um were now added to the list of illuminating materials. The
American whaling fleet, which at the time of Edison's birth mustered
over seven hundred sail, had dwindled probably to a bare tenth when he
took up the problem of illumination; and the competition of oil from the
ground with oil from the sea, and with coal-gas, had made the artificial
production of light cheaper than ever before, when up to the middle
of the century it had remained one of the heaviest items of domestic
expense. Moreover, just about the time that Edison took up incandescent
lighting, water-gas was being introduced on a large scale as a
commercial illuminant that could be produced at a much lower cost than
coal-gas.

Throughout the first half of the nineteenth century the search for a
practical electric light was almost wholly in the direction of employing
methods analogous to those already familiar; in other words, obtaining
the illumination from the actual consumption of the light-giving
material. In the third quarter of the century these methods were
brought to practicality, but all may be referred back to the brilliant
demonstrations of Sir Humphry Davy at the Royal Institution, circa
1809-10, when, with the current from a battery of two thousand cells, he
produced an intense voltaic arc between the points of consuming sticks
of charcoal. For more than thirty years the arc light remained an
expensive laboratory experiment; but the coming of the dynamo placed
that illuminant on a commercial basis. The mere fact that electrical
energy from the least expensive chemical battery using up zinc and
acids costs twenty times as much as that from a dynamo--driven by
steam-engine--is in itself enough to explain why so many of the electric
arts lingered in embryo after their fundamental principles had been
discovered. Here is seen also further proof of the great truth that one
invention often waits for another.

From 1850 onward the improvements in both the arc lamp and the dynamo
were rapid; and under the superintendence of the great Faraday, in 1858,
protecting beams of intense electric light from the voltaic arc were
shed over the waters of the Straits of Dover from the beacons of South
Foreland and Dungeness. By 1878 the arc-lighting industry had sprung
into existence in so promising a manner as to engender an extraordinary
fever and furor of speculation. At the Philadelphia Centennial
Exposition of 1876, Wallace-Farmer dynamos built at Ansonia,
C