JUNCTION SAFETY CATCH BOX.

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faces, one inch square, which are arranged symmetrically around the centre of the box and equi-distant from it. The terminals of the mains are arranged in three other circles, each respectively on the same level as the corresponding polar ring, but of larger diameter, and the safety fuses, also provided with gold-plated terminals, connect each pole piece with the terminal of the main radially opposite to it. The electric tubes containing the mains enter the box two feet below the surface of the street, and the connection between them and the box is made water-tight. If from any reason—a short circuit or a heavy leak-the current through any of the mains becomes too strong, the safety fuse connecting that main with the feeder melts and interrupts the current until the damage has been repaired and a new fuse inserted.

Another system which has already passed the first experimental stages is that of the American Sectional Underground Company. It is intended for the accommodation of telephone, telegraph, electric light, and electric power wires, all in the same duct, but separated from each other by shelves. The largest size duct yet made is a cast-iron pipe of rectangular section, ten inches by fifteen inches, costing £3,000 per mile when laid. The pipe is provided at every street-corner with a man-hole large enough for one or more men to enter for the purpose of hauling in the wires and making the necessary connections. There are further, at convenient distances along the line of conduit, hand-holes for tapping the wires for house-to-house supply. The connection with the house wires and mains are made at the nearest man-hole, and the house-wires are run along an upper shelf in the duct devoted for that purpose until the hand-hole is reached, where they are taken out and across to the house. It is

claimed as a special feature of this system, that through the interposition of shelves the telephone wires are guarded from induction from the electric light and power wires. On the other hand, it seems doubtful whether the insulation of heavy cables, after they have been dragged along the shelves, will remain perfect. To provide against water the man-holes are provided with sumps connected to the street drains, and open gratings are placed at certain man-holes, by which means sweating and condensation in the duct itself are prevented.

The Brooks Underground Conduit.-The conductors are laid in wrought-iron pipes with suitable splice-boxes, hand-holes, and outlets. To protect the pipes from oxidation they are laid in a wooden trough, into which hot pitch is poured so as to completely envelop the pipes. The conductors are made up into bundles, soaked in hot mineral oil, and drawn into the pipes in 2,000 feet lengths. A heavy mineral oil is then forced into the conduit for the purpose of excluding moisture and increasing the insulation. To show the efficacy of this oil as a means of insulation, Mr. Brooks, at the Philadelphia Exhibition, showed the following experiment. Two wires were attached to a Holz induction machine, and their extremities dipped into the oil. They were so placed as to be

inch apart in the oil and 11⁄2 inch apart at the surface. On turning the machine the spark passed through the 11" of air-space at the surface, but not through the oil, although there the leaping distance was much smaller.

In all the systems above described the leading idea is to provide for the conductor, in the first instance, an insulation so perfect and of such thickness that moisture cannot get to the metal of the conductor, and so cause leakage.

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The Continental Underground Cable Company prefer to use for their conductor a cheap and thin insulation, but they endeavour to surround it with an atmosphere of perfectly dry air under pressure. This is done by building conduits with walls of asphalte blocks or other antimoisture material, and providing them with iron supports and semicircular wrought-iron troughs for the accommodation of these lightly insulated mains. The mains are hauled through from one man-hole to the other by means of a cord, which has, in the first instance, been sent through the conduit by a carriage propelled by an electric motor. Very light wires can be laid direct by this carriage. It is proposed to close, as hermetically as possible, the whole of the conduit, and to force air into it which has been deprived of all moisture by being passed over some chemicals. Safety-valves are fitted at the end of the conduit where this air may escape if the pressure rises beyond a safe limit. As far as the author is aware this system has not yet been practically applied.

Lead-Covered Cables.-Perhaps the most simple, and certainly a very efficient way of keeping cables dry, is that of surrounding each cable with a continuous sheath of lead. The cable, after having received the usual insulation, is passed through a machine which, by hydraulic pressure, surrounds it with a cylindrical coating of lead free from any open joints, flaws, or other imperfections through which moisture might enter. The cable, thus protected, can be laid either directly into the ground or into a trough made of brickwork filled with loose sand, and then covered over by flags or brickwork. M. Marcel Deprez has used forty-five miles of lead-covered cable in his Paris-Creil experiments on the electric transmission

of energy.' If special protection is required a second lead sheathing is put over the first. The following Table gives the weight of single and double lead-covered cable of different cross-sectional area.

1 This was, however, a mistake, because with the high pressure employed the lead covering of the cable acted as an enormous condenser and gave rise to heavy electro-static induction. It seems that lead-covered cables would be only applicable for currents of low electro-motive power.

CHAPTER IX.

Possible Applications of Electric Transmission of Energy-Best Field for it is Long Distance Transmission-Comparison with other SystemsHerr Beringer's Investigation-Hydraulic Transmission-Pneumatic Transmission-Wire-Rope Transmission-Comparative Tables of Efficiency and Cost-Practical Conclusions.

If we would judge fairly the merits of a new invention, we should not only look upon it by itself, but compare it with all that has gone before and might be superseded by it. This is especially the case if we have to deal with a new thing that has many rivals, and the electric transmission of energy is precisely in this position. Ever since man began to use tools worked by other than manual power, he had to employ some system of transmission of energy, and as a natural consequence the number of systems is not only very large, but each has in the course of time been brought to great perfection. Electric transmission has therefore to compete with a host of mechanical devices, and it becomes important to compare it with them. Some enthusiasts predict that in the near future all belts, pulleys, shafts, ropes, and cog-wheels will be superseded by electric wires and motors. Thus Mr. Walker, in "The Electrician" of Jan. 8, 1886, says: "How easily and how quickly, and with little occasion for repairs, can two cables be laid, in almost any position, for mines, ironworks, docks, factories, as compared with shafting, ropes, steam-pipes, compressed air. I have