THE KINETIC THEORY OF GASES. 345 



Prof. Loschmidt do hot agree with his formula in a manner corresponding to 

 the accuracy of his experiments. They agree in a very remarkable manner with 

 the formula derived from the kinetic theory. 



I have recently been revising the theory of gases founded on that of the 

 collisions of elastic spheres, using, however, the methods of my paper on the 

 dynamical theory of gases (Phil. Trans. 1866) rather than those of my first 

 paper in the Phil. Mag., 1860, which are more difficult of application, and 

 which led me into great confusion, especially in treating of the diffusion of 

 gases. 



The coefficient of interdiffusion of two gases, according to this theory, is 



D - -i=-Z 



where w l and w t are the molecular weights of the two gases, that of hydrogen 

 being unity. 



s a is the distance between the centres of the molecules at collision in centi- 

 metres. 



V is the " velocity of mean square " of a molecule of hydrogen at C. 



r = I = 185,900 centimetres per second. 



P 



N is the number of molecules in a cubic centimetre at C. and 76 cm. B. 

 (the same for all gases). 



D u is the coefficient of interdiffusion of the two gases in * ^ - 

 measure. 



We may simplify this expression by writing 





Here o is a quantity the same for all gases, but involving the unknown 

 number N. 



o- is a quantity which may be deduced from the corresponding experiment 

 of M. Loschmidt. We have thus 



*i = <ur tt (3), 



VOL. n. 44 



