264 Mr KELLAND, ON THE MOTION OF 



a firmer foundation than any other. The hypothesis I should adopt 

 from the formula ^j = Z) {1 + c(Z} — l)\ would be that the air consists 

 of aggregations of different kinds of particles about a fluid which i 

 attractive or repulsive, or, perhaps, of aggregations about two fluids. 

 The particles themselves might be indifferent to each other's action, 

 and obey the pressure of this fluid. Thus we should reduce the 

 problem of pressure to that of particles in contact. 



30. The result of our foregoing calculations has gone to shew, 

 that, if we may suppose the phenomenon of sound due to the action 

 of the repulsive energies of particles varying according to the New- 

 tonian Law, there is no necessity for introducing an auxiliary hypo- 

 tliesis of the developement of Heat, but that the modifications, which 

 the forces themselves produce, supply the requisite change in the 

 energies of the action. The fact, that the same supposition is in- 

 applicable d'u-ectlij to Pressure, is no argument against its validity for 

 Sound ; as it is clear, that, if these attractive particles be not the 

 particles of air itself, but of some one or two media, exerting pres- 

 sin-cs on those of iiir, we must refer the statical pressiu'e of the 

 atmosphere to that of the particles of air, uniformly acted on ; but 

 the motion, at least the vibratory one, must be attributed to the con- 

 densation or rarefaction of the attracting particles, and therefore to 

 the variation of the action of these particles on each other, and on 

 the air. 



