Wireless Telegraphy and Telephony Simply Explained / A Practical Treatise Embracing Complete and Detailed Explanations of the Theory and Practice of Modern Radio Apparatus and Its Present Day Applications, Together With a Chapter on the Possibilities of Its Future Development

by Alfred Powell Morgan

FIG. 128.—The vocal when relaxed.

Speech is the sound produced by the vocal chords of a human being, modified by the movements of the lips, tongue, and cavity of the mouth. The consonants are made by movements of the tongue and lips obstructing the sounds at their beginning or end, while the vowels are formed by a steady voice modified by the resonance of the different shapes or sizes given the parts of the mouth. The waves produced in this manner are transmitted to the ear, and the sensation of sound is caused by the impact of the otoconia against the auditory nerve, giving a series of impressions, musical or unmusical, pleasing or displeasing, as the case may be. Many interesting experiments showing the nature of the sounds of the human voice may be performed by means of a simple apparatus invented by Koenig of Paris. A box is separated into two compartments by a rubber membrane. Gas is led into one of these compartments by a rubber tube, and then allowed to issue to a burner. The other compartment is connected to a megaphone.

FIG. 129.—Koenig's manometric flame apparatus.

FIG. 130.—Appearance of manometric flames in a revolving mirror.

Two pieces of mirror are arranged so as to revolve in front of the lighted jet or burner. When the human voice is produced in front of the megaphone, the air waves strike the membrane and cause changes of pressure in the gas. The height of the flames varies with each change in the pressure, and when viewed in the mirror resemble a band of light having an edge like a saw. The teeth are faithful representations of the changes in the voice, and immediately take on a new appearance when a new sound is emitted. The shape of the teeth changes with the tone, and the number of teeth with the pitch. Fig. 130 shows the flames produced by singing the sound oo, as in tool. The same sound an octave lower in pitch will show as in B, where there are just one-half as many teeth or vibrations. The sound of oo is a simple sound. If o on the note is sung into the megaphone, the image in the mirror will appear like that shown by C, being made up of alternating large and small teeth, the former corresponding to every alternate vibration of the octave of the higher sound coinciding with a vibration of the octave below.

FIG. 130 a.

The sound causing the flame to appear, as in D, is made up of two simple vibrations combined.