314 Lord "Rayleigh on Conduction of Heat in a Spherical 



thermal capacity of unit, volume. This thermal capacity is 

 to be taken with volume constant, and it will be less than the 

 thermal capacity with pressure constant in the ratio of 7 : 1. 

 Accordingly v/y in (6) represents the latter thermal capacity, 

 of which the experimental value is "00128 x *239, the first 

 factor representing the density of air referred to water. 

 Thus, if we take the calorimetric conductivity at '000056. we 

 have in c.G.s. measure 



j>='258, v/ 7 =-183; 



and thence 



^ = -102« 2 . 



In the present apparatus a, determined by the contents, is 

 16*4 centim., whence 



£=27*4 seconds. 



The agreement of the observed and calculated values is 

 quite as close as could have been expected, and confirms the 

 view that the transfer of heat is due to conduction, and that 

 the part played by radiation is insensible. From a com- 

 parison of the experimental and calculated curves, however, 

 it seems probable that the effect of gravity was not wholly 

 eliminated, and that the later stages of the phenomenon, at 

 any rate, may still have been a little influenced by a downward 

 movement of the central parts. 



XXY. On tlie Conduction of Heat in a Spherical Mass of Air 

 confined by Walls at a Constant Temperature. By Lord 

 Rayleigh, F.R.S.* 



IT is proposed to investigate the subsidence to thermal 

 equilibrium of a gas slightly disturbed therefrom and 

 included in a solid vessel whose walls retain a constant 

 temperature. The problem differs from those considered by 

 Fourier in consequence of the mobility of the gas, which 

 may give rise to two kinds of complication. In the first 

 place gravity, taking advantage of the different densities 

 prevailing in various parts, tends to produce circulation. In 

 many cases the subsidence to equilibrium must be greatly 

 modified thereby. But this effect diminishes with the amount 

 of the temperature disturbance, and for infinitesimal dis- 

 turbances the influence of gravity disappears. On the other 

 hand, the second complication remains, even though we limit 

 ourselves to infinitesimal disturbances. When one part of 

 the gas expands in consequence of reception of heat by 



* Communicated by the Author. 



