THE 



LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XVL FOURTH SERIES. 



I 



LV. On the Theory of Sound. By J. J. Waterston, Esq.* 



IN a paper on the Integral of Gravitation that appeared in the 

 Philosophical Magazine of May last, I endeavoured to draw 

 attention to the principle of physical causation supplied to us by 

 the mechanical theory of heat, — how it leads us to study natural 

 phsenomena in their dynamical sequence, and suggests the 

 arranging of problems of molecular statics so that they may pre- 

 sent the aspect of motor transition to the mathematical inquirer. 

 It may perhaps be of advantage, as testing the general argument, 

 to discuss the question, Can the theory of the propagation of 

 sound developed by Newton and Laplace be viewed, consistent with 

 the modern idea of heat, as a correct exposition of the actual mode 

 in which pulses are transmitted tlirough air ? It appears from 

 recent memoirs, that this opinion is still generally entertained by 

 physicists; and the theory of Laplace has in some instances 

 been considered so perfect as to afford the means of deducing 

 the specific heat of air from the velocity of sound, and this by 

 zealous professors of the mechanical theory of heat. 



The ideas upon which Laplace's theory was constructed are 

 to be found in the second chapter of the second book of the 

 Mecanique Celeste. The following extracts show how very re- 

 mote they are from those now universally prevalent : — 



Page 105, line 8. "Doubtless it is necessary to admit that 

 between the molecules of air there is a repulsive force which is 

 only sensible at imperceptible distances : the difficulty consists 

 in deducing from it the laws of elastic fluids. This may be done 

 by the following considerations." 



P. 105, line 4 from bottom. "I suppose then that these mo- 

 lecules retain the heat by their attraction, and that their mutual 

 repulsion is due to the repulsion of the molecules of the heat 

 which I assume to extend to an insensible sphere of activity." 



P. Ill, line 9. "But what ought we to understand by the 

 temperature u, and what is its measure ? It appears natural to 

 * Communicated by the Author. 



Phil. Mag. S. 4. No. 110. Suppl. Vol. IG. 2 I 



