in the Titeory qfSouml 105 



controul which wind exercises over the intensity of sound, and 

 which is tlie more remarkable, considering tJie vast dispropor- 

 tion of their velocities. It is generally suptx)scd that the rela- 

 tive velocity of sound and wind is not affected by the motion 

 of tlie latter ; but this opinion stands much in need of confir- 

 mation. It is clear, that the effect of wind on sound is very 

 different from merely bearing it along, as a current in the ocean 

 does a floating body. For in this way, the intensity would un- 

 dergo no sensible change ; whereas, we know, that, in most cases, 

 wind annihilates sound, when opposed to it, and magnifies it pro- 

 digiously when moving in the same direction. The most natu- 

 ral inference which we can draw from this is, that wind reflects 

 sound in the opposite direction ; something in the way that the 

 tide sends the bore up a river. 



The tremendous explosion of the Stobbs Powder Mills in 

 1824, shewed, in a very striking light, how feebly, and to how 

 short a distance, sound moves against the wind, while it is pro- 

 digiously strengthened to leeward. A moderate breeze then 

 blew from the south-west, and, although in the opposite direc- 

 tion, the report was loud, and the houses sensibly shaken, to 

 the distance of thirty miles, yet very few heard it, and that 

 feebly, three miles to windward. 



Chap. III. Book xii. of the Mecanique Celeste, is devoted to 

 the theory of sound, and forms a continuation of the author's 

 speculations on heat and gases contained in the two preceding 

 chapters. In it, particularly pages 127, 128, occur some of the 

 formulae that are employed in the memoir of M. Poisson on the 

 same subject; and which are closely allied to what I commenced 

 with in the Number of this Journal for October 1826. I then 

 pointed out an error into which these eminent mathematicians 

 had fallen, in determining the proper form of the integral of a 

 differential equation ; and which error arose from their intro- 

 ducing a needless and erroneous hypothesis, at variance with 

 the conditions of the problem. The mistake to which I allude 

 admits of being placed in a still clearer point of view ; and this 

 becomes the more necessary, considering the very unfair repre- 

 sentation which Mr Ivory has given of what, in the Phil. Afaff. 

 for April last, he calls the equations of the Mecanique Celeste ; 

 though, in fact, the equations which he has prothiced there, to- 



