REPORT ON RADIANT HEAT. 
283 
of Count Rumford, on increased intensity of combustion, and 
on the coalescing of several flames. ( Essays, i. 304.) 
7. ) Melloni states, {Ann. de Chim. Dec. 1831, p. 385,) that 
by using his thermomultiplier he has found the permeability of 
transparent bodies to heat to be also dependent on their re¬ 
fractive power. He has compared twenty such media, and finds 
the order of permeability constantly the same, whatever be the 
temperature of the source. Chloruret of sulphur has the 
greatest power, oil next, and water least; he exposed them to 
the rays of a candle, an Argand lamp, or the sun. He finds 
the differences of permeability less, the higher the temperature. 
The full account is promised in another memoir. 
All this obviously applies only to luminous hot bodies. 
MM. Melloni and Nobiii, in their former paper, (Annales de 
Chimie , Oct. 1831, p. 211,) also speak of the heat from phos¬ 
phorus having been by these means found sensible, though it 
is often supposed to give light without heat. 
8. ) For information on various points connected with the 
subject, and on the theories of the evolution of light and heat, 
the following references may be useful. 
Wedgewood, Phil. Trans. 1792, p. 28, thinks that light from 
attrition is produced by a heat of from 400° to 600° Fahr. 
Dize on Heat as the Cause of shining, Journ. de Phys. 
xlix. 177. Gilbert, Ann. iv. 410. 
Fordyce on Light from Inflammation, Phil. Trans , 1776, 
p. 504. Morgan, Phil. Trans. 1785, p. 190. M. Hermstaedt, 
Nicholson s 4tto Journal , v. 187. 
Mr. Davies on Flame, Annals of Phil. Dec. 1825. 
Mr. Deuchar on Flame, Edinb. Phil. Journ. iv. 374. 
M. Seguin on Heat and Motion, &c., Edinb. Journ. of Sci¬ 
ence, xx. 280. 
Division III. 
Heat of the sun’s ravs. 
ml 
Speaking according to our ordinary sensations, we are ac¬ 
customed to say .that the sun communicates both light and 
heat. Light is transmitted in a way which we term radiation. 
The heat from nonluminous hot bodies is transmitted to a di¬ 
stance in a way closely analogous ; and to which the same name 
has been applied. 
In the first instance, we might suppose that the sun sends 
out two separate emanations, one of light, and another distinct 
from it, and similar to that of radiant heat from a mass of hot 
water ; and this, perhaps, was the first view taken of the sub- 
