45 
had preceded the author in the same investigation, parti- 
cularly those of Dulong. Dr. Apjohn’s own method was 
then detailed. In a paper read by him before the Academy 
in April, 1835, the equation* f” = f <a x 
to include the solution of the dew-point problem. But the 
factor a in this expression, which is obviously equal (when 
the air or gas is dry, or in other words, when f”=0) to 
was proved 
Md had is the specific heat under a given volume of the 
43d" p 
gas which is supposed to be the subject of experiment. 
Hence if f’ and d be determined for the various aeriform 
fluids by observation, their relative capacities for caloric 
can be compared. Such is the principle of the method. 
Two distinct series of experiments were then detailed, 
from the second of which, as comprehending those which he 
conceives to be most accurate, the author has deduced the 
following table of specific heats : 
Specific Heats of equal Volumes. 
Atmospheric Air,. . . . . 1.000 
Nitrogen, . . - . 1.048 
Oxygen, (by cleaaton) af piping 
Hydrogen, . . . eeheny | kee 
Carbonie-Acid,..j.. - . « -. 195 
Carbonic Oxide -.. . .' . .996 
Nitrous Oxide, ~~... 3 *. 1.193. 
Dr. Apjohn conceives himself justified in drawing from 
his researches the following conclusions : 
1°. All gases have not under equal volumes the same 
specific heat. 
2°, This law is not even true of the simple gases. 
*d=t —t' the difference of the temperatures shown by a wet and dry ther- 
mometer, and f" is the elastic force of vapour at temperature t’. 
