The Idaho Republican. [volume] (Blackfoot, Idaho) 1904-1932, 1911-06-16

The electro-magnet 1t not permanent.
1t is a magnet only so long as an cleo
trio current is flowing through its
coil.
The permanent magnet has never
advanced much beyond the toy stage
except in compasses. The compass Is
small permanent magnet made in
the shape of needle, or an arrow,
and balanced on pivot SO that it can
swing around and obey its impulse
to point north and south or to parallel
the lines of magnetic influences be
tween the north and south poles of
this magnetic earth.
The electro-magnet is indispensable
to almost every modern application
of electricity. Without the electro
magnets the dynamos and motors
could not run; the telegraph would
refuse to carry it's messages around
the world; the telephones would not
transmit your voice the length of the
room; wireless would not work; fire
alarms would be worthless and door,
bells would refuse to ring. The per-
manent magnet is a bar of rather
hard iron or steel which, once mag
|netized, will retain it's magnetism for
long time, although its lifting or at
tractive power is comparatively weak
at best. The electromagnetic is what
might be termed an artificial mag
nett; that is, we may put the mag
netizing force into it or take the force
away at will.
This is the secret of the electro
magnet. We know that wire carry
|! ing current has formed around it
field of magnetic force, which is
strong in proportion to the strength
of the current flowing in the wire.
The theory is that this field of force
| is of the nature of invisible lines OF
| force encircling the wire, and as you
look along the wire in the direction
in which the current flows the lines
are circling around the wire in the d.
rection in which the hands of a clock
move.
This you must understand is theorF
so far. No one can see the lines OF
force, but the theory fits the facts OF
phenomena which we are able to OBJ
serve, and as long as the theory does
not "fall down" before the results
of actual experiment we may safely
base our arguments upon it.
If you take that same wire which
, is carrying current and form it into
spiral coil you have what is called
"solenoid.'' Remember that the
lines of force are still encircling the
wire in each individual turn of the
spiral. Therefore the tendency is for
all these lines of force to thread down
through the hollow spiral and up
along the outside, or vice versa, de-
pending ON which end of the solen-
did Won are looking at. Then, strange
to saw. the solenoid, as a whole, taxes
on the properties of a bar magnet
That is. one end of the solenoid is
a north pole and the other a south
mole. Suspend it carefully by its mid
die and it will point to the north
magnetic pole of the earth the same
as compass needle. All this, re-
member. is due to the current flow
ing in the wire.
Then, Just one step further and we
have an electro-magnet-slip INSIDE
the coil a bar of iron. Now turn or
the current and the iron bar becomes
a nowerful magnet-hundreds, per
hans thousands, of times stronger
than any permanent magnet evel
made. depending upon the strength
Of the current flowing in the wire ane
the number of turns of wire IN the
coil. called the "ampere-turns.T luri
off the current and the iron ceases
to be a magnet except for very little
magnetism left in it, called reslaua
magnetism. The explanation is ina
the lines of force threading througs
the coil saturate the iron with mag
netism to far greater extent thai
anv other known way of magnetizlng
Thus, you see, an electro-magne
means simply bar OF iron arouh'
which is wound coil OF insulated
wire. the wire carrying a current 0
electricity.
This discovery made practicable dy
namos and motors for the fields 0
| these machines are nothing more thar
, electromagnetic wound with man
turns of wire and forming between
/ their poles magnetic fields of great in
, tensity in which the armatures turn
The sounder of telegraph lnstru