Telegraph Lines
Construction of telegraph lines was a work of no ordinary undertaking. The country through which
the lines had to pass has to be explored, and the services of experienced engineers
were engaged. The shortest route was generally chosen, running along a highway or railway if possible; forests
and sudden turns were avoided; where curves were necessary, they
were designed as long as possible, so that the solidity of the supports
were not endangered. The posts were made 150 to 200 feet apart ; new supports
were added if the weight of the wires was too great. Sometimes
posts were charred to avoid decay, and across them arms placed, on which porcelain or glass cups
were fixed in a reversed position to avoid accumulation of moisture. The wire
passed around these cups, and was thus insulated from the earth. The wire
was galvanized, size from 9 to 12, a mile of wire weighing about 375 pounds. When wire
was being run, the ends were twisted firmly together by means of a tackle and vise. When wire runs through damp places like tunnels, it
was covered with gutta percha.
Telegraph Offices
Each office had a call or signal for itself. Any one or two letters of the alphabet
suited, and served in working over the line as the name of whatever office it
was applied to. One office desiring to communicate with another
wrote on the line the call of that office three or four times, followed by his own call, and
repeated this operation indefinitely, or until it was answered by the office called. The office answering the call
made the letter "I" three or four times, and signed his own call. The receipt of a communication
was answered by the signal "O. K." followed by the signal or call of the office receiving it. If the receiver, from any cause,
failed to read or understand any portion of the communication, he
called for a repetition by "breaking in" and saying "G. A." (go ahead), and giving the last word understood by him. If he
wished it repeated entirely he says "R. R" (Repeat).
With wires of many miles in length, main batteries, containing a large number of cells
were placed at the end stations. The return circuit was made through the entire distance of the earth, and each office connected with the line in the manner here described. The means employed to "tap" a telegraph line (which is sometimes done in case of railway accidents and for other purposes)
were very simple. The wire was cut, and its two ends connected to a portable instrument in the hands of a "sound" operator, who
was then easily able to read all that passed over the wire.
As lightning was frequently attracted to out-door lines, and thereby
would sometimes enter the offices, damaging the instruments
and even setting fire to curtains or other inflammable material about the instrument table, a simple instrument called "Lightning Arrester and Cut-out"
was used for the purpose of intercepting and carrying to the earth such discharges of lightning as would be liable to cause damage. This apparatus
was entirely effective, and was a complete safeguard against lightning.
Relay
The relay was used only on main lines, and
was made with greater or less resistance, according to the length of the wire. It
was connected in the main line, and operated by the key. The
armature of the relay closed the local circuit by striking the screw above the magnet, and
was simply the key to work the local sounder.
In the previous description it is assumed that the instrument was worked directly by the current sent along the line. In long circuits, however, direct working could only be accomplished by great battery power, as, owing to inevitable loss by leakage, a current loses greatly before it reaches its destination. It
was found to be a much better arrangement to have the instrument worked by a "local current" derived from a local battery at the receiving station.
When two stations far apart were to be connected by telegraph, it
was usual to transmit the signal to a half-way station, and thence to re-transmit it. This
was done by making the intermediate instrument act as a relay.
Arrangement of a Way Station
The annexed plan shows the instruments and connections of a way station. The line
entered at L, passed through the lightning arrester, X, and thence through the relay,
M, key, K
, and back to the lightning arrester, and thence to the next station by the
line L. The button C, arranged as shown in the figure, is called a "Cut-out." When turned so as to connect the two wires leading into the office, it
allowed the line current to pass across from one to the other without going through the instruments. The instruments
were always cut out, by means of this apparatus, when leaving the office temporarily or for the night, and also during a thunder-storm, to avoid damage to the apparatus. The local circuit
commenced at the X pole of the local battery, E', and through the platinum points of the relay by the binding screws 3, 4, thence through the sounder coils, S, and back to the other pole of the battery.
Other essential parts were the Pony Sounder (used in offices to receive from), the
Key, with circuit-breaker, and the Battery, by means of which action
was produced. If the battery was a gravity battery, it had the copper in the bottom of a glass jar, and the zinc suspended in the top. The circuit
was formed by connecting with wire the copper (or positive pole) to the binding screw of the key, and the zinc (or negative pole) to the binding screw of the sounder. A small quantity of blue vitriol
was placed in the bottom of the jar, and the jar filled with water to cover the zinc; the instrument is then in condition for operation.
