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188 His discovery of the "law of the retardation" of electric currents, and the invention of the mirror galvanometer and the syphon recorder, rendered submarine telegraphy possible.

The Atlantic cables of 1858 and 1865 broke, the latter after a fortnight's use. This, according to the late Mr G. H. Smith, was due to strains caused by the "paying out of the cable from coils instead of from reels. During the gales encountered by the Agamemnon the upper part of the main coil shifted, and became a mere shapeless tangled mass. Kinks were produced, and breakage was the result." Ultimately the cable was laid in 1866, and Thomson received the honour of knighthood.

He invented a mariner's adjustable compass (suitable for iron ships), i.e. the compass was constructed so as to neutralize the effect of terrestrial magnetism on iron. The compass was first adopted by the mercantile service, and afterwards by the Admiralty. At first the Admiralty would not look at Kelvin's compass! It may be mentioned that the same authorities resisted the use of lime-juice for scurvy—and thereby thousands of men lost their lives!

Among Kelvin's inventions are his quadrant electrometer for measuring minute electric currents, his tide-predicting machine, his deep-sea sounder, his kilowatt balance, his multicellular electrostatic voltmeter, etc. Kelvin patented his inventions, and thereby reaped a