74 



THE DYNAMICAL THEORY OF OASES. 



The numbers given are the ratios of the transpiration-times of mixtures to 

 tliat of oxygen as determined by Mr Graham, compared with those given by the 

 equation (140) deduced from our theory. 



Conduction of Heat in a Single Medium (y). 

 The rate of conduction depends on the value of the quantity 



where f, rf, and * denote the mean values of those functions of 17, for 

 all the molecules in a given element of volume. 



As the expressions for the variations of this quantity are somewhat compli- 

 cated in a mixture of media, and as the experimental investigation of the con- 

 duction of heat in gases is attended with great difficulty, I shall confine myself 

 here to the discussion of a single medium. 



Putting 



Q = M(u + t){tf + * + vf+Zu+taHi + tool + $(? + if + ?)} ......... (142), 



and neglecting terms of the forms 7 and f 1 and rf when not multiplied by 

 the large coefficient &,, we find by equations (75), (77), and (54), 



(143). 



The first term of this equation may be neglected, as the rate of conduction 

 will rapidly establish itself. The second term contains quantities of four dimen- 



