127 
a half square inches of zinc surface, this magnet would sustain four- 
teen pounds. He then wound upon the core a second and similar 
wire, the ends of which were connected to the same cell; and now 
the magnet lifted twenty-eight pounds. With a single pair of 
plates 4x6 inches this magnet lifted thirty-nine pounds, or more 
than fifty times its own weight. This increase of power by multi- 
plying the number of wires without increasing the length of each, 
as Henry points out, produces its effect in two ways: ‘first, by 
conducting a greater quantity of galvanism, and secondly, by giving 
it a more proper direction.’’** Thus was constructed what Henry 
called his ‘‘ quantity ’’ magnet. 
Still larger electromagnets were constructed upon this plan 
in 1830 and 1831. The former magnet consisted of a bar of soft 
iron two inches square and twenty inches long, bent into the form 
of a horseshoe, and weighing twenty-one pounds. Around this was 
wound five hundred and forty feet of copper wire arranged in nine 
coils of sixty feet each; each strand being coiled in several 
layers, and occupying about two inches of the length of the core. 
The ends of these coils being left separate and numbered, 
the coils could be combined in any way desired so as to form one 
continuous coil, or a double coil of half the length, a triple coil 
one-third the length, etc. When a single pair of coils were put in 
series the electromagnet lifted sixty pounds; but when the coils 
were arranged in multiple, forming a double circuit, a lifting power 
of two hundred pounds was developed. ‘The cell used with this 
magnet was composed of two concentric cylinders of copper, having 
a zinc cylinder between them ; the exposed zinc surface being about 
0.4 square foot, and the acid required about half a pint. With all 
the coils in parallel the magnet with this battery lifted six hundred 
and fifty pounds; and with a pair of plates exactly an inch square 
the magnet lifted eighty-five pounds.f 
The 1831 magnet was made for the laboratory of Yale College. 
The iron horseshoe was about a foot in length, and was made from 
a bar of octagonal iron three inches in diameter. It was wound 
with twenty-six strands of copper wire, each about twenty-eight feet 
* Am. Jour. Science and Arts, xix, 402, Jan., 1831. 
+Am. Jour. Science and Arts, xix, 404, 405, 1831. See also the excellent memorial ad- 
dress on ‘‘The Scientific Work of Joseph Henry,” delivered before the Philosophical 
Society of Washington, Oct. 26, 1878, by Wm. B. Taylor, to which the author would here 
acknowledge his indebtedness. Bull, Phil. Soc., Washington, Vol. ii, p. 230. 
t Am. Jour. Science and Arts, xx, 201, April, 1831. 
