St. Tammany farmer. [volume] (Covington, La.) 1874-current, 1891-06-27
WHAT A DYNAMO IS.


WHAT A DYNAMO IS.
Explssassoa q the Aetssa - Alternating
Curreats In Electric Lighting.
The first dynamoelectric machine
ever constructed was that made BY
Faraday. This great physicist the
prince Of cxperimenters. rs he has been
called, discovered that when disc o.
fiat plate of copper was made to rotats
between tho poles of . powerful mag
net currents were produced in the
plate from the center outward by
making . wire touch the revolving
plate with one of its ends and bringing
the other one in contact with the rim
he found that . current of electricity
passed along the wire and could Be
made to indicate its existence BY defect
ing the needle of . galvanometer, de.
composing . chemical solution, or by
any of the well-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 il
might be put, but he did not himself
stay to develop it; he left that to others,
and with il the wealth which might
thus be acquired. and himself went ON
to investigate other obscure and little
known phenomena connected with ply
sizes and electricity, regarding this rs 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 illumina-
ton of the North Foreland lighthouse
he said. after looking At the large mag
neto-electric machines there: II gave it
to yoa IN infant; you have made it .
giant"
Dynamo and magnetic electric ma
chimes consist essentially of . coil Of
wire-''the armature," n It is called
rotating 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 q permanent magnet of
hard steel or an elcctro-magnet consist
ing Of wire coiled round = soft iron core,
q current of electricity being made to
circle round the wire coil, and thus
magnetising the iron core while it lasts.
II is the latter arrangement which is
almost universally used now, though the
magnetic machines with permanent
magnets were the earliest form.
A magnet produces an influence in
the neighborhood around it, and this
ncighborhood is known as
the field of force" Of the magnet-i. e..
the sphere in which its influence can be
felt. A magnetic needle or bit of IRON
fling placed in this field sets itself to
point along the ''lines of force" of the
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 curv-
ing round to the other. Any one may
see the form of these lines Of force for
BY placing . bar-magnet un-
derncath q sheet of paper and then
iron-filings on the paper.
On tapping this the filings will set
along the lines of force in
beautiful regular curves Here the small
fragments Of iron are themselves made
magnets while under the influence of
the powerful magnet in whose field"
they are, and therefore place them
selves 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 . coil of wire or armature is
made to rcvolve 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-
lion through the coil every time the lat
ter changes its position with reference
70 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 ''alternste current" dynamo
nachine. a ID . f-.f--f-
great speed-some hundreds Of revolur
Hons per minute-these cuzenta in al-
sernating directions. Succeed each other
rery rapidly, and II IN electric arc-lsmp
s placed ON the circuit i will be lit mp
n this csae it j. mot necessary that the
current be; sent round the circuit in one
direction onlyy but although the termin-
lis Of the lamp ars conatantly changing
heir polarity-that is, the north pole
where the current enters the next in
'tant becomes the south pole where the
current leaves-yet - this occurs many
lines In one second, the effect produced
. the same - Il the current was In one
,niiogu direction. va t. 7r F-s-7
The lamp has 70 time 70 get cool; II
loes not 60 ont before the oppositely
lirected current passes through il and
produces the same effect ~ the previous
me. No Aiekering l. observable. The
produced BY the glowing
.afbon On the human eye isretained BY
he retina for . far longer period than
hs anraaion Of one surge q electricity
hroagh the lamp and - not gone be-
ore the effect produced By the susceed-
ng opposite wave nahes it, inpressios
" our nerveA The Jablochlko6 lamps
ised lately on the Thames embanknent
re meant for. this system Of electric
lighting With alternating currents
In >''eoo1inuous current" dynamo.
vhich- = 'ascessaky for come purposes,
neh - elestfoplatine. where the eject
lesireA copA - b prodoosd II The d..
ection of the current IVES ceatinually
the electric snxEsat is made to
ass always anew wsy rounG The exter-
laaShsuiA Fh6resslt is'got by using
he ingsuioaS Aev1ce Of . comi93tator,
vhlel ldso esie1ny dk4ectT. a. cut:
ent 50 - always to send L in IN un-
'sEying. digeotiya thfssgh ths plsting
Datk or the electric lamp - the case
nay b. 40 .ss>Sss