210 
DR. SIMONS ON THE COEFFICIENT OF THE FORMULA 
The degree of accuracy with which experiments on the velocity of sound are 
now conducted, naturally led to a supposition that some of the elements of the 
theoretical formula were susceptible of a greater degree of correctness ; and 
thus natural philosophers were rather inclined to attribute the difference 
between experiment and calculation to some deficiency of the analytical 
expression, than to error in the observation. 
It has been shown in a recent volume of the Philosophical Transactions, 
that the experiments on the velocity of sound, made by Captain Parry in the 
polar regions, lead to the same conclusions with those made by Drs. Moll and 
Van Bef.k, under widely different circumstances ; and this coincidence would 
tend to confirm our doubts as to the correctness of some of the elements of the 
computation. 
A very able experimentalist, M. Dulong, lately published some experiments 
on the specific heat of the gases*, in the investigation of which he recurs to 
Laplace’s analytical formula. M. Dulong’s reasoning is nearly this : If it be 
admitted that the velocity of sound in atmospheric air is obtained by multi- 
plying the Newtonian formula by the square root of the ratio between the two 
specific heats of the air, under a constant pressure, and under a constant 
volume, it must follow, that this ratio, or the coefficient with whose square 
root the original formula must be multiplied, may also be deduced from the 
velocity of sound as given by observation. Accordingly, M. Dulong com- 
puted this ratio or coefficient from actual observations on the velocity of sound, 
bv the formula v V 2 
g-P 
D 
in which K is the ratio between the specific heat of air under a constant 
pressure, and the specific heat of air under a constant volume, whilst V is the 
velocity of sound as obtained by experiment. 
The object of this paper is to compare the inquiries of M. Dulong with the 
experiments on the velocity of sound made by Drs. Moll and Van Beek, 
which were published in the Philosophical Transactions. 
The following Table contains only such of the observations of Drs. Moll and 
Van Beek, in which the guns were fired on both stations exactly at the same 
Annales de Physique et de Chimic, t. xli. p. 118 . 
