[Illustration: FIG. 3.]

This latter apparatus has in this case the form shown in Fig. 4.

[Illustration: FIG. 4.]

The spiral, _s m b_, is movable, and the core, N _o s_, is kept in a
position of equilibrium by virtue of its weight, and is provided with
rollers. For the sake of greater clearness, the front part of the
armature is supposed to be removed. The current does not circulate in
the spirals to the right of the diameter, W O, which latter is not
absolutely vertical. The position of the rubbers and armature is
regulated once for all. We do not know just what were the means
devised by Kravogl to suppress the current in the spheres to the
right. At all events, it is probable that the system has grown old
since Gramme invented his collector. In the application of the Kravogl
motor to the generation of continuous currents, Professor Pfaundler
now proposes to ingeniously utilize the Gramme collector. In such a
case the arrangement shown in Fig. 5 would be adopted. Let us suppose
an ordinary collector having as many plates as there are sections in
the ring, these plates being connected as usual with the entrance and
exit wires of the sections. The diametrically opposite touches that
are in the line, W O, are divided, and one of the halves is connected
at the entrance, _c a'_ (Fig. 4), with the corresponding section,
while the other communicates with the exit, _c' a_, of the neighboring
section. Each of these halves is prolonged by a piece of metal bent
into the form of an arc of a circle and embracing a little less than a
semi-circumference. Between these prolongations there is an insulating
part. In the rotary motion of the spiral, at least one of the touches