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Ü~C raree n~s ,'"ni\t rroullC(.d ;lny paniculJ.r calour in the
('Iblong pi8ure 1'1' ;are lhe r..tys fhat produce lhe f2me
<:ulour in lhe ¡nverted pitlure 'p ; 2S woulJ be e',i<!cnt
(rom intcn:.:pting any pdrlicular colour al 1'1': ror ir rhe:
nrcen T3P t lor inll.iOcC', are iñtcn:cpted al 1'1', Ihc.:rc: wl lI
be no gr~ ..n at I/': or if lhe red ale unerccprC'd.t PT,
thert \ViII lhen appcar no red cotour ;t( '/' : and Ihe ["me:
thing \Vdl h~ppen upon intercept ing the fay!> of any olhcr
colour al PT, [or then th... t colcur \ViII vonirh al Ip.
C, louTI may l'e pror/uud by comp ?Jition ,ha f nre lldlher
~xn{11; h~" aIJJ of Ihe prilll,"y olleJ, nor lilll;' 'UJhit~.
1r lhe ud ray5 of one coloured piélure ...re mi:<cd \Virh
the violct rays of anothcr, according to lhe various pro·
portions in which they are: mi~ ~~ , vuiou$ pu:-p1es \\ ¡JI
be produccd. (uch as are not likc in ~ppearanc~ tO the
colour of any homogeneous Jight; :nd o~ the::r~ purples,
mix.d ",i,b yellow aod blue, OI ay be made o,her ntw eo–
lours.
By mixing the coloured powders which painters uf!',
though ,he powders ,hemfel ves «f<mble ,he prim"y eo–
lours, yet ,he mixture may be grey, or duo, or rulfet–
brown, luch as are the calours of a man's nail, of a moufe,
of afhes, of ordioary llones, of mon ar, of dufl and dirt
; n ,he higb_ways_ T hus one pa" of red lead, and five of
oviride zns, compare a dlln colour like that of a moure.
If ,oor pimen" whieh is yellow, a full brigh, purpl. po"'·
der ufed by pain,ers is added, ,he mix,ure may be made
cf a pale red; aod with the additioo of a liltle viride zris,
which, as the Dame imports, is greeo, and of a little blue
bife, ,hi. pale red will ehange 10 grey or pale wbi,e, fuch
as is lhe coloue of a(hes, or of wood newJy cut, or of .a
man's lkin.
T hefe grey, dun, and rurre, colou rs are only impcrfeél
fons of whi,e. And we may uoderfland, why ,he mix–
' ure of ,heCe coloured powders Ihould produce an imper–
feél whi,e, and no, a full brigh , ooe, from ,he fullowinj!
<lbferu,ion. A Il coloured powders Cuppref, aoo flop grea,
part of ,be ligh, ,ha, falls upon ,hem : ,hey ..fl, él mOre
of thore rays from whence their colour aeifes than of any
o,h·er Con ; bu, ,hey refieél even ,hofe more CpaTingly
than whi ,e bodie. do. R ed lead, for inllanee, ..fi eéls
fe wer red rayo ,han whi,e paper does ; for if red lead and
",hite p' per are bo,h of ,hem plaeed in homogt neous red
Jigh" ,he p'per will appear of a brigh,er red ,han ,he lead.
Bu, if red lead fupprefres many red rays. i, may weJl he
fuppofed ' o Cupprefs many more ray' of o,her colotl,,;
fin ce its rednefs is owing to its HBcai ng red rays mOre
eopiouOy, and all o,her rayo more Craringly. From henee
it folJows, that in a mixrure of coloured powJers, Ihough
they rcA 'll rayo of all fOrls iu a due propon ion, Co ,h.,
the campound light will not be more of one colour than
another, bUI will be white; yet the white::nefs will be
mueh lef. bright ,han ,ha, of paper; .beeaufe ,he mix,u re
of powders fupprerre, ano f10ps many ray', "here.. ,he
p'per "Olél. almo!! .11 ,he rays ,ha, fall "Fun i" aud
fupprdrcs (ca ree any. Thus the whitt: ncrs in lhe mixture
ofpowders, and thewhiu.nefs ¡nthe paper, ::. rt:uothoC Ihe
fame ron , and diIFt:r {rom one anolher only in dt"grec, oe
in lhe quantity of light. T hrrc(ore, ir fome:: of IhlS mix-
1ure of powders is placcd In {unJhin~, aDd a piccc
-()f white p.apcr is pl:tced in lhe fhaJ:, the rllixturc hy Ih us
V OL . JI!. N° 87.
1 e s_ 4 F
illcle,IG0ci th~ ]ight, ud ~,e p~pcr by ,bus diminjOlíng ¡t.
nHy o: ruade tu appl ar t!'qlJ.1l1y whlte.
T ,íc ro/(mrJ o/ all hodi ..·.J nre ~Ílh("r Iht .filllplt cD/fwrJ fJ(
hOIl¡og~J1~?tJJ light . or [ueh (o1ll/,ollnd ( olourJ al arif:
fram a mix(ur~ of hOJJ/ogelJ(~Ul lighl.
EACH ron of light has:t p'!culiar colour of ¡rs owr:,
which no rcfról~ion or refl<élion can ch angc. " he:refore
t h~ colour of no narunl body COlO b: any other than either
th! c.,lmu of fome fort of homcneneous I¡Ch t, or a como.
p~,unJ colocr z.rillng from a mi xtllre of [he Cc\'t::ral fons 1
F'úr bodi., ' ppear eoloJ red only by rtOeéling lig~' ; and
no reficélion can give any othcr colours to the ra}'s bllt
\\'ha, ,hey had bdore.
Oj Ih, COLOURS.j TII'S TRAS SP.UENT PLAT OS.
I-Voler, Dir. g/afi, or (troj olh" Ir r<nl jubjlo1/et,
rwh~n d,.a"W11 out ifllo ¡hi/} pla/u, b(come coloured.
WAT E R., when it is made tenacioU5 by h:wing ,foap
mixed wi,h i" may be blowo up io,o a bubble A, (No. 38.)
fueh as ehildr<n play wi,h . 1f ,hi. bubble is Ce, under a
glafs, fo that the mation of the ..ir may not afF..:ét it, lhc",
as ,he wa,er glides down ,he fideo of i" aod ,he ,op of i,
at A grows th¡nner, {everal colours will lQcceffivcly app~:tr
at A., and will Cpread themCelves from thence iD rings fur~
rounding A, aod deCeending farther and farrher down ,he
fides of ,he bubbl., ,UI they vanifh 2t BC in ,he Came order
in wh,r h they .ppeared . Thu., forioflanee, ,he firll eolour
,h" appea" at A, ,he ,op of lhe bubble, is red : ,hlS red Cpot
fpreads i,felf io,o a circular ring round A, 2nd ,hen , he
,op of ,he bubbl. A becomes blue: ,h is blue fpo, fpread.
itfdf in the fa tle manner round A , and then A becomes
red a fccond lime. Before we go 00 lO coofider what o·
ther eolours arife at A, we wiJl obrerve what becomes of
,hoCe whieh arife 6rfl. The red, whieh firfl appeared
a' A, fpr..ds itfelf io,o a circular ring roand A : ,his
ring: grows larger, a, the WAter glidcs down lhe lid«:s oC
,he bubbJe; fo ,h.. ,he eolourcd ring glides down ,be
bubble along wi,h ,he wa,er, , ill i, fink. a, Ja!! 'o nc,
and ,here eneomparres ,he bubble. In like manner ,he
blue, whieh ariCes a' A af,er ,he red, fpread, i,felf aod
defeeod. down ,he bubb!e, •• ,he red ring did. The co–
lour which arife3 next at A, is red a fecond lím~ ; this
fpre.d, i,felf in ,he fame mann«, and is fu ecceded by bJue
a Cecond ,ime. Thefe are followed by a grea, varie,y of
colours, wh~ch appear fu cceffively at A, ami Cpread lhcm·
fdves from lheace in this order : Red¡ yello\V, greea, blue.
purple ; then again red, yellv\V, green. btue, violet; and
Iallly, red, yello\\', white, blue. This ült blue eolour i.
fu ceeeded a' A by a blaek fpot, wh ich retleéls fearce .ny
Jíghl : this fpot dil.ues itrdf, bm nOI inlo 3 circular ring
as (he coJours had done; lt becomes beoarler and broarler,
,¡II ,he bubble break•.
A thin pIafe of water of lhe f:tllle fort with this hu!.> ·
ble, bUl more: laning, may be otherwife procuréJ . Ir1\
pieee of plane r ulrlhell claC, is placed upon ,he ohjcél·
AlaC. of a long ,clefeope, as in (No. 39.) ,he pl.lne lur–
{a ce of onc glar9, and thc convcx. one of the oth ~r, will
touch one another only in a lingt<: ftoint; ano if ,he inter–
val bctween them ís filled with water, as lhe bl",K's are
prcrrcd ,o~e,her, ,he (dOle eoJours a,ife JI ,hc poin, of
t 5 Q.. ,· .'!