Idaho semi-weekly world. [volume] (Idaho City, Idaho Territory) 1875-1908, 1891-08-18
ELECTRIC DYNAMOS.
MACHINERY THAT CAUSES THE AZ
IeRNATiNo CURRENT.

Compari.on Between the f''''
wheel and the Present P"weri"i @''
observation-disclosures in the '~'
Currcnts-The Machine
Thu first DYNAMO electric machine
ever constructed was made oy r@a"e
This great physicist, the prince Oh us
,x,r;nenters, rs he has been called us
a,rsr.3 that when u disc or fiat plate OF
conner was made to rotate between 'ne
poies of powerful magnet currents we,s
produced in the plate from the center OUT
ward. BY making wire touch .ne ~
yolying plate with one of Its ehus anu
bringing the other one in contact Win
the rim he found that current OF eieo
tricity passed along the wire, ana couiu
be made to indicate its existence ns NC
Nact,np the needle of galvanometer,
decomposing a chemical solution or oy
any of the well known effects produeeu
by electricity in motion. -,
Faraday saw the Importance OF TINS
discovery and the great uses IN the way
of practical application to wnich !.
might be put, but he did not himself
stay to develop it; he left that to others,
and with it the wealth which might
thus be acquired, and himself went on
to investigate other obscure ana nttie
known phenomena connected with phys
les and electricity, regarding this AS his
proper work, and exhibiting in his con-
duct the true scientific spirit. When
many years afterward he went to see
the first application of this discovery OF
his to the production OF the illumiha-
ton of the North Foreland lighthouse,
he said. after looking at the large mag
neto-electric machines there, 81 gave 1t
to YOU an infant; you have made 1t
giant"
Dynamo and magnetic electric ma
chimes consist essentially of coil of wire
the armature," as it is called-rotat-
ing between the poles of large mag
net. the poles being bent round so as to
approach each other and have the arma-
ture between them. This magnet may
be either a permanent magnet of hard
steer, OF al "a
wire coiled round soft iron core, cur
rent of electricity being made to circle
round the wire coil, and thus magnetic
ing the iron core while it lasts. 1t is the
latter arrangement which is almost uni
versally used now, though the magnetic
machines with permanent magnets were
the earliest form.
THE EI4ECTRO-MAGNET.
A magnet produces an influence in the
neighborhood around it, and this sur
rounding neighborhood is known as the
''field of force" of the Magnet. e., the
sphere in which its influence can be felt.
A magnetic needle or bit of iron filing
placed in this field sets itself to point
along the Zines of force of the field
that is, the lines along which the mag
netic 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 forco for him
self by placing bar magnet underneath
a sheet of paper and then sprinkling
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
magnet while under the influence of the
powerful magnet in whose field they
are, and therefore place themselves
lengthwise along the lines of force-that
is, along the line of action of the result
ant magnetic force at the place where
each one is.
When coil of wire or armature is
made to revolve rapidly in the strong
field Of force which occupies the space
between the poles of powerful electro
magnet currents are produced in the
coil. These currents alter their direc.
ton through the coil every time the lat.
ter changes its position with reference
to the poles of the magnet. The side of
the coil, which was opposite the north
pole, Is after half revolution opposite
the south pole, and the influence Of the
south pole tends to produce an opposite
current to that of the north pole. Here
we have an alternate current" dynamo
machine
PROCESSES OF USING THE CURRENT.
AS the coil or armature rotates with
great speed-some hundreds of revolu-
tlons per minute-these currents, in al.
ternating directions, succeed each other
very rapidly, and if an electric arc lamn
Is placed on the circuit it will be lit mn
In this case it is not necessary that the
current be sent round the circuit in ono
direction only, but although the ter1ni.
nais OF the lamp are constantly changing
thelr polarlty-that is, the north mole
where the current enters the next in.
stant becomes the south pole where the
current leaves-yet, as this occurs MANY
tlmes IN one second, the effect produced
Is the same as if the current was in one
uniform direction.
Inc lamp has no time to cool; it doe.
not go out before the oppositely directed
current passes through it and prodncas
tne same effect as the previous one. No
nlcker1ng Is observable. The impression
produced by the glowing carbon on the
human eye is retained by the retina 70,
Tar longer period than the duration ot
one surge OF electricity through tho
lamp, and is not gone before the effect
produced by the succeeding opnos;te
wave makes its impression on our nerves
In a continuous current" dynamo
winch Is necessary for some purnoaes
snch as electro plating, where the effec,
desired could not be produced if the Al
lection OF the current was continually
altering the electric current is made 70
pass always one way round the externsi
circuit circuit; This result is got by using the
ingenious device of commpta,or