Mr. J. J. Waterston on the Theory of Sound. 483 



dence in Laplace's views, such conviction of their truth to nature, 

 that he considers them entitled to supersede the result of direct 

 observation ; and no attempt is made to reconcile the statical 

 theory of caloric with the vis viva theory of heat ; nor is a neces- 

 sity for doing so apparently even felt as a preliminary step to the 

 adopting of one of the deductions of the former as an ally to the 

 deductions of the latter. 



As Mr. Joule's name is conjoined with that of Professor 

 Thomson in this memoir, it is perhaps beceseary to assume that 

 he also approves of this manner of dedacing the ratio of specific 

 heats. .; . 



Another instance of the commingling of statical and dynamical 

 theories is to be found in a memoir by M. Masson, " On the Cor- 

 relation of the Physical Properties of Bodies," which appeared in 

 a recent number of the Annales de Chimie. M. Masson also 

 adopts the mechanical theory of heat (see, § III. chap. 2). Yet 

 in the beginning of the same chapter he writes, " Laplace has 

 discovered the true mathematical expression of the velocity of 

 sound in gas." Further, M. Masson states that he has found, 

 by experimenting according to the method employed by MM. 

 Gay-Lussac and Welter, that the value of k is actually what is 

 required to make Laplace's formula agree exactly with the best 

 observations on the velocity of sound. No details are given, 

 although the amount of compression in such experiments is of 

 some importance, as the ratio increases with this amount ; and 

 the formula has only to do with the initial ratio, or when the 

 change of density is infinitely small. M. Masson has also com- 

 puted the velocity of sound in a considerable number of compo- 

 site gases and vapours from the pitch of the sound given by an 

 organ pipe while immersed in them; and thence, employing 

 Laplace's theorem, obtains the respective values of k, which are 

 thus found to range from 1-36 to 1"42 in the composite gases, 

 and from 1-06 to 1-27 in the vapours. 



Thus all authorities, both of the statical and dynamical school, 

 seem to agree that Newton and Laplace's theory of sound is a 

 perfect representation of nature, and that its success is as com- 

 plete as the theory of gravitation. 



Newton, in several parts of the Principia, calls upon us to 

 keep in mind that his principles are mathematical, not philoso- 

 phical. At the beginning of Book 3 he thus expresses him- 

 self: — "In the preceding books I have laid down the prin- 

 ciples of philosophy ; principles not philosophical, but mathema- 

 tical, such to wit as we may build our reasonings upon in philo- 

 sophical inquiries." Again, after proving in Prop. 23, Book 2, 

 that " particles flying each other with forces that are reciprocally 

 proportional to the distances of their centres, compose an elastic 

 2 12 



