The Marietta journal. [volume] (Marietta, Ga.) 1866-1909, 1889-01-17
ELECTRIC LIGHTS.
THREE KINDS AND THEIR COST.
BY D. "A. ToMPKINs, CHARLOTTE, N. C.
From the Manufacturers Record.

of electric lighting, viz: arc, alter
mating current incandescent and d.
rect current incsndescent.
The arc system is that in which
two carbon rods are used and the
lamps are, mostly so-called 1900 to
1000 candle power each. The cur
rent generated on an arc light ma
chine is very high pressure, being
usually over 1000 volts electro-mo-
tive force and is very '~ngerous, in
asmuch as 600 volts 9ould in many
cases kill man. The greater the
pressure of the current the more
dangerous it is, but also the smaller
the wire required to!convey it and
therefore the cheaper is the plant.
Arc lamps can only be operated
with success by means of currents
Of high pressure. The lamps can
only be made so called 1900 or up
wards candle power with CONNER
cial success. Therefore, because of
the high pressure used and the
small-sized wire required, the lamps
may, with reasonable expense, be
put in circuit 10 to - miles (and
more) long, and thus distributed
over large territory. But the
lamps are very powerful, and if
placed close together make more
light than is required, and if put
far apart make more light than is
generally desired near the lamp and
too little at places remote from the
lamp.
The arc light is made by the as
sage of the current from one carbon
to another, they being drawn slight
ly apart by mechanism, and the
name arc light comes from the fact
that the light between the two points
has an arc shape and is supposed to
be small arc of fused carbon over
which the current is flowing, and is
kept heated te. white holiness and
from this white hot arc OF gas light
is radiated.
The incandescent light is made
by forcing current over "a small
carbon filament in sufficient quaint
ty to heat the filament to white hot
ness The filament must be in va
CUM, otherwise the carbon at white
heat would unite with the oxygen
OF the atmosphere and be consumed.
The pressure of the current must
be low, for just as small wire will
convey high currents, SO a small car
bon will convey high currents and
therefore high current would be
conveyed, but would not make the
carbon hot which it must do to pro-
duce light. Thus while arc lights
require currents of 1000 to 5000
volts pressure, incandescent lights
require a current of so to 100 volts
only.
While high currents are the most
dangerous to human life, on the
other hand high pressure currents
can be conveyed over very small
wires without heating or melting
them, and the lower the pressure
the greater the wire required
to convey it without heating
or melting. In other words, the et-
feet Of clerical pressure on human
beings and on copper wire may be
said to be opposite, viz: man may
take large quantities of low pres
sure current without injure or in
convenience which, at high pres
sure, would kill him, while on the
other hand copper wire will take
a high pressure current which
would melt with the current at low
pessure.
Therefore, for incandescent light
ing it is desirable to keep the cur
rent as high as possible in order to
keep down the size OF wire, and
thereby the expense, but it cannot
much exceed 100 volts, for at a
greater pressure than this the car
bon flament would convey it with
out heating and therefore no light
would be made.
Because Of the above the flament
is usually made as small as it can be
from mechanical point of view.
Late improvements have made i