1 -1 



747 



d — da — 



and 



:n:[/jT a a <t 



in which z^ = z^ -{- o cos y. 



Hence the number of the collisions in question per second and 

 per surface unity of tiie hiyer is: 



— e «- \\,coxii(y t<ui y dy d[-idz . (o) 



in which n (ienotes tlie number of molecides per cm\, iv the relative 

 velocity of molecule II with jespect to molecule I, and /< the angle 

 between the direction of i>,. and the central line, so that: 



v^,. COS (I := [u.^ — ii^) .sm 7 cos ,5 | {i\ — y,) siii y shi ;•? [- (w^ n\) cos y 

 i\t each of tljese collisions the .r-componejit of the quantity of 

 motion, which is instantaneously transferred from above downwards is : 



■y . nt i\. COS (.1 shi y cos ^ . . (4) 



The condition that really transfer of momentum through the 

 chosen plane is to take place is : 



^0 or y <^ Bg cos 



-z. 



a 



Hence i] is found by multiplication of (3) by (4), and then by 

 integration with respect to: 



y between and Bq cos - — 



l^ „ „ 2.^ 



?/,.... 10, ,, — 00 „ +00 



-, „ — ^ „ 



We have then still to multiply the ex[)ression by 2 for the 

 transfer from below upwards. We must, however, still pay attention 

 to something else. In the limits set above collisions have'been taken 

 into account which are impossible in reality. Only those combinations 

 of values of the independent variables can occur, for which (i is 

 obtuse, hence cos !i<^0. It is simpler to inti'oduce the condition that 

 i\.cosn <:^0. This condition can be introduced in the way of Dirichlkt 



I / sin p<i' 

 bv mnlliplicalion bv \f''i'r d(f 



