80 MOTIVE POWER OF SEAT. 



the l&w <vf Mariotte.* In fact, the densities of the 

 two gases maintaining always the same ratio for 

 similar positions of the pistons, and the tempera- 

 tures being always equal in both, the total pressures 

 exercised on the pistons will always maintain the 

 same ratio to each other. If this ratio is, at any 

 instant whatever, unity, the pressures will always 

 be equal. 



As, furthermore, the movements of the two pis- 

 tons have equal extent, the motive power produced 

 by each will evidently be the same; whence we 

 should conclude, according to the proposition on 



* The law of Mariotte, which is here made the founda- 

 tion upon which to establish our demonstration, is one of 

 the best authenticated physical laws. It has served as a 

 basis to many theories verified by experience, and which 

 in turn verify all the laws on which they are founded. 

 We can cite also, as a valuable verification of Mariotte's 

 law and also of that of MM. Gay-Lussac and Dalton, for a 

 great difference of temperature, the experiments of MM. 

 Dulong and Petit. (See Annales de CMmie el de Physique, 

 Feb. 1818, t. vii. p. 122.) 



The more recent experiments of Davy and Faraday can 

 also be cited. 



The theories that we deduce here would not perhaps be 

 exact if applied outside of certain limits either of density 

 or temperature. They should be regarded as true only 

 within the limits in which the laws of Mariotte and of 

 MM. Gay-Lussac and Dalton are themselves proven. 



