200 THE ELECTRIC TELEGRAPH. 



the " dutch tongs/' or " devil's claw," b, attached to the 

 leather strap c, which is wound upon the drum d of the winch 

 by turning the handle h. A pair of pulley- blocks and line may 

 be used for stretching, but the winch is more convenient. 



Fig. 111. 



When the wire is sufficiently stretched, it is made fast to 

 the insulator on the stretching-post, and the following length 

 to the next stretching- post served in the same way. 



Phenomenon of Charge in Overland Wires. When a gal- 

 vanic battery is connected to one end of an overland line, the 

 other end being insulated, the wire becomes charged with 

 electricity, whose tension depends upon the strength of the 

 battery, just in the same way as a Leyden jar, or condenser, 

 or submarine cable would under the same circumstances. 

 The wire, stretched from post to post, forms the inner coating 

 of a jar, the air acts as dielectric, and the earth, the neigh- 

 bouring houses, trees, &c., form the outer coating. 



Dr. Siemens has determined the distances of faults in 

 overland lines by measuring the discharge currents. To 

 determine the capacity of a jar formed by a line of telegraph, 

 he erected, in the yard of his factory at Berlin, an iron wire, 

 121 metres long and 2 lines diameter, at an average height 

 of 8 metres above the ground. The points of suspension 

 were carefully insulated ; one end of the wire was carried 

 directly to the instrument with which the measurements were 

 made, and the other insulated. In comparing the charge of 

 this wire with that of a condenser formed by a glass plate, 



