Kelvite sounding machine

Printed tables were provided to calculate the depth of water when the ship was in motion; these showed variations for different forward speeds to allow for the wire's deviation from straight up-and-down.

[7] In early versions of the machine, there was no dial indicating the length of wire paid out; the movement of a spring-loaded plunger (corresponding to the water pressure) in a tube mounted on the sinker left a mark that could be read when brought to the surface.

[8] In a refinement, which was considered to be more accurate than the dial, Thomson used a small brass pipe containing a thin, replaceable glass tube, closed at the top end, that was attached just above the sinker.

[8][10] When the sinker was back on deck, the glass tube was removed and the position of the mark in the chemical was measured against a boxwood scale, inscribed directly in fathoms, to determine the depth.

[12][13] Kelvin & James White Ltd., located at Hillington, Glasgow,[7] was well situated to supply the flourishing Clydeside shipbuilding industry, and many vessels worldwide carried the Kelvite machine.

[14][15] After the British Admiralty conducted trials in 1904, the Mark IV model, with provision for an optional electric motor for winding in the line, was developed.