Page:Popular Science Monthly Volume 71.djvu/30

tube is preferably made of rubber and braided fabric upon a spiral foundation of wire, by which the tube retains its circular form. The tube is suspended from a supporting wire of sufficient strength to stand the strain of severe wind and the weight of accumulated ice and snow. The wires, which may be either well insulated or even the ordinary braided or double-wound wire, can be drawn in singly or in groups and connections made at the cupolas. The tube, being impervious to moisture, the channel inside will remain perfectly dry. Since the last report of the committee, it has been introduced on a limited scale in the city of Boston and it will soon be extended.

While no underground system satisfactory to telephone men was available in 1880-3, a few wires had been laid underground and some experience of an expensive character gained. For instance, the Western Union carried out some costly experiments with underground wires in New York City during the four years, 1876-80. In 1876, two 4-inch iron pipes were laid from the main office to Pier 18, a distance of one third of a mile. In each pipe

was placed a cable of sixty conductors, the wires insulated with gutta-percha, and wound separately with a layer of tarred tape, the whole covered with a double layer of heavy tape tarred and run through sand to prevent sticking to the pipes.

These cables were connected to the submarine cables running to Jersey City. In 1876, a 12-conductor cable about 2,200 feet in length was laid between the main office, 195 Broadway, and the branch office on Broad Street. Owing to the proximity of steam pipes and the destructive effect of gas on the insulation, these cables were short-lived. In 1880, a new 28-conductor cable was laid between the same offices. Before the end of 1882, eleven of the conductors were useless. In May, 1882, sixty circuits were laid between 195 Broadway and 134 Pearl Street, only to be abandoned within a year, every circuit having failed within seven months. On November 28, 1888, it was stated that the result of the Western Union

experiments during the past twelve years proves that there is no form of underground cable and conduit which can be depended upon to give more than four or five years' service under the most favorable circumstances.

In 1878, John P. Barrett, superintendent of the city telegraph system, placed the fire-alarm and police signal wires underground for a distance of 840 feet on a handsome residence street in Chicago. Two-inch iron pipe, the interior of which was heavily coated with tar, was laid underground and into this pipe two kerite insulated wires were drawn. Ten years later it was stated that these wires had given no trouble and were in 'practically as good a condition to-day as when so placed.'

Submarine telegraph cables were in use thirty years before the first telephone exchange was opened. Referring to the first one used in this country, Henry A. Reed said:

This cable was of No. 9 iron wire, insulated to the thickness of half an inch and was made in 1847 by Stephen Armstrong in Brooklyn, N. Y. It was laid