S-l-O Prof. Apjohn on the Specific Heats of the Gases, 



than that assigned to it by these philosophers in the ratio very 

 nearly of 5 to 3. 



4. There does not seem to be any simple relation between 

 the specific heats of the gases and their specific gravities, or 

 atomic weights, and philosophers in searching for such are 

 probably pursuing a chimera. 



From this exposition of my method, and summary of my 

 experiments, I now turn to the more recent researches of 

 Suerman. These researches have appeared in the form of 

 an inaugural essay, which was published by the author upon 

 the occasion of his taking a degree in the university of 

 Utrecht. He had, he informs us, for a long time determined 

 upon making the specific heats of the gases the subject of his 

 thesis ; but when after many interruptions he had at length 

 begun to provide himself with the necessary apparatus, he 

 was much chagrined at finding, upon looking into a re- 

 cent number of the Philosophical Magazine, that I had al- 

 ready investigated the same question, and by the very method 

 which it was his intention to have employed. He would, in 

 fact, have turned to something else were it not for the per- 

 suasions of Professor Moll, who urged him strongly to per- 

 severe in his undertaking. This he was fortunately induced 

 to do, and the result has been a most elaborate and lucid hi- 

 story of the various attempts which have been made towards 

 the solution of this very difficult problem in physics, followed 

 by a detailed account of a number of experiments instituted 

 by himself with a similar object. 



His method I have stated to be the same with that which 

 I had previously adopted. This is strictly true. The formula, 

 however, which he used in calculating his observations, and 

 which he stated to be due to Gay-Lussac, is slightly different 

 from that which I have employed. In part retaining the 

 notation already used, and slightly changing the form of his 

 expression, it will become 



_ fe SO 



an equation differing in no respect from formula (C) which 

 I have used, save in the substitution of p—J"' for p I do not 

 of course admit the correctness of this expression ; p—J' is 

 certainly the elasticity of the gas when saturated with vapour 

 at temperature t'. But it is the pressure of the dry gas which 

 should enter into the formula, and this is p, provided p re- 

 presents the height of the barometer at the time of the ex- 

 periment. If this be a true view of the question, it is clear 

 that Suerman's results are all a little too high, and should, in 



