

1SOPERI METRICAL PROBLEMS. 591 



problem of dynamics involving only two freedoms 

 to move, I am sure you will understand suffi- 

 ciently to admire the great beauty of this theorem. 



The doctrine of isoperimetrical problems in its 

 relation to dynamics is very valuable in helping 

 to theoretical investigation of an exceedingly im- 

 portant subject for astronomy and physics the 

 stability of motion, regarding which, however, I 

 can only this evening venture to show you some 

 experimental illustrations. 



The lecture was concluded with experiments 

 illustrating 



1. Rigid bodies (teetotums, boys' tops, ovals, 

 oblates, &c.) placed on a horizontal plane, and 

 caused to spin round on a vertical axis, and found 

 to be thus rendered stable or unstable according 

 as the equilibrium without spinning is unstable 

 or stable. 



2. The stability or instability of a simple 

 pendulum whose point of support is caused to vi- 

 brate up and down in a vertical line, investigated 

 mathematically by Lord Rayleigh. 



3. The crispations of a liquid supported on a 



