sion of any one of which would probably
have resulted eventually in failure.

[Footnote 8: As a practical illustration of these facts it
was calculated by Professor Barker, of the University of
Pennsylvania (after Edison had invented the incandescent
lamp), that if it should cost $100,000 for copper conductors
to supply current to Edison lamps in a given area, it would
cost about $200,000,000 for copper conductors for lighting
the same area by lamps of the earlier experimenters--such,
for instance, as the lamp invented by Konn in 1875. This
enormous difference would be accounted for by the fact that
Edison's lamp was one having a high resistance and
relatively small radiating surface, while Konn's lamp was
one having a very low resistance and large radiating
surface.]

Continuing the digression one step farther in order to explain the term
"multiple arc," it may be stated that there are two principal systems
of distributing electric current, one termed "series," and the other
"multiple arc." The two are illustrated, diagrammatically, side by side,
the arrows indicating flow of current. The series system, it will be
seen, presents one continuous path for the current. The current for the
last lamp must pass through the first and all the intermediate lamps.
Hence, if any one light goes out, the continuity of the path is broken,
current cannot flow, and all the lamps are extinguished unless a loop
or by-path is provided. It is quite obvious that such a system would be
commercially impracticable where small units, similar to gas jets, were
employed. On the other hand, in the multiple-arc system, current may be
considered as flowing in two parallel conductors like the vertical sides
of a ladder, the ends of which never come together. Each lamp is placed
in a separate circuit across these two conductors, like a rung in the
ladder, thus making a separate and independent path for the current in
each case. Hence, if a lamp goes out, only that individual subdivision,
or ladder step, is affected; just that one particular path for the
current is interrupted, but none of the other lamps is interfered with.
They remain lighted, each one independent of the other. The reader will
quite readily understand, therefore, that a multiple-arc system is the
only one practically commercial where electric light is to be used in
small units like those of gas or oil.

Such was t