FIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORY
Copyright, 1904, by Byron, N. Y.
FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870
Copyright, 1904, by William J. Hammer
FIG. 60–FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880
The carbon thread in the incandescent light is heated to a white heat, and because it is so heated it gives out light. In air such a tiny thread of white-hot carbon would burn in a fraction of a second. The carbon must be in a vacuum, and so the air is pumped out of the light bulb with a special kind of air-pump invented not long before Edison began his work on the electric light. This pump is capable of taking out practically all the air that was in the bulb. Perhaps a millionth part of the original air remains.