288 OUTLINES OF NATURAL PHILOSOPHY. 



ternate condensations and rarefactions of that fluid, 

 in consequence of which the particles go and re- 

 turn, or oscillate backwards and forwards for some 

 time, even though there is no renewal of the im- 

 pulse of the sonorous hody, yet every such oscilla- 

 tion acts only once, or by a single impulse on the 

 ear. AVere it otherwise, sound would be always 

 something inarticulate and ill defined. 



388. The velocity with which vibrations are 

 propagated through the air, is the same that a 

 heavy body would acquire by falling through half 

 the height of the homogeneous atmosphere, or that 

 which the atmosphere would be reduced to, if it 

 were every where of the same density, and the 

 same temperature with the air at the surface of the 

 earth. 



The height of this homogeneous atmosphere has been 

 formerly computed at 4343 fathoms, when the tem- 

 perature is that of freezing. If this height be call- 

 ed H, then v 9 the velocity of the aerial vibrations, 

 = V^^H. Hence V 1057, which is too small, 

 as it is found by experiment to be 1142 feet per 

 second. 



The nature of the vibrations of an elastic fluid, was 

 first considered by NEWTON, and their velocity de- 

 fined, as in the preceding proposition, by compa- 

 ring them with the vibrations of a pendulum, 

 2 Princip. 



