656 



with the straight line for •/« = oo {a =: go), when x or « are above 

 a certain small value. With regard to the precision of the measure- 

 ments all cases in which x ]> 5 X 10-^ (« > 0.01) may be treated 

 as if ï< = 00 (« = ODj. If the observations agree with the theory for 

 y, =z GO, we may consequently only conclude from this that r. is 

 larger than this small value. 



The quantity x occurring above has the dimension of a velocity 

 and to know what the values of y. mentioned before mean, we have 

 to find out with what velocity x has to be compared. So we have 

 to enter into a closer investigation of the physical meaning of x, 

 also to decide whether y. may assume all values between zero and 

 infinity as has been tacidly supposed up till now. 



From the way in which (XIX) is deduced, follows : 



'^ = y.Fio,t) (XX) 



at 



dill 



Now bearing in mind, that represents the number of the 



dt 



particles that sticks to the wall in a unit of time, it naturally 

 suggests itself to compare this witli the number of the particles that 

 collides against the wall. This number, as is known from the kinetic 

 theory of gases and liquids, amounts to : 



^i^(o,0 = >c, /'(o,0'), ..... (XX7) 



where v is the mean velocity of the particles that is given by the 

 known formula: 



.==1 /^ i^XXlI) 



V Nm 



Here ti, T and N have the known meaning and m is the mass 

 of the particle. With the help of the values given by Brillouin we 

 find for the number of the collisions in a second: 



y.^ F {o, t) = 0.1 F {o,t) 



From this follows, that of the particles, colliding against the wall 

 only a very small fraction 8 sticks. This s, that consequently represents 

 the probability that a colliding particle adheres, is to be found from : 



') When we want to take the change of the concentration with the distance from 

 the wall into account, we have to substitute Fp=o + ^ I aT ) ,=o ~ ^ ^^^ F/j=o = 0, 

 where A is a length of the order of magnitude of the mean free path of a particle. 

 As J5(^)_^j= K F/j=o, the ratio of the correction to the used value is 

 2jr , i-e. always very small. 



