Alexandria gazette. [volume] (Alexandria, D.C.) 1834-1974, 1889-09-25
Electric Light and How it is Made.

without tho Use OF technical terms, diagrams
or mathematics, is not az easy matter. My
obj ct, however, is 10 remove these stumbling
blocks aad prepare for the general public q
clear and simple description of the appara
tua used to produce the arc light such as
we have in this city. will begin with the
dynemo, which is q machine for converting
mechanical energy into electrical energy.
1t consists essentially of four parte, viz A
puIly with which to apply the mechanical
force, an eectro.magnet with which TO pro.
duce the magnetic field, an armature to ro
tate in the magnetic isld and set of brush
es to collect the current generated in the
armature Before proceeding further, it
will be we'll to explain the meaning OF mag
netic fed Every school boy is familiar
with The red horseshoe magnet which can
br purchased at any hard~are store. just
why the manufacturers Of these toys persist
in painting them red ls profound mystery
However, If iron filings be sprinkled on q
piece Of paper and the same be carried near
magnet they will be instantly
attracted aud assume o peculiar shape.
The ings show exactly how the magnetic
lluFS III IOtCc AOW OuU llOm q ooSbOij VIC
suace surrounding g magnet through which
these / mes of force flow is called the mag
netic 6s!d." Faraday in 1881 discovered
tha. If piece of wire be moved across
| magnetic field &c that it's movement will cut.
| or alter the lines of force. the lines thus cut
| will surround the wire and produce feeble
current of electricity n the wire. This in
| fuence around the wire is generally defined
as magnetic whirs; these whirls can be
shown by passing wire up through piece
| Of card board, and sprinkling few iron
| filings around the wire. When current of
electricity is passed through the wire the
| iron filings will Immediately assume the
| form OF concentric circles around the wire. Ii
| ieebl. current is produced in single wire
| by moving il through magnetic field, it is
reasonable to suppose that if long wire be
coed upon Itself many times and rapidly
| ed in a magnetic field it will cut more
,..r, Of force than single wire more meg
netic Iines os forcs will encirole the wire,
| consequently more electricity will be pro-
duced in The wire. Il will thus be seen that
| the amount cf current generated is directly
proportional TO the number Of turns of wire
rotated in the magnetic field. This arrange
| ment is called the armature, the wire being
| woucd on en iron core in direction psrsl.
I Iel with the shaft upon which it is mounted.
| In the construction of SO armature instead
| Of one continuous wire, it is generally di.
| y,dsd into several sections, the ends of each
section being carried to one end of the shaft
and tbere connected to metallic ring; this
ring ia divided into sections or &c gments, the
lumber Of which correspond with the pum.
Der of coils 10 the armature. Upon this ring,
or commutator, as it is technically termed,
| bo hrpSbal uhi0h P0llopt tho QnrrQnt
as 1t is generated in the armsture II is then
made to pass around the coils of the field
magnet and thence to the lamps. II. in
stead of using the steel horseshoe or perma.
ueut magnet, we substitute bar of soft iron
and upon this col several layers of covered
wire, we have an electro magnet which can
be very highly msgnetized by passing an
electric current through the coil of wire. In
the manu ecture of dynamos the mechanical
construction of this magnet is so arranged
| that its poles lie exactly opposite each
other with sufficient space between to allow
! the armau ure 10 be freely rotated on its axis.
This magnet produces the magnetic field,
and is called the "ield magnet" All iron
contaius email amount of permanent mag
netism When the armeture is made to re-
volve in the isld produced by this perma.
nent magnetism it causes very feeble cur
rent to be generated in the srmature; this
feeble current passing around the full mag
| net causes it to become stronger, and the
stronger tbs field magnet becomes the more
lines of force will be cut by the armature,
cons seuenFSy more electricity will be pro.
duced. This action continues until the
field magnet becomes thoroughly magnet
lied, when it is then said to be saturated,
and the dynamo doing it's maximum work.
In good dynamo only ten per cent. of the
mechanical power is lost; 1t is therefore
seeu that we have as available electrical
energy ninety per cent of the power ex
pended in producing it. The arc
lamp is an arrangement for holding
two sticks of carbon in vertical
line, one above the other; the lower carbon is
generally stationary, while the upper one is at.
tsched to brass rod capable Of being freely
moved up and down. In the body of the lamp
are two electro. magnets, which control the move.
| ment OF the upper carbon. Through one magnet
the entire current passes this is called the lifting
magnet The other is so arranged that only a
small portion of the current passes through it;
this is known as the feeding magnet. When
! there is no current passing through the lamp the
point of the upper carbon rests on that OF the
! wer simply by force of grsvitation. When the
current is made to pass through the lamp the
lifting magnet Immediately raises the upper car
bon at the same time the socalled "arc" is form.
ed between the ends of the csrbons. As the car.
bons burn the space between them is gradually
increased, until at length thearc would be broken
were it not for the feeding magnet which, when
the src has reached predetermined length causes
the upper carbon to descend little This burn
ing and feeding continues as long as q current
tio rs through the lamp. Some lamps are provided
with two sets OF carbons 80 arranged that when
I one set burns out the other by automatic do
vice is switched in circuit. In practice there are
several other mechanical detail s. but those men
! t;annd are the nrincinal nnes