The telegraph is an instrument used to send messages to a distance by means of electricity. It is usually worked by electrical current or by an electromagnet. The instrument is made up of four separate parts :

(1) the generator, or battery to generate the electricity;

(2) the conductor, or insulated wires by which the electric current is carried to any distance; (3) the transmitter, or instrument which regulates the flow of electricity; and (4) the register, which records the signals. The generator is made up of one or more voltaic batteries, each of which is composed of a number of cells connected in a series. The Grove cell was formerly much used and then the Daniell cell; but a cell called the gravity cell, which is as good as either of these two and a great deal cheaper, is now commonly employed. To send a message a long distance a stronger battery is needed than to send one a short distance. A battery can be made stronger by adding more cups or cells to it.