1261 



For the equation with the second member we must add to it the term 



-— RT 1 

 A' = — 



N 6jtga ' 



When we again write - — for r', it appears that for t of the 



m 



order 1 sec. the argument of /^ and Y^ becomes of tiie ordei- 10\ 



For such large arguments the terms with the Bessel's functions may 



be neglected, so that equation (Ic) is left. 



Remark 1. The equation {€) on p. 1256 -^= — p^ '^' H- 7 ^'^s 



been derived by Miss Snethi.age and me from equation {A): 



^ .T = 



and used for the calculation of A'. Ohnstkin and Zernike have 

 advanced objections to this equation and the use we have made of it. 

 Erroneously as it seems to me. But the fact that they make objec- 

 tions to it shows that the validity of this and simular equations 

 requires further elucidation. In itself equation (6') is of course not 

 inaccurate, but nothing can be derived from it. It only gets its meaning 

 from the significance that rs assigned to p' and q. 

 When we multiply {C) by mx, we get'): 



. d)t . . 



m X — = — mp^ x^ -\- rn q X . 

 dt 



When we then average over all the particles, and when equation 

 (B) is taken into account, we find : 



— il" =. — m p^ x^ -{- mq x . 



Up to now we have left p^ and ^entirely undetermined. When 

 we now, however, choose 



P' = -= . . W 



mx* 



it appears that : 



qx^O . . . (E) 



p* z= constant for a swarm of suspended particles that are in a 

 stationary state. Hence the equation (C) simply means this that for 



a definite particle I separate the — p into two terms. 1 choose as 



') I owe this derivation to an oral communication by Mr. Zernike. 



87 

 Proceedings Royal Acad. Amsterdana. Vol. XX. 



