Heroes of the Telegraph | Page 9

and
ingenious. He cut the wire at the middle, to form a gap which a spark
might leap across, and connected its ends to the poles of a Leyden jar
filled with electricity. Three sparks were thus produced, one at either
end of the wire, and another at the middle. He mounted a tiny mirror on
the works of a watch, so that it revolved at a high velocity, and
observed the reflections of his three sparks in it. The points of the wire
were so arranged that if the sparks were instantaneous, their reflections
would appear in one straight line; but the middle one was seen to lag
behind the others, because it was an instant later. The electricity had
taken a certain time to travel from the ends of the wire to the middle.
This time was found by measuring the amount of lag, and comparing it
with the known velocity of the mirror. Having got the time, he had only
to compare that with the length of half the wire, and he found that the
velocity of electricity was 288,000 miles a second.
Till then, many people had considered the electric discharge to be
instantaneous; but it was afterwards found that its velocity depended on
the nature of the conductor, its resistance, and its electro-static capacity.
Faraday showed, for example, that its velocity in a submarine wire,
coated with insulator and surrounded with water, is only 144,000 miles
a second, or still less. Wheatstone's device of the revolving mirror was
afterwards employed by Foucault and Fizeau to measure the velocity of
light.
In 1835, at the Dublin meeting of the British Association, Wheatstone
showed that when metals were volatilised in the electric spark, their
light, examined through a prism, revealed certain rays which were
characteristic of them. Thus the kind of metals which formed the
sparking points could be determined by analysing the light of the spark.
This suggestion has been of great service in spectrum analysis, and as
applied by Bunsen, Kirchoff, and others, has led to the discovery of
several new elements, such as rubidium and thallium, as well as
increasing our knowledge of the heavenly bodies. Two years later, he

called attention to the value of thermo-electricity as a mode of
generating a current by means of heat, and since then a variety of
thermo-piles have been invented, some of which have proved of
considerable advantage.
Wheatstone abandoned his idea of transmitting intelligence by the
mechanical vibration of rods, and took up the electric telegraph. In
1835 he lectured on the system of Baron Schilling, and declared that
the means were already known by which an electric telegraph could be
made of great service to the world. He made experiments with a plan of
his own, and not only proposed to lay an experimental line across the
Thames, but to establish it on the London and Birmingham Railway.
Before these plans were carried out, however, he received a visit from
Mr. Fothergill Cooke at his house in Conduit Street on February 27,
1837, which had an important influence on his future.
Mr. Cooke was an officer in the Madras army, who, being home on
furlough, was attending some lectures on anatomy at the University of
Heidelberg, where, on March 6, 1836, he witnessed a demonstration
with the telegraph of Professor Moncke, and was so impressed with its
importance, that he forsook his medical studies and devoted all his
efforts to the work of introducing the telegraph. He returned to London
soon after, and was able to exhibit a telegraph with three needles in
January, 1837. Feeling his want of scientific knowledge, he consulted
Faraday and Dr. Roget, the latter of whom sent him to Wheatstone.
At a second interview, Mr. Cooke told Wheatstone of his intention to
bring out a working telegraph, and explained his method. Wheatstone,
according to his own statement, remarked to Cooke that the method
would not act, and produced his own experimental telegraph. Finally,
Cooke proposed that they should enter into a partnership, but
Wheatstone was at first reluctant to comply. He was a well-known man
of science, and had meant to publish his results without seeking to
make capital of them. Cooke, on the other hand, declared that his sole
object was to make a fortune from the scheme. In May they agreed to
join their forces, Wheatstone contributing the scientific, and Cooke the
administrative talent. The deed of partnership was dated November 19,
1837. A joint patent was taken out for their inventions, including the
five-needle telegraph of Wheatstone, and an alarm worked by a relay,
in which the current, by dipping a needle into mercury, completed a

local circuit, and released the detent of a clockwork.
The five-needle telegraph, which was mainly, if not entirely, due to
Wheatstone, was