Wireless Telegraphy and Telephony

IIO WIRELESS TELEGRAPHY smoothness or abruptness of the changes in pressure. Therein lies the difficulty of the production of sound by means of a phonograph or telephone, for the sound waves n min i mu min min 11 Fig. I26—Illustrating the action of air waves. must resemble each other in every detail in order that the result may be like the original. The mechanism with which we speak or sing is com- posed of two flexible membranes, stretched side by side across a small cylindrical box located at the top of the wind- pipe. The membranes are called the vocal chords, and the Fig. 127.—The vocal cords in position for making a sound. box the larynx. The chords are so arranged and controlled by muscles that their tension may be changed at will. In breathing, the air to and from the lungs passes freely be- tween the chords. When the controlling muscles are tight- ened, so as to stretch the chords, the edges are also brought parallel and quite close to each other. If the breath from the lungs is then forced through the narrow slit between them, they vibrate like the reed of a musical instrument, and produce the sounds of the voice. The multitude of sounds which it is possible for a human being to produce