y of electricity.'
In this he demonstrated the identity of the laws governing the
distribution of electric or magnetic force in general, with the laws
governing the distribution of the lines of the motion of heat in certain
special cases. The paper was followed by others on the mathematical
theory of electricity; and in 1845 he gave the first mathematical
development of Faraday's notion, that electric induction takes place
through an intervening medium, or 'dielectric,' and not by some
incomprehensible 'action at a distance.' He also devised an hypothesis
of electrical images, which became a powerful agent in solving problems
of electrostatics, or the science which deals with the forces of
electricity at rest.

On gaining a fellowship at his college, he spent some time in the
laboratory of the celebrated Regnault, at Paris; but in 1846 he was
appointed to the chair of natural philosophy in the University of
Glasgow. It was due to the brilliant promise he displayed, as much as
to the influence of his father, that at the age of twenty-two he found
himself wearing the gown of a learned professor in one of the oldest
Universities in the country, and lecturing to the class of which he was
a freshman but a few years before.

Thomson became a man of public note in connection with the laying of the
first Atlantic cable. After Cooke and Wheatstone had introduced their
working telegraph in 1839; the idea of a submarine line across the
Atlantic Ocean began to dawn on the minds of men as a possible triumph
of the future. Morse proclaimed his faith in it as early as the year
1840, and in 1842 he submerged a wire, insulated with tarred hemp and
india-rubber, in the water of New York harbour, and telegraphed through
it. The following autumn Wheatstone performed a similar experiment in
the Bay of Swansea. A good insulator to cover the wire and prevent the
electricity from leaking into the water was requisite for the success
of a long submarine line. India-rubber had been tried by Jacobi, the
Russian electrician, as far back as 1811. He laid a wire insulated with
rubber across the Neva at St. Petersburg, and succeeded in firing a mine
by an electric spark sent through it; but india-rubber, although it is
now used to a considerable extent, was not easy to manipulate in those
days. Luckily another gum which could be melted by heat, and readily
applied to the wire, made its appearance. Gutta-percha, the adhesive
juice of the ISONANDRA GU