1000000031

432

conraa. an:l fprca.1

thefntclvcs

in circular'rings round

in ,he

f.me

order

in ,he foap_bubble.

HC (No

40)

fcétion of ,he pl"ne glafs, . nd D AE

rdlion of ,he

conYcx one;

when they

are

prefr.!d clore'

wgether,

the thin

pi,HC

of ware r

lhat 11115 [he

ioterval

bl!lWeCn them \Vi II

hay

blaek fpo, at

" od ,his fpot will be enoolnp"(fed

with

rin~s

co lours, in (he fame order {hat

th.:y.

fiana

in ,hat fi g'ue upon ,he line BC, on eaeh fide of A . If ,he

colours are reckoned in (he order

which

they

Cland on

the pl, ' e of water after ,he blaek fpot "pp.ars a' A, anJ

we re(.kon thcm from (he

(pot

A tow.trds (he edges of the

plate at

and C; then we mull e"1I blue ,he fid l eolour.

Eut

\Ve::

re~kon

them in the order in which they

arore:

A, and fpread

themrel ves;

then

we muO:

begin

from

[he edces of the

ate.

and go

0 0

towards /\, and in

chis

n:ckooing

\Ve muU

c.tll

red

rhe lidi

colour.

lhere is no water bet\Vccn lhe

two gli([es, then the

interval will

bt:

illled wil h air, and this thin pl cHe of air

will

h"ve lhe Came colours that the

ate

of w ater had ;

Wilh (his difl'erence onl y, chal each of

Ihe

coloured rings

is larger io [he

pl.t.te

of air

~han

in lhe

pl.t.te

of wate r.

W hen

gl~rs

is blown very thin al a laOlp-fl1rnacc, thin

plates of it lhus fo rmed will exhibit eolours ; and fo like–

wj,fe will thin plale. of

Mufeovy-gl.fs

. M elals, when lhey

are heated , feod out to their furfilces rcoria or vitrified

.puts. which cover the metals io form of a thin llcin; aod

tLeCe fcoria or thin plates caufe colours upon (he Cu rface

of l he metal,

.fueh

as are nlitde toa ppear on polifhcd (l eel

by heating it, or on bell_Olelal by melting it firll- "od lhen

pouring; it

the ground to cool in the ai ro

Wh~n

Ihe

thin

pl:lle

ÍJ

denftr Ihan the

lIudiu1II

Ihal ¡lI r–

r (,undI jI ,

Ihe colours are ",(¡re

",ivid

Iha1J

Ih~J

Ilre

~hen

t he }/ale

rarer thtJ1J Ihat

lIudium .

A lhin bubble is a piate of water eneompa(fed with air ;

where lhe fubnance of lhe plate, which is water, is den..

fer than the air, which

the medium that furrollnds ir.

On the eontrary. the pIate of air belween the two gla[.

1..

B AC , D AE, (No.

40.)

is eneompa(fed with g!ar. ;

a nd here the fubClaoee of ,he plate ·is rarer ,han tha¡ of

t he circumambient medium; and the colours on the

bllbble of water

are

more vivid than thofe

the tllin

plate of air.

Whi n Ihin IranjpaNnl plalu

rejldi

"1<

forl o) rap, Ih"

IranJmil Ih, N/l .

the plate of air betwe<n lhe ' wo gla(fes BAC, D AE,

(No.

40.)

is viewed by , efleékd light, the eolours of it

are thofe exprcffed on

the

upper part of lhe figu re from

but

¡ook through it, that is,

we view

tritnC!l,itled J;ght, or ir the tranfnlitted lighl fall s upon

white

paper,

lhe colours that

ft:e

throll ~h

lhe pLH\!,

lhat

f¡sll

0 0

l he papero are thofe ex.prdl'ed on l he Jow–

cr pan of

lhe

ligure. Now, any

the tranfOliucd colours

Olre

whar

would Hife from

mixture of all lhe rC01í1.ining

rd}

aftc::r thure of lhe refleéled colour are reparatcd Crolll

,h'! flln's ht·lcrogene;;t llíght. Thus, for innance, tha fCl\\rth

«ftd lcu eolour

C'om

,he bl2ek fpot

inclulivcly is yellnw,

,iu!

tranfu,;u ctl coluur i!:J viole\. '1"he ycllow rtlys. ano fome

uf \he or.;ngc and (!ret'o, tire refleélcd ht:re, ro Ihat th!!

J.lixt ure of lhe rt.f1;;étcd

li ~ht

\\ill he yd l()'.V. l "hc miy.–

lure uf

the

tranrtf,ine, ..d

I:C1.l

th~

rc[orc \"Idl ltc \'ivlct, (,I r

rather fu'oh a purple as is not exaélly like any

the pri–

m:t ry colours; for we

ohferve~ .

thac from red

r.J.ys

, VIO–

Ic:t.

anJ blue, new pllrp't's

may

prodllc~d.

Th is is

the:

cafe

fome

natural bodies,

a:i

well

as in

thefe tranfparent artificial pbtes ; for if le:tf-gold, whien

is made thin enollgh tO tranfmít ligh t, is held agaion the:

flrong light of lhe fun's rays, th\! gold, wi1Ích is ydlo\v

when feen by ,he r. lleéled lighl, will be blue wheo tbu,

feen by tr"nfmiltee! ligh t.

The feven,h r. fi<éled eolour inclufively from the blaelc

fpat is

blue,

the te \'enth tranfmiu ed colour is yellow.

\Vhen ihe rays which make the blue calour are takcn

oul of che fun's heterogeneous Iight. the remaining ray5

wdl be ycllow .'

l~hus

li.t.ppens Irkewife

fome natural

bodics ; for ao -i nfufion of lignum nephriti..cum, wh:ch is

bl 'e when feen by refleéted lignl, is yellolV IVheo feeo by

trt\nrOliued

light.

The blaek rpot A reAeéls fe"ree .ny light: and'as ray'

of ..

colours are tranfmitted thete, lhe tranC1nitted co ..

lour is whitt> ; (he thi rd refle'élcd colour fro·m the black

(pot inclufively

while . Thcrefore, fince all the ray'

are rd h:fted there, no colo'.H ought to be feen lbere,

when

W t!

look through tbe plate ; and accordiogly that

pUl of ,he plate is

bl.ek

H t::nee we fee the reafoo why. if there

two

Jiquo.rs

of fu ll eolours in

:,vo

diff~rent

glars ve(fd" fuppofe ree!

and ,blue; though each is tranfparent when we look thro'

it fepa rately,

we fhould not be able

fee through

both of thom ,ogether if one was held bebind the

I,hcr. For ir

lhe

blue liquor, for in(h nce, is beld towards

the ligllt, and the red cowards lhe eye ; fince ooly blue

rays pafs lhrough ,he firH liql1or, and come to the fe·

eond ; and (inee lhe fecond lil1uor

\ViII

traofm it no blue

rays,

bUl

only red o nes; it follows, lhat no rays at aU

can

come tO the eye.

Indeed fome tranfparen' bodies

app.ar

of the fame eo–

lour, w hether \Ve fee ehem by reRe8:ed or rraoCmitted

ligh'. Of lhi. fort i. morl painted glaf.. But \Vhen

lhis is the cafe. che coloured rays are refleéted from the

feeond furf. ee ofthe body. Thus, if a piece ofpainted

glafs is yellow eilher wheo feen by refteéled ligh, or when

feen by traofmitted light, all ,he .rays but the yerIow

ooes are rupprefled as they pafs through ,he glafs: of

the yello\V rays, morl are tranfmilted a' , he feeond fu ro

f"ce; the feIV \Vhieh "re refteéled from thenee \ViII be fu f–

Geien, 'o tinge

all

the light yellow, whieh is refieéled

from the

firll

fUI

facé. T his will be evident from m.tking

,he body thiek, and pilehing it on lhe baekfide: for by

this mCilns lhe reneéted colour will be Jon; whereas,

had b"en reOdled from lhe lórfl fudace, the piteh at ,he

fecond

fUT

face could oot have ahered

it.

T he

",. re

dmft

tb, Jub/lance il oul O) which a tbin

pl./le

¡,

1JJüd" Ih,lc¡S

j¡

the

Ihic~ne¡S

o( Ih, plale

'Wh.er~

i l

rejlcllJ

all) clrt ain

c~'our.

T h::

colo\1rs are

[he

r.~me'

whctller thcre is ai ror water

b<tween ,he t \Vo gl. fli:s R AC.

DAE,

(No.

40)

only

eh!.! c!JJourl'd ei l'cles are fm allcr in

the

plate ofwíl.ter than

in che pille of

.,ir.

Tltus lhe ydlo.v, (orin(hnce.

which

lhe fouflh eoloure:u circle (rol11 the black rpot.

iS ,il

J...fs

(';r..:h', or i:l nC4'lrl'r to the hlack fp:lc, whl'n there is a

lJllt.::

uf water

b !t\','~;:n t h~ !;1 .dT~s ,

tha:) W!lcn tlH're is a

p!.'I<