451 
the velocity of sound, made in Holland. 
The French philosophers found a difference between their 
experiments of 23d and 24th of June, 1822, of ■§—. But the 
difference of which we obtained, if we reduce the obser- 
vations of both days to what they would have been in per- 
fectly dry air, and in temperature of o 0 cent, is still remark- 
ably lessened. The formula by which the velocity of sound in 
given hygrometrical circumstances, and a given tempera- 
ture of the air, is reduced to what it would be in dry air of 
o 0 cent, temperature, calling U 7 the velocity of sound in dry air 
of o° temperature ; U the velocity of sound at a tension of 
aqueous vapour = F, is as follows: 
u 
y / { 1 + °> 0 °37S * } X { i "°’ 37 6 5 i ) — ■ 
The 27th of June, 1823, we had 
U = 34o m ,o6 = 1116,032 English feet 
t = 11 0 , 16 cent . 
F =0,00925307 
p = 0,74475 metres. 
Substituting these quantities in the formula, we have 
U'= 332 tn ,38 = 1090,827 English feet. 
The 28th June, 1823, we had 
U = 339 m ,34 = 1113,669 feet 
t = ii°, 215 
F = 0,00840465 ;j 
which being substituted in the formula, we have 
U'= 33i m ,72 zb 1088,661 English feet. 
Thus the difference between the observations of both days, 
when reduced to dry air, and o° cent, is o m ,66 = 2,166 feet ; 
or of the mean of the observations of both days. It 
appears also, that by our experiments of the 27th and 28th 
