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