through Gases between Parallel Plates. 



665 



may be reduced to a form which is independent of both 

 i and q by putting 



and 



The equation then becomes 



2f— (i*i){ 



(*) 



*y(R,+ft 2 ) 2 



('+&SX' 



8tt <Wj ' 



(3) 



The writer also showed that for any gas for which R x and 

 R 2 are unequal there exist two pressures at which this 

 equation takes a soluble form. The solution is 



4-7T f — e r das 7 ] , i— "1 



y=-^- a \T=e —. ~jt +M cosh »* 



cosh 1_€ 



Rg — R t 



j-^Jj^ + A.J, 



(4) 



in w 



hich 



€ = 



Hi 



R, 



or = 



R x + R 2 Ri + H 2 



according as the pressure is such as to make 

 a, = 47reR 1 or = 47r^R 2 . 

 The integrals which here occur can only be evaluated in 

 finite form when -z— - is an integer, and when accordingly 



the velocity of one ion is an exact multiple of that of the 

 other:** This is not, however, usually the case, and for air 

 the ratio R 2 : R t is very nearly 5:4. It seemed desirable 

 to render my former paper more useful by calculating the 

 values of the integrals in this case. - 



Different physicists have obtained slightly different values 

 for the ratio, and we can hardly as yet say whether R 2 : R x 

 in the case of air is greater or less than 5 : 4. 



The tables which follow are calculated on the supposition 



that R 2 : R x = 5 : 4, 



and that the pressure is such that 



a = AireH^ 

 Phil. Mag. S. 6. Vol. 10. No. 60. Dec. 1905. 2 Z 



