azilian coast cables in 1873,
and introduced his method of deep-sea sounding, in which a steel
pianoforte wire replaces the ordinary land line. The wire glides so
easily to the bottom that 'flying soundings' can be taken while the ship
is going at full speed. A pressure-gauge to register the depth of the
sinker has been added by Sir William.

About the same time he revived the Sumner method of finding a ship's
place at sea, and calculated a set of tables for its ready application.
His most important aid to the mariner is, however, the adjustable
compass, which he brought out soon afterwards. It is a great improvement
on the older instrument, being steadier, less hampered by friction,
and the deviation due to the ship's own magnetism can be corrected by
movable masses of iron at the binnacle.

Sir William is himself a skilful navigator, and delights to cruise in
his fine yacht, the Lalla Rookh, among the Western Islands, or up
the Mediterranean, or across the Atlantic to Madeira and America. His
interest in all things relating to the sea perhaps arose, or at any rate
was fostered, by his experiences on the Agamemnon and the Great Eastern.
Babbage was among the first to suggest that a lighthouse might be made
to signal a distinctive number by occultations of its light; but Sir
William pointed out the merits of the Morse telegraphic code for the
purpose, and urged that the signals should consist of short and long
flashes of the light to represent the dots and dashes.

Sir William has done more than any other electrician to introduce
accurate methods and apparatus for measuring electricity. As early as
1845 his mind was attracted to this subject. He pointed out that the
experimental results of William Snow Harris were in accordance with the
laws of Coulomb.

In the Memoirs of the Roman Academy of Sciences for 1857 he published a
description of his new divided ring electrometer, which is based on
the old electroscope of Bohnenberger and since then he has introduced
a chain or series of beautiful and effective instruments, including the
quadrant electrometer, which cover the entire field of electrostatic
measurement. His delicate mirror galvanometer has also been the
forerunner of a later circle of equally precise apparatus for the
measurement of current or dynamic electricity.

To give even a brief account of all his physical researches would
require a separate volume; and many of them are too abstruse or
mathematical