Edison's next important work was the adaptation of the electric light
for domestic illumination. At the beginning of the century the Cornish
philosopher, Humphrey Davy, had discovered that the electric current
produced a brilliant arch or 'arc' of light when passed between two
charcoal points drawn a little apart, and that it heated a fine rod of
charcoal or a metal wire to incandescence--that is to say, a glowing
condition. A great variety of arc lamps were afterwards introduced; and
Mr. Staite, on or about the year 1844-5, invented an incandescent lamp
in which the current passed through a slender stick of carbon, enclosed
in a vacuum bulb of glass. Faraday discovered that electricity could be
generated by the relative motion of a magnet and a coil of wire, and
hence the dynamo-electric generator, or 'dynamo,' was ere long invented
and improved.
In 1878 the boulevards of Paris were lit by the arc lamps of Jablochkoff
during the season of the Exhibition, and the display excited a
widespread interest in the new mode of illumination. It was too
brilliant for domestic use, however, and, as the lamps were connected
one after another in the same circuit like pearls upon a string, the
breakage of one would interrupt the current and extinguish them all but
for special precautions.
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