30 INFLUETSCE OF LIGHT ON THE PROPAGATION OF SOUND. 



duced by the rarefaction the presence of the sun occasioned; 



but the situation of my windows, and the usual direction of 



the morning breeze, militated against this argument. 



I, reol J nr>t bo '^'^^e action of the wind miL,!it be supposed capable of 



ov-.r.jj lo ihe jacrea^ing the propagation of sound, when, blowing in the 



line from the sonorous body to the ear, it could impart its 



ovvn velocity to the vibrations of the sound ; but it appeared 



to inc, tiiat its action must be jiuU, when its motion was 



perpendicular to that line*. The velocity of sound too, 



-which is 1065 feet per second, nearly excludes the influence 



of the f»ind, the action of whiclj is slower, and operates only 



on large musses of the atmospheref. 



SpTjrvibaspcr- Sound is propagated by infinitely small vibrations ac- 



iu^ap'.-culiarj,Q^^i;, to the theory of Mr. De la Gran^e"^ ; and it is pro- 



bable, that this takes place in the particles of a very light 



elastic fluid of a peculiar nature, and which should not be 



confounded with the gasses, that compose what we know of 



the atmosphere. 



* Hi5t. of the Royal Acad, of Sciences of Paris, 17S8. 



+ Misccl. Phil. Mat. Societ. Turin, torn. 1. 



With respect to the action of wind on the propagation of sound, Mr, 

 Perrauli, formerly member of the Academy of Sciences of Paris, ex- 

 presses himself as follows. 

 Wind cannot " The invisible particles of bodies, which by their structure and con- 

 fejtTie auith <:f- figuration occasion their essential difF£rences, are themselves com- 

 ferEonscno- posed of atoms still smaller, and less different in different substances 

 than those particles. Both the atoms and particles are endued with 

 elasticity. When the particles are agitated fn such a manner, that this 

 elasticity comes to act, on their recoil they strike the particles of the air 

 that touch tkem with the greatest velocity they can impress upon 

 them, since it is produced by the spring of their elasticity ; and 

 ■* this vHocity is so great, it exceeds ihat which the air commonly has 



for withdiawing behind the substance that strikes it. Besides, as the 

 space in which the spring has acted is extremely sn-iail, the air can pass 

 this short space forward with greater facility than retire behind the atom. 

 The patticle of air struck advances a space equal to that, to which 

 the spring has stretched, pushing that next to it, and so on to the ear. 

 Mencc the sound is propagated with so much velocity ; and other agita- 

 nioBS of the a.ir, as the wind, prevent its propagation but very little, as 

 fcb«y are too slow with re.«pect to it." .Hi.st. de I'Acad., vol. 1, p. 22ii. 



X Inquiries conceTning the Nature and Propagatiou of Sound, by Lewis 

 ife]» Grange. ■• 



Full 



