of revolutions of the street car axle when running at the rate of ten
miles an hour. Take all these wastes, and you find in practice that
you do not utilize more than 40 per cent. of the energy given by the
steam engine. But this is quite sufficient to make this system much
cheaper than horse traction.

It is well known that we can discharge the storage battery _ad
libitum_ at the rate of 2 amperes or 200 amperes. I can get out of a
storage battery almost any horse power I like for a short space of
time. I have not the least objection to the direct system. But when
you come to run twenty or thirty or fifty cars on one line, you will
require very large conductors or dangerously high electromotive force.
The overhead system is applicable to its own particular purposes.
Where there are only five or ten, or even twenty, cars running on one
line, and that line runs through a suburb or a part of a city where
there are not many houses, that system is to be preferred. The
objection to the overhead system is not so much the want of beauty,
but the want of practicability. You have to put your posts very high
indeed, so as to let great wagon loads of hay and all sorts of things
pass underneath. Most of the trouble comes in winter, and when it is
snowing hard a great many difficulties arise. As regards the loss,
suppose that the resistance of the overhead lines is one ohm. To draw
one car it will take an average of 20 amperes, and the only loss will
be 20 multiplied by 20, that is, 400 watts through line resistance.
But if there are ten cars on that line, you get 40,000 watts loss of
energy, unless you increase the conductor in proportion to the number
of cars. If you do that, you get an enormous conductor, and have a
sort of elevated railroad instead of a telegraph wire, as most people
imagine an overhead conductor to be.