local authority are themselves the undertakers, of certain inhabitants, who may at any time require the undertakers to extend their operations over any part of such area.

The fuel required would be a serious item, so that means should be taken to secure a low rate of transport by fixing the position of the station near the siding of a railway or on the banks of a canal.

In large cities like London there would be some difficulty, and a site sufficiently central would cause an enormous outlay for purchase of land. This was partly overcome in the installation of the Edison light at New York, by sinking considerable depth below the surface of the street, and fixing the engine and boilers in a sub-basement, somewhat similar to the position of the engines on board ship. Sir William Siemens proposes to utilise the area of the public squares, which would be excavated to a depth of about 25 feet, and arched over to the present ground level. In the covered space would be fixed the engines, boilers, and dynamos, the only erection above the surface being the chimney, which would be of ornamental design, and combined with ventilating arrangements for the subterranean chamber.

THE ELECTRIO MAINS.

Although it is quite possible to use, as in telegraphy, the earth as the return conductor, it is far better to have two cables; one starting from the machines being called the positive, and that returning to them the negative.

Electricity for lighting purposes can be transmitted by wires in the same manner as those now used for telegraphy, which are carried either above ground or underneath. In some cases the return current may be made by a wire in connection with the earth, but the use of earth returns, though not prescribed by the clauses of the Order, requires the special sanction of the Board of Trade.

For temporary purposes, electric light wires may be also taken overhead, but as copper has a far less breaking strain than iron, the spans should be much shorter, or an extra wire used for a support.

A very excellent wire has lately been introduced for multiplex telegraphy in the United States. It consists of a steel wire round which copper is electrically deposited to the required section. It

thus gives great strength with the high conductivity of a copper -wire.

OVERHEAD WIRES.

At present the legislation as regards overhead wires is not at all clear, and from the continual increase of such wires for telephone purposes the introduction of electric light wires would constitute an element of danger; where such wires have been erected without opposition from the local authorities, it is a question whether they can now interfere in the matter. In the case of electric light wires, if such are likely to be dangerous, local authorities should have summary jurisdiction, and it is very necessary to see that in the hurry to push forward the work of distributing electricity overhead wires are not fixed so as to be prejudicial to workmen engaged in house repairs. As a general rule, all overhead wires should be coated with an insulating material wherever they are likely to be touched or may come in contact with any portion of the building; they should also never be less than 7 feet clear from any part of the roof, and never approach or even cross any wires used for telegraphy or telephones.

As the cable such as would be used from a main generating station would be of considerable size, it is not probable that overhead wires will be employed to any great extent, and the second plan, namely, that of carrying the wires underground, will be generally adopted.

UNDERGROUND MAINS.

A subway probably offers the easiest mode of laying electric mains, and affords a means of access to them at all times.

Only large cities have subways, and these generally are confined to the principal thoroughfares, but if such can be used, the cables would be suspended from the top or sides by means of a strong form of telegraphic insulator. In places where no such provision exists, tubes, either of metal or stoneware, must be fixed of such a size as to allow plenty of clearance to enable the cable to be dragged through.

Several special kinds have been devised, and some, where the tube is divided into two halves, enable the positive cable to be carried in a separate chamber from the negative. The size of the tubes varies according to the number of wires to be carried; for instance,

a tube 6 inches in diameter will take four cables 1 inch in diameter each, and allow for hauling out. At suitable intervals, boxes must be provided where the connections to the houses can be made: that is to say, the cables, both positive and negative, are bared and a smaller cable soldered or clamped on to each so as to form a service line or branch to the consumer, on a continuation of which the incandescent lamps are fixed in what is called the "parallel system."

It will not, however, be necessary to always have a box at each house, as the branch wire can be large enough to supply a group of houses by means of smaller branches. At each point of junction with the main circuit a "switch" should be fixed in order to shut off the current at will, also a "fusible plug," which is a piece of metal so proportioned, that in the event of an excess current being turned on, the increase of temperature melts the fusible plug, and prevents the wires from becoming dangerously over-heated. A plug similar to this will have to be fixed at one end of the wires leading to each house, so as to not only afford a safeguard against increased current being turned into the house, but also to prevent the inhabitants acquiring more electrical current than has been contracted for.

The great difficulty to contend with in underground wires is the leakage of electricity due to water collecting in the pipes. A question thus arises as to whether it is better to lay the mains in water-tight pipes or to simply protect them in such a manner that they shall be fixed as it were in a drain which would conduct all water away. If a water-tight pipe is required it should always be caulked at the joints, and laid with a fall towards the connecting boxes, which may be open at the bottom and connected with a drain.

Water is decidedly the bête noire of the electrical engineer; not only does it cause leakage of current, but also in the case of two positive and negative mains being laid close together, water touching two unprotected parts would be sufficient to establish an arc, and speedily destroy the current. For this reason the so-called fireproof materials are to be avoided as the covering for the mains. Although their electric insulation may be good, the ease with which they are affected by damp would speedily render them unserviceable. All underground mains should therefore have a good covering of guttapercha or some equally good moistureresisting insulator.

Underground pipes are being dispensed with altogether in the mains laid by the Swan United Company. The mains are simply uncovered stranded wires covered with bitumen and placed in the centre of wood frames, which are filled in with asphalte. The branches are insulated wires fixed in grooves cut with solid planks, which are of sufficient thickness to allow of the wires resting well in the grooves and being permanently fixed in them by means of hot tar or pitch. Suitable junction boxes are provided at intervals in the form of pillars of cast iron, kept either by the side of the curb, as the sanitary boxes now in use, or close to the wall. Into these all the mains are led, so that in the event of a fresh house connection having to be made it will not be necessary to disturb the street, but only to run a subsidiary wire to the nearest box. The mains themselves are to be laid, wherever possible, in the pavement, so as to be out of the way of the existing gas and water pipes.

Where a new street has to be made, the curb might be utilised so as to contain the mains by making it of cast iron and hollow. Cables coated with a thick envelope of lead are also supplied, and, according to the inventors, can be laid directly in the earth. These cables are not to be recommended except on private property, as this would be very liable to be destroyed by accident, and after a time the lead would be subject to corrosion.

The arrangement of the mains and service lines are shown in the accompanying plan, Fig. 1, which illustrates the streets adjoining the Victoria district generating station of the Swan United Company. The main cables are shown at M, the line of the curb stones C, and the service mains to houses S. The round black circles are the distributing boxes, and the small square ones the testing boxes. The generating station is shown at G, connected with the railway, R. The distributing boxes, one of which is shown at Fig. 2, consist of round pillars of cast iron, about 3 feet 6 inches high by 20 inches diameter. Inside are a number of connectors uniting the service mains to the main cable, each connection being made through a switch and a duplex Fusible Cut Out on the author's plan, which admits of a second fuse being brought into action should one become melted.

The plan of keeping these connections above ground is preferable to that of Edison's, which may be interfered with by water collecting in the boxes.