Incident Light not decomposable into the prismatic Colours. 193 
monstrate the presence of alcohol in wine; but we must begin 
by isolating the foreign substances which are mixed or combined 
with it, and which oppose its separation. The process which I 
consider as the most advantageous for this purpose, consists in 
shaking the wine with well pounded litharge : it speedily becomes 
limpid like water, by giving to the litharge its colouring and ex- 
tractive matter: the subearbonate of potash then very easily de- 
monstrates the presence of alcohol. 
1 can give another proof of the existence of alcohol in wine, 
equally conclusive, by distilling wine in vacuum at the tempera- 
ture of 15°, which, as is well known, is very inferior to that which 
is developed during fermentation, for 1 obtain a product deci- 
dedly alcoholic. 
These two experiments’ prove beyond doubt that alcohol is 
not formed during fermentation, as was generally supposed pre- 
viously to M. Fabroni’s experiments. 
I shall terminate my memoir, which is about to appear in the 
third volume of the Mémoires d’Arcueil, by showing that we 
may obtain the pure alcohol of Richter by employing quicklime, 
or rather barytes, in place of muriate of lime. 
XXXVIL. Experiments tending to prove, that neither Sir Isaac 
Newton, HerscuEL, nor any other Person, ever decomposed 
incident or impingent Light into the prismatic Colours. By 
JoserH Reapr, M.D. 
Cork, January 24, 1814. 
Sirs, —OrR Isaac Newton, for the purpose of decomposing 
light, made a small hole in his window-shutter a quarter of an 
inch in diametér, and, having placed a prism so as to refract and 
receive a spectrum on a sheet of white paper, perceived seven co- 
lours in the following order: red, orange, yellow, green, blue, in- 
digo, and violet : these he supposed to be primary colours, which 
when combined in certain proportions gave white or transparent 
lights. The necessary shortness of a letter will not permit me 
to enumerate his experiments; I therefore refer to his Optics. 
That this philosopher was mistaken in supposing he analysed in- 
eident light, will appear evident from the following experiments 
and observations. When we look with a prism at a window, the 
light passes through the panes, and likewise through the prism, to 
the eye, undecomposed, and consequently colourless ; but when we 
look to the frames, we perceive an artificial rainbow of reflected 
blue, red, and yellow. Any opaque substance, as a piece of black 
cloth or paper, when pasted on the window, will produce the same 
effect; and the more dense or dark, the deeper the tints or fringe*. 
* T use the word fringe as much more appropriate than penumbra, whose 
derivation is absurd. 
Vel.43, No.191. March 1814. N The 
