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XXVIII. Ohservaiions on Marquis Laplace's Communica- 

 tion to fJif Royal Academy of Sciences " Siir rAttractiou des 

 Spheres, et sur la Repulsion des Fluides olastiques." By 

 John IIerapath, Esq. [Continued tVom p. 60".] 



1\/T LAPLACE tells us that an air thermometer may be 

 ItX. i-egarded as the true thermometer of nature, and finds 

 that his function n[f) is proportional to the expansion of a given 

 volume of gas under a constant pressure. From this it follows 

 that his et|uation P= isn{t) becomes 



F=ig{F-{-U8); 

 F denoting the Fahr. temj^eratine, and i being as with him 

 a constant. Taking therefore for granted, what has been ex- 

 jjeriLuentally demonstrated over and over; namely, that vapours 

 at all tempeiTitures equal to and above, that of their tensions, 

 follow the same laws as gases ; this equation of M. Laplace 

 coincides with the theorem I have delivered, p. 269, Annals for 

 October 1821, when discussing the experiments of Sharpe and 

 Southern ; for my squares of true temperature have the same 

 ratio as M. Laplace's simple temperatures. It is likewise the 

 same theorem that I have given. Annals for June 1822, p. 422, 

 which Dr. Apjohn and Mr. Silvester imagined to be erroneous. 



I have before mentioned that M. Laplace has in effect de- 

 termined the point of absolute cold to be the same as I had ; 

 which I have lately been informed coincides likewise with the 

 joint determination of two other French philosophers, MM. 

 Clement and Des-ormes. 



It is a curious fact that these two results of my theory, which 

 have been corroborated by the subsequent inquiries of such a 

 man as Laplace, are the identical cases which some of our 

 English philosophers have opposed. 



M. Laplace observes, " It results from equation 2, " 

 |^gc- = (^'Z7(^)| "that the temperature remaining the same, the 

 heat c diminishes by an increase of density ; and consequently 

 that the compression of a gas must develop caloric, in order 

 to be brought to the same tenjperature, which experience con- 

 firms." It is true that the temperature is elevated or depressed 

 by raj)idly compressing or rarefying an air, but M. Laplace is 

 too much of a philosopher to imagine that so vague and inde- 

 finite an appearance of agreement as he has here adduced can 

 add any thing to the probability of his views. The same re- 

 mark I might make on his preceding paragraph. 



He immediately afterwards tells us " that a quadruple com- 

 pression will express half the caloric of an}' mass of gas." 

 Indeed by his 2d equation equal compressions of a given mass 

 of gas, whether rapid or slow, will always evolve the same 



quantity 



