happy manner in
which William Siemens, above all others, turned his varied knowledge to
account, and brought the facts and resources of one science to bear upon
another. As early as 1860, while engaged in testing the conductor of the
Malta to Alexandria telegraph cable, then in course of manufacture, he
was struck by the increase of resistance in metallic wires occasioned by
a rise of temperature, and the following year he devised a thermometer
based on the fact which he exhibited before the British Association
at Manchester. Mathiessen and others have since enunciated the
law according to which this rise of resistance varies with rise of
temperature; and Siemens has further perfected his apparatus, and
applied it as a pyrometer to the measurement of furnace fires. It forms
in reality an electric thermometer, which will indicate the temperature
of an inaccessible spot. A coil of platinum or platinum-alloy wire is
enclosed in a suitable fire-proof case and put into the furnace of which
the temperature is wanted. Connecting wires, properly protected, lend
from the coil to a differential voltameter, so that, by means of
the current from a battery circulating in the system, the electric
resistance of the coil in the furnace can be determined at any moment.
Since this resistance depends on the temperature of the furnace, the
temperature call be found from the resistance observed. The instrument
formed the subject of the Bakerian lecture for the year 1871.

Siemens's researches on this subject, as published in the JOURNAL OF THE
SOCIETY OF TELEGRAPH ENGINEERS (Vol. I., p. 123, and Vol. III., p. 297),
included a set of curves graphically representing the relation between
temperature and electrical resistance in the case of various metals.

The electric pyrometer, which is perhaps the most elegant and original
of all William Siemens's inventions, is also the link which connects his
electrical with his metallurgical researches. His invention ran in two
great grooves, one based upon the science of heat, the other based upon
the science of electricity; and the electric thermometer was, as it
were, a delicate cross-coupling which connected both. Siemens might have
been two men, if we are to judge by the work he did; and either half
of the twin-career he led would of itself suffice to make an eminent
reputation.

The success of his metallurgical enterprise no doubt reacted on his
telegraphic business. The making and laying of the