32 



Lord Kelvin on the 



and in (f3) they are in simple proportion to the velocity of its 

 centre of inertia when it leaves F or returns to it. 



Fig. 8. 



Pi 





/ \ / / 



{J 



1 { 



§ 48. In the cases of §§ 46, 47, we have to consider the 

 time-integral for each flight of the kinetic energy of the 

 component velocity of the particle perpendicular to F, and of 

 the whole velocity of the centre of inertia of the rotator, 



