Laplace proved that by multiplying Newton’s velocity by the square root of the ratio of the specific heat of air at constant pressure to its specific heat at constant volume, the actual or observed velocity is obtained.
Conversely, from a comparison of the calculated and observed velocities, the ratio of the two specific heats may be inferred.
The mechanical equivalent of heat may be deduced from this ratio; it is found to be the same as that established by direct experiment.
This coincidence leads to the conclusion that atmospheric air is devoid of any sensible power to radiate heat. Direct experiments on the radiative power of air establish the same result.
The velocity of sound in water is more than four times its velocity in air.
The velocity of sound in iron is seventeen times its velocity in air.
The velocity of sound along the fibre of pine-wood is ten times its velocity in air.
The cause of this great superiority is that the elasticities of the liquid, the metal, and the wood, as compared with their respective densities, are vastly greater than the elasticity of air in relation to its density.
The velocity of sound is dependent to some extent upon molecular structure. In wood, for example, it is conveyed with different degrees of rapidity in different directions.