132 Scientific Intelligence. 
ration, 
above alluded to. But I must remember that you are not met here 0 — 
listen to generalities of whatever nature, but that we have plenty of real 
and special business before us. i. 
10. An account of some experiments on Radiant Heat, involving an@ — 
tension of Prévost’s Theory of Exchanges; by Mr. B. Srzwarr, (Prom 
Brit. Assoc., Ath. 1614).—These experiments were performed with the 
aid of the thermomultiplier, the source of heat being for the most patt 
bodies heated to 212°. Four groups of experiments were considere® 
Group the first contains those experiments in which the quantities of heat 
radiated from polished plates of different substances at a given tempe® — 
ture, are compared with the quantity radiated from a similar surface of | 
lampblack at the same temperature. The result of this group of expel 
ments is, that glass, alum and selenite, radiate about 98 per cent of whab 
lampblack does—thick mica, 92—thin mica, 81—and rock salt only 15 | 
per cent. The second group of experiments was designed to comp! 
together the quantities of heat radiated at the same temperature 7 
polished plates of the same substance, but of different thicknesses. i 
result of this group was, that while the difference between the radials” 
power of thick and thin glass is so small as not to be capable of being 
irectly observed, there is a perceptible difference between the raaial ‘e 
from thick and thin mica, and a still more marked difference between®™ 
radiation from plates of rock salt of unequal thickness. The third apa 
of experiments was made with the view of comparing the radiations ™ 
ually diathermanous for all — of heat is therefore unt 
The fourth group of experim 
eory of exchanges, somewhat extended. This extension cons! 5 ¢ 
following laws:—1. Each particle of a substance has an 
