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Page 25
[Illustration: FIG. 2.]
[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
is always outside of the arc comprised between the brushes, R. In
order to secure a continuity of the circuit in the effective arc, W S_ o_,
it is only necessary to arrange a rubber, M, in such a way as to
establish a communication between the two parts of the divided touch
as soon as this latter enters the arc under consideration.
In order to produce a current in the direction of the arrows shown in
Fig. 4, the spiral and axle must revolve from right to left. In this
case the rubber, M, occupies the position shown in the same figure,
the brushes embracing an arc of a little less than 180�. As soon as
the lower touch comes in contact with the brush, R, when the
revolution is being effected from left to right, the rubber, M,
establishes a communication between the two halves that have until now
been isolated, and the current is no longer interrupted. The second
touch during this time is at any point whatever of the arc, W N _o_,
and the spirals corresponding to the latter arc outside of the
circuit. In short, thanks to the rubber, M, we have an ordinary Gramme
collector in that portion of the circuit comprised between the
brushes, and a collector with a breakage of the circuit in the portion
to the right.
[Illustration: FIG. 5.]
This type of machine is entirely theoretical. In the apparatus used
for Prof. Pfaundler's experiments in 1870, the armature revolved with
the solenoid. The core and armature were of soft iron, and the core
was arranged in a manner analogous to the preceding, and remained in
place under the action of its weight, and the shell, forming a
complete circle, revolved with poles fixed in space.
Practically, the machine that we have just described would prove
inconvenient to realize, and would present serious inconveniences. In
the first place, it seems to us quite difficult to transmit the motion
of the solenoid to the axle, supposing the former to revolve within
the armature. In the second place, considerable friction would surely
occur between the spirals and core, and the axle, being submitted to a
lateral stress, would be placed in a poor condition for work. It is
even allowable to doubt whether such a type could be practically got
up. At all events, no trial has as yet been made of it.
Compared with the Gramme machine, from an absolutely theoretical point
of view, the Pfaundler apparatus presents undoubted advantages. A
theoretically perfect dynamo electric machine would be one in which
there was a complete reciprocity between the magnetizing action of the
current and the inductive action of the magnetic field. Now, such is
not the case in the Gramme machine. In this apparatus the soft iron
core is at the same time a magnet through favorable induction and a
disadvantageous electro-magnet. This double polarization is only
remedied to a certain extent by the adjustment of the brushes. In the
Pfaundler machine, on the contrary, the electro-magnetism and
magnetism through induction act in the same direction, and concur in
effecting a polarization that favors the production of the current.
Looked at it in this light, the latter machine more nearly approaches
the type of perfection than does that of Gramme.
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