64 WRITINGS OF JOSEPH HENRY. [^831 



ON A HECIPROCATING MOTION PRODUCED BY MAGNETIC AT- 

 TRACTION AND REPULSION. 



(Silliman's American Journal of Science, July, 1831, vol. XX, pp. 340-343.) 



To the Editor: 



Sir : — I have lately succeeded in producing motion in a 

 little machine by a power, which, I believe, has never before 

 been applied in mechanics — by magnetic attraction and 

 repulsion. 



Not much importance, however, is attached to the inven- 

 tion, since the article, in its present state, can only be con- 

 sidered a philosophical toy; although, in the progress of 

 discovery and invention, it is not impossible that the same 

 principle, or some modification of it on a more extended scale, 

 may hereafter be applied to some useful purpose. But with- 

 out reference to its practical utility, and only viewed as a 

 new effect produced by one of the most mysterious agents of 

 nature, you will not, perhaps, think the following account 

 of it unworthy of a place in the Journal of Science. 



It is well known that an attractive or rejDulsive force is 

 exerted between two magnets, according as poles of different 

 names, or poles of the same name, are presented to each 

 other. 



In order to understand how this principle can be applied 

 to produce a reciprocating motion, let us suppose a bar mag- 

 net to be supported horizontally on an axis passing through 

 the centre of gravity, in preciselj'^ the same manner as a dip- 

 ping needle is poised ; and suppose two other magnets to be 

 placed perpendicularly, one under each pole of the hori- 

 zontal magnet, and a little below it, with their north poles 

 uppermost; then it is evident that the south pole of the 

 horizontal magnet will be attracted by the north pole of one 

 of the perpendicular magnets, and its north pole repelled by 

 the north pole of the other: in this state it will remain at rest, 

 but if, by any means, we reverse the polarity of the hori- 

 zontal magnet, its position will be changed and the extremity, 



