532 



VISCOSITY. 



[CHAP, xi 



fundamental assumptions are very different. In the former case inertia was 

 predominant, and viscosity neglected ; in the present problem these circum- 

 stances are reversed. 



If X be the extraneous force acting on the sphere, this must balance the 



resistance, whence 



(xiv). 



It is to be noticed that the formula (xiii) makes the momentum and the 



