ercially. Still, electricity generated
by chemical action, even in a very perfect cell, was both feeble and
expensive, and, withal, only applicable in a comparatively limited
field. Another important scientific discovery was necessary before such
things as electric traction and electric lighting on a large scale were
to become possible; but that discovery was soon made by Sir Michael
Faraday.

Faraday, the son of a blacksmith and a bookbinder by trade, had
interested Sir Humphry Davy by his admirable notes on four of Davy's
lectures, which he had been able to attend. Although advised by the
great scientist to "stick to his bookbinding" rather than enter the
field of science, Faraday became, at twenty-two years of age, Davy's
assistant in the Royal Institution. There, for several years, he devoted
all his spare hours to scientific investigations and experiments,
perfecting himself in scientific technique.

A few years later he became interested, like all the scientists of
the time, in Arago's experiment of rotating a copper disk underneath a
suspended compass-needle. When this disk was rotated rapidly, the
needle was deflected, or even rotated about its axis, in a manner quite
inexplicable. Faraday at once conceived the idea that the cause of this
rotation was due to electricity, induced in the revolving disk--not only
conceived it, but put his belief in writing. For several years, however,
he was unable to demonstrate the truth of his assumption, although he
made repeated experiments to prove it. But in 1831 he began a series
of experiments that established forever the fact of electro-magnetic
induction.

In his famous paper, read before the Royal Society in 1831, Faraday
describes the method by which he first demonstrated electro-magnetic
induction, and then explained the phenomenon of Arago's revolving disk.

"About twenty-six feet of copper wire, one-twentieth of an inch in
diameter, were wound round a cylinder of wood as a helix," he said,
"the different spires of which were prevented from touching by a thin
interposed twine. This helix was covered with calico, and then a
second wire applied in the same manner. In this way twelve helices were
"superposed, each containing an average length of wire of twenty-seven
feet, and all in the same direction. The first, third, fifth, seventh,
ninth, and eleventh of these helices were connected at their extremities
end to end so as to form one helix; the others were connect