"The motors are so light that they develop two horse power for
every pound of their weight; while, to keep the frames thin, the
necessary power is obtained by terrific speed of the moving
parts, as though a steam engine, to avoid great pressure in its
cylinders, had a long stroke and ran at great piston speed,
which, however, is no disadvantage to the rotary motion of the
electric motor, there being no reciprocating cranks, etc., that
must be started and stopped at each revolution.

"To obviate the necessity of gearing to reduce the number of
revolutions to those possible for a large screw, this member is
made very small, and allowed to revolve three thousand times a
minute, so that the requisite power is obtained with great
simplicity of mechanism, which further decreases friction. The
shafts, and even the wires connecting the batteries with the
motors, are made large and hollow. Though the primary battery
pure and simple, as the result of great recent advances in
chemistry, seems to be again coming up, the best aeroplane
batteries are still of the combination- storage type. These have
been so perfected that eight ounces of battery yield one horse
power for six hours, so that two pounds of battery will supply a
horse power for twenty-four hours; a small fifty-horse-power
aeroplane being therefore able to fly four days with a battery
weight of but four hundred pounds.

"Limestone and clarified acid are the principal parts of these
batteries. It was known long ago that there was about as much
imprisoned solar energy in limestone as in coal, but it was only
recently that we discovered this way of releasing and using it.