The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 322. SINGLE NEEDLE TELEGRAPH INSTRUMENT, DOUBLE
TAPPER FORM.

Fig. 323. DOUBLE TAPPER KEY FOR SINGLE NEEDLE TELEGRAPH.
C and Z are two strips of metal to which the positive and negative poles
of the battery are respectively connected. E and L are two metallic
springs; E is connected to earth, L is connected to the line; at rest
both press against Z. If L is depressed so as to touch C, the current
from the battery goes to the line by the key L, goes through the coils
of the distant instrument and deflects the needle to one side, and then
goes to the earth. If the key E is depressed, L retaining its normal
position, the direction of the current is reversed, for the other pole
of the battery is connected to the earth and the reverse current going
through the coils of the distant instrument deflects the galvanometer
needle to the other side.
In the drop-handle type an analogous form of commutator worked by a
single handle produces the same effects.
521 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Wheatstone, A. B. C.
A magneto-electric telegraph of the dial system. An alternating current
magneto-generator is turned by hand and by depressing keys its current
is admitted to or cut off from the line and receiver's instrument. The
message is received by a dial instrument working by the escapement
motion described under Telegraph, Dial.
Telegraph, Writing.
A telegraph in which the message is received in written characters. The
transmitter includes a stylus which is held in the hand and whose point
bears against the upper end of a vertical rod. The rod is susceptible of
oscillation in all directions, having at its base a spring support
equivalent to a universal joint.
The stylus is moved about in the shape of letters. As it does this it
throws a series of resistances in and out of the circuit.
At the receiving end of the line the instrument for recording the
message includes two electro-magnets with their cores at right angles to
each other and their faces near together at the point of the angle. An
armature is supported between the faces and through it a vertical rod
carried by a spring at its bottom rises. These magnets receive current
proportional to the resistances cut in and out by the motions of the
other rod at the transmitting end of the line. These resistances are
arranged in two series at right angles to each other, one for each
magnet. Thus the movements of the transmitting stylus and rod are
repeated by the end of the rod in the receiving instrument. A species of
pen is carried at the end of the rod of the receiving instrument, which
marks the letters upon a riband of paper which is fed beneath it.
Telemanometer. Electric.
A pressure gauge with electric attachment for indicating or recording
its indications at a distance.
It is applicable to steam boilers, so as to give the steam pressure in
any desired place.
Telemeter, Electric.
An apparatus for electrically indicating or recording at a distance the
indications of any instrument such as a pressure gauge, barometer or
thermometer, or for similar work. The telemanometer applied to a boiler
comes into this class of instrument.
Telephotography.
The transmission of pictures by the electric current, the requisite
changes in the current being effected by the action of light upon
selenium. The picture is projected by a magic lantern. Its projection is
traversed by a selenium resistance through which the current passes.
This is moved systematically over its entire area, thus constituting the
transmitter, and synchronously with the motion of the selenium a contact
point at the other end of the line moves systematically over a sheet of
chemically prepared paper. The paper, which may be saturated with a
solution of potassium ferrocyanide and ammonium nitrate, is stained by
the passage of the current, and by the variation in intensity of
staining, which variation is due to variations in the current, produced
by the effects of the light upon the selenium, the picture is
reproduced.
522 STANDARD ELECTRICAL DICTIONARY.
Telepherage.
An electric transportation system, hitherto only used for the carrying
of ore, freight, etc. Its characteristic feature is that the electric
conductors, suspended from poles, supply the way on which carriages
provided with electric motors run. The motors take their current
directly from the conductors.
There are two conducting lines, running parallel with each other,
supported at the opposite ends of transverse brackets on a row of
supporting poles. At each pole the lines cross over so that right line
alternates with left, between consecutive pairs of poles.
The cars are suspended from pulleys running on one or the other of the
conductors. A train of such cars are connected and the current is taken
in near one end and leaves near the other end of the train. These
current connections are so distant, their distance being regulated by
the length of the train, that they are, for all but an instant at the
time of passing each of the poles, in connection with segments of the
line which are of opposite potential. To carry out this principle the
distance between contacts is equal to the distance between poles. Owing
to the crossing over of the lines the contacts are in connection as
described and thereby the actuating current is caused to go through the
motors.
Cars running in one direction go on the electric conductors on the one
side, those running in the other direction go on the other conductor.
A great many refinements have been introduced, but the system has been
very little used.
Telephone.
An instrument for the transmission of articulate speech by the electric
current. The current is defined as of the undulatory type. (See Current,
Undulatory.)
The cut shows what may be termed the fundamental telephone circuit. A
line wire is shown terminating in ground plates and with a telephone in
circuit at each end. The latter consists of a magnet N S with a coil of
insulated wire H surrounding one end. Facing the pole of the magnet is a
soft iron diaphragm D, held in a frame or mouthpiece T. Any change of
current in the line affects the magnetism of the magnet, causing it to
attract the diaphragm more or less. The magnet and diaphragm really
constitute a little electric motor, the diaphragm vibrating back and
forth through an exceedingly short range, for changes in the magnetic
attraction.
The principle of the reversibility of the dynamo applies here. If the
magnet is subjected to no change in magnetism, and if the diaphragm is
moved or vibrated in front of its poles, currents will be induced in the
wire bobbin which surrounds its end. If two such magnets with bobbins
and diaphragms are arranged as shown, vibrations imparted to one
diaphragm will send currents through the line which, affecting the
magnetism of the distant magnet, will cause its diaphragm to vibrate in
exact accordance with the motions of the first or motor diaphragm. In
the combination one telephone represents a dynamo, the other a motor.
If the vibrations of the diaphragm are imparted by the voice, the voice
with all its modulations will be reproduced by the telephone at the
distant end of the line.
523 STANDARD ELECTRICAL DICTIONARY.

Fig. 324. DIAGRAM OF BELL TELEPHONES
AND LINE WITH EARTH CONNECTIONS.

Fig. 325. SECTION OF BELL TELEPHONE.
The above gives the essential features of the Bell telephone. In
practice the telephone is used only as the receiver. As transmitter a
microphone is employed. To give the current a battery, generally of the
open circuit type, is used, and the current in the line is an induced or
secondary one.
The microphone which is talked to, and which is the seat of the current
variations which reproduce original sound, is termed the transmitter,
the telephone in which the sounds are produced at the distant end of the
line is termed the receiver.
Fig. 325 shows the construction of the Bell telephone in universal use
in this country as the receiver. M is a bar magnet, in a case L L. B B
is a bobbin or coil of insulated wire surrounding one end of the magnet.
D is the diaphragm of soft iron plate (ferrotype metal), and E is the
mouthpiece. The terminals of the coil B B connect with the binding
screws C C. The wire in the coil is No. 36, A. W. G., and is wound to a
resistance of about 80 ohms.
524 STANDARD ELECTRICAL DICTIONARY.
As typical transmitter the Blake instrument may be cited. It is a carbon
microphone. It is shown in section in the cut; a is the mouthpiece and e
is a diaphragm of iron plate, although other substances could be used; f
is a steel spring, with a platinum contact piece at its end. One end
bears against the diaphragm, the other against a carbon block k. The
latter is carried by a brass block p, and pressure is maintained between
these contacts by the spring g and weight of the piece c, which by
gravity tends to press all together. The current passes by way of the
spring f, carbon button k and spring g through the circuit indicated.
A battery is in circuit with these parts. If a telephone is also in
circuit, and the transmitter is spoken against, the diaphragm vibrating
affects the resistance of the carbon-platinum contact, without even
breaking the contact, and the telephone reproduces the sound. The heavy
piece of metal C acts by its inertia to prevent breaking of the contact.
The position of this piece c, which is carried by the brass plate m, is
adjusted by the screw n.

Fig. 326. SECTION OF BLAKE TRANSMITTER.
In practice the transmitter and battery are usually on a local circuit,
which includes the primary of an induction coil. The line and distant
receiving telephone are in circuit with the secondary of the induction
coil, without any battery.
Telephone, Bi-.
A pair of telephones carried at the ends of a curved bar or spring so
that they fit the head of a person using them. One telephone is held
against each ear without the use of the hands.

525 STANDARD ELECTRICAL DICTIONARY.
Telephone, Capillary.
A telephone utilizing electro-capillarity for the production of
telephonic effects. The following describes the invention of Antoine
Breguet.
The point of a glass tube, drawn out at its lower end to a capillary
opening dips vertically into a vessel. This vessel is partly filled with
mercury, over which is a layer of dilute sulphuric acid. The end of the
immersed tube dips into the acid, but does not reach the mercury. One
line contact is with mercury in the tube, the other with the mercury in
the vessel. The arrangement of tube and vessel is duplicated, giving one
set for each end of the line. On introducing a battery in the circuit
the level of the mercury is affected by electro-capillarity. The tubes
are closed by plates or diaphragms at their tops, so as to enclose a
column of air. It is evident that the pressure of this air will depend
upon the level of the mercury in the tube, and this depends on the
electro-motive force. On speaking against the diaphragm the sound waves
affect the air pressure, and consequently the level, enough to cause
potential differences which reproduce the sound in the other instrument.