658 



When f =: 1 or is at least not too small, we get very approximatelj 

 ^ = 1 and (XXV) becomes: 



drif 



— ^ = 4rri?Z)»„ {XXVo) 



(it 



as is also found by v. Smoluchowski. If f is however very small, then 

 the same formulae remain valid as is also remarked by v. S., when 

 we only multiply t with a constant factor. This factor however is 



8Xj R 



not, as V. S. assumes t, but -. So, as long as t does not 



sTt^R -f- D 



become very small, the formula (XXV'^) of v. Smoluchowski holds 



good. When however f becomes a very small fraction, then the 



number of particles that sticks per unit of time also becomes smaller, 



80 that in this way the slow coagulation may be explained. 



Finally I wish ro express my sincere thanks to Prof.Dr. L.S. Ornstein 



for his kind help and advice at the composition of this communication. 



Utrecht, April 1917. Institution for Theoretical Physics. 



