he nature of the problem that confronted Edison at the outset.
There was nothing in the whole world that in any way approximated a
solution, although the most brilliant minds in the electrical art had
been assiduously working on the subject for a quarter of a century
preceding. As already seen, he came early to the conclusion that the
only solution lay in the use of a lamp of high resistance and small
radiating surface, and, with characteristic fervor and energy, he
attacked the problem from this standpoint, having absolute faith in
a successful outcome. The mere fact that even with the successful
production of the electric lamp the assault on the complete problem
of commercial lighting would hardly be begun did not deter him in the
slightest. To one of Edison's enthusiastic self-confidence the long
vista of difficulties ahead--we say it in all sincerity--must have been
alluring.

After having devoted several months to experimental trials of carbon,
at the end of 1878, as already detailed, he turned his attention to the
platinum group of metals and began a series of experiments in which he
used chiefly platinum wire and iridium wire, and alloys of refractory
metals in the form of wire burners for incandescent lamps. These metals
have very high fusing-points, and were found to last longer than the
carbon strips previously used when heated up to incandescence by the
electric current, although under such conditions as were then possible
they were melted by excess of current after they had been lighted a
comparatively short time, either in the open air or in such a vacuum as
could be obtained by means of the ordinary air-pump.

Nevertheless, Edison continued along this line of experiment with
unremitting vigor, making improvement after improvement, until about
April, 1879, he devised a means whereby platinum wire of a given length,
which would melt in the open air when giving a light equal to four
candles, would emit a light of twenty-five candle-power without fusion.
This was accomplished by introducing the platinum wire into an all-glass
globe, completely sealed and highly exhausted of air, and passing a
current through the platinum wire while the vacuum was being made.
In this, which was a new and radical invention, we see the first step
toward the modern incandescent lamp. The knowledge thus obtained that
current passing through the platinum during exhaustion would drive out
occluded gases (i.e., gases mechanically hel