e
electric light--or, more correctly, the subdivision of the electric
current--was not only possible but entirely practicable.

It will have been perceived from the foregoing chapters that from the
time of boyhood, when he first began to rub against the world, his
commercial instincts were alert and predominated in almost all of the
enterprises that he set in motion. This characteristic trait had grown
stronger as he matured, having received, as it did, fresh impetus and
strength from his one lapse in the case of his first patented invention,
the vote-recorder. The lesson he then learned was to devote his
inventive faculties only to things for which there was a real, genuine
demand, and that would subserve the actual necessities of humanity; and
it was probably a fortunate circumstance that this lesson was learned
at the outset of his career as an inventor. He has never assumed to be a
philosopher or "pure scientist."

In order that the reader may grasp an adequate idea of the magnitude and
importance of Edison's invention of the incandescent lamp, it will be
necessary to review briefly the "state of the art" at the time he
began his experiments on that line. After the invention of the voltaic
battery, early in the last century, experiments were made which
determined that heat could be produced by the passage of the electric
current through wires of platinum and other metals, and through pieces
of carbon, as noted already, and it was, of course, also observed that
if sufficient current were passed through these conductors they could be
brought from the lower stage of redness up to the brilliant white heat
of incandescence. As early as 1845 the results of these experiments were
taken advantage of when Starr, a talented American who died at the early
age of twenty-five, suggested, in his English patent of that year, two
forms of small incandescent electric lamps, one having a burner made
from platinum foil placed under a glass cover without excluding the air;
and the other composed of a thin plate or pencil of carbon enclosed in
a Torricellian vacuum. These suggestions of young Starr were followed
by many other experimenters, whose improvements consisted principally in
devices to increase the compactness and portability of the lamp, in
the sealing of the lamp chamber to prevent the admission of air, and
in means for renewing the carbon burner when it had been consumed. Thus
Roberts, in 1852, proposed to cement the neck o