Page:Popular Science Monthly Volume 24.djvu/522

506 continued to work, and from this grew the system now used in Paris. Up to 1870 the above-described attempts, as well as many others (not recounted), had proved a series of complete failures. Since that, however, several lines have been built in England that have continued to work successfully; and in Germany successful under-ground cables have been laid down connecting together all of the principal cities of the empire. The present complete system, as used between Liverpool and Manchester, was constructed as follows: Iron or stoneware pipes were laid from one to two feet below the level of the road-side with flush-boxes coming to the surface every two hundred yards. Into these was drawn a cable of gutta-percha-covered wires. The joints were carefully made in the pipes, and they were smoothed inside to prevent any possible abrading of the cable. The route was especially selected through a low and marshy section of country, so that the pipes were almost constantly filled with water—this being the best possible condition for the preservation of the gutta-percha. The present European system dates from 1875. The cable is similar to that used for submarine purposes. It consists of seven copper wires, each coated with two layers of gutta-percha and two of Chatterton's compound, and the whole covered with an armor of galvanized-iron wires. This cable is laid in a trench by the road-side, and comes to the surface only inside the telegraph-offices in the cities. Its cost was nearly twenty times the cost of a well-built pole line.

Although both the English and the German systems are successfully working lines of telegraph, they are far less efficient than pole lines of the same length. The speed of working even the ordinary instruments is limited; serious trouble appears in attempting to use fast-working machines, or automatic senders, and the use of the telephone is impossible.

I think these facts have sufficiently demonstrated that for long lines of telegraph, stretching from city to city, here in America, pole lines, which can be cheaply built, easily repaired, and where the wires can be removed from the retarding influence of the earth and the inductive influences on each other, are decidedly superior to underground lines.

Within our large cities the problem presented is somewhat different. During the last few years the number of electric wires has rapidly increased, especially since the introduction of the telephone and electric light, and the probability is that the next few years will show a further large increase. If these wires are run on poles, they not only disfigure the streets, but seriously interfere with the operations of firemen in case of fire, as we have repeatedly seen during the last few years. A cobweb of wires running over the house-tops requires the linemen to continually tramp through the houses and over the roofs, causing annoyance to the tenants and damage to the buildings. Moreover, wires fixed to house-tops are subject to removal at