Alexandria gazette. [volume] (Alexandria, D.C.) 1834-1974, 1892-10-07
The Trolley System.

In the preparation of this article 1t Is
the purpose of the writer to avoid the
use of technical terms and give those
unfamiliar with the subject q general
idea of what is commonly known as the
trolley system.
In an article prepared by the writer
and published in the GAZETTE when
the electric light was introduced in this
city, it was explained that the dynamo
was q machine for converting mechanl-
cal force into electricity. I'll 1.-THE present
case, we deal with identically the same
machine although in an entirely differ
ent role, its function being to transform
electricity into mechanical power.
The motor which propels the car
consists of heavy bar ofsoft iron, call
ed the core, shaped so that its two ends
will face each other, something like 4
horse shoe. Around this is wound several
layers of covered wire. When electric
ity flows through this wire the iron
core becomes q powerful magnet, It's
maximum strength being at its ends,
which are called poles, and the space
surrounding the poles, within their
magnetic influence, is called the mag
netic field.
Between the poles of this field-pro-
ducing magnet is placed another iron
core wound longitudinally with num-
Der of sections of covered wire, each
section of which becomes & magnet
when electricity flows through it this
arrangement is called the armaturec,
and is mounted upon shaft so that 1t
can freely revolve between the poles OF
the field magnet, which is stationary. !.
When the electric current is passed
through the field magnet and armature
they become strongly magnetlzed and
according to well established law OF
magnetism, that unlike poles attract,
the armature sections are successfully
attractcd by the field magnet, which
causes them to rotate.
On the end of the shaft to which the
armature is attached, is affixed cog
wheel, which operates upon similar
wheel gcared to the car axle. so long
rs the current flows the armature re,
wolves and with it The Car axle and
wheels; when the current is cut of, by
means ofthe regulating device on the
car platform, the field and armature
cease to be magnets and the car stops.
The speed of the car is governed by
the amount of current allowed to pass
through the regulator to the motor,
the power OF which varies in direct
proportion TO the current strength.
By the peculiar manner in which the
cars are supplied with electricity the
running is not materially affected even
should the trolley wire break.
The current is taken from the over
head wire by metallic trolling wheel,
and conveyed to the motor by means OF
"a wire running through the trolley pole
and car; after passing through the mo-
tor it leaves the car by way of the
wheels and track, thence back to the
generating dynamo at the power house;
BY means of the earth, which is a good
conductor. The system used in TINS
city is called the overhead, as distin-
guished from the underground and
storage battery system, all of which
have been tried with varying success.
While the storage is unquestionably
the ideal systems the overhead is the
most practical, and is in general use
where electricity is employed for the
propulsion of street cars.
CHAs. F. THOMSON.
Alexandria Va