Electro-Magnet. a See 
other battery was then substituted for the above, containing about 
three times the same quantity of zinc surface ; with this, at the first 
instant of immersion, the magnet sustained 1600 Ibs. ; 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 experiments, that this magnet required a consid- 
erably larger quantity of zinc surface in proportion to its weight, to 
magnetize it to saturation, than that described in the former paper. 
Accordingly the two batteries, before mentioned as containing 43 
square feet, were prepared. With one of them, at the first immer- 
sion, the magnet readily supported 2000 Ibs. A sliding weight was 
then attached to the bar; the battery was suffered to become per- 
fectly dry, and on immersing it again, the magnet supported 2063 
- The effect of a larger battery was not tried. 
To test its power of inducing magnetism on soft iron, two pieces 
of round iron 11 inches in diameter and 12 inches long, were inter- 
posed between the extremities of the magnet and the armature— 
with this arrangement, when one of the batteries was immersed, the 
Pieces of iron became so powerfully magnetic as to support 155 lbs. 
To exhibit the effects produced by instantaneously reversing the 
Poles, the armature was loaded with 56 Ibs. which added to its own 
Weight made 89 Ibs.; one of the batteries was then dipped into the 
acid and immediately withdrawn, when the weight of course continued 
to adhere to the magnet ; the other battery was then suddenly im- 
mersed, when the poles were changed so instantaneously, that the 
Weight did not fall. That the poles were actually reversed in this 
€Xperiment, was clearly shown by a change in the position of a large 
needle placed at a small distance from the side of one extremity of 
the horse-shoe. 
P.S. Last autumn, I commenced a series of observations on the 
magnetic intensity of the earth at Albany, and intend to begin a new 
Setles next month ; the apparatus used was that sent by Capt. Sabine 
to Prof, Renwick, and was mentioned in the Journal, Vol. xvi, p. 
145. T have constructed a similar apparatus for myself, and intend 
'0 pay considerable attention to the subject. 
* The armature of 23 Ibs. applied when the battery is immersed, only for an inch 
and an j nt, remains, day after day, without falling. although the galvanic coils 
he Perfectly q ry. —Ed. 
