About 1874 Professor Alexander Graham Bell, of Boston, seized upon an idea similar to that of Bourseul's. Bell saw in the vibrating disk a resemblance to the drum of the human ear. In imagination he beheld "two iron disks, or ear drums, far apart and connected by an electrified wire, catching vibrations of sound at one end and reproducing them at the other." With this conception in mind he went to work to construct an apparatus that would actually catch the sounds of the voice and reproduce them at a distance. Bell, like Morse, was without means to conduct his experiments, but friends came to his aid and furnished him with the necessary money and by 1876 his labors had resulted in making a machine that would carry the human voice; he had invented the telephone. At first the telephone was only a toy and would operate at only short distances, but as improvements were made the distances grew greater and greater until at last one could talk in Boston and be heard in Denver, or talk in New York and be heard in London. The telephone grew rapidly into favor as a means of communication and in a short time it was used more than the telegraph. It is estimated that in the entire world about ten billion conversations are held over the telephone in the course of a single year. [Illustration: FIG. 13.--PROFESSOR ALEXANDER GRAHAM BELL SPEAKING OVER THE FIRST LONG DISTANCE TELEPHONE BETWEEN NEW YORK AND CHICAGO.] As wonderful as the telephone was it was quickly followed by an invention even more wonderful. Almost as soon as men had thoroughly mastered the art of sending messages by the aid of wires they set about trying to find a way by which messages could be sent long distances without any wires at all. In 1889, Heinrich Hertz, a German scientist, showed that electric waves could be sent out in all directions just as light waves go out in all directions. He also showed how these waves might be produced and how they might be detected or caught as they passed through space. In 1896, William Marconi, an Italian electrician, making use of the facts discovered by Hertz, sent a message a distance of 300 feet without the use of wires. This was the first _wireless telegraph_. Marconi continued his experiments, sending wireless messages between places further and further apart, and by 1911 he was able to signal without cables across the Atlantic Ocean. [Illustration: FIG. 14.--A WIRELESS TELEGRAPH STATION.] And now it seems that the wireless telegraph is to be followed by an invention still more wonderful. Men are now working upon a _wireless telephone_. Already it is possible to talk without the aid of wires between places so far apart as Newark and Philadelphia, and many inventors believe that it is only a matter of time when the wireless telephone will be used side by side with the wireless telegraph. FOOTNOTES: