1000000031

the intcrnices, or of hOlh,

wiJl

prevenl lhe mixture:

(rom boing

op.ke

Sinee ,hordore all uodies will be Iranfparen" i( ei, hcr

(h~ir

pan s: CJr lheir intcrllices are tOO

{m~ lJ ,

fc.l lows

that lhe pans, and Jikcwlfe lhe pOTes, o(

fueh

bodics as

are nOI lrilnfparcnt hUI

op.,ke and coloured,

muft nOl

lcr,

lh...

o of a ccuain and Jt:tcrminatc bigoefs .

T h, "/Or/N oí",rtura/ bodio d'pmd u/,on lb,

ji=,

oí

Ihlir

par/ida.

DI F FE k ENT

paru of thin ....

aDfparent

pl.ue

according

to Ihe differenl lhickncfs of (hem. are of different

colou r5 .

Now if any

par'

of fueh a ,hin pl..e of Clars, for innance,

""here

appears of one uniform colour

fhould

be Cplit

ioto threads, or broken

¡Oto

fmall particles, all

mere

par–

liele. would O1ah a heap of powder of ,he (.me eolour.

And ,he f01. 11 partielc. of natu ,,1 bodies, finee ,h ey are

Iranfparen" like fo

m.oy

fragments of. , hin

pl.te

, muel

exhibit colcurs in ,he Came manner.

T h, parll oí bodi", on . uhich Ih(Ír c%r/rl d,pmd,

are fIIuch

áenft r Ihan Ihe llIeáiulII rwhich

fillJ

Ihdrp~reJ.

where ,he Iranfparen' plate or partide eonfill. of

• rarer CubO"nce than the medium lhat encompaífes it,

,he eolou" are lef. vivid lhan ,hofe of n.,ur. 1 bodies

commonly arC.

For this reafon it is that the colours of

lilks or cloths, whrn they are wetted with oil or water,

becomc more

fain!;

becaure theCe Jiquors are mOre n('lr·

Iy of ,he

f.me

denfi,y Wil h ,he par,icles, lhan ,he medium

is whieh fi lls ,he in,erniees when lhey are dry. Bdides,

, he eolours upon a tronfparen' plate change very fenfibly,

uolef, lhe piate confin. of a fubll.nee mueh denfe r ,han

,he medium ,hal eneompalfes i, ; bu, moll na,ural bodie.

Ire of lhe fame colour in Wh3teVer pofition of the eyc

they are ,iewed . Therefore their tranfpareot particles,

upon which ,heir eoloun dependo are mueh denfer ,han

•he medium whieh eneompaifes , hofe partides or fills ,he

interOiees between

them.

Nor is ,he eafe o,herwife eveo in ,hofe bodies whieh

do change eolour upon being viewed obliquely, fueh as

chaoge.ble filk., or ,he fea,hers of • pe.eock's ,. il or of

pigeon's neek. For ,bis ehaoge of eoloor, upon ,he

fi luation of

the

eye beiog cl12oged, is no reafon (or con–

cludinc that lhe medium which fi l!s the interllices or

pores is more nearly of ,he fame denfi, y ",i,h ,he par,

.iele., upon which lhe eolours depend, in ,hefe bodies

, han in o,hen ;' fin re lhe ehange of colour is plainly ow–

inC 'o our feeing a diff<renl part of ,he body in different

pofi,ions of ,he eye. T hus, in ehangeable filb , lhe warp

is o( one colour, and the \Voo( of anotner ; and

one po·

{jlion o( the eye more of the w.;¡,rp is fceo, anO in anolher

pora,ion of i, more of ,he woof is feen . In like m.nncr,

if a pigeon's ncek appears blue in one pofi,ion of ,he eye,

and crimfoD in anothcr. it is becaufc: in there difLreot

pofilion, we f.. d./feren, pans of ,he fa me fea,:,.rs.

lI'f

Car.n~t

Ji'cm

Ih~

CI)/Ollr

01"

hfJd"

filaN

"'J}

cOllj, flure

116 ul Ih,

ji=,

oí Ih, parllela upon 'Which

I1I

<%url

tI,!,,,,d.

Su, roSE, (rom lbe 'pp.arance of ,he colour in any

yellnw body. lha! we had de,crmined its yellow 'o

lhe fame fort w\th .ha, whieb i, nex' 'o

,h~

block (fo:

V OL .

I!I.

N° .S7.

435

plale of . ir, or W.ler, or gl. fs. T he ,hieknefs of a

ate,

where

appean of this colcur, is ddfc:rent accord–

ing

lhe

difrucnt denfity

of the

futlllaoce out of

which

that

pi are is

mtlde;

Ihe

lhickners

of a

pbue

air wh('re

it appears of this coluu r.

greater than

lhat

plate

of water

were

appears

lhe {ame

colour,

and

much

grea,er nill ,han , ha, of. plate of clafs. Suppofe ,hfre–

fore f;anhcr, that

\Ve wue

ablt

determine

exatlly wh:n

is Ihe

thickners

of a

p);:tte

ai r

or water

glafs,

where

caeh of

,he....

is ,inged wi,h ,he fame yellow eolour ,ha,

aoy nat'J r:t1 boriy exhil>its; yet wc cannot determine

whcther the diameter of

lhe

panicles,

upon

which

this

body's eolou r depends, i. equal 'o , he ,hieknefs of ,he

pla,e of .i r, or of water, or of glaf. , unlefs we eou ld

firll determine \Vhe,her ,he denfi,y of ,hofe partides is e–

quaJ

lhe

dcnfity of air, or

l O

that of water, or to

that

of gl. fs : 'finee ,he particles mun be J.rger, if ,heir deo·

fi,y is equal 'o ,he denfi,y of . ir, ,h. n if i, is e.q<lal 'o

lhe

denlityofwater; and

l..

rger,

¡fil

is equal

tO lhatofwa–

,er ,han if i, is equal ' o ,ha! of

gl.fs.

And indeed

\Ve

h.ve

good reafoillO eonelude, ,ha, lbe deDfi,y of ,he par.., upon

whích Ihe colours of natural bodíes deprnd , is greater even

,han ,ha, of Clafs; .nd eonfequently ,ha, ,he di.meler of

, hofe par" is O1"eh lefs,han ,he ,hieknefs

0( .

pla,eof glafs ,

where i, appears of ,he fa me

c~lour

Wilb ,he bod y'. jo'or,

upon being viewed obliquely, ,hin piates of "gl. fs 'ehange

colour, whertas natu ral bodics do not : and

lhe

colour

of na,ural bodies is mode more uneh.ngeable ,han ,ha, of

,hin plat.s of glafs, by ,heir particles beiac more denfc

,h.n glaf •.

Ih,

RA.l<» OW.

When Ihe ray¡

oí

Ih, íun jall

~pon

a drop oí rain and

enler inlo jI, fome o/

Ih~Jh,

o/Ier OTU re!e{}jon aná

/ tUJa

rifr"fiiolll, lIIay come lo lhe el e

[pet1al()r

rwh~

hal hit

bac~ Ivwartll l~,

íunandhitíace lo'Ward 1h, drop•

I r XY (

43.)

is a d rop of rain, .r:d ,he fun fhi"es

upon i, io any Jin..

If, Id, ItI ,

&e. moll of , he rays will

en'er iOlO ,be drop: fome fe w of ,hem only will be re–

fl eéled (rom ,he 6rll furfaee ; lhof. r.y', whieh are re–

flrlled from thence, do not come unoer ou r prcCent con–

fider. ,ion, becaufe ,hey are never refraéled a, all . The

gre."n part of ,he

r.ys

,hen en'er ,he drop, >.nd ,hofe

paffing on 'o lhe feeond

furf.ee

wil! moC! of ,hom be

tranfmitted ,h rou¡;h ,he drop; bl1l nei,her do ,llofe r.y.

whieh are ,hes tranfmitted fall under Our preCen, eon–

(jderalion, fince {bey are nol refle(ted .

For tfle rays ,

which are deferibed in , he propoG,ion, are fueh as are

l\Vice

refraéled and once reflcéted. However, ;u lhe fe–

cond

fUIf.ce

, or hioder pan of ,he drop,

f'g

r.'me few

roys wil! be renea ed, whilCl ,he rays are tranfinitted: ,hofe

rays procced in fome fuch lines as

lI",l1f;

and coming as-t

of ,he drop in ,he lines

rll,

91,

m.y fall upon

eye of

a fp: éla,or, who is plaeed aoy where in lhofe Ilnes. wi,h

bis faee 'o vards ,he d rop, .nd confequently wi,h his back

,owards ,he fun, \Vhieh is fu ppofed ' o fhinc upon ,he drop

:he

lioes

Jf.ld

Ja,

&c. T heCe rays are t\Vice re(ral'ted,

and once refloéled: , hey are refraéled ":'!:<n ,hey pafs

ou, of ,he air io,o ,be drop; ,hey are "neéled fmm , he

recond f.. rface, aod are r<fraéled again,

W!l<D

, hey p.f.

O" of

,he

tlrop io;o

,b••

ir.

5 R

¡';-' o;