ILLUSTRATIONS OF THE DYNAMICAL THEORY OF GASES. 403 



By choosing pairs of gases of equal density, and ascertaining the amount 

 of diffusion in a given time, we might determine the value of I in this expres- 

 sion. The diffusion of nitrogen into carbonic oxide or of deutoxide of nitrogen 

 into carbonic acid, would be suitable cases for experiment. The only existing 

 experiment which approximately fulfils the conditions is one by Graham, quoted 

 by Herapath from Brande's Quarterly Journal of Science, Vol. xvm. p. 76. 



A tube 9 inches long and 0'9 inch diameter, communicated with the 

 atmosphere by a tube 2 inches long and 0'12 inch diameter; 152 parts of 

 olefiant gas being placed in the tube, the quantity remaining after four hours 



was 99 parts. 



/ 

 In this case there is not much difference of specific gravity between the 



gases, and we have a = 9x(0'9) 2 - cubic inches, 6 = 00, c = 2 inches, and 



= (0'12) 4 square inches; 



a 



= 0-00000256 inch =^^Vo7 inch .................. (58). 



PROP. XXI. To find the amount of energy which crosses unit of area in 

 unit of time when the velocity of agitation is greater on one side of the area 

 tlian on the other. 



The energy of a single particle is composed of two parts, the vis viva 

 of the centre of gravity, and the vis viva of the various motions of rotation 

 round that centre, or, if the particle be capable of internal motions, the vis 

 viva of these. We shall suppose that the whole vis viva bears a constant 

 proportion to that due to the motion of the centre of gravity, or 



where /8 is a coefficient, the experimental value of which is T634. Substituting 

 E for M in Prop. XIV., we get for the transference of energy across unit 

 of area in unit of time, 



512 



