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o p T
",111 be reBe(lcd at the furface nc. The rays, which·pafs
throu~h ,he bafe, f~nn '0 oblong coloured p¡dure ~IK,
whcre MH i. a mere refraogible rayo aod MK • lefs ;'e·
fraogible one. If ,he few raj's of lbe ; which are
i from M in the dir~étion ~lNJ are made to pais
throunh aoo,her prifm XYV. they wiJl likewife form ao
o~long eoloured pidure PI, whcre p i. ,h. mo(\ refrao–
¡;ible and I ,he leall refrangible rayo This Pldure wiJl
be a very faint one, bec3ufe [bere are but few' rays re·
Jle{led from M .
No," if the prifm ACB rs turned OowlY ' round upoo
in axis io ,he direllion ACB, ,he obJiquilY of the rayo
EM 'o the bafe Be wiJl kcep inereafing, tiJl at lall thi,
obliquity may becom~ fo great, tbat no rayo will p.f.
out at M, bet all of them will be reBeded. Wheo thi.
total reBellion is made, the oblong pillure PI, v'hieh was
f';nt before, wiJl boeome mlleh brighter, beeaufe then
not ooly a few rays, but aJl the beam, wiJl be reBelled
thi,htr. Thia total «Bection will no' be. made aJl at
once; bot al tbe prifm is turoed llowly rOllOd upon its
lxi., the moa refrangible rays MH will be 6rn refleeml,
for the viol.. eolour will difappear in the oblong pidure
flK, whila aJl the o,her eolour. cootinue as bright as
they were befar.; and WAen this colour difappearo at
HK, the eolour at p wiJl b<come brigh', "nd aH
tbe other colours at p' wiJJ conlinue as fainl as tbey were
before. Wheo ,he prifm i. ,uroed & little farther upon
ira ,xís, lh!! indigo colour J which confins of nys lhat bave
Ihe next greatell degre< of refrangibili,y. will be reRe.e.
ted, fa that thi. eolour will difappear at HK .od wllI
beeome bright at pI. The fame thing will happen '0 .11
tbe tily!t in their order ; as the priem is turoed round,
<aeh differen. fort of r ays will be reBected foooer as Ihe
ra)'s have a greater degree of refrangibili,y, or la.ler a•
•hey have a lef..tegree . The red rays at K, whieh are the
leaa refrangible of all, "ill b, reBecled laa of all. From
hence therc::fore it appears, that the rays of the fun are
differenily reflekible. aod ,h>! thofe whieh are moa re·
frangible ate likewife inDa reflexible .
JI.",ogen.ouI lighl ;1 rifroOed regulorly 'Wilhoul any di.
lola/jon or [caJJerh-g of Ibe ra)/.
W HE H the tay. of .ny one particular eolour lo Ihe ob·
long pictore of the fUD, as the greea uys, ror ¡atlaDce,
.re feparated from ooe another; if fome of th'efe green
rays which are homogeneal, 01 are all equaJJy refraogible.
are tranfmitted ,hrough a very fmal! round hole in a CliíF
".ncbond, and ate refncted by a prif... on Ihe other fide
df the hole, the ?ieture formed by lhefe green rays afler
tefraction upon a white paper "cid beyond ,he prifm will
not be oblong, but circular, a. the hale i. tb.rougb which
Ihoy pall'ed. Therefore ,hi. homogeneouo light is '!lot
dilated, nor are the rayo of it fea"ered by thi. refraction .
The <o»j'ufod 0IP,oronu oj' ohjeElJ, ""hm theJ are jnn
~Ihroughrifra(/ing hodi", iJ vwing lo Ihe difftre/11 re–
j'rong;6i!;IJ oj' l;g~l.
Jy Bie., Or the lelt.n of a fmall prin<, or any Other
minute objee.., are pl.«d in heterogeneallight, fueh as a
direct beam of the fun'., which has never been fe""raled
by any refraction mIO ila hornogencous parto; ,hefe ob·
e S. 'P9
j.: cts being viewed ,hrough a glafs. p •¡fOl will be fe,n <on–
¡ufedly. lh,ir edg.. will appear fo m,ny that lhe fmdiler
p"ts of minute animals canhoreafily lie dillingu;nled from'
on! anothcr, and the Jetters of the rm~1l priot canDOt be
read. J~ut if the fam.e objeets are plaeed ¡o a boam of
homog.ncous light, whieh is fepara,ed from all other raya
of. differen, refraogibili,y in the macner al ready deferi.
bed. they will arpear as di(tinct through a p,ifm as il
Ihey were viewed Wilh the n. ked eye. Thererore w~
may conclude, thar this confui'ioD 's owitg to the diff~rent
refrangibility of thofe rays which come (rom tbe objee" ;
finee objeeto never appear confufed when they are feea
,hroltgh refraeting bodies, unlof. they are enlightened
with feveral fons of rays whieh have dilfereot degreea
of refraogibility.
II i, prohable Ihal any jingle ray oj' Ihe Itajl rifrongi.
hle forl containl o greale.r fuan/¡,y' of rnoller than an,J
jingl. ro)' oj' lh. moJI rifrangihlejorl.
W. have already feeD, that at ,he fame angles of iD·
cidence violet rays will be more refracted or more turoed
out of the way than fed ray', And we have likewife Ceen..
lhat raya are rdracted when they pafs out oí ooe mediuru
into aDother. by being either more or leCs attractcd in 000
medium tban they are in the oiher. Now finec, wheD
all other circum(tanees are equal, when red rays and ,iol<l
rayo r.1I al equal obliquities, and are 'o paf. out of Elaf.
into air, fo lbal the mediums, and confequently the at·
tractive force or caufe of refractton, is giveD; if the Carne
caufe can turo {he violet u'Y' mbre OUt of 'rhe way. or
refract them more, thao it does the red rays, Ihefe ray,
mull hate difFerent moments; the refrangible rays,
or thofe which are mon eafily turned out of ,he w'y, h...
,he leaa moment; and the leaa refrangible rayo, or thofe
which are moO difficult to turn OUt of tbe way, ha\"e'the
greatea But if all fons o( rayo ha.e lhe
vc:locity, thdr refpecrive qU3Qtities of matttor will be .,
tbeir n10mento; and eonfequently any fingle ra y of tbe
moa refrangible fort contain. a lefs quanüly of mauet
than any fingle ray of the lean refraogible fort .
lt may be upon this account that a red colour, or a
pale purple, is lefs pleafant to the eye than a bluc, greeo,
ur a yello,", The red rayo fhike the eye w¡lh fo grea!
a force a. to be offenfive to it ; and Ibe fmall (orce of
,he pale purple ones will produce too faim a fcofation to
be agreeable. The intermediate colours are tberefore
more pleafaDt to the eye, as the force of lhe nys is neithc:r
too grea. 10 be off"DGve, nor 'DO fmaJl to prodoce a quid:
Qod Ji,ely feofatlon.
The coloU" if homogmeou, lighl are jo invariahlt, Iha'
neilhtr (In; rifratlion n~r an) rtfi,{]j()1J can alter
Ihem .
Ir a bum of homogeneous light pall'<. through a round
hole in a paa eboard, and ,hen i. refraaed by • prifm 00
the other fideoof the hole, thi. refradioa will no
aheration iD lhe colour of the rays; ir lhey were red. oi
Wal their colour, before they enlered ,he prifm,
their colour will mil be tbe fame, wh, n they ha,e pall'<d
through it, and fall upon a white p'per held b"yood the
prifm. This prOfts the fira part of ,he prorofi,ioo, th...
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