368 On the component Parts of Light, 
Another objection to this hypothesis is, that heat has never 
been discovered in the light from the moon. But this has been 
ably shown by Sir Humphry Davy*, and other philosophers, to 
deserve no weight. The small degree of light which is received 
from the moon in comparison with that from the sun, as 1 to 
300000, perfectly explains how, in the experiments hitherto 
published on the subject, no heat has been discovered. It must 
also be remembered, that the lens probably stops a greater pro- 
ortion of a small quantity of rays of light transmitted through 
it, than of a larger quantity, its attraction for it being stronger 5 
consequently, it has not an equal power in concentrating rays of 
light from the moon, as from the sun. 
The prismatic colours once separated, are not further divisible 
by a second prism; and this fact has been urged as a proof of 
the distinct and homogeneous nature of each of the colorifie 
rays. But the passing of a coloured ray a second time through 
a prism, does not separate from it the calorific or chemical rays; 
and therefore, it does not prove that they are unnecessary to vi- 
sion. For since they do remain united, notwithstanding the de- 
gree in which they are usually refracted, it is certainly possible 
that the cause of their continued union may be the only cause 
of their continued colour. If it be supposed that they remain 
in combination from an attraction for the calorific ray, why not 
suppose an attractiou between the calorific and chemical rays? 
The different colours would then arise from a combination of 
the calorific and chemical rays taking. place in definite propor- 
tions, analogous to innumerable chemical attractions. The con- 
tinued union of the invisible rays, whether there be distinct _co- 
lorific rays or not, tends to show that there is no repulsion be- 
tween the particles. 
_ There are on the other hand very great objections to the sup- 
position that the colorific rays are homogeneous. In most cases 
¥-10,000dth part. For, as a more practised and experienced one than that 
of Dr. Herschel cannot reasonably be expected, the discrepancies evident 
upon these experiments may prove its impossibility. Thus, out of 1000 parts, 
he found that 
Coach glass one side rough, stopped 464 parts of heat and 854 of light. 
Crown glass ditto 571 - 825 3 
Coach glass both sides rough 667 2 952 : 
Crown glass ditto 735 " 946 Ps 
All together they stopped 854 995 - 
But if a calculation be made from the quantity which they stopped sepa~ 
rately, it will be found that they ought all together to have stopped 979.8 
parts of heat, and 999.938 of light. Ii another part of the same paper in 
the Philosophical Transactions, it would appear that the coach glass with 
one side rough stopped more heat from the taper when alone, than the 
same coach glass when assisted by crown glass also rough on one side. 
* Elements of Chemical Philosophy, vol. i. part i. p. 202. of 
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