592 
OPT 
all foreign light was carefully excluded, neither he nor 
any other perfon could perceive it.’ To try whether 
white bodies refteft more light than others, he held a fheet 
of white paper in a fun-beam admitted into a darkened 
room, and obferved that it reflefted a far greater light 
than a paper of any other colour, a confiderable part of 
the room.being enlightened by it. Further, to (how that 
white bodies reflect the rays outwards, Mr. Boyle adds, 
that ‘common burning glades will not of along time 
burn or difcolour white papers.’ When he was a boy, he 
fays, he took great pleasure in making experiments with 
thefe glafles ; he was much furprifecTat this remarkable 
circuinftance, and it fet him very early upon gueding at 
the nature of whitenefs, especially as he obferved that the 
image of the fun was notfo well defined upon a white pa¬ 
per as upon a black one; and as, when he put ink upon 
the paper, the moiltifre w'ould be quickly dried up, and 
the paper, which he could not burn before, would pre- 
fently take fire. He alfo found, that, by expofmg his hand 
to the fun with a thin black glove upon if, it would he 
fuddenly and more cpnfiderably heated, than if he held 
his naked hand to the rays, or put on a glove of thin white 
leather. To prove that black is the reverfe of white, 
with refpeft to its property of reflecting the rays of the 
fun, Mr. Boyle procured a large piece of black marble; 
and, having got it ground into the form of a large fphe- 
■rical concave fpeculum, he found that the image of the 
fun reflected from it was far from offending or dazzling 
his eyes, as it would have done from another fpeculum ; 
and, though this was large, he could not, in a long time, 
fet a piece of wood on fire with it, though a far lefs fpe¬ 
culum of the fame form, and 'of a more reflecting fub- 
ftance, would prefently have made it flame. To fatisfy 
himfelf ftill farther with refpeft to this fubjeft, he took a 
broad and large tile, and, having made one half of its 
furface white and the other black, he expcfed it to the 
III miner fun ; and, having let it lie there fome time, he 
found, that, while the white part remained cool, the part 
that was black was grown very hot: for his farther fatis- 
faclion he (ometimes left part of the tile of its native red, 
and, after expofmg the whole to the fun, obferved that this 
parr grew hotter than the white, but was not lo hot as the 
black part. 
“ Mr. Boyle not being aware of the faft, lately nfcer- 
tained by the experiments of Herfchel and others, that 
luminous and calorific rays are Separate and diffinCt, and 
as all his reafpning depends on the identity of heat and 
light, we mult look on his facts and experiments as in- 
conclufive, efpecially when cppofed to thole direft ones 
on which I found my opinion. In my laft paper lent to 
NichoUon’s Journal, I mentioned my having formed a 
perieft black by mixing the leven different colours; of the 
rainbow in different proportions; and that, after drawing 
lines with this compofition on white paper, I anajyfed 
them by means of a powerful plano-convex lens, or prilVn, 
into indigo and orange; which two colours contain the. 
three primary rays, yellow, red, and blue, or indigo, from 
which all the others might be formed. Sir Isaac Newton, 
in looking through a teiefcope at a black body, obferved 
thole colours ; but he was lb impreffed with iiis own beau¬ 
tiful theory, that ‘ he fuperficiaily examined the circum- 
ftance : he fays, ‘If a black objeCI be lurrounded with a 
-white one, the colours which appear through tlie prilin 
are to be derived from the light of the illuminated one 
fpreading into the regions of the black ; and therefore 
they appear in a contrary order to that in which they are 
feen when a white objtCt is lurrounded with a black one.’ 
To lhow the 1 allacy of this reafoning, I made the follow¬ 
ing experiments. 
•: i. | drew..! line with a perfect-black ink on a fheet 
of red paper; and, on applying my lens or prilin, I ana¬ 
lysed it into a beautiful orange and indigo.; the red rays 
reflected from the illuminated paper added to the bril¬ 
liancy ot the orange. -Whence was the indigo derived ? 
.certainly not from the red paper. If lir Ifaac Newton’s 
I c s. 
theory were cor reft, nothing but red fhould have met 
the eye. 
“ 2. I drew a line with red ink on a fheet of white pa¬ 
per, and obtained, by analyfis, only the primary red. If 
fir Ifaac Newton’s theory were correft, where were the 
other fix colours of the illuminated white paper ? 
“ 3. I drew a line with black ink on a fheet of yellow 
paper, and, on analyfing it in afnnilar manner, perceived 
the orange, indigo, and a beautiful green ; the yellow 
rays of the illuminated paper had blended with the blue 
of the indigo, and formed a green. 
“ 4. I drew a line with black ink on a fheet of blue pa¬ 
per, and obtained only indigo and orange. 
“ 5. I mixed up fome red and yellow paint, and, having 
formed an orange ink, I drew lines on white paper, and, 
on analyfing them, obtained only red and yellow! On fir 
Ifaac Newton’s theory, I fhould have perceived the other 
five colours reflefted from the white paper. 
“6. I mixed blue and yellow, and, having formed a 
green, analyfed it into yellow and blue. 
“ 7. I drew two lines, one of orange, the other of in¬ 
digo, parallel to each other ; and, on condenfing them by 
a powerful concave lens, I law the orange and indigo 
uniting by degrees to form a black line. I did the fame 
with the different colours of the rainbow. 
“From thefe experiments, and many others which the 
fhortnefs of this communication will not allow me to 
enumerate, I venture to conclude, that blacknefs ordark- 
nefs arif’es from the condenfed refleftion of orange and 
indigo; the orange and indigo containing the three pri¬ 
mary colours, red, yellow, and blue, which, being blend¬ 
ed in different proportions, form the four others. Thus, 
however furprifing it might appear, black and white are 
produced by the refleftion of the fame colours. It has 
often occurred to me, that, however beautiful the Newto¬ 
nian theory of light, it was inadequate to account why 
a candle, placed in a room entirely lined with black, 
fhould enable a perfon to fee the different (hades and an¬ 
gles. If the light were abforbed by the black, the room 
fhould be inviiible. It alfo appeared furprifing x t)iat, on 
blowing out the light, the room full of fluid light, how¬ 
ever attenuated or lubtle, fhould vanifh, or be abforbed 
into the pores of thefturrounding bodies, and that with¬ 
out any changes of property or chemical agency. 
“ It likewife mutt appear furprifing, if not impoffible, to 
any thinking mind, that the fun, eternally emitting an 
inconceivable quantity of fluid light,'fhould never he 
exhaufled ; and, on the other hand, that thole bodies re¬ 
ceiving- fuch a fupply fhould never be increafed in fize. 
Should my ideas of light be adopted, they account in a 
latistackory manner tor thofe incongruities. Let us fup- 
poie the earth conftantly furrounded with a large quan¬ 
tity of fluid light. The fun riles in the heavens, and 
modifies it into vifibility ; he fets, and condenfes it into 
the blacknefs or darknefs of night.” 
The laft difcovery we (hall notice under this head is 
that of prcfeltor Morichini of Kome, who has found 
that the violet rays of the prifmatic fpeftrum poflbfs the 
extraordinary power of communicating the magnetic pro¬ 
perty to needles. The late profeffor Playfair of Edin¬ 
burgh, in whole prefence the experiment was performed, 
during his vifit to Italy, by Dr. Carpi, gives this account 
of the procefs: A lolar ray, entering a room by a circu¬ 
lar hole made in the fhutter, was received upon an ordi¬ 
nary prifin. The fpeftrum relulting from the refraftion 
was caught upon a fcreen ; a book was then fet up in 
fuch a manner a-s to intercept the whole of the fpeftrum 
excepting the violet rays, in the prolongation of which 
a fupport was fixed for the needle to be magnetifed, which 
was a thin piece of fieel, taken from among feveral 
others, and which, when tried, manifefted neither pola¬ 
rity nor any power of attraftion for iron-filings. It was 
fattened with wax horizontally upon the fupport, and in 
a direction interfefting the magnetic meridian nearly at 
right angles. The whole of the violet ray was collefted 
by 
