But the aerial telegraph was soon to have a most dangerous rival. This rival was _the electric telegraph_. Many years before the invention of Chappe men had been experimenting with electricity with a view of sending messages by means of an electric current. These experiments began in 1728 when an Englishman named Gray caused electricity to produce motion in light bodies located at a distance of more than 600 feet. In 1748, the great Benjamin Franklin, who conducted so many wonderful experiments in electricity, sent an electric current through a wire which was stretched across the Schuylkill River and set fire to some alcohol which was at the opposite end of the wire. We may regard the flash of alcohol as a telegraph, for it could have been used as a signal. In 1819, Professor Oersted of Copenhagen brought a magnetic needle close to a body through which an electric current was passing and he observed that the needle had a tendency to place itself at right angles to the electrified body. In 1825, William Sturgeon of England coiled a copper wire around a bar of soft iron and found that when a current of electricity was sent through the wire the bar of iron became a temporary magnet; that is, the bar of iron attracted a needle when the current was passing through the wire and ceased to attract it when the current was broken (Fig. 8). These discoveries of Oersted and Sturgeon led to the invention known as the _electro-magnet_ and the electro-magnet led rapidly to the invention of the electric telegraph, for by means of the electro-magnet a signal can be sent to a distance as far as a current of electricity can be sent along a wire. In 1831, Professor Joseph Henry, one of America's most distinguished scientists, discovered a method by which an electric current could be sent along a wire for a very great distance. The next year Henry constructed and operated an apparatus which was essentially an electric telegraph (Fig. 9). "I arranged," he said, "around one of the upper rooms of the Albany Academy a wire of more than a mile in length through which I was enabled to make signals by sounding a bell. The mechanical arrangement for effecting this object was simply a steel bar permanently magnetized, supported on a pivot and placed with its north end between the two arms of a horse-shoe magnet. When the latter was excited by the current the end of the bar thus placed was attracted by one arm of the horse-shoe and repelled by the other and was thus caused to move in a horizontal plane and its further extremity to strike a bell suitably adjusted." Thus by 1832 the electric current had been used for sending signals at a distance and the electric telegraph had been invented. [Illustration: FIG. 9.--PROFESSOR HENRY'S ELECTRO-MAGNET, 1832.]