The importance of the telegraph in working railways was manifest, and yet the directors of the company were so purblind as to order the removal of the apparatus, and it was not until two years later that the Great Western Railway Company adopted it on their line from Paddington to West Drayton, and subsequently to Slough.  This was the first telegraph for public use, not merely in England, but the world.  The charge for a message was only a shilling, nevertheless few persons availed themselves of the new invention, and it was not until its fame was spread abroad by the clever capture of a murderer named Tawell that it began to prosper.  Tawell had killed a woman at Slough, and on leaving his victim took the train for Paddington.  The police, apprised of the murder, telegraphed a description of him to London.  The original “five needle instrument,” now in the museum of the Post Office, had a dial in the shape of a diamond, on which were marked the letters of the alphabet, and each letter of a word was pointed out by the movements of a pair of needles.  The dial had no letter “q,” and as the man was described as a quaker the word was sent “kwaker.”  When the tram arrived at Paddington he was shadowed by detectives, and to his utter astonishment was quietly arrested in a tavern near Cannon Street.

In Cooke and Wheatstone’s early telegraph the wire travelled the whole round of the circuit, but it was soon found that a “return” wire in the circuit was unnecessary, since the earth itself could take the place of it.  One wire from the sending station to the receiving station was sufficient, provided the apparatus at each end were properly connected to the ground.  This use of the earth not only saved the expense of a return wire, but diminished the resistance of the circuit, because the earth offered practically no resistance.

Figure 45 is a diagram of the connections in a simple telegraph circuit.  At each of the stations there is a battery B B’, an interruptor or sending key K K’to make and break the continuity of the circuit, a receiving instrument R R’to indicate the signal currents by their sensible effects, and connections with ground or “earth plates” E E’ to engage the earth as a return wire.  These are usually copper plates buried in the moist subsoil or the water pipes of a city.  The line wire is commonly of iron supported on poles, but insulated from them by earthenware “cups” or insulators.

At the station on the left the key is in the act of sending a message, and at the post on the right it is conformably in the position for receiving the message.  The key is so constructed that when it is at rest it puts the line in connection with the earth through the receiving instrument and the earth plate.

The key K consists essentially of a spring-lever, with two platinum contacts, so placed that when the lever is pressed down by the hand of the telegraphist it breaks contact with the receiver R, and puts the line-wire L in connection with the earth E through the battery B, as shown on the left.  A current then flows into the line and traverses the receiver R’ at the distant station, returning or seeming to return to the sending battery by way of the earth plate E’ on the right and the intermediate ground.