David Brooks patent for insulating underground cables

Underground Telegraph Wires.

Mr. Wm. Radde, the owner of the patent for the admirable invention of glass-lined iron water pipes, has applied the same principle to underground telegraph wires. For this purpose each iron tube is filled with from 10 to 20 glass tubes, as long and of as small a diameter as practicable, and the spaces between the glass tubes are filled with an isolating cement. Through these interior glass tubes metallic conducting wires are passed, and length after length attached to one another, with appropriate connecting boxes.

This is only one of the many devices invented for this purpose. We will here describe another now practically applied in Chicago, which the local papers call "greased lightning." It is the invention of Mr. D. Brooks, of Philadelphia, who several years ago invented what is known as the "Brooks insulator."

A small copper wire is wound with cotton to secure insulation. Several of these insulated wires are bound into one cable, which is then wound with a heavy coating of cotton. The cable is then drawn into a pipe, to he afterwards completely filled with oil, which, especially at a low temperature, is a good non-conductor. When the pipes have been laid, perpendicular tubes will be connected with them, for the purpose of keeping them full. In crossing rivers it is proposed to have the pipes made to fit the bottom of the streams. It is not intended to put the wires in the country underground, but only those inside the limits of large towns. One difficulty in the way of the perfect working of the plan at present is that the insulating quality of the oil decreases very rapidly as its temperature rises, and during hot weather this may cause some trouble; but a more perfect insulating fluid may be found which will remedy this fault. Another is that whenever lightning strikes the cable it carbonizes the oil at the point of greatest conductivity, or of the least resistance, and makes a little string of carbon to the pipe, which furnishes an excellent "escape." This can be remedied, however, by having the pipe made in sections, 50 that when such an escape is formed in any one section, the oil can be taken out, and in, and out, until the thread is broken, when the section will be as good as before.