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83
Meanwhile, however, Edison staked his money and reputation on a large-scale
installation in the middle of New York. He bought a site on Pearl Street, moved into
it with a small army of technicians, and built six large direct-current generators,
altogether of 900 h. p., powered by steam-engines. Several miles of streets were dug
up for the electric cables – also designed and manufactured by Edison – to be laid,
and eighty-five buildings were wired for illumination. On 4 September 1882 New
Yorkers had their first glimpse of the electric age when 2,300 incandescent lamps
began to glow at the throwing of a switch in the Pearl Street power station. Electric
lighting had come to stay. And what was most important: Edison had finally
established a practical method of supplying electricity to the homes of the people.
Pearl Street was not the first generator station to be built. A 1-h. p. generator
for the supply of current for Edison lamps was built in 1881. In Germany, Werner
von Siemens did more than any other engineer for the introduction of electric
lighting, in which he had first refused to believe, by perfecting his 'dynamo', as he
called the generator for continuous current.
Spectacular as the advent of electric lighting was, it represented only one aspect
of the use of electricity, which was rapidly gaining in popularity among industrial
engineers. For a century, the reciprocating steam-engine had been the only important
man-made source of mechanical energy. But its' power was limited to the place
where it operated; there was no way of transmitting that power to some other place
where it might have been required. For the first time, there was now an efficient
means of distributing energy for lighting up homes and factories,, and for supplying
engines with power.
The engine which could convert electric energy into
mechanical power was
already in existence. As early as 1822, nearly a decade before he found the principle
of the electric generator, Faraday outlined the way in which an electric motor could
work: by placing a coil, or armature, between the poles of an electromagnet; when a
current is made to flow through the coil the electro-magnetic force causes it to rotate
– the reverse principle, in fact, of the generator.
The Russian physicist, Jacobi built several electric motors during the middle
decades of the 19th century.
Jacobi even succeeded in running a small, battery-powered electric boat on the
Neva river in St. Petersburg. All of them, however, came to the conclusion that the
electric motor was a rather uneconomical machine so long as galvanic batteries were
the only source of electricity. It did not occur to them that motors and generators
could be made interchangeable.
In 1888, Professor Galileo Ferraris in Turin and Nikola Tesla – the pioneer of
high-frequency engineering – in America invented, independently and without
knowing of each other's work, the induction motor. This machine, a most important
but little recognized technical achievement, provides no less than two-thirds of all the
motive power for the factories of the world, and much of modern industry could not
do without it. Known under the name of 'squirrel-cage motor'
1
– because it resembles
the wire cage in which tame squirrels used to be kept – it has two robust circular
;rings made of copper or aluminium joined by a few dozen parallel bars of the same
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