By E. L. VOICE.
The remarkable researches and experiments of Professor Hughes clearly
show that magnetism is totally independent of iron, and that its
molecules, particles, or polarities are capable of rotation in that
metal. It would also appear that by reason of the friction between
magnetism and iron, the molecules of the latter are only partially
moved, such movement being the result of the tendency of iron to retard
magnetic change.
I have found that the magnetic molecules also possess inertia, that they
are capable of acquiring momentum, and that their rotation continues
for a considerable time after the exciting cause of their rotation has
ceased.
These facts may be proved in a very evident manner, inasmuch as induced
electric currents are generated by this _after_ rotation, which may be
made to light incandescent lamps.
In this case the magnetic rotations are produced in an electro magnet by
means of alternate currents supplied by alternating Gramme machine.
In order to better explain the action, it will be necessary to refer
to a new electro-motor, which was the subject of an article in the
_Electrical Review_ of February 19 last. It is of that type of motor in
which the field magnet and armature poles are alternately arranged, and
which requires a periodical reversibility of magnetism in the armature
to cause the latter to revolve, as in the Griscom motor. The insulating
strips in the commutator are sufficiently wide to demagnetize the whole
of the machine before reversibility in the armature takes place, and
this demagnetization sets up a _direct_ induced current, which is caught
in a shunt circuit by the aid of a second commutator, which only comes
into action when the first commutator goes out.
When this motor is supplied by a continuous current, it is easy to
understand that the induced current which passes through the shunt
circuit, and which is caused by the demagnetization, is proportional
to the mass of iron and wire of which the machine is composed, or
proportional to its inductive capacity. This current is purely a
secondary effect, of short duration, and only occurs once at each break
of the commutator.
The motor is of such a size that when supplied with a continuous current
of proper strength the induced electrical effect in the shunt circuit
will light one incandescent lamp. If, however, it is supplied with an
alternating current of the same power, it will light eight lamps, and
the mechanical power given off is even more than with a continuous
current, provided that the alternations from the dynamo do not exceed
6,000 a minute.
At first I was considerably puzzled by this great difference, because in
both cases it is impossible for the lamp circuit to be acted upon by the
main current. It occurred to me, however, that the rapid alternations
of the exciting current from the dynamo, and the consequent speed of
magnetic molecular rotation, gave the latter a certain momentum, and
that by widening the insulating strips of the first or main current
commutator, and proportionately increasing the width of conducting
surface in the shunt commutator up to certain limits, this effect would
be increased. I found such to be the case, from which I inferred that
the increase of induced current in the shunt circuit was on account of
its longer duration, by reason of the acquired momentum of the magnetic
molecular rotations _after_ the alternating exciting current had ceased.
[Illustration]
Those who have facilities for carrying out experiments may prove it in
the following manner:
E, in the inclosed drawing, is an electro-magnet whose brushes press on
two metallic bands, B and B¹, fixed to but insulated from the spindle,
A. The band, B, is in electrical circuit with the shunt commutator, S,
and the main commutator, M; while the band, B¹, is in contact with
shunt commutator, S¹, and main commutator, M¹. This contact is made
by conducting rods, as indicated. The commutators, as regards their
brushes, are so arranged that when M and M¹ are in action, S and S¹ are
out of action, and _vice versa_. The spindle and commutators are rotated
by the pulley, P. L is an incandescent lamp in the shunt circuit.
Let us now suppose the apparatus at rest, and the brushes in electrical
contact with the main commutators, M and M¹. The current from an
alternating dynamo passes into the magnet, E, and rapidly reverses its
polarity. By actuating the pulley, P, the commutators are rotated, when
M and M¹ go out of, and the shunt commutators, S and S¹, come into
action, enabling the _after_ current set up in the magnet to light the
lamp, L, in the shunt circuit.
In order to make comparative tests, the same apparatus may be supplied
with continuous instead of alternating currents. The after current in
the former case, however, is much smaller, consisting of one electrical
impulse only at each break of the commutator, whereas in the alternating
system these impulses are practically continued; the result being that,
all things being equal, a far greater number of lamps may be used in the
shunt than when supplied by continuous current only, and it would
appear that this difference can only be attributed to the fact that the
rotatory motion of magnetic molecules, or polarity of the magnet, E,
acquires momentum when acted upon by a suitable physical cause, such as
alternating currents of electricity; this momentum lasting a sensible
time after the cessation of the acting cause.
If we had the gift of magnetic sight, and could see what is going on in
the electro-magnet when it is excited by alternating currents, we should
probably see the molecules or polarities tumbling over each other at an
enormous rate. I do not think, however, that we should see anything but
a vibratory motion as regards the iron molecules.--_Elec. Review_.
* * * * *
[AMER. MICROSCOP. JOUR.]