10 REPORT-—-1840. 
5. The limits of dispersion are open to further inquiry 3 but 
the dispersion in the case of sources of low temperature ap- 
pears to be smaller than in that from luminous sources. 
Reflexion of Heat: Melloni. 
A short paper, by M. Melloni, entitled ‘“ Note on the Reflexion 
of Heat,’”’ was read to the Royal Academy of Sciences, Nov. 2, 
1835, and published in the Ann. de Chim. ix. 402, of which a 
translation appears in Taylor’s Sci. Memoirs, Part III. p. 383. 
After referring to the experiments of Leslie, to show that the 
reflexion of heat depends materially on the texture, polish, &c. 
of the reflecting surfaces, he proceeds to consider what 
takes place in diathermanous substances, as in rock salt ; where, 
there being no absorption, the difference of the heat trans- 
mitted gives the quantity reflected at the first and second sur- 
faces. With other media—as glass, rock crystal, &c.—very 
thin plates exercise no sensible absorption : hence heat, after 
traversing a thick plate, being intercepted by a very thin plate, 
the loss which this occasions is due solely to the two reflexions. 
These considerations afford the means of estimating the inten- 
sities of reflected heat from different substances; and the 
author, in conclusion, gives a comparative statement of the 
reflexions from rock crystal and copper. 
Analogies of Light and Heat: Melloni and Forbes. 
M. Melloni’s “ Observations and Experiments on the Theory 
of the identity of the Agents which produce Light and Heat,” 
were read to the Academy of Sciences, Dec. 21, 1835, pub- 
lished in the Ann. de Chimie, No. 50, p. 418, and translated 
in Taylor’s Scientific Memoirs, Part III. p. 388. 
In this paper the author combats the views of M. Ampére, 
who had proposed some ingenious speculations for explaining, 
on the theory of undulations, the identity of light and heat, 
the difference of effect being dependent solely on the different 
wave-lengths ; those producing heat being supposed longer 
than those giving rise to light. Athermanous media, such as 
water, intercept the longer waves, but not the shorter. Thus 
the aqueous humour of the eye prevents the retina from being 
affected by heat as well as light. 
The author admits that many phenomena may be sufficiently 
accounted for by the mere supposition of the difference of 
wave-lengths; but he mentions some experiments in which he 
thinks decisively that this will not hold good. 
The spectrum formed by a rock-salt prism gives the maxi- 
mum of heat considerably beyond the red end. On interposing 
