PERPETUAL MOTION 6l 



4. The friction at the point y, this last being the most 

 serious of all. An " opening of the tube with practically 

 little or no friction, and also without leakage " is a mechan- 

 ical impossibility. In order to have the joint water-tight, 

 the tube must hug the rope very tightly and this would 

 make friction enough to prevent any motion. And the 

 longer the column of water xz, the greater will be the ten- 

 dency to leak, and consequently the tighter must be the 

 joint and the greater the friction thereby created. 



A favorite idea with perpetual-motion seekers is the 

 utilization of the force of magnetism. Some time prior to 

 the year 1579, Joannes Taisnierus wrote a book which is 

 now in the British Museum and in which considerable 

 space is devoted to " Continual Motions " and to the 

 solving of this problem by magnetism. Bishop Wil- 

 kins in his " Mathematical Magick " describes one of the 

 many devices which have been invented with this end 

 in view. He says : " But amongst all these kinds of inven- 

 tion, that is most likely, wherein a loadstone is so disposed 

 that it shall draw unto it on a reclined plane a bullet of 

 steel, which steel as it ascends near to the loadstone, may 

 be contrived to fall down through some hole in the plane, 

 and so to return unto the place from whence at first it 

 began to move ; and, being there, the loadstone will again 

 attract it upwards till coming to this hole, it will fall down 

 again ; and so the motion shall be perpetual, as may be 

 more easily conceivable by this figure (Fig. 15) : 



" Suppose the loadstone to be represented at AB, which, 

 though it have not strength enough to attract the bullet 

 C directly from the ground, yet may do it by the help of 

 the plane EF. Now, when the bullet is come to the top 

 of this plane, its own gravity (which is supposed to exceed 



