10. _The Telegraph Sounder_ (Fig. 29).--This was a toy half a century ago, but since the days of Samuel Finley Breese Morse it has become of vast commercial importance. The Western Union Telegraph Company in 1909 had 211,513 miles of poles and cables, 1,382,500 miles of wire, 24,321 offices, sent 68,053,439 messages, received $30,541,072.55, expended $23,193,965.66, and had $7,347,106.89 in profits. In the United States more than 93,000,000 and in the world at large more than 600,000,000 messages are sent annually, and there are men still living who scoffed at Morse's ideas as _impracticable_. It is interesting to contemplate what would happen to the Stock Exchange, to the newspapers, to the railroads, to the congressman addressing his constituents from the floor of a legislative chamber, to business in general, if the world were deprived of the telegraph. A few years ago a telegraph despatch was sent from New York to San Francisco, Tokio, London, and back to New York, 42,872 miles, in three minutes less than an hour. Electricity can travel around the world in a fraction of a second, the time was consumed in repeating the message. I once sent a message from New York to New Haven to announce that I was coming, and afterward took my train and reached New Haven in time to receive my own message and pay the messenger boy. But I have never lost faith in the beneficent results of Morse's labours. Morse (1791-1872) was an artist and the first President of the National Academy of Design. He was likewise a professor in New York University and constructed his first experimental telegraph line upon the University campus in 1835. His first public line was built from Washington to Baltimore in 1844. The Western Union Telegraph Company was incorporated in 1856. Of course the work of Morse rested upon that of Oersted, in Copenhagen, who, in 1819, discovered electro-magnetism, and upon that of Joseph Henry of Albany, who in 1827 first insulated the wires. [Illustration: Fig. 30] The application of the electro-magnet to producing telegraphic signals will be understood by referring to Fig. 30. _B_ is the generator of an electric current--sometimes a battery and sometimes a dynamo. One wire from this goes to the earth, _E_. The other wire goes through a key, which, like a push button or a switch, serves to open or close the circuit. This is normally closed when not in use. Through this the current passes around the electro-magnet _S_, which attracts the armature _a_, causing it to click against a metal stop, hence it is called the sounder. From this the current passes along the line wire to a distant station and there through the sounder and closed key to the earth. There is likely to be a generator at each station. The current must run continually through the system. If a battery is employed, the copper sulphate, or gravity cell, to be described later, is chosen, because it will endure continued usage better than any other.