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THE POPULAR SCIENCE MONTHLY 



When all the wire of the first drum is laid down, the end of it is 

 roughly spliced on to the wire of the next drum, and the joint secured 

 by means of the conductor (Fig. 7). This consists of two semi-cylin- 

 drical pieces of hard wood a, their flat side being grooved to receive 

 the wire, and covered with a layer of India-rubber h to act as packing, 

 and insulate the joint, in the case of a ground-line, and the whole is 

 held tightly together by the brass collar and screw c c 8 (Fig. 8). 



The line is very rapidly and easily constructed. In the case of a 

 ground-line it is simply paid out from the drums on the hand or wheel- 

 barrow, being buried in a shallow trench or elevated on poles, when it 

 is necessary to cross a road, where the insulation of the cable might 

 otlierwise be injured by the wheels of passing vehicles. During the in- 

 vasion of France the Prussians frequently avoided the roads in order to 

 protect the line from i\iQ franc-tireurs^ and made considerable detours, 

 concealing it in woods, ravines, and water-courses. Where the uninsu- 

 lated wire is used, poles are erected about fifty paces apart, the hole to 

 receive each pole being made by driving a sharp pointed iron bar into 

 the ground with a heavy mallet. As soon as a pole is fixed the wire 



Fig. 5. 



Eabth-coxductor. 



is run through the hook on the top of the insulator, and stretched 

 tight by a man holding it over his shoulder, who keeps it in this po- 

 sition until the next pole is ready to receive it. Wherever there are 

 trees or walls near the line, the work is still further lightened by dis- 

 pensing with the poles, and merely attaching the wire to the insulators 

 specially constructed for this purpose. In this way the line was erected 

 for the Ashantee expedition, the negro laborers carrying only a light 

 ladder to ascend the trees, a small axe to clear away the boughs, and 

 a gimlet to make a hole for the spindle of the insulator. It never 

 took, we are informed, more than five minutes to fix an insulator to a 

 tree ; but, in those few places where trees were not available, fully 

 half an hour was occupied in erecting each pole, and even then it was 

 often unsteady, and had to be propped and guyed. 



In Europe, where there is an extensive telegraph system in opera- 

 tion in every country, there is no need of the field telegraph-lines ex- 

 tending from the front of the army to the base of operations. Far 

 less than this is required. All that is necessary is to connect the head- 

 quarters of the army with the nearest point on a permanent telegraph- 

 line, and in most European countries an army in the field would sel- 

 dom, if ever, be more than ten miles from such a line. Ten miles of 

 the field telegraph can easily be erected in half a day ; indeed, the 



