FREE AND PERFECTLY ELASTIC MOLECULES IN A STATE OF MOTION. 
70 
Appendix II. 
Extract from the Report of the 21st Meeting of the British Association, Ipswich, 
1851. (Transactions of the Sections, p. 6.) 
On a General Theory of Gases. By J. J. Waterston, Bombay. 
The author deduces the properties of gases, with respect to heat and elasticity, from 
a peculiar form of the theory which regards heat as consisting in small but rapid 
motions of the particles of matter. He conceives that the atoms of a gas, being 
perfectly elastic, are in continual motion in all directions, being restrained within a 
limited space by their collisions with each other, and with the particles of surrounding 
bodies. The vis viva of those motions in a given portion of gas constitutes the 
quantity of heat contained in it. 
He shows that the result of this state of motion must be to give the gas an 
elasticity proportional to the mean square of the velocity of the molecular motions, 
and to the total mass of the atoms contained in unity of bulk; that is to say, to the 
density of the medium. This elasticity, in a given gas, is the measure of temperature. 
Equilibrium of pressure and heat between two gases takes place when the number of 
atoms in unity of volume is equal, and the vis viva of each atom equal. Temperature, 
therefore, in all gases, is proportional to the mass of one atom multiplied by the mean 
square of the velocity of the molecular motions, being measured from an absolute zero 
491° below the zero of Fahrenheit’s thermometer. 
If a gas be compressed, the mechanical power expended in the compression is 
transferred to the molecules of the gas, increasing their vis viva; and conversely, 
when the gas expands, the mechanical power given out during the expansion is 
obtained at the expense of the vis viva of the atoms. This principle explains the 
variations of temperature produced by the expansion and condensation of gases—the 
laws of their specific heat under different circumstances, and of the velocity of sound 
in them. The fall of temperature found on ascending in the atmosphere, if not 
disturbed by radiation and other causes, would correspond with the vis viva necessary 
to raise the atoms through the given height. 
The author shows that the velocity with which gases diffuse themselves is propor¬ 
tional to that possessed by their atoms according to his hypothesis. 
