III. The most recent development has been the electronic means of communication, including the wireless telegraph, radio, phone and television. The invention and use of electronic means has solved all the problems mentioned above. They are the most effective methods of communication. People will certainly try their best to invent even more modern and useful methods.

IV. Bell's extensive knowledge of the nature of sound and his understanding of music enabled him to conjecture the possibility of transmitting multiple messages over the same wire at the same time. Although the idea of a multiple telegraph had been in existence for some time, Bell offered his own musical or harmonic approach as a possible practical solution. His "harmonic telegraph" was based on the principle that several notes could be sent simultaneously along the same wire if the notes or signals differed in pitch. He proved that different tones would vary the strength of an electric current in a wire.