48 
THE CANTOR LECTURE, 1890. 
Sturgeon's further work during the next three years is best described 
in his own words :—"It does not appear that any very extensive experi¬ 
ments were attempted to improve the lifting power of electro-magnets 
from the time that my experiments were published in the f Transactions 
of the Society of Arts, &c.,' for 1825, till the latter part of 1828. Mr. 
Watkins, philosophical instrument maker, Charing Cross, had, however, 
made them of much larger size than any which I had employed, but I 
am not aware to what extent he pursued the experiment. In the year 
1828, Professor Moll, of Utrecht, being on a visit to London, purchased 
of Mr. Watkins an electro-magnet weighing about 5 lbs.—at that time, 
I believe, the largest which had been made. It was of round iron, 
about 1 inch in diameter, and furnished with a single copper wire 
twisted round it 83 times. When this magnet was excited by a large 
galvanic surface, it supported about 75 lbs. Professor Moll afterwards 
prepared another electro-magnet, which, when bent, was 124 inches 
high, 24 inches in diameter, and weighed about 26 lbs.; prepared like 
the former with a single, spiral conducting wire. With an acting gal¬ 
vanic surface of 11 square feet, this magnet would support 154 lbs., 
but would not lift an anvil which weighed 200 lbs." 
At the date of Sturgeon's work the laws governing the flow of 
electric currents in wires were still obscure. Ohm's epoch making 
enunciation of the law of the electric circuit appeared in "PoggendorfPs 
Annalen " in the very year of Sturgeon's discovery, 1825, though his 
complete book appeared only in 1827, and his work, translated by Dr. 
Francis into English, only appeared (in Taylor's "Scientific Memoirs," 
Vol. II.) in 1841. Without the guidance of Ohm's law it was not 
strange that even the most able experimenters should not understand 
the relations between battery and circuit which would give them the 
best effects. These had to be found by the painful method of trial and 
failure. Pre-eminent amongst those who tried was Professor Joseph 
Henry, then of the Albany Institute, in New York, later of Princeton, 
New Jersey, who succeeded in effecting an important improvement. 
In 1828, led on by a study of the “ multiplier " (or galvanometer), he 
proposed to apply to electro-magnetic apparatus the device of winding 
them with a spiral coil of wire " closely turned on itself," the wire 
being of copper from ^Vfh to -^th of an inch in diameter, covered with 
silk. In 1831 he thus describes the results of his experiments :—• 
“ A round piece of iron, about J inch in diameter, was bent into the 
usual form of a horse-shoe, and instead of loosely coiling around it a 
few feet of wire, as is usually described, it was tightly wound with 
35 feet of wire, covered with silk, so as to form about 400 turns; a 
pair of small galvanic plates, which could be dipped into a tumbler of 
diluted acid, was soldered to the ends of the wire, and the whole 
mounted on a stand. With these small plates the horse-shoe became 
much more powerfully magnetic than another of the same size, and 
wound in the same manner, by the application of a battery composed of 
28 plates of copper and zinc, each 8 inches square. Another con¬ 
venient form of this apparatus was contrived by winding.a straight 
bar of iron, 9 inches long, with 35 feet of wire, and supporting it 
horizontally on a small cup of copper containing a cylinder of zinc— 
