The after-current had the effect of curbing its precursor. This self-
acting cable key was brought out in 1876, and tried on the lines of the
Eastern Telegraph Company.
Sir William Thomson took part in the laying of the French Atlantic cable
of 1869, and with Professor Jenkin was engineer of the Western and
Brazilian and Platino-Brazilian cables. He was present at the laying of
the Para to Pernambuco section of the Brazilian 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.
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