.S7A 1 ll'/I.UAM .SY/-..J//-.-.YS, I-\K.S. 9 



into the circ.iit, so that each battery had only the resistance of a 

 section of the line wire to contend with. Moreover, a small 

 portion only of the active current required to pass the wire at all, 

 the greater portion being what was commonly called " bad 

 circuit," or " derived current " (and which was produced 

 artificially). 



An important feature in his brother's system was the use of 

 gutta-percha for coating the underground line-wire, which was 

 first suggested by him in the year 1846, and had since been 

 carried out to the extent of upwards of four thousand English 

 miles. 



The advantages of the under-ground system were, that it was not 

 affected by atmospheric influences, such as fog, lightning, aurora 

 borealis, or sudden changes of temperature, which frequently 

 broke the suspended wire ; it was also expected to be more durable 

 when properly protected ; and lastly, it was beyond the reach 

 of mischievous or riotous persons. The gutta-percha coating 

 was attacked by two enemies, atmospheric air, which gradually 

 converted it by a process of oxidation into a hard and brittle 

 mass, through the crevices of which moisture gained access to 

 the wire, and a species of field rats, which gnawed the wire where 

 it obstructed their mining operations. These two causes com- 

 bined had destroyed the insulation of several of the early 

 lines, particularly in dry sandy embankments. It was there- 

 fore found necessary to protect the gutta-percha by an external 

 coating of lead, which was drawn tight over it through a 

 die. The earlier lines were, moreover, laid only 18 inches below the 

 surface of the ground ; but it was found necessary to lay them from 

 2 feet to 2 1 feet deep. The weight and cost of the under-ground 

 line wire per English mile was : 



s. d. 

 Copper wire, 80 Ibs. at Is. . . . . 400 



Gutta-percha, 68 Ibs. at 3s 10 4 



Lead, 600 Ibs. at 'Ad 7 10 



Total . . -21 14 



exclusive of workmanship and delivery. The cost of the trench 

 work differed, of course, with the depth and nature of the soil ; 



