6 REPORT — 1851. 



solids ; seeing that any amount of rigidity, however small, will account for the 

 phsenomena, if we adopt certain suppositions as to molecular forces. 



V. Our knowledge of molecular forces is not as yet sufficiently advanced to enable 

 us to use experiments on the velocity of sound as a means of determining accurately 

 the coefficients of elasticity of solids. 



If we adopt for them the hypothesis already stated with respect to liquids, a theo- 

 retical investigation given in an Appendix shows that the velocity of sound in a cylin- 

 drical rod of an uncrystallized substance, whose surface is absolutely free, will be less 

 than that in an unlimited expanse in a ratio which is sensibly 1 : s/l for a very 

 slender filament, and approaches \/-2 : -V^S as the diameter of the rod increases ; but 

 the absolute freedom of the surface cannot be realized in practice ; the means used in 

 fixing the rod tend to restrain the lateral oscillations and accelerate the velocity of 

 sound. The ratios ascertained by experiment range from V'2 : V Z to near equality ; 

 but they are not sufficiently numerous to form data for any definite conclusions. 



The oscillations treated of in the special problems of the body of the paper being 

 of a kind called nearly longitudinal, a second Appendix is added, containing the 

 general equations of another kind, called nearly transverse, in uncrystallized bodies. 



On a General Theory of Gases. By J. J. Waterston, Bombay. 



llie 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 quan- 

 tity of heat contained in it. 



He shows that the result of this state of motion must be to give the gas an elasti- 

 city 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. Tempera- 

 ture, 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 abso- 

 lute 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 ob- 

 tained at the expense of the vis-viva of the atoms. This principle explains the varia- 

 tions of temperature produced by the expansion and condensation of gases — the 

 laws of their specific heat under difi'erent 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. 



Light, Heat, Electricity, Magnetism. 



On the Cotiduction of Electricity through Water. 

 By F. C. Bakewell. 



Mr. Bakewell stated the results of some experiments on the conduction of electri- 

 tricity by water, made with a view to prove that an electric current may be trans- 

 mitted for a considerable distance through unprotected wires immersed in water. 

 The experiments were conducted on Saturday last in one of the Hampstead ponds. 

 A thin copper wire (No. 20), three hundred and twenty feet long, was stretched across 

 the pond, and two copper plates ten inches square, to which wires were soldered. 



