270 



VII. DYNAMICS OF ROTATING BODIES. 



without (Fig. 83 b) so that if we consider the relative motion, in the 

 former case a point fixed to the herpolhode describes a sort of 



Fig. 88. 



Fig. 83. 



Fig. 88. 



hypocycloid (loops out) on the card attached to the polhode, in the 

 latter a sort of epicycloid (loops in). 



Fig. 83 a. 



Fig. 83 a. 



The recent astronomical discovery of the motion of the earth's 

 pole is probably due to a sort of variable Poinsot- motion, the moments 

 of inertia of the earth being gradually varied. 



Cone 



Fig. 83 b. 



