crease their
size to such dimensions as to eliminate the drop altogether, beginning
with conductors of large cross-section and tapering off as necessary.
This would, indeed, obviate the trouble, but, on the other hand, would
give rise to a much more serious difficulty--namely, the enormous
outlay for copper; an outlay so great as to be absolutely prohibitory in
considering the electric lighting of large districts, as now practiced.

Another diagram will probably make this more clear. The reference
figures are used as before, except that the horizontal lines extending
from square marked G represent the main conductors. As each lamp
requires and takes its own proportion of the total current generated,
it is obvious that the size of the conductors to carry the current for
a number of lamps must be as large as the sum of ALL the separate
conductors which would be required to carry the necessary amount of
current to each lamp separately. Hence, in a primitive multiple-arc
system, it was found that the system must have conductors of a size
equal to the aggregate of the individual conductors necessary for every
lamp. Such conductors might either be separate, as shown above (Fig.
2), or be bunched together, or made into a solid tapering conductor, as
shown in the following figure:

The enormous mass of copper needed in such a system can be better
appreciated by a concrete example. Some years ago Mr. W. J. Jenks made
a comparative calculation which showed that such a system of conductors
(known as the "Tree" system), to supply 8640 lamps in a territory
extending over so small an area as nine city blocks, would require
803,250 pounds of copper, which at the then price of 25 cents per pound
would cost $200,812.50!

Such, in brief, was the state of the art, generally speaking, at the
period above named (1878-79). As early in the art as the latter end of
the year 1878, Edison had developed his ideas sufficiently to determine
that the problem of electric illumination by small units could be solved
by using incandescent lamps of high resistance and small radiating
surface, and by distributing currents of constant potential thereto in
multiple arc by means of a ramification of conductors, starting from a
central source and branching therefrom in every direction. This was
an equivalent of the method illustrated in Fig. 3, known as the "Tree"
system, and was, in fact, the system used by Edison in the first
and famous exhibition of his