209 
containing as a divisor, not p, but p—f’. But, 3rd, prin- 
cipally to Suerman having in no one instance obtained in his 
experiments depressions of such magnitude as those which he 
himself had observed. Dr. Apjohn did not explain the cause 
of this latter circumstance, as it would have required him to 
describe the very elaborate but rather complicated appa- 
ratus of M. Suerman, and to enter upon other details of a 
critical nature, which he conceived unsuited to a general 
meeting. 
In conclusion, Dr. Apjohn stated, that M. Suerman had, 
in one direction, prosecuted the research in question further 
than he himself had done, having experimentally investi- 
gated the specific heat of air ata series of pressures less 
than that of the atmosphere. M. Poisson had given, in his 
Traite de Mecanique, a formula for solving such problems, 
derived from analytical considerations, which however was 
found by Suerman to lead to numbers quite different from 
those to which his experiments had conducted. 
To the preceding abstract of his observations, Dr. Apjohn 
is desirous of appending the following formule :— 
_ fle, 30 
“sly Ragen (1) 
fie. 30 ‘4 
° = "48d * n—f (2) 
In each of these a is the specific heat of the gas compared 
to that of an equal volume of atmospheric air, f’ the tension 
of aqueous vapour of maximum elasticity, at the temperature 
shown by a wet thermometer placed in a current of such 
gas, and d the depression, or difference between the indica- 
tions of the wet and a dry thermometer. Formula (1) is 
that which Dr. Apjohn communicated to the Academy in 
November, 1834, and which he employed in his researches 
on specific heats. Formula (2) is that which has been used 
by Suerman, and the investigation of which he attributes to 
Gay-Lussac, The former formula had been previously ar- 
U 
