Fig. 311. TAPPER.
Target, Electric.
A target registering or indicating electrically upon an annunciator the
point of impact of each bullet.
Taste, Galvanic.
The effect produced upon the gustatory nerves by the passage of an
electric current, or by the maintenance of potential difference between
two portions of the tongue. It is very simply produced by placing a
silver coin above, and a piece of zinc below the tongue, or the reverse,
and touching their edges. A sour, peculiar taste is at once perceived.
It cannot be due to any measurable quantity of current or of
electrolytic decomposition, because the couple can do little more than
establish a potential difference. With a strong current the taste
becomes too strong for comfort, and if on a telegraph line the extra
currents produced by the signaling make the operation of tasting the
current a very unpleasant one. It is said that messages have been
received in this way, the receiver placing one terminal of the line on
his tongue, and a terminal attached to a grounded wire below it, and
then receiving the Morse characters by taste.
504 STANDARD ELECTRICAL DICTIONARY.
Teazer.
Originally a fine wire coil wound on the field magnets of a dynamo in
shunt with the regular winding to maintain the magnetism. It was
originally used in electroplating machines to prevent inversion of the
magnetism, but has since developed into a component part of the winding
of the compound dynamo. (See Dynamo, Compound.)
Tee, Lead.
A lead pipe of T shape used for connecting branches to electric cables.
The tee is soldered by wiped joints to the lead sheathings of the cable
and branches after the wires have been connected, and the junctions
coated with insulating tape or cement, or both.
It is sometimes made in two halves, and is known as a split tee.
Tel-autograph.
A telegraph for reproducing the hand-writing of the sender at the
receiving end of the line. To save time a special spelling is sometimes
used.
Teleautograph.
The special spelling used with the Tel-Autograph telegraph.
Tele-barometer, Electric.
A barometer with electric attachment for indicating or recording at a
distance the barometric readings.
Telegraph, ABC.
This term is applied to alphabet telegraphs indicating the message by
the movements of a pointer on a dial marked with the characters to be
sent. In England the Wheatstone ABC system is much employed.
Telegraph, Automatic.
A telegraph system based on the operation of the transmitting instrument
by a perforated strip of paper drawn through it. The perforations made
by an apparatus termed a perforator, are so arranged as to give
telegraphic characters of the Morse or International Code in the
transmitting instrument. (See Perforator.) Bain in the year 1846 was the
originator of the system. He punched a fillet of paper with dots and
dashes, and drew it between two terminals of the line, thus sending over
the line a corresponding series of short and long currents which were
received by his chemical receiver. (See Chemical Receiver.) The method
was not successful. Its modern development, the Wheatstone Automatic
Telegraph, is highly so. The perforated paper by its perforations
controls the reciprocating movement of two rods, which pass through each
hole in two rows, corresponding to the two rods respectively as the
holes come opposite to the ends of the rods. The rods are kept
constantly moving up and down. If unperforated paper is above them their
upward motion is limited. This gives three positions for the rods, (a)
both down, (b) one up and the other down, (c) both up. These positions
of the rods work a pole changing key by which dots, spaces, and dashes
are transmitted to the receiving instrument, which is an exceedingly
delicate ink-printer. The latter can have its speed adjusted to receive
from 200 to 450 words per minute.
505 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Dial.
A telegraph in which as receiver a dial instrument is used. A pointer or
index hand moves around a dial. The dial is marked with letters of the
alphabet. The movements of the pointer are controlled by the
transmitting operator at a distant station. He by the same actions moves
a pointer on a duplicate instrument before him and the two are
synchronized to give identical indications. Thus a message is spelled
out letter by letter on both dials simultaneously. The motions of the
index are generally produced by what is virtually a recoil escapement.
The scape wheel is carried by the axle of the index, and a pallet or
anchor is vibrated by an electro-magnet whose armature is attached to
the stem of the pallet. As the pallet is vibrated it turns the wheel and
index one tooth for each single movement. There are as many teeth in the
wheel as there are characters on the dial. The two instruments being in
duplicate and synchronized, the pallets move exactly in unison, so that
identical readings of the dials are given. The pallets may be moved by
any kind of make and break mechanism, such as an ordinary telegraph key.
The index moves by steps or jerks, so that the system is sometimes
called step-by-step telegraphy.

Fig. 312. DIAL TELEGRAPH.
In the cut the make and break transmitter is shown at v v, with its
handle and contacts g and t. This mechanism sends impulses of current by
F and Z to the receiving magnet l. This attracts and releases its
armature K from contact into the position indicated by the dotted lines.
This works the rocker n on the pin o, and actuates the double or anchor
pawl s r, which turns the pallet or scrape wheel m.
The system is dropping into disuse, being supplanted by the telephone.
Synonym--Step-by-step Telegraph.
506 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Double Needle.
A telegraph system in which the message is read by the motions of two
vertical needles on the face of the instrument in front of the receiving
operator. An identical instrument faces the transmitting operator. By
two handles, one for each hand, the needles are caused by electric
impulses to swing to right and to left so as to give a telegraphic code.
It has been generally superseded by the single needle telegraph.
Telegraph, Duplex.
A telegraph capable of transmitting simultaneously two messages over one
wire. The methods of effecting it are distinct from those of multiplex
telegraphy. This term is used as a distinction from diode multiplex
telegraphy, in which the work is done on other principles. There are two
systems of duplex telegraphy, the differential and the bridge systems.
Telegraph, Duplex Bridge.
A system of duplex telegraphy employing the principle of the Wheatstone
bridge. The other or differential system depends on equality or
difference of currents; the bridge method on equality or difference of
potentials. The cut shows the system known as Steam's Plan.
At the ends of the line wire are two cross connections like duplicate
galvanometer connections in a Wheatstone bridge, each including a
receiving relay. The rest of the connections are self-explanatory.
When A depresses his key the current splits at the point indicating the
beginning of the bridge. One portion goes through the line to B and to
earth, the other goes to earth at A through the rheostats indicated by
the corrugated lines.
On reaching B's end the current divides at the cross-connection and part
goes through the receiving relay shown in the center of that
cross-connection.
Thus if A sends to B or B to A it is without effect on the home
receiving instrument. Now suppose that both simultaneously are sending
in opposite directions. If the connections be studied it will be seen
that every movement of the transmitting key will affect the balance of
the distant or receiving end of the bridge and so its instrument will
record the signals as they are sent.
As shown in the cut the sending keys are on local circuits, and work
what are known as duplex transmitters. These are instruments which send
line signals without breaking the connection.

Fig. 313. STEARN'S PLAN OF DUPLEX BRIDGE TELEGRAPHY.
In Stearn's plan condensers are introduced as shown. By this plan
different receiving instruments can be used. The inventor once worked a
Morse instrument at one end of the line, and a Hughes' instrument at the
other end.
507 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Duplex, Differential.
A system of duplex telegraphy employing the differential action of two
exciting or magnetizing coils. The general principles are the following.
Suppose that at each of two stations, there is a magnet working as a
sounder or relay. Each magnet is differentially wound, with two coils of
opposite direction, of identical number of turns.
When the sending key at a station A is depressed two exactly equal
currents go through the magnet in opposite directions. One called the
compensation current goes to the earth at the stations. The other called
the line current goes through the line, through the line coil of the
distant station E, thereby actuating the relay or sounder armature.
The instrument of the sender A is unaffected because he is sending
opposite and equal currents through its two coils. A special resistance
is provided on the compensation circuit for keeping the currents exactly
equal in effect. Nothing the sender at A does affects his own
instrument.
Now suppose E desires to telegraph back at the same time that A is
telegraphing to his station. He works his key. This does not affect his
own instrument except by sending the equal and opposite currents through
its coils. When his key is depressed and A's key is untouched, he works
A's receiving instrument.
508 STANDARD ELECTRICAL DICTIONARY.
When A's key is depressed simultaneously with B's key, the two line
currents are in opposition and neutralize each other. This throws out
the balance in the instruments and both armatures are attracted by the
compensation currents left free to act by the neutralization of the line
currents.

Fig. 314. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM
Suppose that B is sending a dash, and it begins while A's key is raised.
The line and compensation currents in B's receiving instrument
neutralize each other and no effect is produced, while A's receiving
instrument begins to register or indicate a dash. Now suppose A starts
to send a dash while B's is half over. He depresses his key. This sends
the two opposite currents through his magnet. His line current
neutralizes B's working current so that the compensation currents in
both receiving instruments hold the armatures attracted for the two
dashes. Meanwhile A's dash ends and he releases his key. At once his
line current ceases to neutralize B's line current, his receiving
instrument is actuated now by B's line current, while B's receiving
instrument ceases to be actuated by the compensation current.
Two assumptions are made in the above description. The line currents are
assumed to be equal in strength and opposite in direction at each
station. Neither of these is necessary. The line current received at a
station is always weaker than the outgoing line current, and it is the
preponderance of the compensation current over the partly neutralized
line current that does the work. As this preponderance is very nearly
equal to the line current received from the distant station, the signals
are actuated by almost the same current, whether it is compensation or
line current.
509 STANDARD ELECTRICAL DICTIONARY.
Both line currents may coincide in direction. Then when the two keys are
depressed, a line current of double strength goes through both receiving
instruments and both work by preponderance of the double line current
over the compensation current. In other respects the operation is the
same as before described.

Fig. 315. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM.