x PRACTICAL PURPOSE 271 



Lord Kelvin's work for submarine telegraphy is another 

 example of a practical problem solved by scientific know- 

 ledge. The first Atlantic cable was laid in 1858, but 

 scarcely had the enthusiasm awakened by it begun to 

 subside when the signals grew more and more feeble, 

 and in a few weeks the cable altogether ceased to trans- 

 mit messages. This failure was sufficient to discourage 

 most people, but Lord Kelvin encouraged a fresh 

 attempt. " What has been done," he said, " will be 

 done again. The loss of a position gained is an event 

 unknown in the history of man's struggle with the forces 

 of inanimate Nature." Faith and courage were both 

 required to attack the problem again. A new type 

 of cable was designed, better adapted than previous 

 kinds to bear the strain of laying, and in 1865 this 

 cable had established telegraphic communication be- 

 tween England and America. The appliance, known 

 as the siphon-recorder, invented by Lord Kelvin to 

 register the electric impulses transmitted by the 

 cable, still remains in universal use as the standard 

 instrument in submarine telegraphy. It was scientific 

 knowledge, and the spirit of converting difficulties into 

 opportunities, that made Trans-Atlantic telegraphy 

 possible. 



When the first iron ships were built, it was found that 

 the compasses were so greatly affected by the magnetism 

 of the ships that accurate navigation was impossible. 

 Long before Kelvin devised his instrument, a method 

 of determining a ship's permanent and temporary 

 magnetic conditions had been worked out, and a means 

 of counteracting them had been found. No magnetic 

 compass would be of any practical use if the effect upon 

 it of the fixed and movable iron of a ship could not be 

 compensated effectively. 



