TRANSACTIONS OF THE SECTIONS. 



35 



the observer kept his eye, armed with a lens, steadily fixed on the ther- 

 mometers, and registered the indications of both as soon as the wet one 

 became perfectly stationary. The height of the barometer being now 

 taken, the necessary data were obtained for calculating from the hy- 



grometric formula /"=/" x r-' t^^ elastic force of the vapour 



still existing in the air of the gasometer. The atmospheric air being 

 now replaced by some one of the gases, and this being left sufficiently 

 long in contact with the oil of vitriol, the manipulations and ob- 

 servations just detailed were repeated. This same experiment, with 

 sufficient intervals to allow in each instance of maximum desiccation, 

 was again and again performed ; and it having been ascertained, after 

 a considerable number of repetitions, that the results were uniform 

 and consistent, and that they might therefore be rehed upon, the 

 mean of all the observations was taken, and from this the specific heat 



of the gas deduced by means of the formula a = (/ ~"/ XjFj^ — ' 



that value being assigned to /" which resulted from the preliminary 

 experiment on atmospherical air. The analysis of the gas was next 

 very carefully performed, and it having been ascertained that n volumes, 

 ex. gr., of atmospherical air per cent, were present, the proper cor- 



rection was applied by the formula a'= a + 



{a—c) n 

 100— « 



, in which c ='267 



is the specific heat of air, a' the true specific heat of the gas, and a the 

 specific heat of mixture of gas and air, as previously determined. Such 

 was the course pursued in the case of each of the gases submitted to 

 experiment, and the following are the final results. The numbers 

 represent the specific heats of equal volumes, and, to facilitate com- 

 parison, the determinations of Dulong, and those also of De La Roche 

 and Berard, are included in the table. 



Having stated his numerical results, and given an outline of the 

 method of investigation which conducted to them. Dr. Apjohn con- 



D 2 



