188 BIOGRAPHIES OF SCIENTIFIC MEN 



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 electro- 

 meter 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 



