CAN A MAN LIFT HIMSELF 129 



A somewhat analogous result, but depending on different 

 principles, is attained in certain curious boat races which 

 are held at some English regattas and which is explained 

 by Prof. W. W. Rouse Ball, in his " Mathematical Recrea- 

 tions and Problems." He says that it 



" affords a somewhat curious illustration of the fact that 

 commonly a boat is built so as to make the resistance to 

 motion straight forward less than that to motion in the 

 opposite direction. 



" The only thing supplied to the crew is a coil of rope, 

 and they have (without leaving the boat) to propel it from 

 one point to another as rapidly as possible. The motion 

 is given by tying one end of the rope to the afterthwart, 

 and giving the other end a series of violent jerks in a 

 direction parallel to the keel. 



" The effect of each jerk is to compress the boat. Left 

 to itself the boat tends to resume its original shape, but 

 the resistance to the motion through the water of the 

 stern is much greater than that of the bow, hence, on the 

 whole, the motion is forwards. I am told that in still water 

 a pace of two or three miles an hour can be thus attained." 



