498 
Notices . 
and those of Herschel’s, which showed that the solar beam was di* 
videdby the prism (according to Newtonian language) into two 
other substances beside the coloured rays, one of which was found 
between the red ray and the direction of the incident rays, and was 
the matter of heat or caloric. The other, a hitherto unknown sub« 
stance, which blackened the salts of silver, and appeared to be that? 
part of the solar ray which causes the colours of vegetables, &c« 
which we know would, if not exposed to it, become white and co- 
lourless These experiments establish the certainty of the Newto- 
nian theory on a ground not to be shaken. Besides, had Dr. Read 
reasoned correctly on his experiments, he would have found that 
the circumstance of the light remaining white in the centre of the 
spectrum, when admitted in large quantities upon the prism, arose 
from the same cause that misled Newton, viz. as to the number of 
the prismatic colours, the aperture being larger than was neces- 
sary to obtain the coloured rays entirely separate, and in Dr. Wool- 
laston’s experiment the aperture was an oblong of the smallest 
breadth that could admit the light free from inflection. In Sir Isaac 
Newton’s experiment the aperture, a quarter of an inch, was suffi- 
cient to blend the colours so as to produce the intermediate shades, 
and in Dr. Read’s the aperture, of four inches, threw the separated 
rays in confusion on the middle part of the spectrum so as to re- 
produce white light. 
This is not the first lime that Sir Isaac Newton’s doctrines 
have been attacked in this point. The celebrated Euler, and many 
others, have opposed the existence of light as a substance altoge- 
ther, and have supposed its appearance to arise from the vibrations 
of an elastic medium. Newton’s optics, however, stand on a basis 
df mathematical demonstration, and their merits will not fall should 
even his deductions from his prismatic experiments be proved to 
be founded on false reasoning. R. 
Dr. Read some years ago, advanced the production of caloric 
by the agitation of water in a close tube : which has not been con- 
firmed. T. C- 
Distilling *. — The method of distilling by steam introduced into 
the wash, is doubtless the best yet found out. Count Rumford 
first shewed how several vessels of water might be boiled by the 
steam conveyed from one boiler common to all of them. He i£ 
the inventor of the process. Whether steam be applied to boil 
water, to boil the liquor in a dyer’s copper, or the wash in a dis- 
