The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

DISCOVERIES OF STURGEON AND HENRY. 117
DISCOVERIES OF STURGEON AND HENRY.
The next grand step taken in the science of electro-magnetism was by Sturgeon in 1825. He bent a piece of iron wire
in the form of a horse-shoe. He
then insulated the iron wire, bent Fig. 4.
as a horse-shoe, by covering it
with varnish; and having thus
covered the iron to be magnetized,
he wound around it a copper wire, s
and placed the spirals so that they
would not touch, in order to prevent the current from passing
from one spiral to the other with- |lUil i
out circulating around the iron.
The result was a complete success. The ends of the bent
iron wire were found to be magnetic when the current was on
the spiral wire; and when off, it was not magnetic. This
experiment was an advance of Arago and Ampere. Fig. 4
represents the plan adopted by Sturgeon. It is an exact copy
of the original drawing published in the "Annals of Philosophy," 1826.
Upon the theory advanced by Ampere, Arago coiled wire
around the glass tube to magnetize the needles; Sturgeon,
instead of using the glass tube to insulate the electric copper
wire from the iron core to be magnetized, used varnish as an
insulator. It was a non-conductor, and separated the electric
wire from the iron. Besides the improvement in the idea of
the insulation, he bent the wire in the form of a u, which was
a very important progress from the straight bar or needle.
Professor Joseph Henry, of America, in his philosophical
researches, in 182S, continued in 1829 and 1830, was led to
Fig. 5. Fig. 6.
make farther advances, and he perfected the construction of
the electro-magnet as now known in the science. He con