum to comp>e ) "o ano!r4 ,us+ ?is app>atus & ins]t+ ! tr\gh ( dilute hyposulphite 9 ! beam1 ! spectrum is ( ! "* usually se5 ) ! electric light2 b on dropp+ ! dilute hydro*loric acid into ! solution ! same hues fall on ! slit ( ! spectroscope :i* fell ^u ! scre5 to =m ! mock sun1 & ! spectrum is se5 to *ange z ! light *anges f :ite to yell[1 & f yell[ to r$4 ,fir/ ! violet w disappe>1 ! blue & ! gre5 be+ dimm$1 ! =m] mo/ h[ev]2 !n ! blue w vani% to ! eye1 ! gre5 becom+ /ill less lum9\s1 & ! yell[ also fad+2 ! gre5 & yell[ w successively disappe>1 leav+ f9ally on ! scre5 a r$ b& alone1 :i* w be a ne> mat* to ! col\r ( ! unanalyz$ light1 z may be se5 by comp>+ x ) ! adjac5t pat* =m$ f ! reflect$ beam4 ,we h "h a pro( t ! succession ( ph5om5a is caus$ by a scatt]+ ( ! %ort] wave-l5g?s ( light1 & t ! %ort] ! waves are ! m !y are scatt]$4 ,x has be5 f\nd !oretically by ,"l ,rayleigh t ! scatt]+ takes place 9 inv]se proportion to ! f\r? p[] ( ! wave-l5g?2 ?us1 if two wave-l5g?s1 :i* may be waves 9 ! gre5 & violet1 are 9 ! proportion ( ?ree to f\r1 ! =m] w be scatt]$ z #a_/7cd7 to #a_/7dd71 or z #bef to #ha1 :i* is approximately z ?ree to "o4 ,consequ5tly if ! gre5 9 pass+ ?r\gh a c]ta9 ?ickness ( a turbid m$ium loses "o-half ! violet 9 pass+ ?r\gh ! same ?ickness w lose five-six?s ( its lum9osity4 ,! inv]se f\r? p[]s ( ! foll[+ wave-l5g?s1 :i* are )9 ! limits ( ! :ole visible spectrum1 are %[n bel[4 ----------------------------------- ,lamda #gjjj #fjjj #ejjj #djjj ----------------------------------- #a_/,lamda#d #a #ejd #bfj #ajg ----------------------------------- ,suppos+ ,lamda#gjjj by ! scatt]+ ( small p>ticles loses "o-t5? ( its lum9osity1 !n ,lamda#fjjj w\ld h #ded ( its orig9al brightness2 ,lamda#ejjj1 #bcd2 & ,lamda#djjj1 #jie2 t is1 :il/ ,lamda#gjjj w\ld lose "o-t5? only ( its lum9osity1 ,lamda#djjj 9 ! violet w\ld reta9 n q "o-hundr$? ( its brightness4 ,dur+ ! ye>s #ahhe1 #ahhf1 & #ahhg1 ! writ] measur$ ! lum9osity ( ! sol> spectrum at diff]5t times ( ! ye>1 & at diff]5t h\rs ( ! day 7see ,phil4 ,trans4 #ahhg3 ,transmission ( ,sunlight ?r\gh ! ,e>?'s ,atmosph]e71 & f ! results he f\nd t ! smalle/ coeffici5t ( scatt]+ = "o atmosph]e at sea-level = ea* wave-l5g? 0 #jjac1 :5 ,lamda-#d 0 = conv5i5ce sake multipli$ by #ajag 7?us ,lamda#fjjj-d on ?is scale 0 #ggb71 & t ! mean 0 #jjag4 ,! foll[+ table %[s ! loss ( light = ! rays d5ot$ by ! pr9cipal l9es giv5 at page #bf1 us+ ?is la/ coeffici5t = diff]5t air ?icknesses4 ,?is is equival5t to giv+ ! int5sity ( ! rays ( sunlight :5 ! sun is at diff]5t altitudes4 ---------------------------------------- ------------------------- #a ,light aft] pass+ ?r\gh atmosph]es ( ,l9e ,wave- - ! foll[+ ?icknesses4 l5g?,lamda-#d--------------------------- ---------- x#ajag #j #a #b #c #d #e #f #g #h #cb ---------------------------------------- ---------------- ,a #geid #cj #aieeijhheghaeggegcfgjgffeajg ,b #fhfg #de #aibfhehgiegcefhdfcbehcedbjhf ,c #fefb #ed #aiabhcbgeificfcbegfebfdhjjai ,d #ehib #hc #ahfhgedfeeefididdbhcgbcbcjja ,e #ebfi #abi #ahjcfddeahdbgccdbfhbafagc -- ,f #dhfa #agi #agchedddjbbifbaiafaaaijhh -- ,g #dcjg #bia #afjicfgbbjacgjhdjeajcajai -- ,h #cifh #djc #aejfbedabhjgajccjafjjhjjd -- ---------------------------------------- ---------------- ,! sun trav]ses ! foll[+ ?icknesses ( atmosph]e :5 x is at ! angles %[n above ! horizon4 #a atmosph]e #ij #b #cj #c #aicj #d #adcj #e #aacj #f #icj #g #hcj #h #gcj ,fig4 #aj4--;,absorption ( ,rays by ! ,atmosph]e4 ,x trav]ses ?irty-two atmosph]es :5 x is v ne>ly sett+4 ,b\gi] & ,=bes h calculat$ t ! extreme ?ickness ( ! atmosph]e1 trav]s$ by its light :5 ! sun is on ! horizon1 is approximately #ce-a_/b atmosph]es4 ,! absorption %[n by #cb atmosph]es w !re=e be v close to t :i* w\ld be obs]v$ at sunset on an ord9>y day1 & x w be se5 t practically all rays h be5 scatt]$ f ! light1 except ! r$1 & a little bit ( ! orange4 ,z to ! lum9osity ( ! sun at ^! diff]5t altitudes1 we c easily f9d x by r$uc+ ! lum9osity curve ( ! sun at "s kn[n altitude by ! factors 9 ! table j giv51 = z _m wave-l5g?s z we please1 & ?us con/ruct ano!r curve4 ,! area ( ! figure ?us obta9$ w\ld be a measure ( ! total lum9osity on ! same scale z ! area ( ! lum9osity curve f :i* x 0 d]iv$4 ,! foll[+ are ! approximate lum9osities ( ! sun :5 ! light %9es ?r\gh #j atmosph]es #a #a #hdj #b #gje #c #eid #d #dif #e #dag #f #cjc #g #bef #h #bae #cb #jjb ,x w ?us be se5 t ! sun is #dbj times less bright j at sunset ?an x is if x 7 to %9e directly ov]head1 & ab\t #cej times bright] ?an x is = a w9t] sun 9 a cl\dless & mi/less sky at twelve o'clock1 = ! altitude ( ! sun 9 our latitude is ab\t #cj at t "t1 & corresponds ) a ?ickness ( two atmosph]es1 ?r\gh :i* ! sun has to %9e4 ,we all "k t to look at ! sun at any "t ne> noon 9 a cl\dless sky dazzles ! eyes1 b t ne> sunset x may be look$ at ) impunity4 ,! r$uction 9 lum9osity expla9s ?is fact4 ,! di/ribution ( ! scatt]+ p>ticles 9 ! atmosph]e is v f> f regul>4 ,z we asc5d1 ! p>ticles get m sp>se1 z is %[n by ! less scatt]+ t takes place ( ! blue rays comp>$ ) ! r$4 ,?us at an altitude ( "s #hjjj feet ! mean coeffici5t ( scatt]+ is ab\t #jjjc1 in/ead ( #jjag1 :i* x is at sea-level4 ,x mu/ be recollect$ t !re is only ab\t ?ree-f\r?s ( ! air above u at #hjjj feet1 & x is less d5se4 ,!re w !re=e be a dim9ution ( p>ticles n only because !re is less air1 b because ! air itself is less capable ( keep+ !m 9 susp5sion4 ,up to #cjjj or #djjj feet !re is no v great m>k$ diff]5ce 9 ! scatt]+ ( light1 z obs]vations c>ri$ on dur+ five ye>s h %[n2 b above t ! scatt]+ rapidly dim9i%es1 & at #bj1jjj feet x mu/ be v small inde$1 if ! dim9ution increases z rapidly z has be5 f\nd x does at ! altitude ( #hjjj feet4 ,we mu/ repeat once m t ! blue ( ! sky is pr9cipally if n entirely due to ! pres5ce ( ^! p>ticles1 ! rays scatt]$ by !m1 :i* are pr9cipally ! blue rays1 be+ reflect$ back f !m1 giv+ ! s5sation ( blue :i* we "k z sky-blue4 ,! great] ! numb] ( ^! f9e p>ticles t are enc\nt]$ by sunlight1 ! great] ! scatt]+ w be1 & ! blu] ! sky4 ,x is m ?an probable t ! blue sky ( ,italy1 s prov]bial = be+ beautiful1 is due to ?is cause1 s9ce f its geographical position ! small p>ticles ( wat] mu/ be v abundant !re4 ,c>ry+ ?is argum5t fur!r1 we %\ld expect t z we m\nt high] ! blue w\ld become m fully mix$ ) ! d>kness ( space1 & ?is ,alp9e travell]s w tell y is ! case4 ,at heights ( #ab1jjj feet or m1 on a cle> day1 ! sky seems almo/ black1 & x is no uncommon ?+ to see ?is admirably r5d]$ 9 photographs ( ,alp9e sc5]y :5 tak5 at a height4 ,_m ( ! late ,mr4 ,donk9's photographs %[ ?is 9 great p]fection1 z also ,signor ,sella's4 ,be=e quitt+ ?is subject we may call att5tion n only to ! col\r ( ! sun itself at sunset1 b also to ! col\r+ ( ! sky :i* accompanies ! sun z x s9ks4 ,?is col\r+ is (t5 diff]5t to ! col\r t ! sun itself assumes2 b we c easily %[ t ! effects s wond]fully beautiful are entirely dep5d5t on ?is scatt]+ ( light by ^! small int]v5+ p>ticles 9 ! air4 ,we (t5 see a ruddy sun1 & p]haps ne>ly 9 ! z5i?1 or ev5 fur!r away f ! sun1 cl\ds ( a beautiful crimson hue1 ly+ on a sky :i* appe>s almo/ pea-gre51 :il/ ne>] to ! sun ! sky is a brilliant orange1 :i* arti/s imitate ) cadmium yell[4 ,let u fix our att5tion fir/ on ! crimson cl\d4 ,! cl\ds ( :i* ! col\r+ is s gorge\s are (t5 n #ajjj feet above u1 & 7 we to be at t altitude we %\ld see ! sun n q s ruddy z we see x f ! e>?1 & ! cl\d w\ld consequ5tly be illum9at$ by ! sun ) a m orange t9t2 b ! light reflect$ f ! cl\d to our eyes has to pass ?r\gh1 say #ajjj feet ( d5se atmosph]e1 & ?us ! total atmosph]e t ! light trav]ses 9 ! latt] case is always great] ?an ! air ?ickness ?r\gh :i* ! direct light f ! sun has to pass2 h5ce m orange is cut (f1 & ! light reflect$ f ! cl\d is r$d]4 ,?is r$1 h[ev]1 w n acc\nt = ! brilliant crimson & purples :i* we s (t5 see4 ,x has to be rememb]$ t n sunlight alone illum9es ! cl\d1 b also ! blue light ( ! sky4 ,! feebl] ! int5sity ( ! r$1 ! m w ! blue ( ! sky be felt 9 ! mixture ( light :i* rea*es our eyes1 & consequ5tly we may h any t9t rang+ f crimson to purple1 s9ce r$ & blue make ^! hues1 accord+ to ! proportions 9 :i* !y are mix$4 ,n[ let u see h[ we get ! brilliant orange ( ! sky itself4 ,:5 ! ev5+ is p]fectly cle> & free f mi/ & cl\d1 ! orange 9 ! sky is v feeble1 %[+ t ! int5sity dep5ds ^u _! pres5ce4 ,n[ a look at ! table w %[ t ! sun is v close to ! horizon :5 x becomes ruddy "u normal conditions2 b t :5 ! light trav]ses a ?ickness ( eight atmosph]es1 ! blue & violet1 & mo/ ( ! gre51 are abs5t1 leav+ a light ( yell[i% col\r4 ,to trav]se eight atmosph]es ! light has only to come f a po9t "s eight degrees above ! horizon4 ,:5 ! sun is ne> ! horizon1 x s5ds its rays n only to u & ov] u1 b 9 e direction2 & an eye plac$ "s few ?\s& feet above ! e>? w\ld see ! sun almo/ ( its midday col\r1 = sunset col\rs ( ! gorge\s "* t we see at sea-level are almo/ abs5t at high altitudes4 ,if a cl\d or mi/ 7 at su* an altitude ! sunlight w\ld /rike x1 & :il/ only a small portion w\ld be selectively scatt]$1 ow+ to ! g5]al grossness ( ! p>ticles1 ! major "p w\ld be reflect$ back to our eyes1 & come f an altitude ( ov] eight to t5 degrees1 & w\ld !re=e1 aft] trav]s+ ! int]v5+ atmosph]e1 rea* u z ! orange-col\r$ light ( :i* we h j spok54 ,! cl\ds :i* are orange :5 ne> ! sun1 are usually high] ?an ^? :i* are simultane\sly r$ or purple4 ,! pea-gre5 col\r ( ! sky is (t5 due to contra/1 = ! contra/ col\r to r$ is gre51 & ?is w\ld make ! blue ( ! sky appe> decid$ly gre5]4 ,sometimes1 h[ev]1 x is due to an absolute mixture ( ! blue ( ! sky & ! orange light :i* illum9ates ! same haze4 ,9 ! high ,alps x is no uncommon occurr5ce = ! sn[-clad m\nta9s to be tipp$ ) ! same crimson we h describ$ z col\r+ ! cl\ds1 & ?is is usually j aft] sunset1 :5 ! sun has sunk s l[ b5ea? ! horizon t ! light has to trav]se a great] ?ickness ( d5se air1 & consequ5tly to pass ?r\gh a l>g] numb] ( small p>ticles ?an x has :5 j above ! horizon4 ,9 ?is case ! r$ ( ! sunlight mixes ) blue light ( ! sky1 & gives u ! crimson t9ts4 ,! deep] & ri*] t9ts ( ! cl\ds j aft] sunset are also due to ! same cause1 ! ?ickness ( air trav]s$ be+ great]4 ,x is wor? :ile to pause a mom5t & ?9k :at extraord9>y s5sual pleasure ! pres5ce ( ! small scatt]+ p>ticles float+ 9 ! air causes u2 t )\t !m ! col\r+ :i* impresses itself ^u u s /rongly w\ld h be5 a blank1 & t arti/s w\ld h to rely ^u =m pr9cipally to convey _! feel+s ( art4 ,inde$ )\t ^! p>ticles !re w\ld probably be no sky1 & objects w\ld appe> ( ! same h>d def9ition z d ! m\nta9s 9 ! atmosph]eless moon4 ,!y w\ld be only directly illum9at$ by sunlight1 & _! %ad[s by ! light reflect$ f ! surr\nd+ bright surfaces4 ,,*apt] ,,vii4 ,lum9osity ( ! ,spectrum to ,normal-ey$ & ,col\r-bl9d ,p]sons--,me?od ( det]m9+ ! ,lum9osity ( ,pigm5ts--,addition ( "o ,lum9osity to ano!r4 ,! det]m9ation ( ! lum9osity ( a col\r$ object1 z comp>$ ) a col\rless surface illum9at$ by ! same light1 is ! det]m9ation ( ! second col\r con/ant4 ,we w fir/ take ! pure spectrum col\rs1 & %[ h[ _! lum9osity or relative brightness c be det]m9$4 ,view+ a spectrum on ! scre51 !re is n mu* d\bt t 9 ! yell[ !re is ! greate/ brightness1 & t ! brightness dim9i%es bo? t[>ds ! violet & r$4 ,t[>ds ! latt] ! lum9osity gradi5t is evid5tly m rapid ?an t[>ds ! =m]4 ,?is be+ ! case1 x is evid5t t1 except at ! brighte/ "p !re are always two rays1 "o on ea* side ( ! yell[1 :i* mu/ be equally lum9\s4 ,if ! spectrum be recomb9$ to =m a :ite pat* ^u ! scre51 & ! slide ) ! slit be pass$ ?r\gh x1 pat*es ( equal area ( ! diff]5t col\rs w successively appe>2 b ! yell[ pat* w be ! brighte/ pat*4 ,if ! pat* =m$ by ! reflect$ beam be sup]pos$ ov] ! col\r pat*1 & ! rod be int]pos$1 we get a col\r$ /ripe alongside a :ite /ripe1 & by plac+ our rotat+ sectors 9 ! pa? ( ! reflect$ beam1 ! brightness ( ! latt] c be dim9i%$ at pleasure4 ,suppose ! sectors be set at #de1 :i* w dim9i% ! reflect$ beam to "o-qu>t] ( its normal int5sity1 we %all f9d "s place 9 ! spectrum1 betwe5 ! yell[ & ! r$1 :]e ! :ite /ripe is evid5tly less bright ?an ! col\r$ /ripe1 & by a slight %ift t[>ds ! yell[1 ano!r place w be f\nd :]e x is m bright4 ,betwe5 ^! two po9ts !re mu/ be "s place :]e ! brightness to ! eye is ! same4 ,?is c be v readily f\nd by mov+ ! slit rapidly backw>ds & =w>ds betwe5 ^! two places ( too d>k & too light1 & by mak+ ! pa? ! slit has to travel less & less1 a spot is f9ally arriv$ at :i* gives equal lum9osities4 ,! position t ! slit occupies is not$ on ! scale beh9d ! slide1 z is also ! op5+ ( ! sectors1 9 ?is case #de4 ,z !re is ano!r position 9 ! spectrum betwe5 ! yell[ & ! violet1 :i* is ( ! same int5sity1 ?is mu/ be f\nd 9 ! same mann]1 & be simil>ly not$4 ,9 ! same way ! lum9osities ( col\rs 9 ! spectrum1 equival5t to ! :ite light pass+ ?r\gh o!r ap]tures ( sectors1 c be f\nd1 & ! results may !n be plott$ 9 ! =m ( a curve4 ,?is is done by mak+ ! scale ( ! spectrum ! base ( ! curve1 & sett+ up at ea* position ! measure ( ! angul> ap]ture ( ! sector :i* 0 us$ to give ! equal lum9osity or brightness to ! :ite4 ,by jo9+ ! ends ( ^! ord9ates by l9es a curve is =m$1 :i* repres5ts graphically ! lum9osity ( ! spectrum to ! obs]v]4 ,9 ,fig4 #aa ! maximum lum9osity 0 tak5 z #ajj1 & ! o!r ord9ates r$uc$ to t scale4 ,! outside curve ( ! figure 0 plott$ f obs]vations made by ! writ]1 :o has col\r vision :i* may be consid]$ to be normal1 z x co9cides ) obs]vations made by ! majority ( p]sons4 ,! inn] curve requires a little explanation1 ?\gh x w be bett] und]/ood :5 ! !ory ( col\r vision has be5 t\*$ ^u4 ,fig4 #aa4--,lum9osity ,curve ( ! ,spectrum ( ! ,positive ,pole ( ! ,electric ,light4 ,! obs]v] 9 ?is case 0 col\r-bl9d to ! r$1 t is1 he _h no p]ception ( r$ objects z r$1 b only di/+ui%$ !m by ! o!r col\rs :i* 7 mix$ ) ! r$4 ,?is be+ premis$1 we %\ld naturally expect t 8 p]ception ( ! spectrum w\ld be %ort5$1 & ?is ! obs]vations fully prove4 ,if x happ5$ t 8 p]ceptions ( all o!r col\rs 7 equally acute ) a normal-ey$ p]son1 !n 8 illum9ation value ( ! "p ( ! spectrum occupi$ by ! violet & gre5 ought to be ! same z t ( ! latt]4 ,! diagram %[s t x is s1 & ! am\nt ( r$ pres5t 9 ea* col\r to ! normal-ey$ obs]v] is %[n by ! defici5cy curve1 :i* 0 obta9$ by subtract+ ! ord9ates ( col\r-bl9d curve f ^? ( ! normal curve4 ,!re are o!r p]sons :o are defective 9 ! p]ception ( gre51 & !y aga9 give a diff]5t lum9osity curve = ! spectrum4 ,^! v>iations 9 ! p]ception ( ! lum9osity ( ! diff]5t col\rs are v int]e/+ f a physiological po9t ( view1 & ?is mode ( measur+ is a v good te/ z to defective col\r vision4 ,we %all allude to ! subject ( col\r-bl9dness 9 a subsequ5t *apt]4 ,! foll[+ are ! lum9osities = ! col\rs fix$ by ! pr9cipal l9es ( ! sol> spectrum1 & = ! r$ & blue l9es ( li?ium1 to :i* ref]5ce has already be5 made4 ---------------------------------------- ------------ ,lum9osity4 ------------------- ,l9e4 ,col\r4 ,normal ,r$ ,eye4 ,col\r ,bl9d4 ---------------------------------------- --------- ,a ,v d>k ,r$ -- -- ,b ,r$ 7,crimson7 #aj #j ,r$ ,li?ium ,r$ 7,crimson7 #he #e ,c ,r$ 7,sc>let7 #bjf #ba ,d ,orange #ihe #ecj ,e ,gre5 #ejj #dij ,f ,blue ,gre5 #gj #gj ,blue ,li?ium ,blue #ai #ai ,g ,violet #f #f ,h ,fa9t ,lav5d] -- -- ---------------------------------------- ------------ ,! failure ( ! r$ col\r-bl9d p]son to p]ceive r$ is v well %[n f ?is table4 ,x w = in/ance be notic$ t he p]ceives ab\t "o-t5? ( ! light at ,c :i* ! normal-ey$ p]son p]ceives4 ,a modification ( ?is plan c be employ$ = measur+ ! lum9osity ( ! spectrum1 & x is excessively useful1 because we c adapt x to ! measurem5t ( col\rs o!r ?an ^! simple ones4 ,9 ! plan already expla9$ x 0 ! col\r 9 ! pat* t 0 alt]$1 to get an equal lum9osity ) a c]ta9 lum9osity ( :ite light4 ,9 ! modifi$ plan ! lum9osity ( ! :ite light is alt]$1 = ! lum9osity ( ! %ad[ illum9at$ by ! reflect$ beam c be alt]$ rapidly at w by op5+ or clos+ ! ap]tures ( ! sectors :il/ x is rotat+4 ,! slit 9 ! slide is plac$ 9 ! spectrum at any desir$ po9t1 & ! ap]ture ( ! sectors alt]$ till equal lum9osities are secur$4 ,! read+s by ?is plan are v accurate1 & give ! same results z obta9$ by ! previ\s me?od employ$4 ,x mu/ be rememb]$ t we h s f> dealt ) col\rs :i* are spectrum col\rs1 & :i* are int5se because !y are col\rs produc$ by ! spectrum ( an int5sely bright s\rce ( light4 ,by an artifice we c d$uce f ?is curve ! lum9osity curve ( ! spectrum ( any o!r s\rce ( light4 ,if by any means we c comp>e1 int] se1 ! int5sity ( ! same rays 9 two diff]5t s\rces ( light1 "o be+ ! electric light1 we c evid5tly f ! above figure d$uce ! lum9osity curve ( ! spectrum ( ! o!r s\rce ( light 7see p4 #aji74 ,we c n[ %[ h[ we c adapt ! la/ me?od to ! measurem5t ( ! lum9osity ( ! light reflect$ f pigm5ts4 ,fig4 #ab4--,rectangles ( ,:ite & ,v]milion4 ,fig4 #ac4--;,arrangem5t = measur+ ! ,lum9osities ( ,pigm5ts4 ,suppose ! lum9osity ( a v]milion-col\r$ surface _h to be comp>$ ) a :ite surface :5 bo? 7 illum9at$1 say by gaslight1 ! foll[+ proc$ure is adopt$4 ,a rectangul> space is cut out ( black pap] 7,fig4 #ab7 ( a size su* t its side is r less ?an twice ! bread? ( ! rod us$ to ca/ a %ad[3 a conv5i5t size is ab\t "o in* broad by ?ree-qu>t]s ( an in* 9 height4 ,"o-half ( ! ap]ture is fill$ ) a :ite surface1 & ! o!r half ) ! v]milion-col\r$ surface4 ,! light ,l 7,fig4 #ac7 illum9ates ! :ole1 & ! rod ,r1 a little ov] half an in* 9 bread?1 is plac$ 9 su* a position t x ca/s a %ad[ on ! :ite surface1 ! edge ( ! %ad[ be+ plac$ accurately at ! junction ( ! v]milion & :ite surface4 ,a flat silv]$ mirror ,m is plac$ at su* a di/ance & at su* an angle t ! light x reflects ca/s a second %ad[ on ! v]milion surface4 ,betwe5 ,r & ,l are plac$ ! rotat+ sectors ,a4 ,! :ite /rip is caus$ to be evid5tly too d>k & !n too light by alt]+ ! ap]ture ( ! sectors1 & an oscillation ( dim9i%+ ext5t is rapidly made till ! two %ad[s appe> equally lum9\s4 ,a :ite scre5 is next sub/itut$ = ! v]milion & aga9 a comp>ison made4 ,! mean ( ! two sets ( read+s ( angul> ap]tures gives ! relative value ( ! two lum9osities4 ,x mu/ be /at$1 h[ev]1 t any diffus$ light :i* might be 9 ! room w\ld relatively illum9ate ! :ite surface m ?an ! col\r$ "o4 ,to obviate ?is ! receiv+ scre5 is plac$ 9 a box1 9 ! front ( :i* a n>r[ ap]ture is cut j wide en\gh to all[ ! two beams to rea* ! scre54 ,an ap]ture is also cut at ! front angle ( ! box1 ?r\gh :i* ! obs]v] c see ! scre54 ,:5 ?is app>atus is adopt$1 its effici5cy is se5 f ! fact t :5 ! ap]tures ( ! rotat+ sectors are clos$ ! %ad[ on ! :ite surface appe>s q black1 :i* x w\ld n h done _h !re be5 diffus$ light 9 any measurable quantity pres5t )9 ! box4 ,! box1 x may be /at$1 is black5$ inside1 & is us$ 9 a d>k5$ room4 ,! mirror arrangem5t is useful1 z any v>iation 9 ! direct light also %[s itself 9 ! reflect$ light4 ,in/ead ( gaslight1 reflect$ skylight or sunlight c be employ$ by v obvi\s artifices1 9 "s cases a gaslight tak+ ! place ( ! reflect$ beam4 ,:5 we wi% to measure lum9osities 9 our /&>d light1 viz4 ! light emitt$ f ! crat] ( ! positive pole ( ! arc-light1 all we h to d is to place ! pigm5t 9 ! :ite pat* ( ! recomb9$ spectrum1 & illum9ate ! :ite surface by ! reflect$ beam1 us+ ( c\rse ! rod to ca/ %ad[s1 z j describ$4 ,! rotat+ sectors mu/ be plac$ 9 ei!r "o beam or ! o!r1 accord+ to ! lum9osity ( ! pigm5t4 ,! lum9osities ( ! foll[+ col\rs 7 tak5 by ! above me?od1 & subsequ5tly we %all h to use _! values4 ,electric ,light4 ,:ite #ajj ,v]milion #cf ,em]ald ,gre5 #cj ,ultram>9e #dd ,orange #cia ,black #cd ,black 7diff]5t surface7 #ea ,suppose we h two or m col\rs ( ! spectrum ^: lum9osities h be5 f\nd1 ! "q imm$iately arises1 z to :e!r1 :5 ^! two col\rs are comb9$1 ! lum9osity ( ! comp\nd col\r is ! sum ( ! lum9osities ( ea* sep>ately4 ,?us suppose we h a slide ) two slits plac$ 9 ! spectrum1 & =m a col\r pat* ( ! mixture ( ! two col\rs & measure its lum9osity1 & !n measure ! lum9osity ( ! pat* fir/ :5 "o slit is cov]$ up1 & !n ! o!r4 ,w ! sum ( ! two latt] lum9osities be equal to ! measure ( ! lum9osity ( ! comp\nd$ col\r pat*8 ,"o w\ld naturally assume t x w\ld1 b ! physici/ is b\nd n to make any assumptions :i* are n capable ( pro(2 & ! tru? or o!rwise is p]fectly easy to asc]ta91 by employ+ ! me?od ( measurem5t la/ indicat$4 ,let u get our answ] f su* an exp]im5t4 ---------------------------- ,col\rs ,obs]v$ ,measur$4 ,lum9osity4 ---------------------------- ,r #bjcj ,g #che ,v #he 7,r ,g7 #bdb 7,g ,v7 #de 7,r ,v7 #bad 7,r ,g ,v7 #bej ---------------------------- ,?ree ap]tures 7 employ$1 "o 9 ! r$1 ano!r 9 ! gre51 & ! ?ird 9 ! violet1 & ! lum9osity 0 tak5 ( ea* sep>ately1 next two toge!r1 & !n all ?ree comb9$1 ) ! results giv5 above4 ,! accuracy ( ! measurem5ts w p]haps be be/ %[n by add+ ! s+le col\rs toge!r1 ! pairs & ! s+le col\rs1 & comp>+ ^! values ) t obta9$ :5 ! ?ree col\rs 7 comb9$4 ,:5 ! pairs are %[n !y w be plac$ 9 brackets2 ?us 7,r ,g7 means t ! lum9osity ( ! comp\nd col\r made by r$ & gre5 are be+ consid]$4 ,r ,g ,v #bejj 7,r ,g7 ,v #beje 7,r ,v7 ,g #bebe 7,g ,v7 ,r #bdhj 7,r ,g ,v7 #bejj ,! mean ( ! fir/ f\r is #bejbe1 :i* is only #a_/aj diff]5t f ! value ( #bej obta9$ f ! measurem5t ( 7,r ,g ,v7 comb9$4 ,o!r measures fully bore out ! fact t ! lum9osity ( ! mix$ light is equal to ! sum ( ! lum9osities ( its compon5ts4 ,x is true t we h "h only be5 deal+ ) spectrum col\rs1 b we %all see :5 we come to deal ) ! mixture ( col\rs reflect$ f pigm5ts t ! same law is univ]sally true4 ,x w be prov$ by & by t a mixture ( ?ree col\rs1 & sometimes ( only two col\rs1 be !y ( ! spectrum or ( pigm5ts1 c produce ! impression ( :ite light4 ,if !n we measure all ! compon5ts b "o1 & also ! :ite light produc$ by all1 !n ! lum9osity ( ! rema9+ compon5t c be obta9$ by d$uct+ ! fir/ measures f ! la/4 ,= in/ance1 r$1 gre5 & violet 7 mix$ to =m :ite light4 ,! lum9osity ( ! :ite be+ tak5 z #ajj1 ! r$ & violet 7 measur$ & f\nd to h a lum9osity ( #dde & #c respectively4 ,?is %\ld give ! gre5 z hav+ a lum9osity ( #ebe4 ,! gre5 0 measur$ & f\nd to be #ec1 :il/ a measurem5t ( ! r$ & gre5 toge!r gave a lum9osity ( #ife in/ead ( #ig4 ,,*apt] ,,viii4 ,me?ods ( ,measur+ ! ,int5sity ( ! ,diff]5t ,col\rs ( ! ,spectrum1 reflect$ f ,pigm5t$ ,surfaces--,templates = ! ,spectrum4 ,fig4 #ad4--,measurem5t ( ! ,int5sity ( ,rays reflect$ f :ite & col\r$ surfaces4 ,we w n[ proce$ to demon/rate h[ we c measure ! am\nt ( spectral light reflect$ by diff]5t pigm5ts4 ,let u take a /rip ( c>d pa9t$ ) a pa/e ( v]milion1 leav+ half ! bread? :ite2 & simil>ly "o ) em]ald gre54 ,if we place ! fir/ 9 ! spectrum s t half its bread? falls on ! r$1 & ! o!r half on ! :ite c>d1 we %all see t app>5tly ! r$ & orange rays are undim9i%$ 9 int5sity by reflection f ! v]milion1 b t 9 ! gre5 & beyond b v little ( ! spectrum is reflect$4 ,) ! em]ald gre5 plac$ simil>ly 9 ! spectrum1 ! r$ rays w be f\nd to be absorb$1 b 9 ! gre5 rays ! full int5sity ( col\r is f\nd1 fad+ (f 9 ! blue4 ,:at we n[ h to d is to f9d a me?od ( comp>+ ! int5sities ( ! diff]5t rays reflect$ f ! pigm5ts1 ) ^? f ! :ite surface4 ,we w comm5ce ) ! second ( ! two me?ods :i* ! writ] devis$ ) ?is object1 & !n describe ! fir/1 :i* is m complex4 ,suppose we h1 say a c>d disc ?ree in*es 9 diamet]1 pa9t$ ) ! pigm5t ^: reflective p[] has to be measur$1 & place x on a rotat+ app>atus ) black & :ite sectors ( say five in*es diamet]1 & capable ( ov]lapp+ s z to %[ diff]5t proportions ( black to :ite 7see ,fig4 #db74 ,if we ?r[ a col\r pat* 7%[n 9 ,fig4 #ad z ! area inside ! dott$ squ>e7 on ! comb9ation ( black & :ite1 & at ! same "t on ! pigm5t$ disc1 x is probable t ei!r "o or o!r w be ! bright]4 ,by mov+ ! slit along ! spectrum x is evid5t1 h[ev]1 t a col\r c be f\nd :i* is equally reflect$ f !m bo? :il/ rotat+4 ,take z an example ! sectors z set at two p>ts :ite1 to "o "p black1 ! c5tre disc be+ v]milion1 ! slit is mov$ along ! spectrum until su* a po9t is rea*$ t ! col\r reflect$ f ! r+ & ! disc appe>s ( ! same brightness1 = x mu/ be recollect$ t !y _c diff] 9 hue1 z ! light is mono*romatic4 ,x w be f\nd t ! place :]e !y mat* 9 brightness is 9 ! r$1 ! exact position be+ fix$ by ! scale at ! back ( ! slide4 ,tak+ ! proportion ( black to :ite z ?ree to "o1 ! mat* w be f\nd to take place 9 ! orange4 ,increas+ ! proportion ( black m & m1 a po9t w be rea*$ :]e ! reflection takes place uni=mly along ! blue end ( ! spectrum1 ?is w be f ! gre5 to ! end ( ! violet4 ,by suffici5tly increas+ ! numb] ( mat*es made1 a curve ( reflection c be made %[+ ! exact proportion ( ea* ray ( ! spectrum t is reflect$4 ,! uni=m reflection along ! blue end ( ! spectrum %[s t a c]ta9 am\nt ( :ite light is reflect$ f ! pigm5t4 ,next tak+ ! em]ald gre5 disc1 if we adopt ! same proc$ure x w be f\nd t = "s %ades ( ! r+ !re are two places 9 ! spectrum f :i* ! col\rs reflect$ give ! same brightness4 ,by plott+ curves 9 exactly ! same way z t %[n = ! curve ( lum9osity at page #gh1 sub/itut+ = ! op5 ap]ture ( ! sector ! angul> value ( ! :ite us$1 we c %[ graphically ! correct reflection = ea* "p ( ! spectrum4 ,sometimes ?ree places 9 ! spectrum w be read1 z giv+ equal reflections f ! col\r$ disc & ! grey r+4 ,! accompany+ figures %[ ! results obta9$ = reflection f v]milion1 em]ald gre51 & ,fr5* blue1 aft] hav+ made a correction = ! :ite by add+ ! am\nt :i* ! black reflects4 ,! scale is t ( ! prismatic spectrum employ$4 ,on page #df we /at$ t a :ite surface c\ld be made to appe> d>k] ?an a black surface1 by illum9at+ ! latt] & cutt+ (f ! light f ! =m]4 ,by plac+ ! black surface 9 place ( "o ( ! col\r$ ones1 z %[n 9 page #hb1 ! lum9osity ( ! black surface c be asc]ta9$4 ,9 ?is case x 0 f\nd t almo/ exactly #e ( ! :ite light f ! crat] ( ! positive pole 0 reflect$4 ,9 ! table ! orig9al measures are %[n1 & also ! correct$ measures1 & = conv5i5ce sake ! int5sity ( e ray ?r\gh\t ! l5g? ( ! spectrum reflect$ f :ite1 has be5 tak5 z #ajj4 ,! position ( ! ref]5ce l9es on ! scale 7,fig4 #ae7 are z foll[s-- ,fig4 #ae4--;,int5sity ( ,rays reflect$ f ,v]milion1 ,em]ald ,gre51 & ,fr5* ,ultram>9e4 ,b#aja1 ,c#ifbe1 ,d#hi1 ,e#gii1 ,f#gae1 ,g#ece4 ,,v]milion4 ---------------------------------------- ------- ,:ite ,sectors4 -----------------------------------,read + ( ,orig9al ,:ite ,cor-,correct$ ,spectrum ,sett+4 rect$ ,= ,:ite ,scale4 -------------- ,black4 #ajj4 ,:ite4,black4 ---------------------------------------- --- #aj #cej #bge #gfe #ga-a_/b #bj #cdj #cgj #ajae #hd #cj #ccj #dfe #abie #hfb #ej #caj #fee #ahaj #hhj #gj #bij #hde #bcej #hhg #ij #bgj #ajce #big #hie #abj #bdj #acbj #cgb #ijc #aej #baj #afje #dej #ia #ahj #ahj #ahij #ebe #iaf #baj #aej #bage #fjb #ibe #bbj #adj #bbgj #fcb #ice #bcj #acj #bcfe #ffb #ide #bdj #abj #bdfj #fhe #if #bcj #acj #bcfe #ffb #igg #baj #aej #bage #fjb #ajjj ---------------------------------------- --- ,,em]ald ,,gre54 ---------------------------------------- ----------- ,:ite ,sectors -------------------------------------- ,read+ ( ,orig9al ,sett+4,:ite ,cor-,correct$ ,spectrum -----------------rect$ ,= ,:ite ,scale4 ,:ite4 ,black4 ,black4 #ajj4 ---------------------------------------- -------- #aj #cej #bge #gfe #ej #bj #cdj #cgj #ajae #ed #cj #ccj #dfe #abie #ee #ej #caj #fee #ahaj #ege #gj #bij #hde #bce #fjj #ij #bgj #ajce #big #fce #aaj #bej #abbe #cdg #fee #acj #bcj #adae #cie #fge #aej #baj #afje #dej #fhe #agj #aij #agie #ejj #ga #aij #agj #aiee #edg #gce #baj #aej #bage #fjb #gej #bbj #adj #bbg #fcb #gf #bbj #adj #bbg #fcb #gh #baj #aej #bage #fjb #hj #aij #agj #aihe #edg #hb #agj #aij #agie #ejj #hc #aej #baj #afje #dej #hd #acj #bcj #adae #cie #he #aaj #bej #abbe #cdg #hfe #ij #bgj #ajce #big #hge #gj #bij #hde #bce #hhe #ej #caj #fee #ahaj #ijj #cj #ccj #dfe #abie #ib #bj #cdj #cgj #ajae #id #aj #cej #bge #gfe #ih ---------------------------------------- -------- ,,fr5* ,,ultram>9e ,,blue4 ---------------------------------------- ------------- ,:ite ,sectors4 --------------------------------------- ,read+ ( ,orig9al ,sett+4 ,:ite ,correct$ ,spectrum ---------------- correct$ ,:ite ,scale4 ,:ite4 ,black4 = black4 #ajj4 ---------------------------------------- ---------- #j #cfj #ahj #ej #hd #aj #cej #bge #gfe #hj #bj #cdj #cgj #ajae #gg #cj #ccj #dfe #abie #ge #dj #cbj #efj #aef #gd #fj #cjj #gej #bjg #gbe #hj #bhj #idj #bee #gje #ajj #bfj #aacj #cbe #fh #abj #bdj #acbj #cgb #ffe #adj #bbj #aeaj #dbc #fbe #afj #bjj #agjj #dgd #eie #agj #aij #agie #ejj #ee #afj #bjj #agjj #dgd #ea #adj #bbj #aeaj #dbc #df #j #cfj #ahj #ej #ie #aj #cej #bge #gfe #ih #bj #cdj #cgj #ajae #ii #cj #ccj #dfe #abie #aaj ---------------------------------------- ---------- ,^! ?ree measurem5ts h be5 giv5 9 full1 s9ce !y w be useful = ref]5ce :5 o!r exp]im5ts are describ$4 ,fig4 #af4--,me?od ( obta9+ two ,pat*es ( id5tical ,col\r4 ,:5 we h to measure ! col\r transmitt$ ?r\gh col\r$ bodies1 we h to adopt a slightly diff]5t plan1 :i* is extremely accurate4 ,! fir/ ?+ necess>y is to make "s arrangem5t :]eby two beams ( id5tical col\r--t is1 ( ! same wave-l5g?--rea* ! scre51 "o ( :i* passes ?r\gh ! transp>5t body to be measur$1 & ! o!r unabsorb$4 ,if we 9 addition h "s means ( equaliz+ ! int5sity ( ! two beams1 we c !n tell ! am\nt cut (f by ! body ?r\gh :i* "o beam passes4 ,! me?od t w\ld be fir/ ?\ght ( w\ld be to use two spectra1 f two s\rces ( light2 b %\ld we adopt t plan !re w\ld be no gu>antee t ! spectra w\ld n v>y 9 int5sity f "t to "t4 ,! po9t !n t _h to be aim$ at 0 to =m two spectra f ! same s\rce ( light1 & ) ! same beam t passes ?r\gh ! slit ( ! collimator4 ,"h we are help$ by ! prop]ty ( ,icel& sp>1 :i* is able to split up a ray into two div]g5t rays4 ,by plac+ :at is call$ a d\ble-image prism ( ,icel& sp> at ! end ( ! collimator1 we get two div]g5t beams ( light fall+ on ! prisms1 & by turn+ ! d\ble-image prism we are able to obta9 two spectra on ! scre5 ( ! cam]a "o above ! o!r1 & if ! slit ( ! slide be suffici5tly long two beams w\ld issue ?r\gh x ( id5tical col\r1 & sep>at$ f "o ano!r by a d>k space1 ! bread? ( :i* dep5ds on ! l5g? ( ! slit ( ! collimator4 ,x is to be obs]v$ t by ?is arrangem5t we h exactly :at we require3 a light f "o s\rce passes ?r\gh ! same slit1 is decompos$ by ! same prisms1 & z ! beams div]ge 9 a plane pass+ ?r\gh ! slit ( ! collimator1 ! l5g? ( spectrum is ! same4 ,! problem to solve is h[ to utilize ^! two spectra n[ we h got !m4 ,we c make ! light f ! top spectrum pass ?r\gh ! col\r$ body by ! foll[+ artifice4 ,let u place a "r-angl$ prism 9 front ( ! top slit1 reflect+ say ! beam to ! "r1 & aft] x has travell$ a c]ta9 di/ance1 cat* x by ano!r "r-angl$ prism1 & ?us reflect x on to ! scre54 ,already 9 ! pa? ( ! ray1 issu+ ?r\gh ! slit f ! bottom spectrum1 ! l5s ,l#d is plac$1 =m+ a squ>e pat* on ! scre54 ,by plac+ a simil> l5s 9 ! pa? ( ! o!r ray aft] reflection f ! second "r-angl$ prism1 we c sup]pose a second pat* ( ! same col\r ov] ! fir/ pat*1 & by putt+ a rod 9 ! pa? ( ! two beams we c h z be=e two %ad[s side by side1 b ?is "t ea* illum9at$ by ! same col\r4 ,"o %ad[ w be m /rongly illum9at$ ?an ! o!r1 ow+ to ! diff]5t int5sities ( beams into :i* ! d\ble-image prism splits up ! prim>y ray4 ,! two1 h[ev]1 c be equaliz$ by plac+ a rotat+ app>atus 9 ! pa? ( "o ( ! beams4 ,:5 equaliz$ ! sector is read (f1 & tells u h[ mu* bright] "o spectrum is ?an ! o!r4 ,?us suppose 9 ! direct beam ! sectors _h to be clos$ to an angle ( #hj1 to effect ?is1 ! bottom spectrum w\ld be #ahj_/hj1 or #bbe times bright] ?an ! bottom spectrum4 ,x %\ld be not$ t z ! two spectra are =m$ by ! id5tical quality ( light1 ?is same ratio w hold good ?r\gh\t _! l5g?4 ,if x does n1 x %[s t ! d\ble-image prism is n 9 adju/m5t1 & t ! same rays are n com+ ?r\gh ! slit 9 ! slide1 & x mu/ be rotat$ till ! read+s ?r\gh\t are ! same4 ,"o ( ! mo/ s5sitive te/s = adju/m5t is to =m a pat* ) orange light1 :5 ! slighte/ deviation f adju/m5t w be se5 by ! two pat*es diff]+ 9 hue4 ,we c n[ place ! col\r$ transp>5t object 9 ! pa? ( ! beam :i* is mo/ conv5i5t1 & by aga9 equaliz+ ! %ad[s1 measure ! am\nt x cuts (f2 ?is we c d = any ray we *oose4 ,z bo? "r-angl$ prisms c be atta*$ to ! c>d or slide :i* moves across ! spectrum1 no?+ besides ! c>d ne$ be mov$4 ,9 ! foll[+ diagram we h ! proportion ( rays transmitt$ by ! ?ree diff]5t glasses1 r$1 gre51 & blue1 9 t]ms ( ! unabsorb$ spectrum4 ,take = in/ance on ! scale ( ! spectrum ! numb] #aa4 ,! curve %[s t at t p>ticul> "p ( ! spectrum :i* lies 9 ! blue1 ! blue glass only all[$ #d_/ajj or #a_/be ( ! ray to pass1 :il/ ! gre5 glass all[$ #aj_/ajj or #a_/aj to pass4 ,s at scale ,no4 #d 9 ! orange1 ?r\gh ! blue only #b 0 transmitt$1 ?r\gh ! gre5 glass #d1 & ?r\gh ! r$ #bj4 ,fig4 #ag4--;,absorption by ,r$1 ,blue1 & ,gre5 ,glasses4 ,fig4 #ah4--,light reflect$ f ,metallic ,surfaces4 ,fig4 #ai4--a4 ,v]milion #b4 ,c>m9e4 #c4 ,m]curic ,iodide4 #d4 ,indian ,r$4 ,f su* curves z ^! we c readily d]ive ! lum9osity curves ( ! spectrum1 aft] ! :ite light has pass$ ?r\gh ! col\r$ object4 ,all we h to d is to alt] ! ord9ates ( ! lum9osity curve ( :ite light 9 ! proportion to ! int5sities ( ! rays be=e & aft] pass+ ?r\gh ! object4 ,x w be se5 t :5 ! lum9osity curve ( ! spectrum ( any s\rce is kn[n1 ?is me?od holds good4 ,fig4 #bj4--a4 ,gamboge4 #b4 ,indian ,yell[4 #c4 ,cadmium ,yell[4 #d4 ,yell[ ,o*re4 ,! int5sity ( ! diff]5t rays ( ! spectrum reflect$ f metallic surfaces c also be measur$1 if = ! fir/ or second "r-angl$ prism a small piece ( ! metal is sub/itut$1 us+ x z a reflect+ surface1 z c also ! rays reflect$ f any surface :i* is bright & poli%$4 ,9 ,fig4 #ah ! dott$ curves %[ ! lum9osity ( ! spectrum reflect$ f ! diff]5t metals1 curve ,v be+ t ( :ite light4 ,^! curves are d]iv$ by r$uc+ ! ord9ates ( curve ,v proportionately to ! int5sity curves4 ,?us at #di brass reflects #gg ( ! light1 & ! lum9osity ( ! :ite is #hj4 ,! lum9osity ( ! light f ! brass is !re=e #gg_/ajj ( #hj1 or #fa4 ,?is %[s ! me?od :i* is adopt$1 ( d$uc+ lum9osities f int5sities4 ,fig4 #ba4--a4 ,em]ald ,gre54 #b4 ,*rom\s ,oxide4 #c4 ,t]re ,v]te4 ,! light reflect$ f pigm5ts c also be measur$ by ! same plan4 ,! proc$ure adopt$ is t c>ri$ out :5 measur+ _! lum9osities1 viz4 to cause ! ray f "o spectrum to fall on a /rip ( a :ite surface1 & t f ! o!r on a /rip ( ! col\r$ surface 7see page #hb74 ,?is is a m conv5i5t me?od ?an t j describ$1 :5 ! col\r$ surface is small4 ,! annex$ figures 7,figs4 #ai1 #bj1 #ba1 #bb7 %[ ! results obta9$ f v>i\s pigm5ts4 ,fig4 #bb4--a4 ,indigo4 #b4 ,antw]p ,blue4 #c4 ,cobalt4 #d4 ,fr5* ,ultram>9e4 ,fig4 #bc4--,me?od ( obta9+ a ,col\r ,template4 ,f curves su* z ^! we are able to produce ! col\r ( ! pigm5t on ! scre5 f ! spectrum itself4 ,?is is a useful pro( ( ! tru? ( ! measurem5ts made4 ,to d ?is we mu/ m>k (f on a c>d 7,fig4 #bc7 ! absolute scale ( ! spectrum along ! radius ( a circle1 & draw circles at ! v>i\s po9ts ( ! scale f its c5tre4 ,f ! same c5tre we mu/ draw l9es at angles to ! fix$ radius correspond+ to ! v>i\s ap]tures ( ! sectors requir$ at ! v>i\s po9ts ( ! scale to measure ! light reflect$ f a pigm5t4 ,:]e ea* radial l9e cuts ! circle drawn ?r\gh ! p>ticul> po9t ( ! scale to :i* its angle has ref]5ce1 gives u po9ts :i* jo9$ give a curv$ figure4 ,su* a figure1 :5 cut out & rotat$ 9 front ( ! spectrum 9 ! prop] position 7z = in/ance by mak+ ! ,d sodium l9e correspond ) t on ! scale71 w cut (f exactly ! same proportion ( ea* col\r t ! pigm5t absorbs4 ,! spectrum1 :5 recomb9$1 %\ld give a pat* ( ! exact col\r ( t measur$4 ,! spectrum mu/ be made n>r[1 z ! template is only !oretically correct = a spectrum ( ! wid? ( a l9e1 z c be readily se54 ,templates l ^! w always enable any col\r to be reproduc$ on ! scre51 & if ! light be us$ = ! spectrum 9 :i* ! col\r has to be view$1 be x sunlight1 gaslight1 />light--:atev] light x is--! col\r obta9$ w be t :i* ! pigm5t w\ld reflect if x 7 view$ 9 t light4 ,! id5tity ( ! col\r produc$ on ! scre5 by ?is plan ) t measur$1 c be readily se5 by plac+ ! latt] 9 ! reflect$ beam ( :ite light alongside ! col\r$ pat* =m$ on ! :ite surface4 ,fig4 #bd4--,template ( ,c>m9e4 ,9 ,fig4 #bd we h a mask or template ( c>m9e1 :i* 0 us$ = det]m9+ if ! measurem5ts 7 "r4 ,! black f+]like-look+ space on ! "r 0 ! am\nt ( r$ reflect$ light1 & ! o!r t ( ! blue & violet2 sc>cely any light at all 0 reflect$ f ! gre5 "p ( ! spectrum4 ,fig4 #bf4--;,absorption ( transmitt$ & reflect$ ,light by ,prussian ,blue & ,c>m9e4 ,on page #ajh we h giv5 ! diagram ( ! lum9osity ( ! spectrum 9 ref]5ce to a /&>d :ite light4 ,x w br+ ?is lum9osity m home if1 9 a simil> mann] to t describ$ above1 we make a template ( ?is curve 7,fig4 #be74 ,we c place a n>r[ slit horizontally 9 front ( ! cond5s+ l5s ( ! optical lant]n1 & ?r[ an image ( x on to ! scre54 ,if 9 close contact ) ?is slit we rotate ! template1 we %all h on ! scre5 a graduat$ /rip ( :ite light1 giv+ 9 black & :ite ! app>5t lum9osity ( ! spectrum z se5 by ! eye4 ,fig4 #be4--,template ( ,lum9osity ( ,:ite ,light4 ,x has be5 /at$ 9 *apt] ,v41 t x is g5]ally immat]ial :e!r a pigm5t is 9 contact ) ! pap] or away f x1 s long z ! light passes ?r\gh ! pigm5t4 ,! above figure 7,fig4 #bf7 %[s ! tru? ( ?is ass]tion4 ,i4 & ,,ii4 are ! curves tak5 ( ! light transmitt$ by ,prussian blue & c>m9e respectively1 & ,,iii4 & ,,iv41 f ! light reflect$ f ^! col\rs on pap]4 ,fig4 #bg4--;,collimator = comp>+ ! int5sity ( two s\rces ( ,light4 ,to measure ! diff]5ce 9 ! int5sities ( ! rays ( diff]5t s\rces ( light we c use a spectroscopic arrangem5t ) two slits 7,s7 7,fig4 #bg7 plac$ 9 a l9e at "r angles to ! axis ( ! collimator4 ,"o slit is a little bel[ ! o!r1 ! rays be+ reflect$ to ! collimat+ l5s ,l1 by means ( two "r-angl$ prisms ,p1 & two spectra are =m$1 "o above ! o!r4 ,by plac+ ! rotat+ sectors 9 front ( "o ( ! s\rces1 ! int5sities ( ! diff]5t p>ts ( ! spectrum c be equaliz$ & measur$4 ,fig4 #bh4--,spectrum ,int5sities ( ,sunlight1 ,gaslight1 & ,blue ,sky4 ,! curves = ! annex$ figure 7,fig4 #bh7 7 d]iv$ f measures tak5 9 ?is mann]4 ,if ! rays ( a ,may-day sun are tak5 at #ajj1 x w be se5 :at a rapid dim9ution !re is 9 ! gre5 & ! blue rays 9 gaslight4 ,gaslight only possesses ab\t #bj ( ! gre5 rays1 :il/ ( ! violet h>dly #e4 ,on ! o!r h& ! light :i* comes to u f ! sky %[s a v m>k$ fall+ (f 9 ! yell[ & r$ rays4 ,a v easy exp]im5t w conv9ce u ( ! diff]5ce 9 col\r betwe5 skylight & gaslight4 ,if we let a beam ( daylight fall on a %eet ( pap] at ! end ( a black5$ box1 & ca/ a %ad[ ) a rod by su* a beam1 & !n br+ a light$ c&le or gas-flame s t x ca/s ano!r %ad[ ( ! rod alongside1 "o %ad[ w be illum9at$ by ! artificial light1 & ! o!r by ! daylight4 ,! diff]5ce 9 col\r w be mo/ m>k$3 ! blue ( ! latt] light & ! yell[ ( ! =m] be+ int5sifi$ by ! contra/ 7see page #aih74 ,fig4 #bi4--;,comp>ison ( ,sun & ,sky ,lights4 ,by a little tr\ble ! blue light f ! sky may be comp>$ ) sunlight4 ,a beam ( light ,b 7,fig4 #bi7 is reflect$ by a silv]$ glass mirror f ! blue sky into ! box ,,hh1 at ! end ( :i* is a scre5 ,e4 ,ano!r mirror ,a1 :i* is pref]ably ( pla9 glass1 reflects light f ! sun on to a second unsilv]$ mirror ,g 7%[n 9 ! figure z a prism71 :i* aga9 reflects x on to ! scre51 & ea* ( ^! lights ca/s a %ad[ f ! rod ,d2 ,k are rotat+ sectors to dim9i% ! sunlight1 & we c make two equally bright %ad[s alongside "o ano!r4 ,! blu] col\r ( ! sky w be v evid5t4 ,,*apt] ,,ix4 ,col\r ,mixtures--,yell[ ,spot 9 ! ,eye--,comp>ison ( ,diff]5t ,lights--,simple ,col\rs by mix+ ,simple ,col\rs--,yell[ & ,blue =m ,:ite4 ,! col\r ( an object 9 nature1 )\t exception we might almo/ say1 is due1 n to "o simple spectrum col\r1 or ev5 to a mixture ( two or ?ree ( !m1 b to ! :ole ( :ite light1 f :i* b&s ( col\r are m or less ab/ract$1 ! absorption tak+ place ov] a consid]able portion or portions ( ! spectrum4 ,not)/&+ ?is we %all n[ exp]im5tally %[ t e col\r c be =m$ by ! simple admixture ( n m ?an ?ree simple col\rs1 if !y be rightly *os51 & f ?is we %all make a d$uction reg>d+ vision itself4 ,we are 9 a position to obta9 ?ree simple col\rs by means ( a slide conta9+ ?ree slits4 ,n[ = our purpose we require t ! ?ree slits c be plac$ 9 any "p ( ! spectrum1 & t !y c be n>r[$ or wid5$ at pleasure4 ,in/ead ( a c>d ! writ] uses a metal slide1 z %[n 9 ,fig4 #cj4 ,fig4 #cj4--,slide ) slits to be us$ 9 ! ,spectrum4 ,x w be se5 t ! ?ree slits c be clos$ or op5$ f ! c5tre by a p>allel motion4 ,!y also slide 9 a c\ple ( grooves1 s t !y c be mov$ along ! frame into any position4 ,! position !y occupy is indicat$ by a scale engrav$ on ! front ( ! slide4 ,beh9d ! grooves 9 :i* ! slits move are ano!r pair ( grooves1 into :i* small pieces ( c>d ,,cccc c slide1 & ?us close ! ap]tures betwe5 ! slits4 ,by ?is arrangem5t all rays except ^? com+ ?r\gh ! slits !mselves are cut (f4 ,! metal frame fits on to an out] wood5 frame1 :i* slides 9 ! grooves us$ ) ! c>d 9 ! app>atus z already describ$4 ,x is conv5i5t always to keep ! scale on ! back ( ?is wood5 slide 9 ! same position z reg>ds ! %ad[ ( ! ne$le-po9t us$ = regi/]+ ! position1 & to move ! slits along _! grooves :5 a *ange 9 position is requir$4 ,us+ ^! ?ree slits ?ree diff]5t col\rs c be ?r[n on ! same squ>e pat* on ! scre54 ,a v crucial exp]im5t is to see if we c make :ite light by ! admixture ( ?ree col\rs1 = if ?is c be done x almo/ foll[s t any col\r c be =m$4 ,we mu/ use ! col\r pat* app>atus1 & beg9 ) plac+ "o slit 9 ! violet ne> ! l9e ,g1 ano!r betwe5 ,e & ,f1 & a ?ird betwe5 ,b & ,c ( ! sol> spectrum1 & fill up ! gaps betwe5 !m ) c>ds z %[n 9 ! figure4 ,= our pres5t purpose x is bett] to make ! col\r pat* & ! :ite pat* t\* ea* o!r1 n us+ ! rod1 z by ?is means we avoid fr+es ( col\r4 ,we %all f9d t ! ap]ture ( ! slits c be s alt]$ t we c produce a p]fect mat* ) ! :ite reflect$ light4 ,by plac+ ! rotat+ sectors 9 front ( ! reflect$ beam we c r$uce its int5sity1 s t ! two pat*es are equally bright4 ,by a tap]+ w$ge we c measure ! wid? ( ! slits1 & ?us get ! proportions ( ^! ?ree diff]5t col\rs :i* mu/ be us$ to give ! :ite4 ,?is is a sample ( ! me?od t we employ :5 we mat* any o!r col\r4 ,suppose1 = in/ance1 x be wi%$ to measure ! col\r ( a solution ( bi*romate ( pota%2 x is plac$ 9 ! pa? ( ! reflect$ light1 & we h an orange /rip ( light :i* we h to mat*4 ,9 ?is case x w be f\nd t ! slit 9 ! blue has to be clos$ entirely1 & only ! gre5 & r$ slits op5$4 ,! int5sities ( ! two lights are equaliz$ by ! rotat+ sectors z be=e4 ,s aga9 ) a solution ( p]manganate ( pota%4 ,9 ?is in/ance no gre5 light w be requir$ 7or if any ( x b a trifle71 & ! col\r ( ! p]manganate w be =m$ by ! rays com+ ?r\gh ! blue & r$ slits4 ,?is plan is a v useful "o = measur+ all k9ds ( transp>5t col\rs 9 t]ms ( ?ree rays4 ,! me?od ( f9d+ ! int5sity ( any ray ( ! spectrum transmitt$ by any su* m$ium has already be5 expla9$4 ,! latt] has "o advantage ov] ! =m]1 9 t ! measurem5ts by x are exact1 :atev] s\rce ( light be us$ to =m ! spectrum4 ,by ! me?od n[ describ$ ?is is n ! case4 ,= in/ance1 ! col\r ( p]manganate ( pota% may be mat*$ 9 ! electric light ) ! r$ & blue slits4 ,if ! limelight 7 sub/itut$ = ! electric light1 x w\ld be f\nd t ! slits w\ld require o!r ap]tures1 n proportional to ^? already =m$1 to mat* ! col\r ( ?is sub/ance4 ,fig4 #ca4--,scre5 on :i* to mat* ,gamboge4 ,if we wi% to regi/] ! t9t ( any pigm5t1 we h to slightly alt] our mode ( proc$ure4 ,suppose1 = in/ance1 we wi% to regi/] ! col\r ( gamboge4 ,9 su* a case we pa9t a small bit ( c>d 7,fig4 #ca7 ) ! pigm5t1 & divide ! :ite space on :i* ! col\r pat*es are ?r[n into two p>ts1 & cov] "o-half ) ! pigm5t$ c>d1 leav+ ! o!r half :ite4 ,! reflect$ beam illum9ates ! pigm5t1 & ! spectrum pat* ! :ite4 ,! wid?s ( ! ?ree slits are !n alt]$ till ! two t9ts agree1 & ! brightness mat*$ by means ( ! rotat+ sectors4 ,!re are c]ta9 sad & /hetic col\rs :i* x might be consid]$ _c be mat*$ by a mixture ( ?ree col\rs4 ,a br[n col\r1 or eau de nil1 might appe> to come out ( ! range ( mat*+4 ,^! col\rs1 h[ev]1 c be mat*$ 9 precisely ! same mann] z ! bright] col\rs are mat*$4 ,?us a br[n pigm5t w be f\nd to require r$ & a little gre51 & a trifle ( blue2 & ! only diff]5ce betwe5 x & a bright] %ade ( ! same col\r1 is t m total light has to be cut (f f x to give ! sombr5ess4 ,a sad col\r only means a pigm5t or dye :i* reflects b little light1 & if t be s x c naturally be mat*$ by us+ b v small quantities ( ! comp\nd+ col\rs4 ,!re is "o curi\s ph5om5on to :i* att5tion may be call$ 9 ?is mat*+1 :i* is wor?y ( rem>k4 ,! mat* w be f\nd to diff] accord+ z ! pat*es are comp>$ f a di/ance ( a c\ple ( feet1 or f a consid]able di/ance4 ,m gre5 w be requir$ 9 ! latt] case ?an 9 ! =m]4 ,if mat*$ at a di/ance ( ab\t six feet1 & ! eyes be !n turn$ s t ! edge ( ! pat* falls on _! c5tres1 x w be notic$ t ! col\r mixture appe>s ( a gre5 hue4 ,?is la/ exp]im5t indicates t ! ret9a is n equally s5sitive = all col\rs ?r\gh\t its area4 ,physiologi/s tell u t :at is kn[n z ! yell[ spot occupies a c5tral position 9 ! ret9a1 & t x absorbs a "p ( ! spectrum ly+ 9 ! gre54 ,n[ :5 ! eyes are close to ! pat*1 its image occupies a consid]able "p ( ! ret9a1 & ! col\r is comp\nd$ z x 7 ( ! col\r z se5 on ! yell[ spot1 & ( t beyond x1 = ! yell[ spot w take 9 an image ( f six to eight degrees 9 angul> measurem5t4 ,:5 view$ at a di/ance we h ! image ( ! pat* fall+ almo/ entirely on ! yell[ spot1 & h5ce a great] quantity ( gre5 is requir$1 z x has to make up ! defici5cy caus$ by ! absorption4 ,:5 ! eyes are turn$ a little on "o side ! image falls on ! outside ( ! yell[ spot1 & ! pat* illum9at$ by ! mix$ light appe>s gre51 comp>$ ) ! pat* illum9at$ ) ! :ite reflect$ beam4 ,x is ?us evid5t t :5 col\r mat*es h to be made1 ! di/ance ( ! eye f ! scre5 %\ld always be /at$1 z also ! dim5sions ( ! pat*es view$4 ,x may be fairly ask$ :y1 if ! half pat* illum9at$ by ! mix$ col\rs appe>s gre5] :5 ! eye is turn$1 ! o!r %\ld n equally d s4 ,?is is a v fair "q to ask4 ,x mu/ be rememb]$ t "o /rip is illum9at$ ) :ite light1 9 :i* e col\r$ ray ( light is comp\nd$1 :il/ 9 ! o!r only ?ree rays are bl5d$4 ,! gre5 ray *os5 happ5s to be tak5 f t "p ( ! spectrum :i* is absorb$ by ! yell[ spot2 b all ( ! gre5 rays ( ! spectrum are n s mu* absorb$1 h5ce 9 ord9>y :ite light1 9 :i* all ! gre5 rays are pres5t1 only a small p]c5tage ( ! total gre5 9 ! spectrum is absorb$1 comp>$ ) t absorb$ f ! s+le gre5 ray ) :i* ! mat* is made4 ,no d\bt bo? pat*es are really gre5] :5 ! eye receives ! impression ( _! images outside ! yell[ spot1 b "o is mu* gre5] ?an ! o!r1 & x is ?us comp>atively gre54 ,x is possible to make a mat* ) "s col\rs ) a blue-gre5 9 :i* ! ph5om5on describ$ does n appe>2 b 9 cases :]e a mat* has to be made ) col\rs 9 :i* b little blue is requir$1 x w\ld be impossible to make x1 ow+ to ! blue exi/5t 9 su* a gre5-blue ray4 ,we w n[ return to our comp\nd+ ( ?ree col\rs to make :ite4 ,:y h we *os5 ! positions ( ! slits :i* we did 9 ! spectrum = its =mation8 ,w\ld n o!r positions answ] z well8 ,let u give our answ] by exp]im5t4 ,let u move ! slit :i* is n[ 9 ! gre5 t[>ds ! r$2 we %all f9d t z we d s--& keep+ ! blue slit ( ! same wid?--t we %all h to close ! r$ slit1 & alt] ! ap]ture ( ! gre5 slit itself4 ,if we reason on ?is po9t we %all be =c$ to ! conclusion t ! gre5 slit lets ?r\gh m r$ light ( "s description1 z less r$ f ! r$ slit is requir$ to make ! mat*4 ,if we move ! gre5 slit almo/ into ! yell[i% gre51 we %all f9d t ! r$ slit has to be entirely clos$1 & t :ite light is =m$ ( ! two col\rs1 yell[i% gre5 & violet4 ,?is %[s u t ! yell[i% gre5 col\r "h us$ is =m$ by a mixture ( ! r$ & gre5 rays :i* pass$ ?r\gh ! two slits 9 _! orig9al positions4 ,if we replace ! slits 9 ^! positions & close ! violet slit1 we are at once able to v]ify x4 ,if we aga9 =m :ite light ) ! slits 9 _! orig9al positions1 & move ! gre5 slit t[>ds ! blue1 we %all f9d t1 keep+ ! r$ slit at a con/ant ap]ture1 ! blue slit w h to be clos$1 & ! gre5 slit alt]$ 9 wid?4 ,! necessity ( less5+ ! ap]ture ( ! blue slit %[s t !re is a c]ta9 am\nt ( blue light com+ ?r\gh ! gre5 slit4 ,at "o po9t1 :5 ! slit has travell$ into ! blue-gre51 ! blue slit may be entirely clos$1 & :ite light be =m$ ( ?is & ! r$1 %[+ t ! blue-gre5 col\r is compos$ ( ! same proportions ( blue & gre5 :i* pass$ ?r\gh ! blue & gre5 slits 9 _! orig9al position4 ,! positions *os5 7 arriv$ at by ! writ] f exp]im5ts made 9 ?is mann]1 mov+ fir/ "o slit & !n ! o!rs1 & ! position ( ! gre5 slit 0 confirm$ by a consid]ation ( ! neutral po9t :i* exi/s 9 a gre5 col\r-bl9d p]son's spectrum4 ,! me?od ( mix+ ?ree col\rs toge!r gives u a means ( imitat+ all k9ds ( :ite light1 z x does ( col\r$ light4 ,at page #aaj we h already giv5 a diagram ( ! relative am\nts ( spectrum col\rs 9 sunlight1 skylight & gaslight4 ,if we by any means ?r[ a pat* ( ! light :i* we wi% to mat* on ! pat* =m$ by ! col\r pat* app>atus1 & int]pose ! rod1 we c measure ! ap]tures ( ! ?ree slits1 & ?us arrive at ! relative proportions ( ea* col\r pres5t4 ,9 an exp]im5t c>ri$ out1 sunlight1 ! electric arc-light1 & gaslight 7 comp>$ 9 ?is mann]4 ,! foll[+ are ! results1 ! r$ be+ ne> ! ,c l9e1 ! gre5 ne> ! ,e l9e1 & ! violet ne> ! ,g l9e ( ! sol> spectrum4 ---------------------------------------- ----------- ,sunlight4 ,electric ,gaslight4 ,skylight4 ---------------------------------------- ----------- ,r$ #ajj #ajj #ajj #ajj ,gre5 #aic #bjc #ie #bef ,violet #bbh #bej #bg #gfj ---------------------------------------- ----------- ,n[ f ! above x might seem t z ?ree simple spectrum col\rs w give u ! col\r ( any pigm5t1 t !re=e two col\rs ought to give u ! same col\r z any int]m$iate simple col\rs 9 ! spectrum :i* lie betwe5 !m2 = in/ance1 t ! simple blue-gre5 ought to be obta9$ by mix+ spectral gre5 & spectral violet toge!r4 ,?is c be asc]ta9$ ) a s+le col\r pat* app>atus1 by cutt+ a slit 9 ! c>d t fills up ! ap]ture betwe5 ! two adju/able slits1 & deflect+ ! beam transmitt$ ?r\gh x by a "r-angl$ prism1 & back on to ! scre5 ?r\gh ano!r simil> prism1 z describ$ 9 *apt] ,,viii4 ,x is m conv5i5t1 h[ev]1 to use a duplicate app>atus precisely simil> to ! fir/1 ) ! exception t no collimator is requir$1 plac+ !m side by side1 & mirrors mak+ ! reflect$ beam f ! fir/ trav]se ! second set ( prisms4 ,!re w be a reflect$ beam f ! second app>atus1 :i* c be utiliz$ 9 ! same way z 0 t f ! fir/ app>atus1 & ! two spectra w v>y toge!r 9 brightness1 z w also ! new reflect$ beam1 s9ce !y all are =m$ by ! light com+ ?r\gh "o slit4 ,a pat* ( ! col\r int]m$iate betwe5 ! two is ?r[n on ! scre5 f ! second app>atus1 & ! second pat* f ! fir/ app>atus ov]laps x4 ,a rod plac$ 9 ! usual mann] ?r[s two %ad[s1 :i* are illum9at$ by ! two diff]5t beams4 ,if blue-gre5 be a col\r x is wi%$ to mat*1 x w be f\nd t no matt] 9 :at "p ( ! violet & gre5 ! slits are plac$1 no mat* c be effect$4 ,b if "s v small quantity ( r$ light be mix$ ) simple blue-gre51 t !n a col\r id5tical 9 e respect z reg>ds ! eye c be obta9$ f ! violet & gre5 ( ! fir/ app>atus4 ,x mu/ be rememb]$ t a mixture ( r$1 gre5 & violet =m :ite1 & t !y are mix$ 9 def9ite proportions4 ,no matt] h[ feeble 9 int5sity ! :ite may be1 ! same proportions w /ill obta94 ,9 ! above exp]im5t1 z ! blue-gre5 mu/ conta9 violet & gre51 ! small quantity ( r$ mu/ comb9e ) ! prop] proportion ( violet & gre51 & w =m :ite light1 s t ! mat* is obta9$ by ! residues ( ! violet & gre5 mix$ ) ! small quantity ( :ite light1 ( :i* ! r$ is ! indicator4 ,we c te/ ! tru? ( ?is argum5t 9 a v simple way4 ,if we add to ! col\r ) :i* ! mat* has to be made a small quantity ( :ite light f ! reflect$ beam1 cutt+ (f m or less by ! rotat+ sectors1 we c get ! exact hue ( ! impure blue-gre5 made by ! mixture ( ! col\rs com+ ?r\gh ! two slits2 & fur!r we %all f9d t ! am\nt ( :ite add$ corresponds ) ! am\nt ( r$ :i* w\ld be requir$ :5 ! compon5ts ( ! :ite light 9 ! t]ms ( ! ?ree col\rs are tak5 into acc\nt4 ,= spectrum col\rs betwe5 ! violet & ! gre5 x may !re=e safely be said t no mat* c be effect$ by ! mixture ( violet & gre5 light2 b t x always gives ! int]m$iate col\r dilut$ ) :ite light4 ,= col\rs betwe5 ! gre5 & ! r$ ( ! spectrum1 a v close1 if inde$ n an exact mat*1 c be made ) ! r$ & gre5 slits1 )\t ! addition ( :ite4 ,if we take f ! second app>atus light f above ! position ( ! violet slit 9 ! fir/ app>atus1 t is1 ne>] ! limit ( visibility1 x w be f\nd t a mat* is made1 = at all ev5ts a v consid]able way ) ! violet slit alone1 by m]ely r$uc+ ! ap]ture1 ?us %[+ t ! col\r is ! same1 only less int5se4 ,9 ! same way x w be se5 t ! rays com+ f any po9t betwe5 ! l[] limit ( ! spectrum to a little bel[ ! ,c l9e are id5tical 9 col\r4 ,z we h arriv$ at ! fact t 9 col\r mixtures ( violet & gre51 :ite light is to be f\nd 9 ! col\r produc$1 x foll[s t ei!r ! violet or ! gre51 or bo?1 mu/ !mselves conta9 "s small proportion ( :ite4 ,x might p]haps be said t violet is really a mixture ( r$ & blue1 & h5ce ! :ite 9 ! mixture ) ! gre52 b if 9 ! fir/ app>atus we place "o slit 9 ! pure/ blue we c f9d1 & ! o!r 9 ! r$1 & ?r[ a violet pat* on ! scre5 f ! second app>atus1 we %all be unable to =m ! same hue ( violet by any means2 x w always be dilut$ ) :ite4 ,n[ z ! v blue we are us+1 if mat*$ z above by gre5 & violet1 requires :ite light to be add$ to x1 & z to mat* ! violet ) ! same blue & r$1 :ite light has also to be add$ to x1 x foll[s t ! violet mu/ be fre] f :ite light at all ev5ts ?an ! blue4 ,!re is "o o!r exp]im5t t mu/ be m5tion$ be=e leav+ = a "t ?is "p ( our subject1 viz4 ! =mation ( :ite by a mixture ( yell[ & blue4 ,if "o ( ! slits be plac$ 9 ! yell[ ( ! spectrum1 a position w be f\nd 9 ! blue :]e1 if a second slit be plac$1 & ! ap]tures are adju/$1 an absolute mat* ) ! reflect$ :ite ( ! app>atus c be secur$4 ,?is exp]im5t w be ref]r$ to lat] on1 :5 consid]+ ! "q ( prim>y col\rs4 ,! above exp]im5ts h a great be>+ on ! !ory ( col\r vision1 & %\ld be consid]$ v c>efully 9 connection ) ! %ort5$ spectrum :i* we h %[n exi/s :5 r$ col\r-bl9d p are obs]v+ its lum9osity4 ,!re is "o po9t to be recollect$ 9 relation to ! mixtures ( ! ?ree or two diff]5t col\rs :i* make :ite light4 ,if diff]5t col\r$ pigm5ts be illum9at$ by ! made :ite light1 !y w n appe> ( ! same hues1 z a rule1 z :5 view$ by ord9>y :ite light4 ,!y w v>y n only 9 col\r1 b 9 brightness4 ,?is might be expect$ :5 ! spectral light :i* !y reflect is tak5 into acc\nt4 ,,*apt] ,x4 ,ext9ction ( ,col\r by ,:ite ,light--,ext9ction ( ,:ite ,light by ,col\r4 ,9 ! la/ *apt] we h %[n ! impossibility ( mat*+ ! hue ( ! simple col\rs betwe5 ! violet & ! gre51 unless a c]ta9 & appreciable quantity ( :ite light be add$ to !m4 ,we w n[ turn to a phase ( col\r measurem5t :i* w mat]ially help u to see :y1 9 "s cases1 ! addition ( :ite light to ! simple spectrum col\rs1 betwe5 ! r$ & gre51 does n appe> necess>y 9 ord] to make a mat* ) a mixture ( r$ & gre54 ,we w ask ourselves two que/ions3 "o is1 :e!r any col\r1 & if s h[ mu*1 c be add$ to :ite )\t appe>+ to ! eye8 & ! o!r1 if any1 & if s h[ mu*1 :ite light c be add$ to a col\r )\t its be+ p]ceiv$8 ,p]haps "o ( ! readie/ me?ods ( expla9+ exactly :at we mean is by a rotat+ disc4 ,suppose we h a r$ disc1 ( n9e or t5 in*es 9 diamet]1 & at e "o in* f ! c5tre pa/e on x a :ite waf] ab\t "o-eigh? ( an in* 9 diamet]1 & cause x to rapidly rotate4 ,on exam9ation we %all f9d t p9k r+s w be =m$ by ! comb9ation ( ! :ite & r$ ne> ! c5tre1 b t t[>ds ! m>g9s no r+s w be visible1 ow+ ( c\rse to m r$ be+ comb9$ ) ! same am\nt ( :ite4 ,?is %[s t ! eye is only s5sitive to a c]ta9 degree1 & _c di/+ui% a v small dim9ution 9 col\r purity4 ,! int5sity ( ! light has some?+ to d ) ! numb] ( ^! p9k r+s :i* are visible1 z may readily be te/$ 9 a room4 ,if ! rotat+ disc be plac$ ne> a w9d[1 & ! numb] ( r+s visible be c\nt$1 a diff]5t numb] w be visible :5 x is plac$ 9 a d>k corn]4 ,a k9dr$ exp]im5t is to place r$ circul> waf]s ^u a :ite disc1 & note ! r+s visible4 ,?is gives ! s5sitiv5ess ( ! eye = ! dim9ution 9 int5sity at ! o!r end ( ! scale4 ,x w be f\nd t !re is a m>k$ diff]5ce betwe5 ! two4 ,fig4 #cb4--;,diaphragm 9 front ( ,prism4 ,x is m in/ructive if we exp]im5t ) pure col\rs1 & s we mu/ resort to our col\r pat* app>atus describ$ 9 ,fig4 #f4 ,if a small circul> ap]ture ab\t qu>t] ( an in* 9 diamet] be cut 9 a c>d1 & plac$ 9 front ( ! prism ne>e/ ! cam]a l5s 7,fig4 #cb71 ! col\r pat*1 in/ead ( be+ an image ( ! face ( ! prism1 w be an image ( ! circul> hole1 & :5 ! slit is pass$ ?r\gh ! spectrum we %all h a col\r$ spot on ! scre51 on :i* we c sup]pose a pat* ( :ite light f ! reflect$ beam4 ,!re are two ways 9 :i* we c r$uce ! int5sity ( ! spot1 by n>r[+ ! slit ?r\gh :i* ! spectral ray passes or by plac+ ! rotat+ sectors 9 front ( ! col\r$ beam4 ,?is la/1 p]haps1 is ! readie/ plan1 z x only involves ! read+ ( ! sector4 ,we c !n dim9i% ! int5sity ( ! col\r$ spot to su* a degree t by its dilution ) :ite light x w entirely disappe>4 ,x w be f\nd t r$ disappe>s at a diff]5t ap]ture ( sector to t requir$ = ! gre51 & ! gre5 to t = ! blue4 ,f our previ\s exp]im5ts 9 *apt] ,,vii4 we "k ! lum9osity ( ! spectrum to ! eye1 & x w be ( int]e/ to see :at relation ! lum9osity at :i* ! spots ( diff]5t col\r disappe>1 :5 !y are s dilut$ ) :ite light1 be> to ! total lum9osity ( ^! rays4 ,9 a set ( measurem5ts made x 0 f\nd t ! r$uc$ angul> ap]tures requir$ = ! col\rs indicat$ by ! foll[+ 73 ,b requir$ #cjj99 ( ap]ture4 ,c #ef ,d #ad ,e #bb ,f #aej ,g #bajj99 ,! l>ge numb]s m>k$ ) an a/]isk 7 obta9$ by plac+ ! rotat+ sectors 9 front ( ! :ite reflect$ beam4 ,! light ( ,d _h to be r$uc$ to #ad be=e x 0 ext+ui%$2 !re=e to ext+ui% ! orig9al light ( ?is col\r 9 ! spectrum w\ld require #ahj_/ad1 or #abi times ! int5sity ( ! :ite light ( ! reflect$ beam4 ,) ! ,e light x w\ld take #ahj_/bb1 or #hb times ! :ite light to ext+ui% x1 & s on4 ,if we tabulate ! results 9 ?is mann]1 & take ! :ite light necess>y to ext+ui% ! ,d light empirically z #ihe1 :i* is its p]c5tage lum9osity 9 ! spectrum ( ! electric light1 we c !n comp>e ! ext+ui%+ factor ) ! lum9osity 9 ea* case4 ---------------------------------------- --------------- ,:ite requir$ ,:ite requir$ to ext+ui% ,lum9osity ,col\r4 to ,ext+ui% ! ,spectrum1 ( ! ,spectrum4) #ej z ,t ,spectrum4 requir$ at ,e4 ---------------------------------------- ------------- ne> l9e ,b #f #ci #di ,c #cb #aie #bjf ,d #abi #gh #ihe ,e #hb #ej #ej ,f #ab #ge #ge ,g #jhg #ef #f ---------------------------------------- ---------------- ,! v close resemblance betwe5 ! la/ two columns indicates t ! same lum9osity ( :ite light is necess>y to ext+ui% ! same lum9osity ( mo/ col\rs1 )9 ! limits ( obs]vation t is to say4 ,inde$ ! me?od ( ext9ction 0 a plan :i* ,drap] & ,vi]ordt essay$1 b ! results1 tabulat$ f exp]im5ts made by !m ) ! app>atus !y employ$1 give a curve ( int5sity v unlike t giv5 9 ,*apt] ,,vii4 ,9 ^! exp]im5ts ! lum9osity ( ! orange light correspond+ to ! ,d l9e com+ ?r\gh ! slit 0 measur$1 & x 0 f\nd to be #cge_/ahj ( ! :ite light4 ,n[ accord+ to ! la/ table b "o #ad_/ahj ( ?is light 0 ext+ui%$ by ! full :ite light1 consequ5tly #cge_/ahj x #ad_/ahj1 or #a_/fb ( ! orange light 0 ext+ui%$ by ! :ite light4 ,9 o!r words1 if :ite light be sixty-two times bright] ?an ! orange light1 ! col\r ( ! latt] :5 ! two are mix$ w be invisible4 ,! ext9ction ( all col\rs requires some:at m light ?an ?is1 & a calculation %[s t ! ext9ction ( e col\r is effect$ by :ite light1 :i* is sev5ty-five times bright] ?an ! col\r4 ,arti/s are well aw>e t a pale wa% ( a pigm5t may be wa%$ ov] draw+ pap]1 & :5 dry is invisible to ! eye4 ,! above exp]im5ts fully acc\nt = x4 ,! o!r exp]im5t :i* 0 to be tri$ 0 to see h[ mu* :ite light c\ld be ext+ui%$ by a col\r4 ,!re are sev]al ways by :i* ?is c be effect$4 ,= in/ance we may sup]pose a :ite dot on ! col\r pat* by plac+ a c>d1 9 :i* a circul> hole is cut1 9 ! reflect$ beam ne> ! prism1 f :i* ! reflection takes place2 or by putt+ a black circul> disc ( small dim5sions pa/$ on a glass 9 ! same position1 by :i* means ! :ite light is sup]pos$ ov] ! :ole ( ! col\r pat*1 ) ! exception ( :at1 :5 ! col\r is cut (f1 is a black spot2 or aga9 by plac+ a rod to %ade half ! pat* f ! :ite light1 b leav+ ! :ole ( x expos$ to ! col\r$ beam4 ,all ^! me?ods h be5 tri$1 & x appe>s t ! size ( ! piece ( ! pat* ov] :i* ! :ite light is ?r[n may h "s effect on ! result+ curve1 b ( "o ?+ !re is evid5ce1 viz4 t a great deal m :ite light c be mix$ unp]ceiv$ ) orange light1 ?an c be ) ! gre51 blue1 or violet4 ,f "o exp]im5t x 0 f\nd t #a_/cf "p ( :ite light ( ! same lum9osity z ! orange c\ld be mix$ ) ! orange & n be p]ceiv$2 b t ) ! gre5 light at ,e #a_/ij w\ld j be visible1 :il/ at ,f 9 ! blue-gre5 ! #a_/abj c\ld be di/+ui%$4 ,look+ at ^! results1 & apply+ !m 9 elucidat+ ! exp]im5ts 9 :i* x 0 attempt$1 b )\t success1 to mat* ! int]m$iate col\rs betwe5 violet & gre5 7( :i* ! light at ,f is a case 9 po9t71 by mix+ !m toge!r1 unless :ite light 7 add$ to ! simple col\r2 & ! success ( ! o!r exp]im5t1 9 :i* orange light c\ld be obta9$ ( ! same hue z t at ,d by a mixture ( ! r$ & gre51 x w be notic$ t #cc times m :ite light c be add$ to ! orange ?an to ! gre5 light at ,f1 )\t its p]ception4 ,! :ite light produc$ by ! mixture 9 ! fir/ case might well %[ :5 mix$ ) ! gre51 b might pass :olly unp]ceiv$ :5 mix$ ) ! orange4 ,,*apt] ,,xi4 ,prim>y ,col\rs--,molecul> ,sw+s--,col\r ,s5sations--,s5sations abs5t 9 ! ,col\r-bl9d4 ,= "s purposes x is advantage\s to %[ exp]im5ts be=e indicat+ ! d$uctions f !m :i* may lead to a !ory4 ,^? describ$ 9 ,*apt] ,,ix4 w enable u to treat ! !ory ( col\r p]ception f a /&po9t ( "s advantage4 ,h[ is x t ! comb9ation ( ?ree col\rs suffices to =m :ite1 or to mat* any col\rs we wi%1 be !y spectrum col\rs to :i* a little :ite is add$1 or ! col\rs ( pigm5ts8 ,! mo/ plausible !ory t c be advanc$ is t x is only necess>y = ! eye to be furni%$ ) a ?ree-col\r-p]ceiv+ app>atus to give ! impression ( e col\r1 & yet ?is w\ld be some:at difficult to believe _h we n _h ! exp]im5ts n>rat$ 9 t *apt] be=e u4 ,we %\ld h almo/ expect$ "s ma*9]y 9 ! eye to exi/1 :i* w\ld answ] to ! rhy?mic sw+ ( ! rays ( e wave-l5g? :i* toge!r make up :ite light4 ,b n[ we h to /& face to face ) ! results ( exp]im5t1 & we f9d t at ! mo/ only ?ree col\rs are necess>y to make up :ite light1 & t f ^! ?ree spectrum col\rs we c =m any o!rs1 ) ! limitation already m5tion$1 :5 "s simple col\rs are 9 "q4 ,we mu/ "h digress = a mom5t1 & notice ! fact t f our exp]im5ts we h d]iv$ ! ?ree prim>y col\rs z !y are call$1 viz4 r$1 violet1 & gre52 ! def9ition ( a prim>y col\r be+ t x _c be =m$ by ! mixture ( any o!r col\rs4 ,we h asc]ta9$ t yell[ & blue make :ite4 ,x is !re=e evid5t t blue1 yell[1 & r$ _c be prim>y col\rs1 s9ce two ( !m =m :ite2 & we h moreov] %[n t yell[ c be made f gre5 & r$2 h5ce x might be fair to assume t ! ?ree prim>y col\rs are r$1 gre51 & blue4 ,b blue1 :5 mix$ ) a v small p]c5tage ( :ite light1 c be made by gre5 & violet4 ,h5ce1 9 ! :ite light =m$ by ! two col\rs yell[ & blue1 we h ! fir/ made by gre5 & r$1 & ! second by gre5 & violet2 h5ce ! ?ree col\rs :i* really make ! :ite light are r$1 gre51 & violet4 ,! approximate positions ( ^! ?ree col\rs 9 ! spectrum are ^? already indicat$2 ?\gh1 z we %all pres5tly see1 x is highly improbable t any p]son ^: eyes are :at are call$ normal1 has ev] exp]i5c$ ! fundam5tal gre5 s5sation4 ,! fact t r$1 yell[1 & blue _c be prim>y col\rs has be5 m5tion$1 z ev5 n[ x is sometimes taught t !y are s4 ,z long z ! !ory ( col\r pr9cipally lay ) arti/s !re 0 reasonable gr\nd = _! assumption1 s9ce !y work$ ) impure col\rs1 viz4 ^? ( pigm5ts2 & z we %all see lat] on ! tru? ( ! assumption agre$ ) su* exp]im5ts z !y w\ld make4 ,:51 h[ev]1 ! "q 0 tak5 up by ! physici/ ) m exact me?ods ( exp]im5t+1 & ) pure col\rs1 ! falsity ( ! old triad 0 soon capable ( pro(4 ,to return f our digression3 h[ x is t ?ree mix$ col\rs c give ! s5sation ( :ite light is at fir/ sight h>d to und]/&2 b a ref]5ce to ! action ( light on a photographic salt helps u 9 "s degree4 ,9 ! case ( a s5sitive salt1 su* z ! bromo-iodide ( silv]1 we f9d t a *emical decomposition is caus$ by ! violet end ( ! spectrum1 & is only feebly affect$ by any o!r "p1 ?\gh ) prolong$ exposure ev5 ! r$ w cause x4 ,! annex$ figure 7,fig4 #cc7 gives ! idea ( ! relative action ( diff]5t p>ts ( ?is violet portion4 ,fig4 #cc4--;,curve ( ,s5sitiv5ess ( ,silv] ,bromo-iodide4 ,! height ( ! curve %[s ! relative effects produc$4 ,n[ ?is curve is n symmetrical1 b has a maximum effect ne>] to ! violet end ( ! spectrum ?an to ! r$4 ,! atomic composition ( ! silv] bromo-iodide is probably two atoms ( silv] & "o ( brom9e & "o ( iod9e oscillat+ toge!r1 & we c conceive ( "s "o atom1 ! p]iod ( ^: sw+s 9 its molecule is iso*ron\s ) "s wave-l5g? ( light4 ,fur!r1 we c conceive t1 l a p5dulum ^: vibrations are increas$ 9 magnitude by well-tim$ bl[s1 ! sw+ ( ! atom is also increas$1 & t ev5tually x gets beyond ! sph]e ( ! attraction ( its p>5t molecule1 leaves x1 & is attract$ to "s neighb\r+ molecule ( diff]5t con/itution1 & t ?us a *emical *ange is induc$4 ,?is we c conceive1 b h[ c o!r waves1 :i* are n iso*ron\s ) ! rhy?mic sw+ ( ! atoms1 alt] ! composition ( ! molecule8 ,if we h an impulse giv5 to a p5dulum exactly tim$ ) ! p]iod ( oscillation1 !re is no d\bt t ! sw+ is increas$4 ,if we h "o ne>ly 9 accord1 x w be f\nd t ?\gh ! sw+s are n increas$ 9 amplitude s greatly z :5 !re is p]fect accord1 yet an increas$ sw+ is giv51 & z exact accord is remov$ fur!r & fur!r1 s ! increase 9 ! sw+ ( ! p5dulum gets small] & small]4 ,9 some:at ! same mann] x is possible t _m s]ies ( waves1 diff]+ 9 wave-l5g?1 & !re=e 9 p]iods ( oscillation1 may be capable ( increas+ ! amplitude ( a sw+1 & ) ! photographic salt ?is probably occurs1 ) ! result :i* we see 9 ! above figure4 ,suppose 9 ! eye we h ?ree su* s5sitive p5dulums :i* are capable ( respond+ to ! beats ( waves ( light1 x requires no great imag9ation to see t "o su* p5dulum w respond n only to t wave ( light :i* is iso*ron\s ) x1 b also ) waves %ort] & long] ?an t p>ticul> wave4 ,! same p5dulum inde$ may respond to ! :ole ( ! visible spectrum1 b :5 f> (f f ! maximum ! response w\ld be v small inde$4 ,we may !re=e assume t ?\gh ea* p5dulum may h its maximum increase ( oscillation at "o "p ( ! spectrum1 yet at o!r p>ts n only x alone answ]s to ! beat+ ( ! waves1 b t ! o!r p5dulums are also affect$ by ! same1 & ?us ! :ole spectrum is recogniz$ by ! sw+s m or less long1 ( ei!r "o1 two1 or ( all ?ree4 ,to ,?omas ,"y is usually attribut$ ! ?ree-col\r !ory1 ?\gh x seems to h be5 promulgat$ 9 an incomplete /ate "s "t be=e2 ,cl>k-,maxwell & ,helmholtz reviv$ x 9 lat] ye>s1 & x is usually kn[n z ! ,"y-,helmholtz !ory4 ,x %\ld be rem>k$ t ! ?ree fundam5tal col\r s5sations are n ( necessity ! same s5sations z are giv5 by ! ?ree prim>y col\rs1 z we %all see fur!r on4 ,! foll[+ figure 7,fig4 #cd7 is tak5 f ,helmholtz's physiological optics1 z diagrammatic ( ! ?ree s5sations4 ,fig4 #cd4--;,curves ( ,col\r ,s5sations4 ,to ?is diagram !re is an objection1 9 "o respect1 viz4 t x gives ! same lum9osity-value to ! blue ( ! spectrum z x does to ! r$ & gre54 ,x has be5 se5 t if we call ! lum9osity ( ! yell[ #ajj1 t ( ! blue is ab\t #e4 ,! objection does n hold if x is rememb]$ t ! ?ree maxima ( impressions are tak5 z equal4 ,if ! ord9ates 7 increas$1 s t ! maxima 7 ( ! same height z t ( ! photographic curve1 ! resemblance betwe5 !m & ?is la/ w\ld be v m>k$4 ,x w be notic$ t ea* ( ! ?ree col\r s5sations is n only excit$ by a limit$ portion ( ! spectrum1 b by all ( x1 ! height ( ! curves be+ a measure ( _! response4 ,n[ assum+ t ?is is ! case1 s9ce a c]ta9 degree ( /imulation giv5 simultane\sly to ! ?ree s5sations causes an integral s5sation ( :ite light1 x foll[s t ! col\r p]ceiv$ 9 e "p ( ! spectrum is due to ! excess ( /imulation ( ei!r "o or two ( ! fundam5tal s5sations1 toge!r ) ! s5sation ( :ite light4 ,if ?is diagram 7 correct1 at no po9t 9 ! spectrum is "o fundam5tal s5sation excit$ alone1 b we believe t ! diagram obta9$ by ,koenig 7,fig4 #ce71 f col\r equations 7:i* w be expla9$ 9 our next *apt]71 is m exact1 & t x is probable t 9 ! extreme violet & extreme r$ ( ! spectrum ! only s5sations :i* are /imulat$ are ! violet & r$ respectively4 ,our measures 9 ! r$ & violet ( ! spectrum make x appe> t ea* ( ! two s5sations c be p]ceiv$ unaccompani$ by any o!rs1 & ! fact t ! r$ col\r bl9d p]son p]ceives a %ort5$ spectrum 9 ! r$ end1 is a fur!r pro( ( ?is d$uction1 s f> z ! r$ is conc]n$4 ,! col\r :i* ! fundam5tal gre5 s5sation excites 9 ! normal eye has probably nev] be5 se51 nor c be se54 ,?is is due to ! fact t all ?ree s5sations ov]lap 9 ! gre52 t is1 t ! p5dulum :i* answ]s to ! gre5 col\r 9 ! spectrum also affects1 b ) mu* less en]gy1 ! o!r two p5dulums1 :i* respond to ! r$ & violet s5sations4 ,! ^w p5dulum has be5 us$ advis$ly1 = x may equally z well apply to a molecul> aggregation z to "o :i* is visible & measurable4 ,)\t ent]+ into ! physiological /ructure ( ! eye1 we may say t x has usually be5 assum$ t ! p5dulums are ! ends ( n]ves :i* vibrate ) ! waves ( light2 b ?is seems r d\btful4 ,gross matt]1 su* z ^! ends are1 comp>$ ) ! molecules ( :i* !y are built up1 _c1 z a rule1 vibrate ) waves ( light1 & !re seems to be no reason :y !re %\ld be an exception 9 ! case ( ! eye4 ,x seems mu* m probable t a *emical decomposition takes place 9 "s sub/ance atta*$ to !m1 & :]e su* decomposition takes place electricity ( "s k9d mu/ be produc$4 ,9 o!r s5sations ( ! body ! n]ves act z telegraph wires1 c>ry+ messages to ! bra91 & x is n improbable t ! n]ves ( ! eye are employ$ 9 some:at ! same mann]4 ,pr(essor ,dew> has %[n t :5 light acts on an extirpat$ eye1 a curr5t ( electricity does trav]se ! n]ves1 & ( su* an am\nt t x c be %[n to a l>ge audi5ce4 ,?is exp]im5t is n1 h[ev]1 conclusive1 z ! effect may be mi/ak5 = ! cause4 ,?is idea1 h[ev]1 is only hypo!tical1 z is inde$ ! hypo!sis ( ! me*anical action ( light on ! gross matt] ( :i* ! rods & cones atta*$ to ! ret9a are compos$4 ,we h 9 a previ\s *apt] /at$ t !re are "s eyes 9 :i* ! s5sation ( "s col\r is altoge!r abs5t1 & 9 o!rs 9 :i* x is m or less defici5t4 ,?us "s eyes appe> to be lack+ :olly 9 ! s5sation ( r$1 o!rs ( gre51 & "s v few ( violet2 & !re h be5 cases kn[n 9 :i* two s5sations1 ! r$ & violet1 h be5 totally abs5t4 ,9 ! fir/ case1 :]e ! s5sation ( r$ is entirely abs5t1 :at is kn[n to ! normal-ey$ z :ite c be mat*$ ) a mixture ( blue & gre51 & !re is a place 9 ! spectrum t is recogniz$ z :ite4 ,simil>ly :ite c be mat*$ by a gre5 bl9d p]son ) a mixture ( r$ & blue4 ,to ^? :o may be curi\s to see ! col\r :i* r$ & gre5 bl9d p]sons w\ld call :ite1 a v simple means is at h& to demon/rate x4 ,us+ ! col\r pat* app>atus ) ! ?ree slits ins]t$ 9 ! slide1 & 9 ! positions we h indicat$ 9 ! violet1 gre51 & r$1 & =m+ :ite light = ourselves on ! scre51 if we cov] up ! r$ slit entirely we %all h a pat* ( sea-gre5 col\r1 :i* a r$ bl9d p]son w\ld call :ite2 & if we cov] ! gre5 slit1 uncov]+ ( c\rse ! r$1 we %all h a brilliant purple1 :i* to a gre5 bl9d p]son w\ld be :ite4 ,!y bo? w\ld call :ite :at ! normal-ey$ p]son sees z :ite1 = ! simple reason t ei!r ! r$ or ! gre5 mix$ ) ! rema9+ col\rs w\ld be unp]ceiv$4 ,! exam9ation ( col\r-bl9d p is ( prime importance = te/+ any !ory ( col\r vision4 ,= in/ance1 if x 7 ass]t$ t ! fundam5tal s5sations did n ov]lap z %[n 9 ! diagram above1 !n x w\ld foll[ t at "s place 9 ! spectrum !re w\ld be a d>k po9t4 ,if !y d ov]lap1 x mu/ foll[ t bo? = ! r$ & = ! gre5 col\r bl9d p]son !re mu/ be "s place 9 ! spectrum :]e :at is :ite light to !m is produc$4 ,col\r-bl9d p 7 te/$ ) ! col\r app>atus4 ,! reflect$ beam & ! col\r pat* 7 made to ca/ %ad[s z be=e1 & ! rotat+ sectors plac$ 9 ! pa? ( ! =m]4 ,a slide ) "o slit 0 pass$ across ! spectrum1 & ! position not$ :]e x 0 said t ! two %ad[s 7 illum9at$ ) :ite light2 to ! normal-ey$ p]son "o %ad[ ( c\rse appe>$ illum9at$ ) ! sea-gre5 col\r1 or blui% gre51 accord+ z ! obs]v] 0 r$ or gre5 col\r bl9d4 ,! ray 9 ! spectrum :i* to ! r$ col\r bl9d is :ite1 has a wave-l5g? ( ab\t #dijj1 & t = ! gre5 col\r bl9d a wave-l5g? ( #ejbj1 :i* corresponds to ! position 9 :i* we usually place ! gre5 slit :5 a normal-ey$ p]son is mak+ col\r mat*es4 ,x may be fur!r rem>k$1 t if ! maxima ( all ! ?ree col\r s5sations are tak51 z 9 ! diagram1 z ( equal value1 t ! place 9 ! spectrum :]e ! :ite light is p]ceiv$ by ! col\r-bl9d is :]e ! two s5sations are ( equal /r5g?1 t is1 :]e ! two curves cut "o ano!r1 & are ( equal height4 ,by obta9+ ! proportions ( ! diff]5t col\rs ) col\r-bl9d p]sons :i* make up :at to !m is :ite light1 ! curves = ! two s5sations c be work$ out 9 ! =m ( simple equations4 ,! exp]im5ts c>ri$ out ) col\r-bl9d p are ( ! mo/ int]e/+ "*1 & a good deal rema9s to be done ) ! data already obta9$ f !m4 ,to ! popul> m9d a col\r-bl9d p]son is usually ?\ght a /range creature1 & x is a matt] ( wond]m5t1 if n ( amusem5t1 t !y _c di/+ui% betwe5 ! r$ ( *]ries & ! leaves ( ! *]ry tree4 ,! physici/1 /udy+ ! !ory ( col\r1 views ! matt] q diff]5tly1 & he looks ^u an intellig5t obs]v] ( ?is class z a boon4 ,x may be rem>k$ t bo? ! r$-bl9d & ! gre5-bl9d p]sons w\ld be unable to di/+ui% betwe5 ! *]ries & ! leaves4 ,! r$-bl9d p]son w\ld see ! *]ries z gre51 z also ! leaves2 :il/ ! gre5-bl9d p]son w\ld see bo? z r$4 ,)\t reg>d+ =m x is probable t ! r$-bl9d w\ld see ! leaves z a bright gre51 :il/ ! gre5-bl9d w\ld see !m z d>k] r$ ?an ! *]ries4 ,failure to di/+ui% betwe5 ! two is m likely to occur ) ! gre5 ( leaves1 & ! r$ ( su* fruits z *]ries1 s9ce ! =m] conta9s a m>k$ proportion ( r$ 9 x1 & ! latt] a small proportion ( gre54 ,"o highly-educat$ g5tleman 0 l$ to "k 8 defici5cy 9 col\r s5se1 by he>+ a companion on a t\r go+ into raptures ov] a sunset4 ,he saw b little diff]5ce betwe5 x & t to be se5 at midday4 ,te/+ 8 vision x appe>$ t he 0 totally bl9d to ! s5sation ( gre51 & t :ite & purple w\ld consequ5tly be mi/ak5 by him = "o ano!r4 ,! crimson on ! cl\ds1 illum9at$ by ! sett+ sun1 w\ld appe> to him z only slightly diff]5t to ! :ite cl\ds :i* he w\ld see at midday2 9 fact he w\ld be always see+ :at to u w\ld be a sunset4 ,= ?is g5tleman to mix spectrum col\rs to mat* o!rs w\ld evid5tly be no guide to normal-ey$ p]sons4 ,we believe t among/ u 9 our daily life we h _m p]sons :o are bl9d to "s col\r1 b :o are n aw>e ( x1 or if !y are aw>e ( x1 hide _! defect z f> z possible4 ,t "s are ignorant ( x to a late p]iod ( _! life we "k4 ,we h said t !re are cases 9 :i* p]sons are only defective 9 col\r p]ceptions1 & n want+ 9 !m altoge!r4 ,! =m] are m common ?an ! latt]1 & to ! exp]im5t] are by no means s int]e/+4 ,!y are only allud$ to "h to indicate t !re are degrees 9 ! defectiv5ess ( eyes to col\r4 ,"o po9t :i* mu/ be rememb]$ "h is t all col\r production = regi/ration by ! mixture ( ?ree col\rs is delusive1 unless ! eye ( ! op]ator is te/$ = its col\r s5se4 ,,*apt] ,,xii4 ,=mation ( ,col\r ,equations--,koenig's ,curves--,maxwell's ,app>atus & ,curves4 ,! plan ( obta9+ col\r equations w by ?is "t h become fairly evid5t4 ,& we may z well illu/rate x by equations obta9$ ) ! app>atus we h be5 us+ 9 our previ\s exp]im5ts4 ,let u suppose we h an individual :o is desir\s ( hav+ 8 eye-sight = col\r te/$1 & t we h ! slide ) ! ?ree slits 9 situ4 ,x w be f\nd t :5 we alt] _! wid? & =m :ite light ) !m1 mat*+ 9 purity ! :ite light ( ! reflect$ beam1 t we %all h to r$uce ! int5sity ( ! latt] v consid]ably1 by means ( ! rotat+ sectors4 ,! ap]ture may sometimes be z small z #d1 & at o!r times p]haps some:]e betwe5 #d & #e4 ,n[ ! v>iation 9 ap]ture betwe5 #d1 & say #dg1 is v consid]able1 b x is highly probable t ! latt] might be e/imat$ z #df1 s9ce only degrees are m>k$ on ! sectors4 ,x !re=e becomes ess5tial to use a less brilliant reflect$ beam = ! comp>ison1 & ?is is secur$ by us+ z a mirror a pla9 unsilv]$ glass4 ,:at be=e read #d w p]haps read #fj1 & #dg w be #gj-a_/b1 :il/ #df w\ld be #fi1 a diff]5ce easily read4 ,we c n[ comm5ce op]ations4 ,let u !n place ! r$ slit at say 7#ce7 ( ! scale1 ! gre5 at 7#bh71 & ! violet at 7#ag71 & make :ite light ( ! same int5sity by alt]+ ! ap]tures ( ! slits4 ,let u d ! same ) ! slits at 7#cd71 7#bh71 & 7#ag71 in/ead ( at 7#ce71 7#bh71 & 7#ag72 & aga9 make :ite light1 & simil>ly ) ! slits at 7#ce71 7#bh71 & 7#ah72 & let ! foll[+ be ! results-- 7#a7 #bj7ce7 #fj7bh7 #dj7ag7 #ajj ,w 7#b7 #aj7cd7 #ee7bh7 #dj7ag7 #ajj ,w 7#c7 #bj7ce7 #ei7bh7 #aj7ah7 #ajj ,w ,subtract+ 7#a7 f 7#b7 we get-- #aj7cd7 #bj7ce7 #e7bh7 or 7#cd7 #b7ce7 #a_/d7bh7 :i* means t ! col\r s5sation at 7#cd7 is made up ( two p>ts ( ! s5sation ( 7#ce71 toge!r ) #a_/d "p ( ! s5sation ( 7#bh74 ,9 ! same way we f9d t ! col\r s5sation ( 7#ah7 is made up ( ! s5sations ( 7#ag7 & 7#bh74 7#ah7 #d7ag7 #a_/aj7bh74 ,9 ?is way all ! diff]5t col\r s5sations c be ref]r$ to ! s5sations :i* we may happ5 to consid] z be/ repres5t+ ! fundam5tal s5sations4 ,:at ^! are is a matt] /ill unsettl$2 ?\gh f ! equations =m$ by col\r-bl9d p1 :o only require really two col\rs to =m equations1 _! places are approximately kn[n2 evid5tly z be=e said1 ! ray 9 ! spectrum :i* ! gre5 col\r-bl9d p]son sees z :ite light1 is t :]e to ! normal eye ! gre5 fundam5tal s5sation is pure/1 be+ free f pr$om9ance ( ei!r ( ! o!r two s5sations1 & might be tak5 z a /&>d col\r4 ,n[ if our lum9osity curve is correct1 & if ! sum ( ! lum9osities ( ea* col\r sep>ately is equal to ! lum9osity ( ! col\rs :5 mix$ 7:i* we h %[n to be ! case 9 *apt] ,,vii471 x foll[s t ! correctness ( ! measures c be *eck$ by us+ ! wid?s ( ! slits z multipli]s ( ! lum9osities4 ,^! lum9osities c !n be add$ toge!r1 & !y %\ld equal 9 lum9osity ! :ite light ) :i* ! comp>ison 0 made4 ,! results c be comp>$ toge!r by r$uc+ ! equations to ! same /&>d ( :ite light4 ,! foll[+ is a set ( obs]vations :i* be> ?is out4 ,! r$ & violet slits 9 ?is case 7 kept at #ce & #agh on ! scale1 & ! position ( ! gre5 slit alt]$4 ---------------------------------------- ------------ ,position ( ,ap]ture ( ,lum9osity ,sum ( ! ,slits4 ,slits4 ( ,col\r4 ,lum9osity -------------------------------- ( ea* ,col\r ,r ,g ,v ,r ,g ,v ,r ,g ,v multipli$ by ! ,ap]ture4 ---------------------------------------- ------ #ce #bhe #aghaae #chaabahagc #fe #dicj #ce #bhj #aghaai #deajjahafaefe #dihi #ce #bggeaghabb #eb #heahaeb #fe #difj #ce #bgceaghabe #fe #gdahadj #fe #dijg #ce #bgj #aghabh #gh #fgahaccbfe #died #ce #bfc #aghaccabe #djahabjcfe #dihg #ce #bfj #aghacdaej #ajahaafgfe #dieb #ce #beheaghaceagj #jahaaejfe #diic -------------- ,mean #diei ---------------------------------------- ------- ,! r$ slit 0 at a po9t 9 ! spectrum betwe5 ,c & ! r$ li?ium l9e1 & excit$ probably ! fundam5tal s5sation ( r$ alone4 ,! violet slit 0 close to ,g1 & probably 9 ?is case ! fundam5tal s5sation ( violet 0 almo/ excit$ alone4 ,) ! gre5 slit ! rev]se 0 ! case1 all ?ree fundam5tal s5sations be+ excit$4 ,at #bfc ! gre5 s5sation 0 probably ! fundam5tal s5sation mix$ ) :ite light alone1 z at t po9t ! gre5 bl9d p]son saw :ite light 9 ! spectrum1 on ! r$ side ( x !re be+ :at he describes z a w>m col\r1 & on ! violet side a cold col\r4 ,an inspection ( ! table w %[ h[ v closely ! sum ( ! lum9osities agree among/ !mselves1 ! :ite light =m$ by !m 9 ea* case be+ ( equal int5sities4 ,x mu/ be recollect$ t :ite light is n necess>y to =m col\r equations2 col\rs may be mix$ to =m any o!r col\r1 :i* may be tak5 z a /&>d4 ,?is is (t5 useful 9 ! case ( ! light betwe5 ! violet & ! blue1 :]e ! lum9osities are small comp>$ ) ! lum9osity 9 ! gre51 yell[1 & r$4 ,fig4 #ce4--,koenig's ,curves ( ,col\r ,s5sations4 ,by tak+ a l>ge numb] ( col\r equations1 ,koenig1 :o works 9 ,helmholtz's laboratory1 has d]iv$ :at he consid]s curves ( ! ?ree fundam5tal s5sations 9 a normal-ey$ p]son1 & also ^? ( ! col\r-bl9d4 ,x may be said t ) ! col\r-bl9d only two ( ! fundam5tal s5sations are se51 & !re=e only two curves are f\nd1 & t ^! agree 9 ! ma9 ) "s two ( ! curves ( ! ?ree belong+ to ! normal-ey$4 ,fig4 #cf4 ,maxwell's ,col\r-box4 ,maxwell 0 ! fir/ to make a def9ite piece ( app>atus = ! purpose ( obta9+ col\r equations1 & we reproduce f 8 pap] 9 ! ,philosophical ,transactions ( ! ,royal ,society = #ah--1 a some:at modifi$ diagram ( x4 ,?is app>atus is (t5 kn[n z ,maxwell's col\r-box1 & is 9 fact a spectroscope rev]s$4 ,) a collimator & prisms we =m a spectrum on ! focus+-scre5 ( ! cam]a 7,fig4 #f71 by light com+ ?r\gh ! slit1 & we c obta9 light on ! di/ant scre51 a pat* ( any col\r1 by plac+ 9 ! spectrum slits z giv5 at ,fig4 #cj4 ,if we 7 to illum9ate ! slits s plac$ ) :ite light1 & look ?r\gh ! slit ( ! collimator1 we %\ld see ! front surface ( ! fir/ prism illum9at$ by ! mixture ( ! col\rs :i* w\ld1 :5 ! light illum9at$ ! collimator slit1 h =m$ "o col\r pat* on ! scre54 ,9 ,maxwell's app>atus1 ! slits ,s#a1 ,s#b1 ,s#c are illum9at$ by ! light reflect$ f a :ite c>d ,c1 plac$ 9 ! sun%9e1 ! rays pass+ ?r\gh !m fall on two prisms ,p#a1 ,p#b1 are reflect$ back aga9 ?r\gh ^! prisms by a concave mirror ,m#c1 are receiv$ on ano!r mirror ,m1 & fall at ,e on to ! eye4 ,at ,a is an ap]ture 9 ! box1 lett+ ?r\gh :ite light on to a mirror ,m#a1 :i* reflects x ?r\gh a l5s ,l on to ,m#b1 :i* aga9 reflects x on to ,m1 & s to ! eye at ,e4 ,?us at ,e an image ( ! prisms1 & an image ( ! ap]ture are se51 & ! :ite light ( ! latt] c be comp>$ ) ! mixture ( ! col\rs =m$ by ! prism pass+ ?r\gh ,s#a1 ,s#b1 & ,s#c4 ,suppose we h "o slit ,s#a1 ! :ite light w be decompos$ by ! prisms1 & w be se5 at ,e z light ( ! same col\r z w\ld be se5 at ,s#a1 if ! light 7 s5t f ,e to ,s#a1 & s ) ! o!r slits4 ,?us :5 two or ?ree ( ! slits are uncov]$1 ! light fall+ on ! eye at ,e w be a mixture ( two or ?ree col\rs4 ,!re are two drawbacks to ! mode ( illum9ation us$1 "o be+ t ! quality ( sunlight v>ies1 & !re=e col\r equations w n be accurately comp>able "o ) ! o!r2 & ! second is t ! light reflect$ f ! c>d is n absolutely ! same 9 all directions1 & x _c be p]p5dicul>ly plac$ to ea* ( ! rays :i* /rike ! prisms1 aft] pass+ ?r\gh ! diff]5t slits4 ,?is latt] is a small objection1 & is n ( mu* acc\nt1 b ! fir/ drawback is a m s]i\s "o4 ,fig4 #cg4--,maxwell's ,curves ( ,col\r ,s5sations4 ,) ?is app>atus1 !n1 ,maxwell =m$ 8 col\r equations1 b he fix$ z ! col\rs :i* may be call$ 8 /&>d col\rs1 portions ( ! spectrum :i* are c]ta9ly n pure1 & h5ce he got curves :i* are n z p]fect z ^? ( ,koenig4 ,x w be se51 = in/ance1 t 8 r$ & violet curves d n ov]lap1 b t\* ea* o!r ne> ,e4 ,7 ?is true1 ! gre5 col\r-bl9d p]son %\ld see a d>k space 9 ! spectrum1 s9ce ! gre5 s5sation is miss+ 9 su* eyes4 ,z a matt] ( fact ! lum9osity ( ! spectrum is v consid]able to su* a p]son at ?is po9t4 ,x w also be se5 t "s ( 8 curves are negative curves ly+ bel[ ! base4 ,?is %[s t ! ?ree /&>d col\rs he took are some:at wrong4 ,! dott$ curve gives ! comb9ation ( 8 ?ree s5sations at e po9t1 & %\ld be ! lum9osity curve2 b ow+ to 8 hav+ tak5 empirically c]ta9 /&>ds ( lum9osity = 8 ?ree col\rs1 x does n repres5t ! tru?1 z may be se5 on comp>ison ) ,fig4 #aa1 page #gi4 ,x mu/ be recollect$ t s9ce ,maxwell's obs]vations ! subject has be5 l>gely exp]im5t$ ^u1 & naturally improv$ appliances & great] k h enabl$ m ne>ly correct views to be ent]ta9$ reg>d+ x4 ,,*apt] ,,xiii4 ,mat* ( ,comp\nd ,col\rs ) ,simple ,col\rs--,all ,col\rs r$uc$ to ,numb]s--,me?od ( mat*+ a ,col\r ) a ,spectrum ,col\r & ,:ite ,light4 ,if we place ! solution ( bi*romate ( potassium 9 front ( ! slit ( ! collimator1 we %all see t on produc+ a spectrum on ! scre51 all rays f ! r$ to ! yell[-gre5 pass2 h5ce bi*romate ( pota% transmits a col\r :i* is a comp\nd col\r4 ,x has be5 %[n t ?is orange col\r & ! spectral yell[ c be mat*$ by mix+ ! simple col\rs ( r$ & gre5 toge!r2 b x w be in/ructive to see if a simple col\r 9 ! spectrum itself c be f\nd :i* c mat* su* a comp\nd col\r z t ( ! bi*romate4 ,if we place ! bi*romate 9 ! reflect$ beam ( ! col\r pat* app>atus & illum9ate "o %ad[ ca/ by ! rod ) ! light transmitt$ by x1 & pass a slit along ! spectrum1 to produce mono*romatic light1 ) :i* ! o!r %ad[ ( ! rod is illum9at$1 a position w be f\nd ne> ! orange sodium l9e ,d1 :]e ! two col\rs app>5tly mat* 9 e respect2 :5 ! int5sities ( ! two illum9at$ %ad[s are equaliz$ z be=e by ! rotat+ sectors4 ,9 ! same way by fill+ ! "p ( ! squ>e ) ! pigm5t on :i* ! %ad[ illum9at$ by ! reflect$ beam falls1 we c see if we c mat* em]ald gre51 cyan9e blue1 & o!r col\r$ pigm5ts4 ,x w (t5 be--m (t5 ?an n--necess>y1 h[ev]1 to dilute ! spectrum col\r ?r[n on ! :ite half ( ! pat* ) a trace ( :ite light4 ,by ref]5ce to our previ\s exp]im5ts we arrive at :at may appe> an unlook$-= result1 t no matt] :at ! col\r may be1 we c ref] x to "o ray ( ! spectrum1 toge!r ) a p]c5tage ( add$ :ite light4 ,x is wor?y ( rem>k1 t ! place 9 ! spectrum :]e ! simple & ! comp\nd col\rs mat*1 v>ies accord+ to ! k9d ( light ) :i* ! pigm5t is illum9at$4 ,?is we c %[ 9 a v simple way4 ,to p]sons :o are totally col\r-bl9d to "o s5sation1 viz4 ! gre5 or ! r$1 ! mat*+ ( a comp\nd col\r ) a simple "o 9 ! spectrum %\ld possess no difficulties4 ,tak+ ! tri*romic !ory ( ?ree s5sations = ! normal-ey$ p]son1 x is evid5t t only ! foll[+ classes ( s5sations are possible 9 ! normal-ey$1 ! gre5 col\r-bl9d & ! r$ col\r-bl9d-- ,normal-eye4 ,gre5 col\r-bl9d4 ,r$ col\r-bl9d4 ,r$ ,r$ -- ,gre5 -- ,gre54 ,violet ,violet ,violet4 ,mixtures ( r$ -- -- & gre5 ,mixtures ( r$ ,mixtures ( r$ -- & violet & violet ,mixtures ( gre5 ,mixtures ( gre5 & violet & violet4 ,mixtures ( r$1 -- gre5 & violet ,if we take z a type ( col\r-bl9dness ! gre5 col\r-bl9d p]son1 we see t e col\r 9 ! spectrum mu/ be ei!r pure r$ or violet1 or else ^! col\rs mix$ ) m or less :ite light1 s9ce ^! two s5sations :5 excit$ 9 c]ta9 proportions give ! s5sation ( :ite4 ,at "o place1 :i* is commonly call$ ! neutral po9t1 ! proportions ( ! two col\rs are su* t ! impression !re giv5 is only :ite2 h5ce x foll[s t1 betwe5 ?is neutral po9t & ea* end ( ! spectrum1 ! rays are mixtures ( violet & :ite1 or r$ & :ite1 ! dilution ( ! col\rs v>y+ f no :ite to all :ite4 ,z e comp\nd col\r mu/ be a mixture ( ! same two col\rs 9 c]ta9 proportions1 x foll[s t ! gre5 col\r-bl9d p]son c mat* e comp\nd col\r ) "s "o ray ( ! spectrum1 & t e col\r mu/ to him be ei!r r$ or violet1 dilut$ ) diff]5t proportions ( :ite light4 ,9 ! same way1 a p]son :o is col\r-bl9d to ! r$ c also mat* any col\r ) a s+le spectrum col\r1 & he w see x z gre5 or violet dilut$ ) m or less :ite light4 ,?is c be readily und]/ood1 b x is n q s pla9 h[ any col\r s5sation felt by ! normal eye c be ref]r$ to ! spectrum4 ,if we take ?ree rays 9 ! spectrum--"o 9 ! r$ betwe5 ,c & ! r$ ,li?ium l9e :i* we w call ,r1 ano!r 9 ! gre5 betwe5 ,f & b :i* we w call ,g1 & a ?ird 9 ! violet ne> ,g b on ! ,h side ( x1 & :i* we may call ,v--!n by v>y+ _! int5sities 7:i* is equival5t to v>y+ ! lum9osities7 & mix+ !m1 we c give ! same impression to ! eye t any comp\nd col\r gives2 & t any int]m$iate simple spectrum col\r gives1 if v slightly dilut$ ) :ite light4 ,) ^! same ?ree col\rs1 b 9 diff]5t proportions1 we c also give ! impression ( :ite light to ! eye4 ,! int]m$iate spectrum col\rs betwe5 ! gre5 & ! violet rays select$ :5 slightly dilut$ are imitat$ by mix+ ^! rays toge!r 9 diff]5t proportions1 & simil>ly ^? ly+ betwe5 ! r$ & ! gre5 by mix+ toge!r ^! rays 9 diff]5t proportions--& !re is "s ray pres5t 9 ! spectrum :i*1 :5 v slightly dilut$ ) :ite light1 has ! same colorific effect on ! eye z ! mixtures ( ! pairs v & b1 & ,g & ,r1 9 any proportions :atev]4 ,let ! lum9osities ( ! rays ,r1 ,g & ,v1 :i* give ! impression ( :ite light1 be a1 b & c units respectively1 & p1 q & r ^? :i* give t ( ! col\r :i* has to be regi/]$ & reproduc$4 ,we !n get ! foll[+ equations--:]e ,w is :ite1 w its lum9osity1 ,z ! col\r1 & z its lum9osity-- a,r b,g c,v w,w--7i472 p,r q,g r,v z,z--7ii472 ,!n evid5tly-- 7a b c7 w2 & 7p q r7 z4 ,let p ,alphaa1 q ,betab1 r ,gammac1 ,!n we may write 7ii47 z-- ,alphaa,r ,betab,g ,gammac,v z,z--7iii474 ,n[ ei!r ,alpha1 ,beta1 or ,gamma mu/ be small] ?an ! o!r two4 ,z an example1 if ,alpha be ! smalle/1 we multiply 7i47 by ,alpha :5 we get-- ,alphaa,r ,alphab,g ,alphac,v ,alphaw,w--7iv47 ,subtract+ 7iv47 f 7iii47 & we get-- 7,beta-,alpha7b,g 7,gamma-,alpha7c,v z,z - ,alphaw,w4 ,n[ x has already be5 /at$ t betwe5 ,v & ,g !re is "s ray :i* gives ! same s5sation ( col\r1 mix$ ) a v small quantity ( :ite light1 z ! above mixture ( ,v & ,g--let u call x ,x & its lum9osity x x be+ evid5tly equal to 7,beta-,alpha7b 7,gamma-,alpha7c1 & ,mu ! lum9osity ( ! small quantity ( :ite add$4 ,we !n get z,z x,x 7,mu ,alpha7 ,w4 ,"h we h ! col\r ,z 9 t]ms ( a s+le ray1 & ( :ite light4 ,?is same holds good :5 9 7ii47 ,gamma is small] ?an ,alpha & ,beta2 b x does n d s %\ld x happ5 t ,beta is ! smalle/1 = !re is no "p ( ! spectrum :i* conta9s simple col\rs giv+ ! same s5sation to ! eye z mixtures ( r$ & blue4 ,!re is1 h[ev]1 a v simple way 9 :i* ! regi/ration ( su* a col\r 7:i* x mu/ be rem>k$ mu/ be ( a purple tone7 c be effect$4 ,x c be fix$ by its complem5t>y4 ,to d ?is we mu/ add to 7ii47 a c]ta9 am\nt ( ,r & ,v1 :i* w make ! :ole :ite4 ,?us1 suppose 9 7iii47 ,alpha to be l>g] ?an ,gamma & ,gamma ?an ,beta1 !n we mu/ add ,phph,phi ,pi mu ,phib,g ,!tac,v & we h ,alphaa,r 7,beta ,phi7b,g 7,gamma ,!ta7c,v n,w ,z ,phib,g ,!tac,v2 b 7,beta ,phi71 & 7,gamma ,!ta7 ea* equal ,alpha ,!re=e n ,alphaw4 ,!re=e ,z ,phib,g ,!tac,v ,alphaw,w4 ,n[ betwe5 ,v & ,g 9 ! spectrum !re is "s s+le col\r :i* gives ! s5sation ( ! mixture ( ,g & ,v4 ,let x be ,x ) lum9osity x1 toge!r ) :ite ^: lum9osity is ,mu1 :i* mu/ equal 7,phib ,!tac74 ,!re=e ,z x,x ,mu,w ,alphaw,w ,z 7,alphaw - ,mu7,w - x,x :i* aga9 is ! col\r express$ 9 t]ms ( :ite light less ! complem5t>y col\r4 ,we h ?us arriv$ at ! v simple d$uction t ! hue & lum9osity ( any col\r1 h[ev] comp\nd$1 may be regi/]$ by a ref]5ce to :ite light & a s+le ray ( ! spectrum4 ,9 practice ?is dom9ant ray is v easy to f9d4 ,suppose we wi% to det]m9e num]ically ! col\r ( a signal-gre5 glass 9 ! electric light1 we %\ld proce$ z foll[s-- ,! col\r pat* app>atus 7describ$ 9 *apt] ,,iv47 is employ$1 & ! col\r$ glass is plac$ betwe5 ! silv]$ mirror :i* reflects ! beam already reflect$ f ! fir/ surface ( ! fir/ prism ( ! spectrum app>atus1 & ! scre51 & a squ>e image ( t surface ( ! prism %[+ ! t9t ( ! glass is =m$ on ! scre5 by means ( ! l5s4 ,t\*+ ?is image is a squ>e pat* ( :ite light =m$ by ! re-comb9ation ( ! spectrum by means ( ano!r l5s4 ,an opaque slide conta9+ an adju/able slit is mov$ across ! spectrum 9 ! mann] describ$ 9 ! *apt] ref]r$ to until ! col\r ( ?is la/ pat* is approximately ! same hue z t ( ! glass4 ,9 ! pa? ( ! reflect$ beam1 b betwe5 ! prism & ! silv]$ mirror1 is ins]t$ a piece ( pla9 glass :i* c be made to reflect "p ( ! beam into ! spectrum pat* ( light1 a squ>e pat* ( ! :ite light be+ =m$ by means ( a ?ird l5s4 ,we ?us h mono*romatic light mix$ ) :ite light4 ,! requisite int5sity ( ! add$ :ite light c be adju/$ by means ( ! rotat+ sectors1 z describ$ 9 ! same *apt]1 :i* op5 & close at w dur+ rotation1 & ! total lum9osity ( ! mix$ beams c be alt]$ by ?is1 toge!r ) ! adju/able slit 9 ! slide4 ,! slit may probably h to be mov$ 9 ! spectrum to make ! hue ( ^! mix$ lights ! same z t ( ! glass1 b by trial ! position ( ! ray ^: col\r :5 dilut$ ) :ite makes ! mat* is readily f\nd4 ,! position ( ! slit 9 ! spectrum is not$1 z also ! ap]ture ( ! sectors4 ,! relative lum9osities ( ! beam reflect$ f ! pla9 glass mirror & ( ! col\r$ ray is next measur$ by plac+ a rod 9 ! pa? ( ! two beams1 & equaliz+ by ! sectors ! lum9osity ( ! %ad[s :i* are illum9at$1 ! "o by ! spectral ray1 & ! o!r by ! :ite light4 ,:5 ! sector ap]ture is not$ ! regi/ration is complete1 z f> z hue is conc]n$1 b ! lum9osity ( ! ray transmitt$ ?r\gh ! glass %\ld be comp>$ ) t ( ! reflect$ beam1 & !n ! lum9osity is also record$4 ,%\ld ! col\r ( a pigm5t be 9 "q1 ! ray reflect$ f ! silv]$ mirror is made to fall on ! pigm5t$ surface & ! same proc$ure adopt$4 ,if a purple glass 7say7 has to be regi/]$1 we proce$ 9 a slightly diff]5t mann]4 ,! pat* ( col\r$ light pass+ ?r\gh ! purple glass is sup]pos$ ov] ! spectrum pat*1 & ! slit 9 ! slide is mov$ till a ray is f\nd :i* w make :ite light :5 sup]pos$ on ! col\r ( ! glass4 ,! lum9osities ( ?is :ite light1 ( ! reflect$ beam1 & ( ! spectral col\r are comp>$ int] se1 & !re are !n suffici5t data ) :i* to make num]ical regi/ration4 ,col\r$ glasses to be us$ at night ) oil or gas1 or pigm5ts to be view$ by ^! lights1 mu/ be regi/]$ 9 ^! lights4 ,z ! spectrum col\rs are always ! same1 x is conv5i5t to use ! electric light spectrum1 & ! only alt]ation 9 ! app>atus is to use two gas-lights to illum9ate two squ>e ap]tures1 9 front ( "o ( :i* ! glass ^: col\r has to be measur$ is plac$4 ,! images ( ^! ap]tures are ?r[n on ! scre51 ! col\r$ image t\*+ ! squ>e image ( ! spectral col\r pat*1 & ! nak$ image ov] ! latt]4 ,! same det]m9ations are gone ?r\gh z ^? j describ$4 ,! foll[+ are ! det]m9ations ( "s glasses-- ---------------------------------------- -------- ,p]c5tage ( ,lum9osity ,wave- ( ,light ,glasses l5g?s (,p]c5tage ,transmitt$ ,measur$4 ,dom9ant ( ,:ite ?r\gh ,ray4 ,light4 ! ,glass4 ---------------------------------------- ------- ,ruby #fbbj #b #aca ,can>y #ehej #bf #hbj ,bottle ,gre5 #eeaj #ca #ajf ,no4 #a ,signal ,gre5 #dibe #cb #fi ,no4 #b ,signal ,gre5 #eajj #fa #aid ,cobalt #dfge #db #cge ---------------------------------------- ------- ,! foll[+ are det]m9ations ( "s col\r$ pigm5ts-- ---------------------------------------- ----------- ,p]c5tage ,p]c5tage( ,lum9osity1 ,wave-l5g?s ( ,:ite ,col\r$ ( ,dom9ant ,:ite ,pap] ,pap]s4 ,ray4 ,light4 be+ #ajj4 ---------------------------------------- ----------- ,v]milion #fajj #be #adh ,em]ald ,gre5 #ebbj #eij #bbg ,fr5* ,ultra- m>9e ,blue #dgbj #faj #dd ,br[n ,pap] #eidj #ejj #bej #ehgj #fgj #aie ,orange #eiae #dj #fbe ,*rome ,yell[ #ehce #bfj #ggg ,blue ,gre5 #ejje #dbe #adh ,eos9 ,dye #fdjj #gbj #ddg 7,sport+ ,times7 ,cobalt #dhbj #eee #ade ---------------------------------------- ----------- ,,*apt] ,,xiv4 ,complem5t>y ,col\rs--,complem5t>y ,pigm5t ,col\rs--,measurem5t ( ,complem5t>y ,col\rs4 ,we are n[ 9 a position to ent] into ! "q ( complem5t>y col\rs1 :i* is "o ( supreme int]e/ to arti/s4 ,a complem5t>y col\r1 9 its /ricte/ s5se1 may be describ$ z ! col\r :i*1 comb9$ ) ! col\r ^: complem5t is requir$1 makes up :ite4 ,9 ?is def9ition we h ?ree *>act]i/ics to take into acc\nt1 viz4 hue & lum9osity1 & dilution ) :ite light4 ,z an example ( :at we mean we ref] to an exp]im5t :i* 0 made & describ$ at page #abe4 ,x 0 said t if ! violet slit 0 plac$ 9 a c]ta9 position 9 ! blue ( ! spectrum1 x 0 possible to move ! gre5 slit into a "p ( ! yell[1 s t ! two col\rs :5 mix$ toge!r w\ld =m :ite4 ,9 t case ! blue is complem5t>y to ! yell[1 & ! yell[ to ! blue1 s long z ! int5sities are ^? :i* make up :ite light4 ,aga91 if x requires ! light com+ ?r\gh ! ?ree slits to make up :ite light1 be x ! :ite ( ! electric light or t ( gaslight1 we c obta9 ! complem5t>y col\r ( ! light issu+ ?r\gh any "o ( !m by cov]+ t slit up4 ,?us suppose ! slits to be 9 ! normal position ! complem5t>y col\r ( ! r$ is a gre5-blue1 =m$ by ! mixture ( ! violet & gre5 rays1 ! complem5t>y col\r ( ! gre5 is a purple1 =m$ by ! mixture ( ! r$ & ! violet light1 :il/ ! complem5t>y col\r ( ! violet is gre5i% yell[1 =m$ by ! mixture ( ! r$ & gre5 rays4 ,x w be evid5t t z ! int5sities ( ! ?ree rays respectively w be diff]5t accord+ z ! :ite light mat*$ is ! electric light or gaslight1 ! complem5t>y col\rs 9 ! =m] w be diff]5t 9 hue & int5sity to ^? 9 ! latt]4 ,fig4 #ch4--;,*romatic ,circle4 ,ano!r c\ple ( /rik+ exp]im5ts :i* ! writ] devis$ to %[ ^! col\rs c be made ) ! col\r pat* app>atus1 & on ! same pr9ciple z t us$ = obta9+ ! int5sity ( ! rays reflect$ f pigm5ts1 & transmitt$ ?r\gh col\r$ transp>5t bodies4 ,in/ead ( ! small slit ) a "r-angl$ prism 9 front to deflect ! beam f ! top spectrum1 :]e two spectra are produc$ 7see ,fig4 #af1 p4 #ie71 a s+le spectrum is us$1 ) a "r-angl$ prism ( su* a size t x deflects half ( x1 :i* is aga9 reflect$ on to ! scre5 by a mirror1 & ?r\gh a l5s to =m a second pat* ( equal size z ! undeflect$ beam4 ,a rod c be s plac$ 9 ! pa? ( ! beams t two col\r$ /ripes are =m$1 toge!r ) a :ite /ripe caus$ by _! ov]lapp+4 ,! two col\r$ /ripes are complem5t>y "o to ! o!r4 ,by mov+ ! prism along ! spectrum v>i\s col\r$ /ripes c be =m$1 9 "s cases "o be+ mu* less lum9\s ?an ! o!r1 & yet !y are complem5t>y4 ,if in/ead ( ! l>ge "r-angl$ prism a small] "o be us$1 ! complem5t>y col\r due to a small "p ( ! spectrum c be %[n 9 ! same mann]4 ,x is cu/om>y to %[ ! complem5t>y col\rs diagrammatically by :at is kn[n z ! *romatic circle4 ,r\ghly x is drawn z 9 ! above figure 7,fig4 #ch74 ,! ?ree col\rs1 r$1 gre5 & blue1 :i* are tak5 = prim>y col\rs1 are plac$ at #abj ap>t 9 a circle1 & l9es drawn f !m ?r\gh ! c5tre1 at :i* :ite is suppos$ to be situat$4 ,:]e ^! l9es cut ! circumf]5ce is plac$ ! complem5t>y col\r4 ,o!r col\rs c be plac$ r\nd ! circle ) _! complem5t>y col\rs opposite1 & s a fairly complete diagram ( ! spectrum c be made4 ,b x mu/ be rememb]$ t ?is is really ( no sci5tific value1 z x conveys no idea ( ! lum9osity ( ! spectrum col\rs1 nor ( ! quantities :i* h to be mix$ toge!r to =m ! complem5t>ies4 ,su* a circle is1 h[ev]1 conv5i5t z a sort ( memoria te*nica1 & c be fill$ up accord+ to ! fancy ( ! obs]v]4 ,! foll[+ are pairs ( mo/ c>efully select$ complem5t>y col\rs ( pigm5ts1 z adopt$ by ,pr(essor ,*ur*4 ,complem5t>ies4 ,pigm5ts4 ,r$ ,madd] r$ or crimson v]milion4 & ,gre5 blue ,viridian1 ! em]ald oxide ( *romium ) a little cobalt4 ,orange ,cadmium yell[1 ( full orange hue4 & ,gre5i% blue ,cobalt gre54 ,orange yell[ ,cadmium yell[1 or deep *rome4 & ,turquoise ,coerulium1 or cobalt blue1 ) a little em]ald gre54 ,yell[ ,lemon yell[1 pale *rome1 or aureol94 & ,blue ,ultram>9e f lapis-lazuli4 ,gre5i% yell[ ,aureol9 ) a little viridian4 & ,violet blue ,fr5* ultram>9e4 ,gre5 yell[ ,lemon yell[1 ) "s em]ald gre54 & ,violet ,fr5* ultram>9e ) madd] c>m9e4 ,yell[i% gre5 ,lemon yell[ ) mu* em]ald gre54 & ,purpli% violet ,madd] c>m9e ) ,fr5* ultram>9e4 ,gre5 ,em]ald gre5 ) lemon yell[4 & ,purple ,madd] c>m9e ) ,fr5* ultram>9e4 ,em]ald gre5 ,em]ald gre5 alone4 & ,r$di% purple ,madd] c>m9e ) a little ,fr5* ultram>9e4 ,z ^! pairs ( pigm5ts are complem5t>y1 x foll[s t if rotat$ toge!r 9 prop] proportions1 !y %\ld make a grey :i* w be indi/+ui%able f a grey =m$ by rotat+ black & :ite sectors toge!r4 7,see *ap4 ,,xv47 ,x w probably happ5 t a good deal m ( "o ( ! pairs ( ! col\rs is requir$ 9 ! disc ?an ( ! o!r1 & suppos+ t ! two are ea* us$ ( ! full brightness :i* ! pigm5ts are capable ( giv+1 x foll[s t 9 a diagram :]e equal areas are fill$ ) ! pigm5ts z complem5t>y1 "s means mu/ be adopt$ to give ! true dep? ( tone to ea*4 ,! mixture ( :ite w height5 ! lum9osity ( ei!r1 or ! admixture ( black w l[] x1 b (t5 alt]s ! hue4 ,"o ( ! mo/ beautiful me?ods ( obs]v+ complem5t>y col\rs is by means ( ! pol>ization ( light1 :i* we ne$ n describe 9 detail4 ,:at is kn[n z ,brcke's s*i/oscope is p]haps "o ( ! mo/ conv5i5t4 ,dove's ,icel& sp> prism is also useful1 :5 two pigm5ts h to be work$ on to pap]1 s z to be complem5t>y4 ,! two squ>es ( pigm5t$ pap] are plac$ side by side1 & two images ( ea* are =m$4 ,"o image ( "o col\r c be caus$ to ov]lap ! second ( ! o!r1 & if ! two :5 sup]pos$ appe> ( a grey !y are complem5t>y "o to ! o!r4 ,if too mu* ( "o col\r appe>s1 x mu/ be ton$ d[n till ! grey is =m$4 ,?is is a v simple piece ( app>atus1 & = exp]im5ts ) pigm5ts w be f\nd to be v h&y4 ,:5 ! "r t9t ( ea* is secur$ 9 ?is mann]1 a fur!r te/ may be made by mak+ ! pigm5t$ surfaces into sectors1 & rotat+ !m toge!r1 :5 if ! d\ble-image prism gives correct results1 ! angul> ap]ture ( ! sectors %\ld be #ahj ea*1 to mat* a grey produc$ by a mixture by rotation ( black & :ite4 ,we h already %[n h[ ! complem5t>ies ( ! spectrum col\rs c be f\nd2 ! "q is c we f9d ! complem5t>ies ( pigm5ts by ! spectrum8 ,!re is "o v self-evid5t way4 ,we c place ! ?ree slits 9 ! spectrum z giv5 9 *apt] ,,ix41 & mat* 9 int5sity ! :ite light ( ! reflect$ beam1 & note ! ap]tures ( ! slits4 ,we mu/ !n 9 ! reflect$ beam place ! pigm5t ^: complem5t>y col\r is requir$1 & mat* its col\r ) ! light f ! ?ree slits1 keep+1 = ! sake ( conv5i5ce1 ! :ite light fall+ on ! pigm5t$ surface ( unalt]$ int5sity1 & aga9 note ! ap]tures4 ,if we d$uct ! la/ measures f ! fir/1 ! diff]5ce ( ap]ture w give ! complem5t>y col\r4 ,?us x 0 f\nd t ) slits 9 a c]ta9 position 9 ! spectrum1 to make :ite light ! foll[+ ap]tures 9 hundr$?s ( a millimetre 7 requir$3 ,r$ #afe 7#a7 ,gre5 #fj ,violet #ajj ,em]ald gre5 0 plac$ 9 ! pat* & 0 mat*$ by ! light f ! ?ree slits1 :5 x 0 f\nd t x requir$ ,r$ #d 7#b7 ,gre5 #ce ,violet #be ,d$uct+ "o f ! o!r we get z ! complem5t>y col\r1 ,r$ #abe 7#c7 ,gre5 #be ,violet #ge ,?is is a complem5t>y col\r1 b l ! gre5 itself x is mix$ ) :ite light2 b we c easily d$uce :at is ! simple/ complem5t>y col\r2 = we h only to d$uct ! possible :ite light f ! second measure4 ,n[ evid5tly ! greate/ am\nt ( :ite light is :5 ! :ole ( ! gre5 is tak5 z =m+ "p ( x1 ) ! prop] proportions ( r$ & violet1 & ^! we c obta9 by tak+ ! proportions ( ! col\rs 9 7#a72 !re=e d$uct-- ,r$ #fi 7#d7 ,gre5 #be ,violet #dae & ?is w\ld leave z ! complem5t>y col\r )\t any admixture ( :ite-- 7#e7 ,r$ #ef ,violet #cce :i* is a purple z w\ld be expect$4 ,n[ to give ! same dilution ( :ite to ! complem5t>y t ! em]ald gre5 has1 we mu/ take away f ! em]ald gre5 all ! :ite mix$ ) x1 & add t quantity to ! complem5t>y4 ,! :ite 9 ! em]ald gre5 c be f\nd by treat+ ! :ole ( ! r$ z go+ to =m ! :ite2 we !n h f 7#a7-- ,r$ #dj 7#f7 ,gre5 #add ,violet #bd ,d$uct+ ^! f 7#b71 we f9d t ! col\r ( em]ald gre51 less ! :ite light1 is #bjf ( gre5 mix$ ) #a ( violet4 ,to f9d ! prop] dilution ( ! complem5t>y col\r we mu/ add ! above proportions ( ! ?ree col\rs1 & z our f9al result we f9d ! complem5t>y col\r1 ( equal impurity1 is a mixture (-- ,r$ #if 7#g7 ,gre5 #add ,violet #ege ,! slits may be set at ^! ap]tures & a col\r pat* ?r[n on ! scre51 & we %all f9d x ( a delicate p9k4 ,! tru? ( ?is c be se5 by us+ a d\ble-image prism to view ! pigm5t$ surface1 illum9at$ by ! same :ite light z t 9 :i* x 0 measur$1 & ! col\r pat* on ! scre5 by its side4 ,! two col\rs may be caus$ to ov]lap1 :5 x w be se5 t :ite is produc$4 ,ano!r example 0 an orange pigm5t1 & ?is we w "w out 9 ! =m ( col\r equation4 ,! same mixture gave :ite1 viz43 #afe ,r #fj ,g #ajj ,v ,w #afe ,r #db ,g ,o ,!re=e ! complem5t>y col\r1 :i* is ,w - ,o #ah ,g #ajj ,v1 or a d>k-blue col\r4 ,9 ?is case !re 0 app>5tly no :ite light reflect$ f ! orange4 ,x 0 slightly glossy1 & z pol>iz$ light 0 us$ = ! reflect$ beam1 x 0 probably some:at qu5*$2 b :at is m probable is t ! gre5 conta9s "s violet z well z r$1 = ! reasons giv5 9 *apt] ,,xi4 ,! reason we h be5 p>ticul> 9 %[+ to :at ext5t complem5t>y col\rs mu/ be dilut$ ) :ite to ! same proportion t ! col\r itself is dilut$1 w be app>5t if consid]$ = a mom5t4 ,a deep br[n is 9 reality orange1 mu* degrad$ 9 tone1 & c be produc$ z a col\r pat* on ! scre5 if a bright orange pigm5t be plac$ 9 ! reflect$ beam ( ! col\r pat*1 & ! light ne>ly %ut (f by ! rotat+ sectors4 ,n[ ! same complem5t>y col\r w be f\nd = bo?1 b if we 7 to use ! bright complem5t>y col\r :i* we obta9$ ) ! orange = ! br[n1 & endeav\r$ to obta9 a :ite ) x by means ( ! d\ble-image prism we %\ld fail1 z ! complem5t>y col\r w\ld pr$om9ate4 ,complem5t>y col\rs c always be =m$ by a mixture ( only two rays1 & al?\gh ! ov]lapp+ images may =m :ite1 yet :5 ! two are plac$ side by side1 x (t5 w be f\nd t ! complem5t>y1 unless dilut$ ) :ite1 is evid5tly too d>k to be satisfactory1 b ! lum9osity may be increas$ by add+ :ite to x1 z any am\nt ( :ite may be add$ to ! mixture ( ! two rays :i* =m ! complem5t>y1 & ( c\rse :ite w /ill be =m$ ) ! orig9al col\r4 ,x is ?us q feasible to give ! complem5t>y ! same lum9osity z ! latt] by add+ :ite light to x4 ,l ! col\r itself1 ! complem5t>y col\r c always be express$ ei!r by a s+le ray ( ! spectrum1 or by :ite light f :i* a s+le ray is d$uct$4 7,see *apt] ,,xiii47 ,,*apt] ,,xv4 ,p]si/5ce ( ,images on ! ,ret9a--,! ,use ( ,col\r$ ,discs4 ,fig4 #ci4--;,disc to cause alt]nate op5+ & clos+ ( two ,slits4 ,by ?is "t we mu/ be ?or\ghly conv9c$ t by ?r[+ "o col\r$ pat* ov] ano!r a comp\nd col\r c be =m$2 our next bus9ess is to demon/rate t ! same effect c be produc$ by successive images ( ^! same col\rs4 ,?us we c %[ t z a mixture ( r$ & blue produces purple1 :5 ! two lights are sup]pos$1 s precisely ! same purple c be produc$ by all[+ ! same two col\rs to /rike ! eye alt]nately1 & 9 v rapid succession4 ,we c make a mat* ( ! beautiful purple ( p]manganate ( pota% z be=e ^u ! scre51 by plac+ "o adju/able slit 9 ! r$ & ! o!r 9 ! violet4 ,if we place 9 front ( ! slits a disc cut out ) equal angul> ap]tures 7,fig4 #ci71 ! slit ,s#a w be cov]$ :5 ! slit ,s#b is op51 & vice v]s1 & ! two w nev] be uncov]$ at ! same "t :5 ! c>d is turn+ r\nd its c5tre4 ,:5 ?is disc is caus$ to rotate rapidly1 we %all h fir/ a pat* =m$ by ! light com+ ?r\gh "o slit1 & !n ano!r =m$ by t com+ ?r\gh ! o!r slit1 ?r[n on ! scre5 on ! same place 9 rapid succession1 & ! effect on ! eye %\ld be precisely ! same z if ! disc 0 n !re1 save 9 ! matt] ( int5sity4 ,apply+ ?is artifice exp]im5tally to ! two slits :i* 7 us$ to give ! col\r ( p]manganate1 ! exp]im5t tells u t su* is ! case4 ,x w\ld be go+ away f ! int5tion ( ?is "w 7 ! physiological aspect ( ?is exp]im5t dwelt ^u2 x ne$ only be /at$ t an impression on ! ret9a la/s an appreciable "t1 ?\gh %ort1 & t ! impression made by ! blue pat* has n _h "t to disappe> be=e !re is an impression made by ! r$ pat*1 & s on4 ,z ! ret9a reta9s ^! two impressions toge!r1 !y produce ! impression ( purple4 ,fig4 #dj4--;,disc pa9t$ ,blue & ,r$4 ,= exp]im5ts 9 col\r ?is duration ( impressions is ( great value1 = we c take advantage ( x to comp\nd ! col\rs ( pigm5ts toge!r 9 a v simple mann]4 ,= in/ance1 we c take a circul> disc pa9t$ 9 sectors ) blue & r$ 7,fig4 #dj71 & produce a purple by caus+ x to rotate r\nd its c5tre4 ,small discs ( two in*es 9 diamet] may be pa9t$ ) diff]5t col\r$ sectors1 & if a p9 be pass$ ?r\gh ! c5tre1 a sm>t movem5t ( a f+] at ! p]iph]y w cause x to rotate suffici5tly quickly to make ! col\rs bl5d4 ,a m conv5i5t plan = exact "w is1 h[ev]1 to h an electro-motor simil> to t :i* moves ! rotat+ movable sectors 7,fig4 #da71 & at ! end ( ! sp9dle to fix a cap ) a screw & nut atta*$4 ,! disc1 p]=at$ at ! c5tre ) a clean-cut hole1 c be slipt ov] ! screw1 & fa/5$ by ! circul> nut4 ,:5 ! armature rotates1 ! disc also rotates at ! same spe$1 & ! col\rs ?us bl5d )\t any ex]tion on ! "p ( ! obs]v]4 ,ord9>y tops c also be us$1 b x is some:at fatigu+ to h to w9d !m up & />t !m afre% = ea* exp]im5t4 ,! motor %[n 9 ! figure rotates suffici5tly rapidly1 ) discs ( eight in*es 9 diamet]1 to bl5d col\rs4 ,x may "h be rem>k$ t ! /rong] ! light 9 :i* su* sectors rotate1 ! quick] ! rotation %\ld be4 ,too sl[ a rotation all[s a sc9tillation :i* is de/ructive ( accuracy ( read+4 ,to bl5d "s col\rs toge!r also requires m rapid rotation ?an ) o!rs4 ,! bright] ! col\r ! m rapid x %\ld be4 ,we le>n f ?is t ! dim9ution ( ! m int5se impressions on ! ret9a is m rapid at fir/ ?an ( ! feebl]4 ,fig4 #da4--;,electro-motor ) ,discs atta*$4 ,fig4 #db4--,me?od ( cutt+ ,disc to all[ an ov]lap ( a second ,disc4 ,v conv5i5t discs = produc+ col\rs by rotation ( sectors may be made by ! foll[+3 v]milion 7,v71 em]ald gre5 7,e71 ,fr5* ultram>9e blue 7,u71 *rome yell[ 7,y71 lamp-black 7,x71 & 7z9c7 :ite 7,w74 ,) ^! ne>ly e col\r c be produc$1 or its value d]iv$4 ,! *rome yell[ disc is some:at sup]flu\s1 b is sometimes useful4 ,! alt]ation 9 ! proportions ( ! col\rs c be readily made by ,cl>k-,maxwell's plan4 ,f ! circumf]5ce to ! c5tre he cut ! discs op51 z at ab 7,fig4 #db74 ,any mod]ate numb] ( discs1 simil>ly cut1 may be slipt ov] "o ano!r1 & only a sector ( ea* is left visible4 ,x %\ld be rem>k$ t ?is necessitates ! rotat+ app>atus be+ view$ ) a direct light1 z 9 ! case ( two or ?ree ov]lapp+ discs x is impossible to keep !m entirely flat1 & %ades are apt to be introduc$4 ,if we wi% to produce a :ite1 or r a grey1 f ?ree col\rs1 we c take ?ree small discs ( ,v1 ,e & ,u1 ( equal diamet]1 & beh9d !m place discs ( black & :ite1 ( l>g] diamet]1 rotat+ ! :ole five on a common c5tre4 ,we %all f9d t by alt]+ ! proportions ( ! ?ree fir/ we c get a grey :i* c be exactly mat*$ by a mixture ( black & :ite1 ,x & ,w4 ,x has already be5 %[n t ev5 lamp-black reflects a c]ta9 am\nt ( :ite light1 s ?is am\nt ( reflect$ :ite light has to be add$ to ! :ite 9 ! outside sectors4 ,9 ! sectors us$ 9 ! foll[+ exp]im5ts x 0 f\nd t ! foll[+ proportions ( ! ?ree col\rs 7 requir$-- ,v #abd ,e #adc ,u #ic ---- #cfj & to make ! same grey x requir$ ,x #bgh ,w #hb ---- #cfj ,n[ ! black reflect$ #cd ( :ite light1 s t really ! proportions ( black & :ite 7 ,x #bfhf ,w #iad ----- #cfjj ,^! mat*es 7 made 9 ! light emitt$ by ! crat] ( ! positive pole ( ! electric light1 & are correct only = ?is light4 ,! greys "h are d>k greys1 & su* greys c be mat*$ exactly by ?r[+ ! :ite light 9 :i* ! comp>isons 7 made on a :ite c>d1 & r$uc+ ! int5sity by means ( ! rotat+ sectors4 ,we c prove :e!r our mat*es are fairly correct f our previ\s measures ( ! lum9osity ( ^! ?ree col\rs1 9 comp>ison ) t ( :ite4 ,! lum9osities ( ,v1 ,e1 & ,u1 z f\nd f ! measures 7pp4 #ic-ie71 are #cf1 #cj1 & #dd1 :ite be+ #ajj2 #abd ( ,v w\ld h a lum9osity ( 7#abdx#cf7_/cfj1 or #abd2 #adc ( ,e w\ld h #aaib2 & #ic ( ,u w\ld h #aad2 :i*1 add$ to ei!r1 give a lum9osity ( #bedf4 ,! lum9osity ( #iad_/cfj ( :ite1 :i* is t ( ! mixture ( black & :ite1 comes to #beci1 s t we may assume our obs]vations h be5 fairly correct4 ,! influ5ce ( ! k9d ( light 9 :i* ! mat* 0 made is well exemplifi$ by tak+ ! mat*$ discs :il/ rotat+ into a room illum9at$ by ! light f ! sky1 :5 x is se5 t ! grey ( ! out] discs is blui%2 or aga91 if ! mat*$ discs be exam9$ 9 gaslight1 ! inn] grey w be f\nd too blue4 ,! mat* ( grey 9 ?is la/ light 0 f\nd to be ,v #aai ,e #adh ,u #ic ---- #cfj :i* mat*$ ) ,x #bdd ,w #aaf 7,9 ?is case ! black & :ite are ! correct$ black & :ite47 ,! importance ( mak+ mat*es 9 a uni=m light is fairly demon/rat$ by ?is exp]im5t1 & we _c be wrong 9 ass]t+ t z skylight & sunlight & cl\dlight 7! la/ be+ (t5 a mixture ( ! two fir/71 are s v>iable no measures made on "o day c be fairly comp>$ ) ^? made on ano!r1 m especially if ! obs]v]s are diff]5t4 ,) an em]ald gre51 a v]milion1 an ultram>9e1 a :ite1 & a black disc any col\r may be reproduc$ 9 ! rotation app>atus1 ! ?ree fir/ ne>ly mat*+ :at we h already /at$ to be ! ?ree prim>y col\rs4 ,x may seem curi\s t bo? black & :ite may h to be mix$ ) ! col\rs1 to produce a pigm5t col\r2 b a little reflection w %[ h[ x is4 ,= in/ance1 suppose we want to "k ! col\r composition ( gamboge 7,y7 9 t]ms ( v]milion 7,v71 em]ald gre5 7,e71 & ultram>9e blue 7,u74 ,we mu/ make a disc pa9t$ ) gamboge1 & also a black & a :ite disc ( ! same diamet]1 b r l>g] ?an ! o!r ?ree discs1 & place !m on ! sp9dle ( ! electro-motor 7,fig4 #dc74 ,we %all soon see on rotat+ !m t no blue is requir$ 9 ! inn] disc1 & t all t rema9s to d is to use ! r$ & ! gre54 ,mix ^! two1 h[ev]1 9 :atev] proportions we may1 ! mixture w nev] atta9 ! same lum9osity1 consequ5tly we mu/ d>k5 ! yell[ ) black4 ,ev5 !n we %all f9d t1 add :at black we may1 ! rotat+ r$ & gre5 sectors w always be a little less saturat$ ) col\r2 :i* means t on rotation !y produce a c]ta9 quantity ( :ite light mix$ ) ! yell[4 ,?is we might expect1 = z em]ald gre51 besides gre5 & r$1 also conta9s a fair proportion ( blue1 & z r$1 gre5 & blue :5 mix$ give :ite1 x foll[s t :5 ,v & ,e are rotat$ toge!r1 a grey or subdu$ :ite light mu/ be mix$ ) ! col\r produc$4 ,turn+ back to ,*apt] ,,xiii4 we also see t z ! em]ald gre5 is expressible by a s+le ray ( ! spectrum1 mix$ ) :ite light ?is result might h be5 =etold4 ,fig4 #dc4--;,arrangem5t to f9d value ( ,gamboge 9 t]ms ( ,em]ald ,gre5 & ,v]milion4 ,?is necessitates add+ "s :ite to ! rotat+ sectors ( ! yell[ & black1 z ! yell[ reflects b little :ite light1 & f9ally we %all get an absolute mat*1 ( :i* ! f9al results are #agb ,v #ahh ,e #ge ,y #de ,w #bdj ,x4 ,?is equation is full ( mean+4 ,x tells u 9 ! fir/ place :at we h already kn[n1 t ,v & ,e are "o or bo? impure col\rs1 & t :5 rotat$ toge!r 9 ! proportions indicat$1 !y produce at lea/ a lum9osity ( :ite equal to #ec_/cfj ( a :ite disc 7z ! black us$ reflect$ j #cd ( :ite light74 ,fur!r1 x tells u t we c obta9 ! lum9osity ( ,y1 :5 we "k ! lum9osities ( ,v & ,e4 ,at page #ahf1 ! lum9osities ( ^! col\rs are giv5 z #cf & #cj respectively1 :ite be+ #ajj4 ,?is makes ! lum9osity ( ! col\rs on ! left h& ( ! equation #agb #aefg1 or #cbhg1 & on ! "r #ge_/cfj ,y #adgf1 & consequ5tly ! lum9osity ( ,y #hfi4 ,9 ! same way we c obta9 any o!r col\r 9 t]ms ( ^! /&>ds4 ,we may "h %[ h[ we c obta9 ! lum9osity ( any col\r by means ( ! ?ree inn] discs1 & ! black & :ite out] discs4 ,we h already %[n t any col\r may be mat*$ by ! comb9ation ( n m ?an two simple col\rs1 aft] d$uct+ :ite f x2 & f ?is we d$uce t any col\r$ pigm5t w =m a grey ) "s two ( ! ?ree col\r$ discs1 ,v1 ,e1 & ,u2 & ?is be+ done we c !n calculate ! lum9osity4 ,= in/ance1 ) an orange-col\r$ pigm5t we %\ld proce$ to make a disc ( ! same diamet] z t ( ! ?ree above2 an inspection w\ld %[ u t 9 ?is col\r r$ pr$om9ates1 & !re=e we c\ld d )\t ! r$ disc4 ,we %\ld !n alt] ! proportions ( ,v1 ,u1 & ,o1 till !y gave a mat* :i* 0 ! same z t ( a grey giv5 by ! rotat+ black & :ite sectors4 ,9 an exp]im5t ) an orange ( ?is k9d1 ! foll[+ results 7 obta9$-- ,e #aae ,u #aej ,w #he ,o #ie ,x #bge ,we c n[ f ^! d$uce ! lum9osity ( ! orange employ$ 9 ?is case4 ,! lum9osities ( ,e & ,u1 z already f\nd1 7 #cj & #dd1 :il/ ! black 7,x7 reflect$ #cd ( :ite light2 we ?us get ! foll[+ equations-- #aae x #cj #aej x #dd #ie ,o 7#he #cd x #bge7 #ajj4 ,?is gives #ie ,o #idce - 7#cdej #ffj74 ,o #ef4 ,t is1 ! lum9osity ( ! orange is #ef t ( :ite2 by direct measurem5t x 0 #eg4 ,9 a simil> way ! lum9osity ( *rome yell[ 7,y7 is f\nd4 ,9 ?is case-- ,e #ce ,u #bjd ,w #aja ,y #aba ,x #bei ,simil> equations 7 =m$ z ! above4 #ce x #cj #bjd x #dd #aba ,y 7#aja #cd x #bei7 #ajj :5ce ,y #ggf4 ,t is1 ! lum9osity ( ! *rome yell[ is #gh2 ! same z 0 obta9$ by direct measurem5t4 ,9 ! same mann] ! lum9osity ( any col\r c be f\nd4 ,?us t ( a purple1 or ( gre51 c be asc]ta9$2 ( ! =m] by us+ ! gre5 disc ) ei!r ! r$ or ! blue disc1 & ! latt] by ! r$ & blue disc4 ,f ?is x is app>5t t we c *eck ! lum9osities d]iv$ f o!r means by ?is plan4 ,a tak+ exp]im5t c be made ) col\r discs to imitate all ! col\rs ( ! spectrum 9 _! prop] ord]1 ?\gh dilut$ m or less by :ite light4 ,?is c be done by rotat+ ,v1 ,e1 & ,u toge!r2 b 9 ord] to get additional lum9osity 9 ! yell[1 we c use *rome yell[ z well4 ,if a disc be made z 9 ! figure 7,fig4 #dd71 x w on rotat+ give a fair imitation ( ! spectrum1 if x be view$ ?r\gh a slit held 9 front ( ! disc4 ,fig4 #dd4--;,disc arrang$ to give approximately all ! ,spectrum ,col\rs4 ,! mixture ( col\rs by means ( rotat+ sectors is "o :i* ! arti/ _c use = arti/ic purposes1 & x might seem t = him any d$uctions made f ?is me?od are useless2 b x is n s4 ,suppose we take black l9es rul$ closely toge!r on pap]1 & exam9e ! surface f su* a di/ance t ! l9es are no long] di/+ui%able x w appe> ( a grey2 & if we take ! am\nt ( black on ! pap] & am\nt ( :ite1 & prep>e two sectors ( black & :ite1 ^: angles are 9 ^! proportions1 & rotate !m alongside ! rul$ surface1 x w be f\nd t ! grey ( "o mat*es ! grey ( ! o!r4 ,if in/ead ( l9es ( black & :ite we h !m ( light yell[ & cobalt blue1 a grey is also produc$ :5 ! surface cov]$ by ! blue is to t cov]$ by ! yell[ 9 correct proportions1 & may be mat*$ by rotat+ sectors conta9+ m]ely black & :ite4 ,n[ "s arti/s employ /ippl+1 fill+ up cross-hat*+ ( "o col\r ) dots ( a totally diff]5t col\r1 or !y place dots side by side4 ,:5 se5 f ! di/ance at :i* ! picture %\ld be view$1 ^! v>i\s col\rs bl5d "o into ano!r1 & =m a t9t :i* is ! same z t :i* w\ld be obta9$ by rotat+ ^! col\rs toge!r 9 ! proportion 9 :i* !y cov] ! gr\nd4 ,arti/s1 h[ev]1 g5]ally mix _! pigm5ts toge!r on ! palette1 & ! result+ mixtures are (t5 totally unlike ^? :i* are obta9$ by rotat+ ! same col\rs toge!r1 a notewor?y example is t ( yell[ & blue4 ,by rotation1 & :5 9 prop] proportion1 ^! two give a :ite1 b :5 mix$ on ! palette a gre5 results4 ,:at causes ?is diff]5ce8 ,exp]im5tal pro( is always ! mo/ satisfactory pro(1 s let u h rec\rse to ! spectrum app>atus to obta9 an answ]4 ,let a spectrum be ?r[n on ! scre51 & 9 x place a /rip ( pap] pa9t$ ) ! yell[1 & !n ano!r ) ! blue4 ,) ! fir/ x w be se5 t ! blue rays are n reflect$1 b only ! gre5 & yell[ & r$1 tak+ ! spectrum z r\ghly made up ( ^! f\r col\rs4 ,) ! latt] ! yell[ is n reflect$1 & b v little r$1 b ! blue & ! gre5 are reflect$ /rongly4 ,n[ we h already said t ! reflection ( col\r f a surface is indicative ( ! col\rs ! p>ticles ( pigm5ts :5 tak5 ?9 en\gh to be transp>5t w\ld transmit2 h5ce we may take x t ! yell[ pigm5t transmits ! r$1 yell[1 & gre51 & ! blue pigm5t sc>cely any?+ b blue & gre54 ,:5 we h a mixture ( ^! f9e p>ticles ( pigm5t on pap]1 "s w und]lie ! o!rs4 ,b let u pay att5tion to :at w\ld happ5 if a yell[ p>ticle 7 at ! top1 & a blue "o b5ea? x4 ,:ite light w\ld imp+e on ! yell[ p>ticle1 b only r$1 yell[1 & gre5 w\ld pass out or be reflect$ f x4 ,?is sift$ light w\ld next fall on ! blue p>ticle &--z we h se5--only blue & gre5 c pass ?r\gh or be reflect$ f x2 b z ! yell[ p>ticle has already depriv$ ! :ite light ( its blue compon5t1 ! gre5 light alone w\ld pass to ! pap]1 & be reflect$ ei!r direct f ! surface ( ! pap]1 or ?r\gh ! p>ticles !mselves to ! eye4 ,if ! blue p>ticle 7 on ! top1 precisely ! same effect w\ld be produc$2 x w\ld only all[ blue & gre5 to pass to ! yell[ p>ticle1 & z ! yell[ is opaque to ! blue1 only gre5 light aga9 w\ld pass4 ,simil>ly if side by side ! same ph5om5a w\ld occur1 s9ce ! light reflect$ f "o on to ! o!r w\ld be depriv$ ( all col\r except ! gre54 ,a v pretty exp]im5tal pro( ( ?is is to place a yell[ solution ( dye 9 front ( ! slit ( ! col\r app>atus1 & hav+ =m$ ! yell[ col\r pat* to place 9 x a piece ( pap] cov]$ ) a blue pigm5t3 ! latt] becomes gre54 ,by plac+ a blue solution 9 front ( ! slit1 & us+ a piece ( yell[ pigm5t$ pap]1 ! same result is obta9$4 ,! arti/ !re=e 9 mix+ 8 pigm5ts calls into play ! law ( absorption1 & f 8 mixtures v naturally assumes t blue & yell[ make gre54 ,he makes a neutral t9t ( blue1 r$1 & yell[1 & z ! r$ cuts (f ! gre51 ?is naturally foll[s f ! above4 ,su* exp]im5ts z ^! l$ him to ! conclusion t r$1 yell[1 & blue are ! ?ree prim>y col\rs1 an assumption :i* _h he us$ simple spectrum col\rs in/ead ( comp\nd col\rs1 su* z pigm5ts1 he w\ld n h v5tur$ to make4 ,,*apt] ,,xvi4 ,contra/ ,col\rs--,measurem5t ( ,contra/ ,col\rs--,fatigue ( ! ,eye--,aft]-,images4 ,fig4 #de4--,me?od ( %[+ ,contra/ ,col\rs4 ,!re is a ph5om5on 9 col\r :i* mu/ be allud$ to1 & :i* possesses m ?an a pass+ int]e/ to ! art _w1 & t is col\r contra/4 ,p]haps "o ( ! be/ me?ods ( %[+ ?is is by our col\r pat* app>atus4 ,if we ?r[ ! reflect$ beam & ! col\r pat* on a squ>e z be=e1 & place a r ?9n] rod 9 front1 s t ! two %ad[s lie on a backgr\nd ( ! comb9$ :ite light & spectral col\rs1 on pass+ a slit ?r\gh ! spectrum1 ! %ad[ :i* is illum9at$ by :ite light w appe> any?+ b :ite4 ,?us if we all[ yell[ spectral light to illum9ate "o %ad[1 ! o!r w appe> decid$ly ( a blue hue2 if a gre5 ray x w be ( a ruddy hue2 if a blue ray ( a yell[ hue2 t is1 all ! contra/ hues w appe> to ! eye to t5d t[>ds a complem5t>y tone to ! spectral light4 ,! k9d ( :ite light illum9at+ ! %ad[ has a m>k$ effect on ! tone1 z might be expect$4 ,! foll[+ table %[s ! contra/ col\r ( ! :ite illum9at$ %ad[ :5 ! :ite light us$ 0 t ( a c&le4 ---------------------------------------- --------------------------- ,contra/ ,contra/ ,spectrum ,col\rs 9 ,spectrum ,col\rs 9 ,col\r4 ,electric light4 ,col\r4 ,gaslight4 ---------------------------------------- --------------------------- ,*]ry r$ ,gre5 gray ,*]ry r$ ,gre5 gray ,sc>let ,blui% gre5 gray ,sc>let ,sap gre5 ,t]ra-cotta ,blue gray ,light r$ ,gre5 gray ,raw si5na ,light blue gray ,olive gre5 ,p9k gray ,olive gre5 ,umb] ,apple gre5 ,mauve black ,em]ald gre5 ,p9ki% lav5d] ,em]ald gre5 ,p9k t]ra-cotta ,grass gre5 ,light p9k ,em]ald gre5 ,p9k t]ra-cotta ,blui% gre5 ,d>k p9k ,blui% gre5 ,p9k] t]ra-cotta ,signal gre5 ,salmon ,peacock blue ,salmon ,cyan9e blue ,yell[ o*re ,prussian blue ,r$di% yell[ ,ultram>9e ,raw si5na ,ultram>9e ,raw si5na ,violet blue ,br[ni% yell[ ,violet blue ,br[ni% ,orange ,blue violet ,gre5 yell[ br[n ,blue violet ,br[ni% yell[ ,violet ,burnt si5na ,violet ,yell[ o*re ---------------------------------------- --------------------------- ,! contra/s "h %[n are n s visible :5 ! two %ad[s ( ! rod occupy ! :ole ( ! :ite squ>e1 b are decid$ly increas$ by ! %ad[s occupy+ only a "p ( ! field1 ! m>g9s be+ illum9at$ ) a mixture ( ! two lights4 ,n only are !re contra/s ) col\r$ light & :ite1 b ! relative position ( "o col\r to ano!r may alt] ! hue ( ea* to ! eye4 ,! foll[+ exp]im5ts indicate :at *ange c be expect$ 9 contra/$ col\rs4 ,! d\ble col\r app>atus 0 us$ z describ$ at page #abb1 & a slit 0 plac$ 9 f\r diff]5t positions 9 ! spectrum1 viz4 9 ! r$1 orange1 gre51 & violet1 to =m pat*es1 & ano!r slit 0 plac$ 9 ! same f\r positions 9 ! o!r spectrum1 & ! contra/s not$4 ---------------------------------------- ----------------------- ,orig9al ,col\rs4 ,*ange due to ,contra/4 ---------------------------------------- --------------------- ,r$ ,orange ,r$ became yell[] ,orange became gre5 grey ,gre5 unalt]$1 b ,gre5 unalt]$1 b bright] bright] ,blue became m ,blue became gre5] orange ,violet became orange ,violet1 no m>k$ *ange ,gre5 ,orange ,gre5 became blu] ,orange became yell[] ,blue became olive ,blue became m violet ,violet became yell[] ,violet became blu] ,orange ,blue ,orange became r$d] ,blue became blu] ,violet became gre5] ,violet became blu] ,violet ,blue ,h>dly alt]$ ,h>dly alt]$ ---------------------------------------- --------------------- ,^! contra/s 7 9 mo/ cases v m>k$1 z w\ld be se5 by caus+ ! same col\rs to fall on a diff]5t "p ( ! scre51 outside t on :i* ! comp>isons 7 made4 ,?is ph5om5on ( contra/ is "o :i* is mo/ valuable = arti/ic purposes1 = x gives a p[] ( increas+ ! value ( ! col\r ( pigm5ts :i* is us$ by ! arti/ almo/ intuitively4 ,?us he c height5 ! tone ( 8 orange pigm5t1 ) :i* he makes a sunset sky1 by plac+ 9 juxtaposition ) x "s bit ( blue col\r$ space4 ,! blue becomes blu]1 & ! orange m orange1 by ?is artifice4 ,all ^! artifices--or r we %\ld say intuitive applications ( sci5ce--are mo/ necess>y :5 ! small range ( lum9osity ( col\rs ) :i* he has to deal is tak5 into acc\nt4 ,= in/ance1 9 a picture ( a sun-light$ sn[ m\nta9 & deep p9e =e/s1 ! utmo/ lum9osity he c give to ! =m] is t ( :ite pap] :5 se5 9 ! %ade1 :i*1 9 comp>ison ) :at he sees1 is really a mixture ( #ij ( black ) ! light f ! sn[1 s t 8 range ( lum9osity is only n9e-t5?s ( t :i* occurs 9 nature4 ,x is 9 adapt+ ?is l[ scale to 8 picture t true g5ius ( ! arti/ is se54 ,x might seem t ^! contra/ col\rs be+ only a physiological effect1 c\ld n be accurately measur$1 b su* is n ! case1 if a little artifice be employ$4 ,if we use ! second col\r pat* app>atus side by side ) ! fir/1 we c v readily & ) v close approximation det]m9e ! contra/ col\rs we see4 ,suppose by ! second app>atus we =m a col\r pat* ( say r$1 & place a ?9 rod 9 ! beam ( ?is ray & ( ! reflect$ beam1 & ab\t six in*es f x =m ano!r pat* ) ! fir/ app>atus1 us+ ! ?ree slits to make col\r mixtures2 by fir/ not+ ! contra/ col\r1 & !n approximat+ 9 ! second pat* to :at ! eye p]ceives1 we c little by little get a fairly exact mat* to ! contra/ col\r1 & c def9itely note x4 ,we n[ give ! results ( ?ree measures made = ! contra/ col\rs :i* pres5t$ !mselves to ! eye :5 !y 7 caus$ by a r$ ray ne> ! li?ium l9e1 ano!r ne> ! ,e l9e 9 ! gre51 & ! ?ird ne> ! ,g l9e 9 ! violet4 ,to make :ite light & ! contra/ col\rs1 ! slits _h to be ( ! foll[+ ap]tures-- ---------------------------------------- - ,col\r4 ,r$4 ,gre54 ,violet4 ---------------------------------------- - ,:ite light #aeg #fe #ih ,contra/ to ,r$ #ace #aah #bbe ,gre5 #aeh #ea #dh ,violet #aei #gb #db ---------------------------------------- - ,?us to =m ! contra/ to r$ took #ace ( r$1 #aah ( gre51 & #bbe ( violet4 ,n[ f ea* ( ^! !re c be d$uct$ ! am\nt ( :ite light1 :i* w leave only two col\rs mix$4 ,calculat+ ?is out we f9d t ! contra/s are-- ---------------------------------------- - ,contra/ ,col\r ,r$4 ,gre54 ,violet4 to ---------------------------------------- - ,r$ -- #ce #afg ,gre5 #aeg #cb -- ,violet #aid #ie -- ---------------------------------------- - ,if ! contra/s 7 exactly complem5t>y col\rs1 ! proportions ( ! two col\rs left %\ld be ! same z ^? ( ! same col\rs z giv51 :i* ) ! orig9al col\r make :ite light4 ,x w be se5 t su* is n ! case4 ,a v simple way ( te/+ ?is is to =m a pat* ( :ite light ) ! ?ree slits 9 ! fir/ app>atus1 & !n to obta9 ! contra/s by ! o!r app>atus1 ) ! same col\rs "o aft] ! o!r t pass ?r\gh ! ?ree slits4 ,if n[ we cov] up ! slit 9 ! fir/ app>atus ?r\gh :i* ! col\r ^: contra/ 9 ! second app>atus is s\ght passes1 we may dilute x ) :ite light z we w1 b 9 no case has ! writ] f\nd t an exact mat* to ! contra/ col\r c be obta9$ 9 ?is way4 ,?us1 suppos+ we want$ to try ! exp]im5t ) ! same r$ light z t :i* comes ?r\gh ! r$ slit1 we %\ld use t same light 9 ! second app>atus1 & =m ! contra/ col\r ) ! :ite beam1 & !n 9 ! fir/ app>atus cov] up ! r$ slit1 leav+ ! violet & gre5 to =m a pat* on ! scre54 ,we %\ld !n dilute ! col\r ( ?is pat* ) :ite light1 & note if x appe>$ ! same z ! contra/ col\r4 ,ano!r ph5om5on :i* pres5ts itself is ! fatigue ( ! col\r-s5sation app>atus ( ! eye1 induc$ by look+ at a bright object4 ,= in/ance1 if we look at a crimson waf] or spot = "s "t1 & !n turn ! eye s t x re/s on a grey surface1 an image ( ! spot w /ill be se51 b z ( a gre5i%-blue col\r4 ,?is is due to ! fact t ! r$-see+ app>atus is fatigu$ & exhau/$1 :il/ ! gre5 & violet-see+ ma*9]y has n be5 l>gely ex]cis$4 ,consequ5tly :5 look+ at grey pap] ! grey ( ! pap] is se5 9 ! ret9a at all p>ts z grey1 except 9 ! small "p ( ! ret9a :i* has got dim9i%$ p[] ( p]ceiv+ a r$ s5sation2 h5ce a sea-gre5 image w be se5 until ! fatigue has pass$ away4 ,?is col\r c be reproduc$ ) v fair accuracy by all[+ only "o eye to be fatigu$1 & !n us+ ! o!r to obta9 a col\r mixture correspond+ to x4 ,x w !n be f\nd t ! col\r is ! same z ! complem5t>y col\r1 mu* dilut$ ) :ite light4 ,to ! same cause may be trac$ positive & negative aft]-images1 z !y are call$4 ,if we look at a /rongly-illum9at$ col\r$ =m1 su* z a *ur* w9d[1 & close ! eyes1 ! w9d[ w /ill be se51 at fir/ ( its orig9al col\r 7a positive aft]-image71 & x w !n fade & be se5 9 its complem5t>y col\rs 7a negative aft]-image74 ,! positive image is due to ! p]si/5ce ( :at we may call n]ve irritation1 :il/ ! negative image is due to ! physiological excitation ( all ! n]ve fibrils1 :i* ord9>ily speak+ give ! s5sation ( a v dull :ite light4 ,! previ\s fatigue ( "o set ( fibrils1 h[ev]1 prev5ts !m be+ excit$ to ! same degree z ! o!rs1 h5ce we get a complem5t>y image4 ,x w\ld be out ( place to pursue ?is subject fur!r1 z we h only dealt ) ! physical measurem5t ( col\r-s5sations1 & ^! are beyond x4 ,,index4 ,absorption by r$1 blue1 & gre5 glasses1 #ec ,absorption ( light 9 ! e>?'s atmosph]e1 #fg ,absorption1 ref]5ce to law (1 #ec ,aft]-gl[1 #gd ,arc light1 #bj ,arti/s & col\rs1 #aie ,balma9's pa9t1 #cc ,black body1 #ah ,bl9dness to gre51 #adb ,bl9dness to r$1 #gi-adb ,bromo-iodide ( silv]1 #acf ,c>bon poles1 #bj ,c>m9e1 light reflect$ f1 #ajg template1 #ajf ,*lorophyll1 gre5 solution (1 #ea ,collimat+ l5s1 focal l5g? (1 #bb ,col\r1 analysis (1 #eb ,col\r-bl9d1 r$ & gre51 #gi1 #hj ,col\r-bl9dness1 #adb-adf1 #aeg1 #aei ,col\r con/ants1 #ae ,col\r equations1 =mation (1 #adg1 #adh ,col\r1 ext9ction (1 by :ite light1 #abf ,col\r mixtures1 #aac ,col\r pat* app>atus1 #da-eb ,col\r s5sation ( ! eye1 #bjb ,col\r$ discs1 use (1 #ahi ,col\r$ glasses1 measurem5t (1 #afb ,col\rs1 complem5t>y ( pigm5ts1 #agj-agb ,col\rs1 complem5t>y ( spectrum1 #afg ,col\rs1 h[ mat*$1 #aef1 #aeg ,complem5t>y col\rs1 measurem5t (1 #agc-agh ,comp\nd col\rs1 def9ition (1 #af ,cont9u\s spectrum1 #ag ,contra/ col\rs1 #aif-bjj ,diffraction grat+s1 #bc spectra1 #bd ,dimness & brightness ( spectrum1 #bi ,discs1 sp9n+1 #ahb ,du/1 p>ticles (1 #fb ,electric light1 contra/ col\rs 91 #aig ,electric light1 crat] ( positive pole (1 #bj ,em]ald gre51 light reflect$ f1 #id ,equations1 col\r1 #adg ,ess5tials ( spectrum1 #bb ,extraction ( col\r by :ite light1 #abf ,extraction ( :ite light by col\r1 #aca ,eye1 s5sitiv5ess (1 #ae ,fatigue ( ! ret9a1 #bjb ,fluoresc5ce1 #ca ,fundam5tal s5sations1 #adj ,gamboge1 mat*+1 #ahi ,glass1 light f %eet (1 #ad ,glass prisms1 #ba1 #bb ,gl[-worm1 #ac ,gre5 col\r-bl9dness1 #adb ,heat+ effect ( radiation1 #ch ,hue1 #ae ,images1 aft]1 #bjb ,images1 p]si/5ce (1 on ret9a1 #agi ,impurity ( simple col\rs1 #abd ,indicator ( sectors1 #dh ,infra-r$ rays1 #cb photography )1 #cd ,ins5sitiv5ess ( ! yell[ spot to gre51 #aah ,int5sities ( limelight1 gaslight1 & blue sky comp>$1 #aaj1 #aba ,int]f]5ce1 #eh1 #ei ,int]f]5ce b&s on soap film1 #fj ,invisible spectrum1 me?ods = %[+ exi/5ce (1 #cb1 #cc ,koenig's curves1 #aea ,koenig's exp]im5ts1 #adj ,law ( ! scatt]+ by f9e p>ticles1 #ff ,light f sun1 imitation (1 #fc ,light1 quality (1 illum9+ object1 #ad ,light scatt]$1 #fb ,limelight1 #ai ,l9es 9 sol> spectrum1 #bf ,lum9osity1 #ac ,lum9osity1 addition ( "o to ano!r1 #he-hg ,lum9osity ( col\r1 #af ,lum9osity ( pigm5ts1 me?ods ( det]m9+1 #ha1 #hb ,lum9osity ( spectrum to normal-ey$ & col\r-bl9d p]sons1 #gf-gh ,lum9osity ( sun at diff]5t altitudes1 #fi-ga ,maxwell's col\r-box1 #aeb1 #aec ,maxwell's discs1 #ahd-ahf ,measurem5t ( am\nt ( light reflect$ by diff]5t pigm5ts1 #hh-ib ,metals1 light reflect$ f1 #ajj ,mock suns1 cause ( *ange ( col\r 91 #fd ,molecul> physics1 #ed ,molecul> sw+s1 #acf1 #acg ,mono*romatic light1 #dg ,negative images1 #bjc ,normal vision1 #gg ,orange1 f9d+ lum9osity (1 #aij ,p]c5tages ( skylight1 sunlight1 & gaslight1 #aaj1 #aaa ,phosphoresc5ce1 #cb1 #ef ,pigm5ts1 absorption by1 #eg1 #eh ,plan ( =m+ spectrum1 #ba ,poli%$ & unev5 surfaces1 #ac ,prim>y col\rs1 def9ition (1 #acc-ace ,prism1 ,icel& sp>1 #if ,prismatic spectrum into wave-l5g?s1 conv]sion (1 #bh ,prisms1 drawback to use (1 #bc ,prussian blue template1 #ajg light reflect$ f1 #ajg ,purity ( col\r1 #af ,rays1 infra-r$1 #cd ,rays1 photography ( d>k1 #cd ,rays1 ultra-violet1 #cd ,regi/]+ t9t ( pigm5ts1 #aaf col\rs1 #aef ,ret9a1 p]si/5ce ( images on1 #agi ,ritt]'s rays1 #cb ,rood's col\r scale1 #bf ,rotat+ sectors1 #df ,scal+ ( spectrum1 #di ,sectors1 rotat+1 #df ,simple col\rs1 h[ obta9$1 #aab1 #aac ,slits plac$ 9 spectrum1 #aac ,soap-bubbles1 #eh1 #ei ,soap-films1 #ei ,spectrum1 absorption (1 #ea1 #eb ,spectrum ( sunlight1 #ah ,sun1 mock1 #fd ,sunset cl\ds1 #fh1 #fi1 #gb1 #gc ,sunset sky1 #gb1 #gc ,!rmopile1 heat+ effects (1 #cf ,!rmopile1 pr9ciple (1 #ce ,ultram>9e1 light reflect$ f1 #ie ,ultra-violet rays1 #ca ,v]milion1 light reflect$ f1 #ic ,vibrations ( rays p] second1 #ee ,violet b&s1 brightness (1 #ba ,visible & invisible p>ts ( spectrum1 #cj ,wat]1 p>ticles (1 #fb ,wave-l5g? ( l9es 9 sol> spectrum1 #bf ,:ite light & contra/ col\rs1 #bjj-bjb ,:ite light1 ext9ction ( by col\r1 #aca ,:ite light1 =mation ( by mixture ( yell[ & blue1 #abe ,:ite light1 h[ made1 #aad1 #aae1 #aai-abc ,:ite light1 impression (1 #ha ,yell[ & blue make :ite1 #abe ,yell[1 *rome1 lum9osity (1 #aia ,yell[ spot1 #aag ,"y-,helmholtz !ory1 #ach ,,! ,,end4 ,ri*>d ,clay ,sons1 ,limit$1 ,london ,bungay4 ,,publications ,,( ,,! ,society = ,promot+ ,*ri/ian ,k4 ,,! ,,romance ,,( ,,sci5ce4 ,a s]ies ( books :i* %[s t sci5ce has = ! masses z great int]e/ z1 & m edification ?an1 ! romances ( ! day4 ,small ,po/ #hvo1 ,clo? bo>ds4 ,coal1 & :at we get f x4 ,exp&$ f ! ,notes ( a ,lecture deliv]$ at ! ,london ,in/itution4 ,by ,pr(essor ,raphael ,meldola1 ,f4,r4,s41 ,f4,i4,c4 ,) sev]al ,illu/rations4 #bs4 #f;d4 ,col\r ,measurem5t & ,mixture4 ,by ,capta9 ,w4 de ,w4 ,abney1 ,l4,b41 ,r4,e41 ,f4,r4,s4 ,) ,num]\s ,illu/rations4 #bs4 #f;d4 ,! ,mak+ ( ,fl[]s4 ,by ! ,rev4 ,pr(essor ,george ,h5sl[1 ,m4,a41 ,f4,l4,s41 ,f4,g4,s4 ,) ,sev]al ,illu/rations4 #bs4 #f;d4 ,! ,bir? & ,gr[? ( ,worlds4 ,a ,lecture by ,pr(essor ,a4 ,h4 ,gre51 ,m4,a41 ,f4,r4,s4 #as4 ,soap-,bubbles1 & ! ,=ces :i* ,m\ld ,!m4 ,a c\rse ( ,lectures by ,c4 ,v4 ,boys1 ,a4,r4,s4,m41 ,f4,r4,s4 ,) num]\s diagrams4 #bs4 #f;d4 ,sp9n+ ,tops4 ,by ,pr(essor ,j4 ,p]ry1 ,m4,e41 ,d4,sc41 ,f4,r4,s4 ,) num]\s diagrams4 #bs4 #f;d4 ,diseases ( ,plants4 ,by ,pr(essor ,m>%all ,w>d4 ,) ,num]\s ,illu/rations4 #bs4 #f;d4 ,! ,/ory ( a ,t9d]-,box4 ,a c\rse ( ,lectures by ,*>les ,meymott ,tidy1 ,m4,b41 ,m4,s41 ,f4,c4,s4 ,) ,num]\s ,illu/rations4 #bs4 ,"t & ,tide4 ,a ,romance ( ! ,moon4 ,by ,sir ,rob]t ,s4 ,ball1 ,,ll4,d41 ,royal ,a/ronom] ( ,irel&4 ,) ,illu/rations4 #bs4 #f;d4 ,,manuals ,,( ,,heal?4 ,fcap4 #hvo1 #abh pp41 limp clo?1 price #as4 ea*4 ,heal? & ,occupation4 ,by ,b4 ,w4 ,ri*>dson1 ,esq41 ,f4,r4,s41 ,m4,d4 ,habitation 9 ,relation to ,heal? 7,!74 ,by ,f4 ,s4 ,b4 ,*aumont1 ,m4,d41 ,f4,r4,s4 ,on ,p]sonal ,c>e ( ,heal?4 ,by ! late ,e4 ,a4 ,p>kes1 ,m4,d41 ,f4,r4,s4 ,wat]1 ,air1 & ,dis9fectant4 ,by ,w4 ,noel ,h>tley1 ,esq41 ,k+'s ,college4 ,,manuals ,,( ,,elem5t>y ,,sci5ce4 ,fcap4 #hvo1 #abh pp41 ) ,illu/rations1 limp clo?1 #as4 ea*4 ,physiology4 ,by ,f4 le ,gros ,cl>ke1 ,f4,r4,s41 ,/4 ,?omas's ,hospital4 ,geology4 ,by ! ,rev4 ,t4 ,g4 ,bonney1 ,m4,a41 ,f4,g4,s41 ,fell[ & late ,tutor ( ,/4 ,john's ,college1 ,cambridge4 ,*emi/ry4 ,by ,alb]t ,j4 ,b]nays4 ,a/ronomy4 ,by ,w4 ,h4 ,m4 ,*ri/ie1 ,m4,a41 ! ,royal ,obs]vatory1 ,gre5wi*4 ,botany4 ,by ,rob]t ,b5tley1 ,pr(essor ( ,botany 9 ,k+'s ,college1 ,london4 ,zoology4 ,by ,alfr$ ,newton1 ,m4,a41 ,f4,r4,s41 ,pr(essor ( ,zoology & ,comp>ative ,anatomy 9 ! ,univ]sity ( ,cambridge4 ,matt] & ,motion4 ,by ! late ,j4 ,cl]k ,maxwell1 ,m4,a41 ,tr9ity ,college1 ,cambridge4 ,spectroscope & its ,"w 7,!74 ,by ! late ,ri*>d ,a4 ,proctor4 ,cry/allography4 ,by ,h5ry ,pal9 ,gurney1 ,m4,a41 ,cl>e ,college1 ,cambridge4 ,electricity4 ,by ! late ,pr(essor ,fleem+ ,j5k94 ,! ,fa!rs = ,engli% ,read]s4 ,a s]ies ( ,monograms on ! ,*ief ,fa!rs ( ! ,*ur*1 ! ,fa!rs select$ be+ c5tres ( influ5ce at important p]iods ( ,*ur* ,hi/ory & 9 important sph]es ( action4 ,fcap4 #hvo1 clo?1 bo>ds1 #bs4 ea*4 ,leo ! ,great4 ,by ! ,rev4 ,*>les ,gore1 ,m4,a4 ,gregory ! ,great4 ,by ! ,rev4 ,j4 ,b>mby1 ,b4,d4 ,sa9t ,ambrose3 8 ,life1 ,times1 & ,tea*+4 ,by ! ,rev4 ,rob9son ,?ornton1 ,d4,d4 ,sa9t ,a?anasius3 8 ,life & ,times4 ,by ! ,rev4 ,r4 ,:el] ,bu%4 7#bs4 #f;d47 ,sa9t ,augu/9e4 ,by ! ,rev4 ,e4 ,l4 ,cutts1 ,b4,a4 ,sa9t ,basil ! ,great4 ,by ! ,rev4 ,ri*>d ,t4 ,smi?1 ,b4,d4 ,sa9t ,b]n>d3 ,abbot ( ,clairvaux1 ,a4,d4 #ajia-aaec4 ,by ! ,rev4 ,s4 ,j4 ,eales1 ,m4,a41 ,d4,c4,l4 7#bs4 #f;d47 ,sa9t ,hil>y ( ,poiti]s1 & ,sa9t ,m>t9 ( ,t\rs4 ,by ! ,rev4 ,j4 ,gibson ,caz5ove1 ,d4,d4 ,sa9t ,j]ome4 ,by ! ,rev4 ,edw>d ,l4 ,cutts1 ,b4,a4 ,sa9t ,john ( ,damascus4 ,by ! ,rev4 ,j4 ,h4 ,lupton1 ,m4,a4 ,sa9t ,patrick3 8 ,life & ,tea*+4 ,by ! ,rev4 ,e4 ,j4 ,newell1 ,m4,a4 7#bs4 #f;d47 ,synesius ( ,cyr5e1 ,philosoph] & ,bi%op4 ,by ,alice ,g>dn]4 ,! ,apo/olic ,fa!rs4 ,by ! ,rev4 ,h4 ,s4 ,holl&4 ,! ,def5d]s ( ! ,fai?2 or1 ,! ,*ri/ian ,apologi/s ( ! ,second & ,?ird ,c5turies4 ,by ! ,rev4 ,f4 ,watson1 ,m4,a4 ,! ,v5]able ,b$e4 ,by ! ,rev4 ,g4 ,f4 ,br[ne4 ,,miscellane\s ,,publications4 s4 d4 ,animal ,creation 7,!74 ,a popul> ,introduction to ,zoology4 ,by ! late ,?omas ,rym] ,jones1 ,f4,r4,s4 ,) #dhh ,woodcuts4 ,po/ #hvo4 ,clo? bo>ds #g #f ,beauty 9 ,common ,?+s4 ,illu/rat$ by #ab ,draw+s f ,nature1 by ,mrs4 ,j4 ,w4 ,:ymp]1 & pr9t$ 9 ,col\rs1 ) descriptions by ! ,au?or ( ,life ,und]gr\nd1 c4 #dto4 ,clo? bo>ds #aj #f ,birds' ,ne/s & ,eggs4 ,) #bb col\r$ plates ( ,eggs4 ,squ>e #afmo4 ,clo? bo>ds #c #j ,briti% ,birds 9 _! ,haunts4 ,by ! late ,rev4 ,c4 ,a4 ,johns1 ,b4,a41 ,f4,l4,s4 ,) #aij engrav+s by ,wolf & ,:ymp]4 ,po/ #hvo4 ,clo? bo>ds #f #j ,ev5+s at ! ,microscope2 or1 ,rese>*es among ! ,m9ut] ,organs & ,=ms ( ,animal ,life4 ,by ,philip ,h4 ,gosse1 ,f4,r4,s4 ,) #aab woodcuts4 ,po/ #hvo4 ,clo? bo>ds #d #j ,f]n ,portfolio 7,!74 ,by ,francis ,g4 ,hea?1 ,au?or ( ,:]e to f9d ,f]ns1 c4 ,) #ae plates1 elaborately drawn life-size1 exquisitely col\r$ f ,nature1 & accompani$ ) descriptive text4 ,clo? bo>ds #h #j ,fi%es1 ,natural ,hi/ory ( ,briti%3 _! ,/ructure1 ,economic ,uses1 & ,capture by ,net & ,rod4 ,by ! late ,frank ,buckl&4 ,) num]\s illu/rations4 ,cr[n #hvo4 ,clo? bo>ds #e #j ,fl[]s ( ! ,field4 ,by ! late ,rev4 ,c4 ,a4 ,johns1 ,b4,a41 ,f4,l4,s4 ,) num]\s woodcuts4 ,po/ #hvo4 ,clo? bo>ds #e #j ,=e/ ,trees 7,!7 ( ,great ,brita94 ,by ! late ,rev4 ,c4 ,a4 ,johns1 ,b4,a41 ,f4,l4,s4 ,) #aej woodcuts4 ,po/ #hvo4 ,clo? bo>ds #e #j ,freaks & ,m>vels ( ,plant ,life2 or1 ,curiosities ( ,vegetation4 ,by ,m4 ,c4 ,cooke1 ,m4,a41 ,,ll4,d4 ,) num]\s illu/rations4 ,po/ #hvo4 ,clo? bo>ds #f #j ,man & 8 ,h&iwork4 ,by ! late ,rev4 ,j4 ,g4 ,wood1 ,au?or ( ,lane & ,field1 c4 ,) ab\t #ejj illu/rations4 ,l>ge ,po/ #hvo4 ,clo? bo>ds #aj #f ,natural ,hi/ory ( ! ,bible 7,!74 ,by ! ,rev4 ,canon ,tri/ram1 ,au?or ( ,! ,l& ( ,israel1 c4 ,) num]\s illu/rations4 ,cr[n #hvo4 ,clo? bo>ds #e #j ,nature & h] ,s]vants2 or1 ,sket*es ( ! ,animal ,k+dom4 ,by ! ,rev4 ,!odore ,wood4 ,) num]\s woodcuts4 ,l>ge ,po/ #hvo4 ,clo? bo>ds #e #j ,ocean 7,!74 ,by ,philip ,h5ry ,gosse1 ,f4,r4,s41 ,au?or ( ,ev5+s at ! ,microscope4 ,) #ea illu/rations & woodcuts4 ,po/ #hvo4 ,clo? bo>ds #c #j ,our ,bird ,allies4 ,by ! ,rev4 ,!odore ,wood4 ,) num]\s illu/rations4 ,fcap4 #hvo4 ,clo? bo>ds #b #f ,our ,insect ,allies4 ,by ! ,rev4 ,!odore ,wood4 ,) num]\s illu/rations4 ,fcap4 #hvo4 ,clo? bo>ds #b #f ,our ,insect ,enemies4 ,by ! ,rev4 ,!odore ,wood4 ,) num]\s illu/rations4 ,fcap4 #hvo4 ,clo? bo>ds #b #f ,our ,isl& ,cont95t4 ,a ,naturali/'s ,holiday 9 ,au/ralia4 ,by ,j4 ,e4 ,taylor1 ,f4,l4,s41 ,f4,g4,s4 ,) ,map4 ,fcap4 #hvo4 ,clo? bo>ds #b #f ,our ,native ,song/]s4 ,by ,anne ,pratt1 ,au?or ( ,wild ,fl[]s4 ,) #gb col\r$ plates4 #afmo4 ,clo? bo>ds #f #j ,selborne 7,! ,natural ,hi/ory (74 ,by ! ,rev4 ,gilb]t ,:ite4 ,) ,frontispiece1 ,map1 & #ej woodcuts4 ,po/ #hvo4 ,clo? bo>ds #b #f ,toil]s 9 ! ,sea4 ,by ,m4 ,c4 ,cooke1 ,m4,a41 ,,ll4,d4 ,po/ #hvo4 ,) num]\s illu/rations4 ,clo? bo>ds #e #j ,wayside ,sket*es4 ,by ,f4 ,edw>d ,hulme1 ,f4,l4,s41 ,f4,s4,a4 ,) num]\s illu/rations4 ,cr[n #hvo4 ,clo? bo>ds #e #j ,:]e to f9d ,f]ns4 ,by ,francis ,g4 ,hea?1 ,au?or ( ,! ,f]n ,portfolio1 c4 ,) num]\s illu/rations4 ,fcap4 #hvo4 ,clo? bo>ds #a #f ,wild ,fl[]s4 ,by ,anne ,pratt1 ,au?or ( ,our ,native ,song/]s1 c4 ,) #aib col\r$ plates4 ,9 two volumes4 #afmo4 ,clo? bo>ds #ab #j ,,london3 ,nor?umb]l& ,av5ue1 ,*>+ ,cross1 ,w4,c42 #dc1 ,que5 ,victoria ,/reet1 ,e4,c4 ,,brighton3 #ace1 ,nor? ,/reet4 ,transcrib]s ,note3 ,page #afb ,! foll[+ equation3 ,!re=e ,z x,x ,mu,w ,alphaw,w ,z 7,alphaw - ,mu7,w - x,x ,is pr9t$ z ,!re=e ,z x#a,x ,mu,w ,alphaw,w ,z 7,alphaw - ,mu7,w - x,x 9 ! orig9al4