free terminal with an object held in the
hand, a current passes through the coil and the copper disc is set in
rotation. If an exhausted tube is put in series with the coil, the
tube lights brilliantly, showing the passage of a strong current.
Instead of the experimenter's body, a small metal sheet suspended on a
cord may be used with the same result. In this case the plate acts as
a condenser in series with the coil. It counteracts the self-induction
of the latter and allows a strong current to pass. In such a
combination, the greater the self-induction of the coil the smaller
need be the plate, and this means that a lower frequency, or
eventually a lower potential, is required to operate the motor. A
single coil wound upon a core has a high self-induction; for this
reason principally, this type of motor was chosen to perform the
experiment. Were a secondary closed coil wound upon the core, it would
tend to diminish the self-induction, and then it would be necessary to
employ a much higher frequency and potential. Neither would be
advisable, for a higher potential would endanger the insulation of the
small primary coil, and a higher frequency would result in a
materially diminished torque.

It should be remarked that when such a motor with a closed secondary
is used, it is not at all easy to obtain rotation with excessive
frequencies, as the secondary cuts off almost completely the lines of
the primary--and this, of course, the more, the higher the
frequency--and allows the passage of but a minute current. In such a
case, unless the secondary is closed through a condenser, it is almost
essential, in order to produce rotation, to make the primary and
secondary coils overlap each other more or less.

But there is an additional feature of interest about this motor,
namely, it is not necessary to have even a single connection between
the motor and generator, except, perhaps, through the ground: for not
only is an insulated plate capable of giving off energy into space,
but it is likewise capable of deriving it from an alternating
electrostatic field, though in the latter case the available energy is
much smaller. In this instance one of the motor terminals is connected
to the insulated plate or body located within the alternating
electrostatic field, and the other terminal preferably to the ground.

It is quite possible, however, that such "no-wire" motors, as they
might be called, could be operated by conduction throug