ge of several thousand amperes without introducing undue
resistance. This was also accomplished.

Objections were naturally made to rails out in the open on the street
surface carrying large currents at a potential of twenty volts. It was
said that vehicles with iron wheels passing over the tracks and spanning
the two rails would short-circuit the current, "chew" themselves up,
and destroy the dynamos generating the current by choking all that
tremendous amount of energy back into them. Edison tackled the objection
squarely and short-circuited his track with such a vehicle, but
succeeded in getting only about two hundred amperes through the wheels,
the low voltage and the insulating properties of the axle-grease being
sufficient to account for such a result. An iron bar was also used,
polished, and with a man standing on it to insure solid contact; but
only one thousand amperes passed through it--i.e., the amount required
by a single car, and, of course, much less than the capacity of the
generators able to operate a system of several hundred cars.

Further interesting experiments showed that the expected large leakage
of current from the rails in wet weather did not materialize. Edison
found that under the worst conditions with a wet and salted track, at a
potential difference of twenty volts between the two rails, the
extreme loss was only two and one-half horse-power. In this respect the
phenomenon followed the same rule as that to which telegraph wires are
subject--namely, that the loss of insulation is greater in damp, murky
weather when the insulators are covered with wet dust than during heavy
rains when the insulators are thoroughly washed by the action of the
water. In like manner a heavy rain-storm cleaned the tracks from
the accumulations due chiefly to the droppings of the horses, which
otherwise served largely to increase the conductivity. Of course, in dry
weather the loss of current was practically nothing, and, under ordinary
conditions, Edison held, his system was in respect to leakage and the
problems of electrolytic attack of the current on adjacent pipes, etc.,
as fully insulated as the standard trolley network of the day. The cost
of his system Mr. Edison placed at from $30,000 to $100,000 per mile of
double track, in accordance with local conditions, and in this respect
comparing very favorably with the cable systems then so much in favor
for heavy traffic. All the arguments that could be urged in