WESTWARD HO ! 275 



enable it to return through earth and water to the 

 startmg-pomt, the conductmg wire, after passing 

 through both instruments, would be carried down at 

 each end to the earth or the sea. 



But as the ordinary way is not in this instance 

 suitable, leakage and ' conduction ' are called into 

 play; and between them the beautiful and highly 

 sensitive ' mirror ' apparatus, invented long ago by 

 Lord Kelvin (when Sir W. Thompson), is made to 

 flash signals, with perfect ease, at the lighthouse 

 from the shore, and vice-versa. 



The reader, if unversed in electricity, may gather a 

 vague idea of the meaning of these terms from the 

 fact that, while the bulk of the electricity sent by 

 cable from Crookhaven flies back to its starting-point 

 without entering the lighthouse at all, a minute 

 portion, sufficient to deflect the mirror, leaks — in 

 other words, darts through the water from the ' mush- 

 room ' anchor, to which the cable is made fast, to one 

 of two wires from the mirror instrument in the light- 

 house, which are fastened to the wall of rock. They 

 are carried down, some distance apart, below low- 

 water mark, and are connected to heavy cylindrical 

 blocks of copper, known as 'centipedes.' These are 

 jammed into the crevices of the rocks, and secured by 

 clamps and bolts. 



So, with a taste of actual electricity, due to leakage, 

 or a sort of shamefaced scuttling over to the rock 

 of a surplus spark or two — vibrations, as it were, 

 from the (jijinnotus, or salt-water electrical eel, nine 



