1866. | Physics. 299 
constitution exercises a paramount influence. The results obtained 
by previous experimenters in connection with this subject are 
illustrated and explained. The reciprocity of radiation and absorp- 
tion on the part of fine powders is also illustrated. It is, moreover, 
shown that the heat emitted from different sources, at a temperature 
of 1,000° C., varies in quality, this being proved by its unequal 
transmission through plates of rock salt of perfect purity. The 
absorption by such plates varies from 4 to 30 per cent. of the 
incident radiation. 
Magnus has published a memoir “On the Difference between 
the Heat Radiated from Polished and Unpolished Surfaces.” The 
author has made the important observation that a plate of platinum 
covered with platinum black radiated twice as much heat as a plate 
of polished platinum of equal extent; and on analyzing the radia- 
tions he discovered that the increase of heat from the unpolished 
metal is not due to a regular increase in all the rays emitted, but that 
the red, and especially the ultra-red, rays are chiefly augmented in 
intensity. The whole paper is of great interest, especially the 
author’s final considerations on the identity of heat and light. 
A notice of an interesting property of sulphocyanide of ammo- 
_ nium has been published by Mr. F. Clowes. He finds that when 
dissolved in water this salt produces intense cold; in a short time 
the atmospheric moisture being deposited like hoar-frost on the sides 
of the vessel. 
This led him to try a few experiments with weighed quantities of 
water and of the salt ; from a few trials with different proportions, it 
appeared that the mixture of equal parts by weight gave the most 
intense cold. By mixing 1,368 grains of the salt with its weight of 
water at 17° C., a cold of —12° C. was obtained ; the temperature 
of the atmosphere at the time of the experiment was the same as 
that of the water employed. 
Exucrriciry.—A very interesting experiment has been described 
by M. Cauderay. He introduces an electro-magnet into the circuit 
of a galvanic pile, and, breaking the circuit at any point, places the 
ends of the two conducting wires, separated one from the other, m 
a box contaming metallic filings, such as silver, copper, brass, or 
iron. The metallic particles will of course complete the circuit. 
If, now, one of the conducting wires be slowly raised, a small chain, 
formed by the juxtaposition of the metallic particles, will be drawn 
out, and if the experiment be made with great care, every particle 
in the box can be drawn out in one long chain. The author states, 
his opinion that the adhesion of the particles is not due to magneti- 
zation, but is the result of a sort of autogenous soldering by a 
superficial fusion of the metallic particies. The same author has 
shown that metallic tilings offer very gieat resistance to currents of 
