[Illustration:  DISTRIBUTION OF ELECTRICITY BY INDUCTION.]

It results from what precedes that each apparatus must be put in in such a way as to permit, of the opening and closing of the corresponding circuit.  This arrangement, moreover, has no need of being dependent upon the apparatus, and may just as well be transferred to any part of this same circuit.  As regards lighting, it is preferable to employ alternating current dynamo machines; yet there is nothing to prevent the use of continuous current ones, provided that there is an arrangement that permits of constantly opening and closing this same circuit.  That portion of the line which is placed under ground is insulated in the ordinary way at the places where it is necessary.  As for the underground circuit and the induction coils connected therewith, these are protected against all external influence, and are at the same time insulated very economically by covering them with a coat of very fine silicious sand mixed with asphalt.

It is only necessary to inspect the annexed figure to get an accurate idea of this system of distribution.  C represents the building in which the generator of electricity, D, is placed; B, the public street, and Q the house of a subscriber.  The principal line, E, starts from the terminals, a, b, of the machine, passes through the primary bobbins, G, and is closed through the earth at F. It will be seen that the primary current communicates through d and c with the internal winding of the bobbins, G, while the secondary currents, H, are connected through e and f with the external winding.  The same arrangement is repeated for the tertiary currents, M, and the quaternary ones, o, p.  In the annexed example all the lines that run parallel with the axis of the streets are closed through the earth, while those that have a direction perpendicular thereto enter the houses of subscribers and form a closed circuit.  In the interior of these houses the wires, as well as the induction coils, are insulated and applied to the walls.  At Q is represented the arrangement that would have to be adopted in the case of a structure consisting of a vestibule, r, and two rooms, s, lighted by two electric lamps, R. In the portion of the figure situated to the left it is easy to see the process employed for insulating the line.  A commencement is made by digging a ditch in the street and paving the bottom of it with bricks.  Upon these latter there is laid a mixture of sand and asphalt, and then the wires and bobbins are put in, and the whole is finally covered with a new insulating layer.