On the Velocity ofSotnuI, fPt 



that the duration of a vibration has nothing to« do with its ex- 

 tent. These are most important points, but which have neither 

 yet l)cen, nor are likely soon to be, proved; and, until some- 

 thing more substantial than opinions or conjectures be advanced 

 in their behalf, the theory must, in a great measure, rest on a 

 slippery foundation. Mankind, it is true, do not all run to the 

 sAme extreme ; for some reject the theory of sound in the lump, 

 just as they do every thing which it would be too troublesome 

 to examine. 



If, as some philosophers suppose, gases and vapours, when 

 mixed, but uncombined, be as if in vacuo to each other, should 

 not each ingredient of a mixed medium have a propensity to 

 propagate the same sound with a velocity peculiar to itself ? and 

 should not the confusion occasioned thereby tend to render the 

 sound indistinct, if not soon to annihilate it altogether ? The 

 remarkable distinctness and audibility of sound at low tempera- 

 tures, may therefore be partly owing to the comparative simpli- 

 city of the medium ; because then the air necessarily contains 

 little moisture. Hence, when the temperature has sunk, and 

 the dew fallen, sound is better heard. Some, to be sure, as- 

 cribe all this to the more uniform temperature of the atmosphere 

 during night; but, so far as mere loudness is concerned, I 

 should rather ascril)e it to the greater density of colder air. 



Since tlie elasticity of air containing tjhe same proportion of 

 moisture is exactly as its density, when under the same tempe- 

 rature, it readily follows, on the theory stated above, that the 

 velocity of sound should, at the same temperature, be precisely 

 the same in air containing a like proportion of moisture, in every 

 latitude, and at every height above the level of the sea. Ano- 

 ther consequence is, that the height of the barometer has no- 

 thing .to do with the velocity of sound in dry air; and, in no 

 case whatever, under the same temperature, should the veloqity 

 increase or decrease when the barometric pressure alone does so, 

 but rather the reverse. All this will be rendered evident by 

 exhibiting the most approved formula for the velocity of sound, 

 as given by Newton, on the principle above stated, and remo- 

 delled by Laplace, viz. 



