The Democratic press. [volume] (Ravenna, O. [Ohio]) 1868-1901, 1891-05-20
WHAT A DYNAMO is.
Explanation of the Action of Alternating
Currents in Electric Lighting.

Explanation of the Action of Alternating
Currents in Electric Lighting.
The first dynamo-electric machine
ever constructed was that made by
Faraday, says Knowledge. This great
physicist, the prince of experimenters,
as he has been called, discovered that
when a disc or fiat plate of copper was
made to rotate between the poles of a
powerful magnet currents were pro-
duced in the plate from the center out
ward. By making a wire touch the
revolving plate with one of its ends
and bringing the other one in contact
with the rim he found that a current
of electricity passed along the wire
and could be made to indicate its ex-
istence by DETECTING the needle of a
galvanometer, decomposing a chemi-
cal soisltion, or by any of the we'll
known effects produced by electricity
in motion.
Faraday saw the Importance of this
discovery and the great uses in the
way of practical application to which
it might be put, but he did not himself
stay to develop it; he left that to 9TH
ers, and with it the wealth which might
thus be acquired, and himself went on
known phenomena connected with
physics and electricity regarding this
as his proper work and exhibiting in
his conduct the true scientific spirit.
When many years afterward he went
to see the first application of this dis
covery of his to the production of the
lighthouse he said, after looking at the
large magneto-electric machines there:
Il gave it to you an infant; you have
made it a giant"
Dynamo and magnetic electric
machines consist essentially of a coil
of wire-''the armature," as it is
collaborating between the poles of
large magnet, the poles being bent
round so as to approach each other
and have the armature between them.
This magnet may be either perma-
nent magnet of hard steel or an cleo
tro-magnet consisting of wire coiled
round a soft iron core, current of
electricity being made to circle round
the wire coil, and thus magnetizing
the iron core while it lasts. 1t is the
latter arrangement which is almost
universally used now, though the mag
neto machines with permanent mag
uets were the earliest form.
A magnet produces an influence in
the neighborhood around it,. and this
surrounding neighborhood is known as
the field of force" of the Magnet.
e.. the sphere in which it's influence
can be felt. A magnetic needle or bic
of iron-tiling placed in this field sets
itself to point along the ''lines of force
of the tield-that is the lines along
which the magnetic force acts, and
which form curves round the magnet,
running out as it were, from pole to
pole, and curving round to the other.
Any one may see the form of these
lines of force for himself by placing a
bar-magnet underneath a sheet of
paper and then sprinkling iron-filings
on the paper.
On tapping this the filings will set
themselves along the lines of force in
beautiful regular curves. Here the
small fragments of iron are themselves
made magnets while under the infiu-
ence of the powerful magnet in whose
field" they are, and therefore place
themselves lengthways along the lines
of force-that is, along the line of
action of the resultant magnetic force
at the place where each one is.
When a coil of wire or armature is
made to revolve rapidly in the strong
field of force which occupies the space
between the poles of a powerful cleo
tro-magnet currents are produced in
the coil. These currents alter their
direction through the coil every time
the latter changes it's position with ref
erence to the poles of the magnet. The
side of the coil which was opposite the
north pole is after half a revolution
opposite the south pole, and the influ-
ence of the south pole tends to produce
an opposite current to that of the north
pole. Here we have an alternate
current dynamo machine.
As the coil or armature rotates with
great speed-some hundreds of revo-
lutions per minute-these currents. in
alternating directions. succeed each
other very rapidly, and if an electric
arc-lamp is placed on the circuit it
will be lit up. In this case it is not
necessary that the current be sent
round the circuit in one direction only.
but although the terminals of the lamp
are constantly changing their polarity
that is, the north pole where the cur
rent enters the next instant becomes
the south pole where the current
in one second, the effect produced is
uniform direction.
The lamp has no time to get cool; it
does not 90 out before the oppositely
directed current passes through it and
produces the same effect as the previ-
Gus one. No Pickering is observable.
The impression produced by the glow
oorbor bo h1n1on nvn iS ra-
tanned by the retina for a far longer
period than the duration of one surge
of electricity through the lamp, and is
not gone before the effect produced by
the succeeding opposite wave makes
it's impression on our nerves. The
Jablochkoff lamps used lately on the
Thames embankment are meant for
this system of electric lighting with
alternating currents.
In continuous current" dynamo
which is necessary for some purposes,
such as electroplating where the effect
desired could not be produced if the
direction of the current was contin-
ually altering, the electric current is
made to pass always one way round
the external circuit. This result is got
by using the ingenious device of a
fleets the current so as always to send
it in an unvarying direction through
the plating bath or the electric lamp,
as the case may be.
This commutator consists simply of
a split tube, which is attached to the
revolving armature, and may be seen
in any dynamo working on the contin-
uous system. This tube revolves with
the revolving armature, and it is di-
vided by an Insulating substance into
two parts; each half is alternately on
the left and right of the space between
the poles of the magnet, and the
brushes" which collect the current
from the armature-i e., the bundles
of copper wire spread out like a brush
which form each end of the outer Cir
cuit-are fixed in position, and the re-
volving commutator attached to the
armature brings alternately one OF its
half-tubes into contact with a brush.
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