99 
for ascertaining the velocity of sound. 
brings out the velocity of sound greater in the proportion of 
ten to nine, or 109 feet more, making the velocity 1088 
feet ; besides, vapours are dispersed through the air, which 
being of a different tone and elasticity, do not partake of the 
motion of the true air, by which sound is propagated ; and 
it is also demonstrated, that the motion of sound will be 
quicker in such an atmosphere than in an atmosphere of true 
air, in the ratio of twenty-one to twenty ; then the velocity 
last found being augmented in that proportion, we shall have 
1142 feet for the velocity of sound in a second, according to 
Sir Isaac Newton's theory. 
La Place, using the Newtonian formula, which he con- 
siders correct, and a theorem which he gives, makes the 
velocity of sound in a second 345,35 metres (or 1133,06 feet 
English) the temperature being 43°. The French Acade- 
micians, as before mentioned, found the velocity 3 3 7, 18 
metres, or no6| feet English. By experiments of Lacaille 
the velocity was 344,42 metres, 1130,1 feet English, but the 
temperature is not mentioned. 
In the above enumeration of the velocity of sound, given 
by different philosophers, very considerable discordances are 
observable ; the actual reason of which cannot, I imagine, be 
discovered without the details of the experiments, and these 
are not in my possession ; but probably, a particular exami- 
nation of the experiments I am about to submit, may furnish 
a clue for the discovery of the cause of these differences. 
Halley and Flamsteed are the only two, whose results 
agree with the theory ; but I am not quite certain whether 
their results were deduced from theory or experiment. Be 
this as it may, the conclusion drawn from the experiments 
