Austrian engineers assert that on favorable ground they could do the work in two hours. In most cases, of course, the advancing army would have to repair the permanent lines which would be partially destroyed by the retreating forces, and in this way twenty-five miles of wire were often erected by the Prussians in a single day. As soon as an army moves forward, the field-telegraph line previously erected is taken down and recoiled on the drums, while a fresh line is laid from the new headquarters to the nearest permanent telegraph. This is done with a view to economizing the material, an enormous amount of which would have to be carried with the army, if the lines it left behind it in its advance were not removed, and the poles, wire, and insulators, employed in their construction again utilized. The hand-barrows of the Austrian telegraph corps are designed to be used in recoiling as well as uncoiling the wire; and for this purpose are fitted with a crank-handle and ratchet-wheels, so as to enable a man to turn the drum and wind the cable upon it.
Besides the ordinary field-telegraph companies, the French army includes a mountain-telegraph corps, organized with a view to operations
| Fig. 6. | Fig. 7. | Fig. 8. |
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| Telegraph-Pole, Socket, and Insulator. | Wire-connector. | Marié Davy Battery. |
on the mountainous frontiers of the south, or to be ready to carry a line over a range of hills in an ordinary campaign, thus avoiding a long détour in the valleys, or securing lateral communication with troops divided from the main army by the hills. As the mountain line would have to be laid along narrow, rocky paths, and through lofty passes, all carriages and wagons are dispensed with, and their place is taken by a train of mules. In a mountain-telegraph company several of the mules are each laden with two drums of the insulated cable, the instruments and batteries are carried on pack-saddles on the backs of others, and others again transport the baggage, provisions, and forage of the company, and also a light tent to form a station whenever messages are to be sent along the line.
While the field telegraph affords a commander a rapid and certain
