108 



tiie f'iHKMion of the fieqiiention of tlie axes has been deduced for 

 the case of molecules (particles) wliicii turn in a liquid, which is 

 acted upon bj an external couple and by a couple resulting from 

 the molecular impacts. The deduction of the results obtained there 

 follows immediately from our formulae. We need only S|)]it up 

 tiie couple exerted by the molecular movement into two parts, the 

 one — o<( {(( be the angular velocity of the particle) q = S jt ii<(^ 

 {(I radius of the particle) and into a second part of which the average 

 value (case average) is zero. For the motion of the axis we get then 



P'('(=i — Q a + X 



where P is the moment of inertia of the particle. 



If we take a z= u,--= i^, - z=: F, we get for u equation (1), from 

 P o 



which appears that the function of frequention can be deduced from 



a differential equation of the form (24a). 



Penally it may be observed that it offers no difficulties to extend 



our considerations to the Brownian motion of coordinates in systems 



with an arbitrary number of degrees of freedom. 



■ Utrecht, Dec 8 1917. [nstitute for Theoretical Phydcs. 



