FIG. 9.
FIG. 10.
These handles can be placed in eight positions (besides the upright one) by a single movement of each hand, as may be seen in [fig. 7]; and these eight signals if repeated, or made twice in rapid succession will make eight more, and by being repeated three times will constitute a third eight, making twenty-four; finally, by a rapid motion right and left, they may be caused to signify a fourth eight, or thirty-two signals, which are found to be sufficient for every purpose, and by practice may be both produced and read off with facility. Before a message is about to be delivered the commutator is so placed as to ring a bell, which is done by the same arrangement as in a common alarm-clock, but the action is set in motion by a peculiar contrivance, which depends upon the property a bar of soft iron has of becoming magnetic when a wire is wound round it and a current of electricity passed through this wire; this magnetic property exists only as long as the current passes, and stops the instant it is cut off. The catch of the alarm is disengaged by the movement of a bar of iron being drawn to the magnet while the current passes, and forced back again by a spring when it is stopped, thus setting in action the mechanism of the alarm, or in some cases there is a simple contrivance for causing a rapid flow and stoppage of the electricity, so that the bar is alternately attracted by the magnet and released by the spring, and this motion of the bar rings the bell as long as it is continued. The bell is always rung to give notice that a message is about to be sent, and at the station where the bell rings, the bell at the former station is rung in return, to show that they are prepared to receive the message; the message is then spelt letter by letter, by moving the handles into the proper positions, and as the message is being sent, the eye is kept on the dials having the needles which will communicate any message in return from the station to which the message is being sent, such as “repeat,” “not understood,” &c., &c., for which certain single signs are made and recognised.The wires which convey the electricity from station to station, are made of galvanized iron (iron coated with zinc), and must be kept from all communication with the earth by some substance incapable of conducting it; they are therefore stretched between wooden poles ([fig. 8]), and rest upon sockets or supports of glass or glazed earthenware, which are both substances incapable of conducting the electricity to the earth ([fig. 9]). In certain localities, as in towns, the wires are coated with gutta percha (another non-conductor), and laid side by side in a tube under ground; this is also done in the longer tunnels. In the cables which conduct the electric power along the bottom of the sea as from Dover to Calais; the wires are first coated with gutta percha, then bound with yarn soaked in tar, and finally coated with galvanized iron wires wound round spirally like the strands of a rope ([fig. 10]), the whole forming a cable which is coiled up in the hold of a vessel, and let out as the vessel crosses from one side to the other; in this way the cable is deposited on the bed of the sea or channel, forming an electrical connection from country to country. These cables are made in one piece by machinery. That from Dover to Calais is twenty-five miles long, contains four copper conducting wires, and weighs about 175 tons; that from Dover to Ostend contains six conducting wires, is seventy miles long, weighs nearly 500 tons, and cost about £30,000; its structure (the real size) is shown at [fig. 10].
ELECTRIC TIME BALL, CHARING CROSS.
The electric cable now constructed to be laid down between Ireland and America, is composed of seven small copper wires twisted into one, and surrounded by gutta percha; this is then surrounded by eighteen small wire-ropes, each composed of seven small wires twisted together, the whole being in its section not larger than a four-penny-piece; 2000 miles of this cable are now ready to be laid down. A plan was some time ago put in practice by which the correct time could be kept at various places by electric communication with the time at Greenwich; a clock thus regulated, is situated at Charing Cross, and a ball placed at the top of the electric telegraph station there, is caused by the same means to fall exactly at one o’clock. A contrivance has of late been patented to work the electric telegraph by steam, and the following account of it is extracted from the “Times:”—
“A series of gutta percha bands, about six inches wide and a quarter of an inch thick, are coiled on wheels on drums arranged for the purpose. These bands are studded down both sides with a single row of holes at short intervals apart. When a message is to be sent the clerks wind off these bands, inserting in the holes small brass pins, which, according to their combinations in twos or threes (with blank holes between), represent certain words or letters. In this manner the message is, as it were, “set up” in the bands with great rapidity, and if the number of bands employed is sufficiently large—say as numerous as the compositors employed in a large printing-office—messages equal in length to five or six columns of this journal could be set up and ready for transmission in the course of a single hour. Of course this operation in no respect interferes with the telegraph wire itself, which continues free for use until the bands of messages are actually being despatched. The gutta percha bands when full are removed to the instrument-room, a most simple appliance preventing any derangement or falling out of the pins while being moved about. In the instrument-room the bands are connected with ordinary steam machinery, by which they are drawn in regular order with the utmost rapidity between the charged poles of an electrical machine in such a manner that, during the moment of each pin’s passing, it forms electrical communication between the instrument and the telegraph, and a signal is transmitted to the other end of the wire, where the spark perforates a paper and records the message. The only limit to the rapidity of the operation is the rate at which the bands can be drawn, since the electrical contact of each pin, even for the 200th part of a second, is more than sufficient to transmit a word or signal from London and register it in America. Of course, as the message is recorded (we will say in America) with the same rapidity as that with which it is transmitted from London, a number of reading clerks will be requisite in order to translate it, by dividing it into small portions, with almost as much facility as it has been sent.”