52 WRITINGS OF JOSEPH HENRY. [1831 



nesses of wire, and on the ends or near the poles it is wound 

 so as to form six thicknesses. 



Two small galvanic batteries are soldered to the wires of 

 the magnet, one on each side of the supporting frame, in 

 such a manner as to cause the poles to be instantaneously- 

 reversed, by merely dipping the batteries alternately into 

 acid. To render these as compact as possible, they are 

 formed of concentric copper cylinders, with cylinders of zinc 

 plates interposed, and so united as to form but one galvanic 

 pair. Each of these batteries presents to the action of the 

 acid, (measuring both surfaces of the plate,) 4|- square feet: 

 they are 12 inches high and about 5 inches in diameter. 



In experimenting with this magnet, a battery containing 

 -§■ of a square foot of zinc surface was first attached to the 

 wires ; with this the magnet could not be made to support 

 more than 500 lbs. Another battery was then substituted 

 for the above, containing about three times the same quan- 

 tity of zinc surface; with this, at the first instant of immer- 

 sion, the magnet sustained 1600 lbs.; after the acid was 

 removed, it continued to support, for a few minutes, 450 

 lbs.; and in one experiment, three days after the battery- 

 had been excited, more than 150 lbs. were added to the 

 armature* before it fell. It was evident from these experi- 

 ments, that this magnet required a considerably larger 

 quantity of zinc surface in proportion to its weight, to mag- 

 netize it to saturation, than that described in the former 

 paper. Accordingly the two batteries, before mentioned as 

 containing 4^ square feet, were prepared. With one of 

 them, at the first immersion, the magnet readily supported 

 2000 lbs. A sliding weight was then attached to the bar ; 

 the battery was suffered to become perfectly dry, and on im- 

 mersing it again, the magnet supported 2063 lbs. The effect 

 of a larger battery was not tried. 



To test its power of inducing magnetism on soft iron, two 



* [The armature of 28 lbs. applied when the battery is immersed, only for 

 an inch and an instant, remains day after daj'- without falling, although 

 the galvanic coils are perfectly dry. — Editor of Journal.'] 



