128 
long. With asingle cell of the construction just described, and 
exposing about five feet of active zinc surface, this magnet lifted 
twenty-three hundred pounds. It was of this magnet that Sturgeon 
himself wrote thus: ‘‘ By dividing about eight hundred feet of con- 
ducting wire into twenty-six strands, and forming it into as many 
separate coils around a bar of soft iron about sixty.pounds in weight, 
and properly bent into a horseshoe form, Prof. Henry has been 
enabled to produce a magnetic force which completely eclipses every 
other in the whole annals of magnetism; and no parallel is to be 
found since the miraculous suspension of the celebrated Oriental im- 
postor in his iron coffin.’’* 
In his ‘‘ quantity’? magnet Henry sought to reduce the resistance 
to a minimum, and so to obtain a very considerable current even 
from a very small pair of plates. But he perceived that this was 
not the whole truth. And in January, 1831, he published a re- 
markable paper ¢ in which he showed for the first time that a coil 
composed of several short circuits in parallel, while least effective 
with a battery of many pairs of plates, was most responsive, on 
the contrary, to a single voltaic cell ; and, on the other hand, that a 
coil whose parts were all in series, which produced only trifling 
effects with a single pair, was highly effective with a battery of 
many pairs. Employing for example a small electromagnet having 
a core of quarter inch iron wound with about eight feet of copper 
wire, Henry found that with a single zinc plate, exposing about 
fifty-six square inches of surface, this magnet lifted four and one- 
half pounds. On interposing five hundred feet of copper wire be- 
tween the magnet and the cell it lifted only two ounces; and with 
one thousand feet interposed only half an ounce. On using a 
trough battery of twenty-five pairs of plates, on the other hand, 
the zinc surface exposed being the same as before, the magnet lifted 
only seven ounces when directly connected. But when the one 
thousand feet of wire was interposed the magnet sustained eight 
ounces. In other words, the current from the battery produced 
a greater magnetic effect after traversing this length of wire than it 
did without it. He calls an electromagnet having its coil contin- 
uous in length an “intensity ’’ magnet; and he says: ‘‘In de- 
scribing the results of my experiments, the terms ‘ intensity’ and 
‘quantity ’ magnets were introduced to avoid circumlocution, and 
* Phil. Mag. and Annals of Philosophy, xi, 199, March, 1832. 
+ Am. Jour. Science and Arts, xix, 400, Jan., 1831. 
