Page:Popular Science Monthly Volume 5.djvu/322

308 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-cylindrical pieces of hard wood a, their flat side being grooved to receive the wire, and covered with a layer of India-rubber b 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 s (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 wheelbarrow, 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 otherwise be injured by the wheels of passing vehicles. During the invasion of France the Prussians frequently avoided the roads in order to protect the line from the franc-tireurs, and made considerable détours, concealing it in woods, ravines, and water-courses. Where the uninsulated 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



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 position 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 dispensing 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 operation in every country, there is no need of the field telegraph-lines extending 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 headquarters of the army with the nearest point on a permanent telegraph-line, and in most European countries an army in the field would seldom, 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