Sound and Telephony.
Until the invention of the telephone, the distance over which the human voice could be used for
communication was limited by the lung power of the speaker and the ear sensitivity of the hearer. This limited distance
could be extended by a device which concentrates voice power in a given direction. The device is called a megaphone.
Notice that the word "mega-phone" and "tele-phone" are made up in part from the Greek word "phone," which means
sound. The word "megaphone"--simply means a "big sound" while the word "telephone" means sound at a distance or far
a. The telephone solves the problem of distance limitation of point to point sound transfer. Many stages of
development were necessary to bring the telephone to its present efficiency and flexibility. Development was rapid and
today the service provided by the telephone reaches almost everywhere. A business executive or a commanding general,
by picking up a telephone, can communicate with an associate in the next room, in his immediate area, or on the other side
of the world.
b. The sound of a speaker's voice is not actually transmitted over long distances. But the small voice power of
the speaker is converted into electrical energy, transmitted over wires to a distant point and reconverted back to a sound
like that generated by speaker. While in the form of electrical energy this sound may be amplified at will and transmitted
over wires to any given point.
Radio communication, developed later as a better solution to the same problem, transmits electrical energy
without wires and therefore in its early stages of development was called the wireless to distinguish it from the telephone
and telegraph. The radio telephone, a more recent development, uses both wire and wireless forms of transmission.
c. Any telephone system begins and ends with sound; therefore, this chapter will concern itself with the origin
and characteristics of sound waves and will also serve as an introduction to the elements and operational techniques of the
basic telephone system. A major portion of this manual is devoted to an analysis of local-battery and common battery