PERPETUAL MOTION 41 



perpetually. Many years ago I made a pair of these col- 

 umns which kept a ball in motion for nearly two years, and 

 Professor Silliman tells us that " a set of these bells rang 

 in Yale College laboratory for six or eight years unceas- 

 ingly." How much longer the columns would have con- 

 tinued to furnish energy sufficient to cause the balls to 

 vibrate, it might be difficult to determine. The amount of 

 energy required is exceedingly small, but since the columns 

 are really nothing but a voltaic pile, it is very evident that 

 after a time they would become exhausted. 



Such a pair of columns, covered with a tall glass shade, 

 form a very interesting piece of bric-a-brac, especially if the 

 bells have a sweet tone, but the contrivance is of no prac- 

 tical use except as embodied in Bohnenberger's electroscope. 



Inventions of this kind might be multiplied indefi- 

 nitely, but none of these devices can be called a perpetual 

 motion because they all depend for their action upon energy 

 derived from external sources other than gravity. * But 

 the authors of these inventions are not to be classed with 

 the regular perpetual-motion-mongers. The purposes for 

 which these arrangements were invented were legitimate, 

 and the contrivances answered fully the ends for which 

 they were intended. The real perpetual-motion-seekers 

 are men of a different stamp, and their schemes readily fall 

 into one of these three classes : I. ABSURDITIES, 2. FAL- 

 LACIES, 3. FRAUDS. The following is a description of 

 the most characteristic machines and apparatus of which 

 accounts have been published. 



