209 



containing as a divisor, not p, but p —/'. 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 at a 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 formulae : — 



48g? p—J ^ \ 



In each of these a is the specific heat of the gas compared 

 to that of an equal volume of atmospheric air,/' 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-* 



