WESTWARD HO ! 277 



positively or negatively, according to the direction 

 of the current. The sea around each earth-plate is 

 similarly charged. Now, if the merry-thought, or 

 rock circuit be so arranged that one of its ends is in 

 the charged area of the main cable, and the other 

 end, or earth-plate, is more or less out of the charged 

 area, a current ^yill flow through it, because of a 

 difference of ' potential ' between its two ends or 

 earth-plates. 



It will, I hope, be evident from the foregoing 

 paragraph that the two earth-plates of the second, or 

 rock, circuit act as the two plates of a battery (of 

 extremely small electromotive force), and consequently 

 the mirror of the receiving instrument at the apex 

 of the merry-thought is deflected, the instrument 

 acting as though the two ends of the rock circuit 

 were connected direct to the two plates of an ordinary 

 cell. 



Of course, when the rock ' sends ' and the shore 

 ' receives,' the same law holds good, the nearest 

 'centipede' affecting the 'mushroom,' although there 

 is a watery gap of a hundred and twenty feet between 

 them. 



In this way the difficulty, held until lately to be 

 insuperable, of electrically connecting isolated light- 

 houses or lightships with the shore seems to be in a 

 fair way of being permanently overcome. Mr. Preece, 

 C.B., has stoutly averred before a recent committee 

 of the House of Commons, that the word ' impossible ' 

 as regards electrical matters does not exist. 



