4.62 Royal Society :— 
June 21.—Sir Benjamin C. Brodie, Bart., President, in the Chair. 
The following communications were read :— 
*‘ Experimental Researches on various questions concerning Sen- 
sibility.” By E. Brown-Séequard, M.D. 
“On the Construction of a new Calorimeter for determining the 
Radiating Powers of Surfaces, and its application to the Surfaces of 
various Mineral Substances.”?’ By W. Hopkins, Esq., M.A., F.R.S. 
When the author's Memoir on the Conductivity of various sub- 
stances was presented to the Society, it was intimated to him on the 
part of the Council of the Society, that it might be advisable to de- 
termine absolute instead of relative conductivities, the latter only 
having been attempted in his previous experiments. It is partly 
in consequence of this intimation, and partly from the desire to make 
his former -investigations more complete, that the author has given 
his attention to the construction of a calorimeter which might serve 
for this purpose. His present memoir contains a description of this 
instrument, with the results obtained from its application to the 
surfaces of various substances. 
The apparatus used by Messrs. Dulong and Petit was more deli- 
cate and complete than the simpler instrument devised by the author 
of this paper, but it was calculated only to determine the radiatimg 
powers of substances of which the bulb of a thermometer could be 
constructed, or with which it could be delicately coated. The only 
substances to which, in fact, it was applied, were glass and silver, 
the radiation taking place, in the first case, from the naked bulb of 
the thermometer, and, in the second, from the same bulb coated 
with silver paper. In these cases, too, it was the whole heat radi- 
ating In a given time from the instrument, and not that which radiated 
from a given area, that was determined. For this latter purpose the 
apparatus was not well calculated, on account of the difficulty of ob- 
taining with accuracy the area of the surface from which radiation 
took place. The instrument here described can be easily applied to 
any plane radiating surface, while the area of that surface can be easily 
determined to any required degree of accuracy. The quantity of 
heat radiating under given conditions, froma unit of surface ina unit 
of time, can thus be easily ascertained. The paper contains a detailed 
description of the instrument, and of the experiments made with it. 
The following are experimental results thus obtained,—the unit 
of heat being that quantity of heat which would raise 1000 grs. of 
distilled water 1° Centigrade. ‘The formula is that of Dulong and 
Petit, where 
0= temperature of the surrounding medium (the air in these ex- 
periments), expressed in Centigrade degrees ; 
¢= the excess of the temperature of the radiating surface above 
that of the surrounding medium, in Centigrade degrees ; 
p= pressure of the surrounding medium (the atmosphere in these 
experiments), expressed by the height of the barometer in metres ; 
a= 1:0077, a numerical quantity which is always the same for all 
radiating surfaces and surrounding media. 
