On the Velocity of Sound, 29 



80g' . (P-l/)g . ■ p, ■ D _ 16(P-i/)ff D/ 

 480° • 448"' + < " "- (44«+i)g/ 



The Jast factor is constant, and its value may be had by insert- 

 ing those of ^' and I> for any place where they are known. 

 Those for London will make it about 48.3. Hence, Laplace's 

 general formula becomes, for any place, 



V=48.3j^^^^^\ in English feet. 



Here, since /"is always small compared with P, it is manifest, 

 that when P alone varies, it must do .so in a great degree to af- 

 fect V ; and, even then, V will vary in the opposite direction. 

 It is therefore evident, that Newton and Laplace did not, as 

 some suppose, make the velocity of sound vary as the square 

 root of the barometric pressure, when t and/ are constant. 



I am not aware of any experiments having been made which 

 could enable us to ascertain whether or not the variations of ba- 

 rometric pressure, considered separately, affect the velocity ; for 

 either the ranges have been too short, and of course the velocity 

 uncertain, from the uncertainty of at least a tenth of a second 

 in the minute interval of elapsed time ; or the effects of wind 

 have been left undetermined, in all cases with which I am ac- 

 quainted where the barometer has been known to have varied 

 materially. As, however, I suspect the velocity to be greater 

 when the sound is more intense, I should expect that the baro- 

 metric pressure will be found to have some influence ; and that, 

 for the same reason, the velocity should vary in a less ratio than 

 V(4!48°+^) for temperature. A comparison of Mr Golding- 

 ham's experiments in the torrid zone with those which have been 

 made in the Arctic expeditions, goes far to establish the latter 

 conjecture. Experiments could even be made through a consi- 

 derable range, both of temperature and pressure, within the 

 temperate zones, by operating at different seasons of the year, 

 and at different heights above the level of the sea. Careful ex- 

 periments, varied in this way, would throw infinitely more light 

 on the subject than all the abstract theories in the world. 



