the Kinetic Theory of Gases. 143 



through wide ranges of pressure, and between 18° C. and 

 100° 0. 



In a mixture of equal numbers of two kinds of particles, of 

 diameters s ly s 2 , I find that for s 3 in the above formula we 

 must put 



i( Sl 3 + 2 s 3 + §2 3 ), 



where s=(s 1 + 5 2 )/2. Thus the "ultimate volume" is in- 

 creased if the sizes of the particles differ, though the mean 

 diameter is unaltered. 



(2) For the coefficient of viscosity in a single gas the value 

 found is 



PrcQi = P \ . 112 



37T71S 2 s/h s/ll ' 



where p is the density, and X the mean free path. The pro- 

 duct p\ is the same at all temperatures, so that the viscosity 

 is as the square root of the absolute temperature. 



(3) The steady linear motion of heat in a gas is next 

 considered, temperature being supposed to be higher as we 

 ascend, so as to prevent complication by convection. It is 

 assumed, as the basis of the inquiry, that : — 



Each horizontal layer of the gas is in the " special " state, 

 compounded with a vertical translation which is the same for 

 all particles in the layer. 



The following are the chief results: — 



(a) Since the pressure is constant throughout, we have 



Pn 



so that n/h is constant. 



(b) Since the motion is steady, no matter passes (on the 

 whole) across any horizontal plane. This gives for the speed 

 of translation of the layer at as, 



= [ v (tl n+d £l v ) v/S( 



(c) Equal amounts of energy are (on the whole) transferred 

 across unit area of each horizontal plane, per unit of time. 

 The value is 



By the above value of p, and its consequence as to the ratio 



