Electricity

by W. H. McCormick

With the invention of the voltaic cell, inventors’ ideas took a new direction. In 1812 a telegraph based upon the power of an electric current to decompose water was devised by a German named Sömmering. He used a number of separate wires, each connected to a gold pin projecting from below into a glass vessel filled with acidulated water. There were thirty-five wires in all, for letters and numbers, and when a current was sent along any wire bubbles of gas formed at the pin at the end of it, and so the letters or numbers were indicated. This telegraph, like its predecessors, never came into practical use. Oersted’s discovery in 1829 of the production of magnetism by electricity laid the foundation of the first really practical electric telegraphs, but little progress was made until the appearance of the Daniell cell, in 1836. The earlier forms of voltaic cells polarized so rapidly that it was impossible to obtain a constant current from them, but the non-polarizing Daniell cell at once removed all difficulty in this respect. In the year 1837 three separate practical telegraphs were invented: by Morse in the United States, by Wheatstone and Cooke in England, and by Steinheil in Munich.

Fig. 26.—Dial of Five-Needle Telegraph.

The first telegraph of Wheatstone and Cooke consisted of five magnetic needles pivoted on a vertical dial. The letters of the alphabet were marked on the dial, and the needles were deflected by currents made to pass through wires by the depression of keys, so that two needles would point towards the required letter. [Fig. 26] is a sketch of the dial of this apparatus. This telegraph was tried successfully on the London and North-Western Railway, over a wire a mile and a half in length. Wheatstone and Cooke afterwards invented a single-needle telegraph in which the letters were indicated by movements of the needle to the right or to the left, according to the direction of a current sent through a coil of wire. Wheatstone subsequently produced an apparatus which printed the letters on paper.

In the United States, Morse had thought out a scheme of telegraphy in 1832, but it was not until 1837 that he got his apparatus into working order. He was an artist by profession, and for a long time he was unable to develop his ideas for lack of money. After many efforts he succeeded in obtaining a State grant of £6000 for the construction of a telegraph line between Baltimore and Washington, and the first message over this line was sent in 1844, the line being thrown open to the public in the following year. Amongst the features of this telegraph were a receiving instrument which automatically recorded the messages on a moving paper ribbon, by means of a pencil actuated by an electro-magnet; and an apparatus called a relay, which enabled the recording instrument to be worked when the current was enfeebled by the resistance of a very long wire. Morse also devised a telegraphic code which is practically the same as that in use to-day.

The great discovery of the German Steinheil was that a second wire for the return of the current was not necessary, and that the earth could be used for this part of the circuit.

In reading the early history of great inventions one is continually struck with the indifference or even hostility shown by the general public. In England the electric telegraph was practically ignored until the capture of a murderer by means of it literally forced the public to see its value. The murder was committed near Slough, and the murderer succeeded in taking train for London. Fortunately the Great Western Railway had a telegraph line between Slough and London, and a description telegraphed to Paddington enabled the police to arrest the murderer on his arrival. In the United States too there was just the same indifference. The rate for messages on the line between Baltimore and Washington was one cent for four words, and the total amount taken during the first four days was one cent!

One of the simplest forms of telegraph is the single-needle instrument. This consists of a magnetic needle fixed to a spindle at the back of an upright board through which the spindle is passed. On the same spindle, but in front of the board, is fixed a dial needle, which, of course, moves along with the magnetic needle. A coil of wire is passed round the magnetic needle, and connected to a commutator for reversing the direction of the current. By turning a handle to the left a current is made to flow through the coil, and the magnetic needle moves to one side; but if the handle is turned to the right the current flows through the coil in the opposite direction, and the needle moves to the other side. Instead of a handle, two keys may be used, the movement of the needle varying according to which key is pressed. A good operator can transmit at the rate of about twenty words a minute with this instrument. The Morse code, which consists of combinations of dots and dashes, is used, a movement of the dial needle to the left meaning a dot, and one to the right a dash. The code as used in the single-needle instrument is shown in [Fig. 27].

Fig. 27.—Code for Single-Needle Telegraph.