447 
on the velocity of sound , made in Holland. 
The ratio of the specific heat of the air when the volume is 
constant, to the specific heat of air at a constant pressure, 
or— , is, according to the experiments of Gay Lussac and 
In Sir Isaac Newton’s formula v/£. by which the ve- 
locity of sound is expressed, D is the density of air, that of 
mercury being taken for unit. 
By Biot’s and Arago’s experiments, the density of per- 
fectly dry air was found at o ra ,7 6 barometrical pressure to 
be equal to unity divided by 10466,82. 
But when the barometrical pressure alters and becomes p , 
and the temperature becomes t, we have by the law of Ma- 
RIOTTE D = p 
And introducing into this formula the correction for the 
aqueous vapour existing in the air, and calling F the tension 
of aqueous vapour existing in the air, we find 
10466,82 xo ra 3 76 | i-j-£. 0,00375 j 
This value of D being substituted in Sir Isaac’s formula, 
we have the velocity of sound by theory 
According to Laplace, this formula must be multiplied by 
the square root of the ratio between the specific heat of air at 
Welter, equal to 1,3748 = — 
D = 
P-T F 
