1831] 



WRITINGS OP JOSEPH HENRY. 



55 



which was before attracted, will now be repelled ; if the 

 polarity be again reversed, the position will again be changed, 

 and so on indefinitely: to produce, therefore, a continued 

 vibration, it is only necessary to introduce, into this arrange- 

 ment, some means by which the polarity of the horizontal 

 magnet can be instantaneously changed, and that too by a 

 cause which shall be put in operation by the motion of the 

 magnet itself; how this can be efifected, will not be difficult 

 to conceive, when I mention that instead of a permanent 

 steel magnet in the moveable part of the apparatus, a soft 

 iron galvanic magnet is used.* 



The change of polarity is produced simply by soldering to 

 the extremities of the wires which surround the galvanic 

 magnet, two small galvanic batteries in such a manner that 

 the vibrations of the magnet itself may immerse these alter- 

 nately into vessels of diluted acid ; care being taken that the 

 batteries are so attached that the current of galvanism from 

 each shall pass around the magnet in an opposite direction. 



Instead of soldering the batteries to the ends of the wires, 

 and thus causing them at each vibration to be lifted from 

 the acid by the power of the machine, they may be perma- 

 nently fixed in the vessels, and the galvanic communication 

 formed by the amalgamated ends of the wires dipping into 

 cups of mercury. 



3 



[Electro-magnetic Engine.] 



*For a method of constructing the galvanic magnet on an improved plan, 

 see my paper in vol. xix, p. 400 of this Journal. [Ante, p. 37.] 



