The speech of adults has a mean pitch lower than that of children; of adult males, lower than that of females.

There is no close analogue for the voice-organ in artificial mechanism, but the use of the lips in playing a bugle, trumpet, cornet, or trombone is a fairly close one.  Here the lips, in contact with each other, are stretched across one end of a tube (the mouthpiece) while the air is blown between the lips by the lungs.  A musical tone results; if the instrument be a bugle or a trumpet of fixed tube length, the pitch will be some one of several certain tones, depending on the tension on the lips.  The loudness depends on the force of the blast of air; the character depends largely on the bugle.

Human Ear.  The human ear, the organ of hearing in man, is a complex mechanism of three general parts, relative to sound waves:  a wave-collecting part; a wave-observing part, and a wave-interpreting part.

The outer ear collects and reflects the waves inwardly to beat upon the tympanum, or ear drum, a membrane diaphragm.  The uses of the rolls or convolutions of the outer ear are not conclusively known, but it is observed that when they are filled up evenly with a wax or its equivalent, the sense of direction of sound is impaired, and usually of loudness also.

The diaphragm of the ear vibrates when struck by sound waves, as does any other diaphragm.  By means of bone and nerve mechanism, the vibration of the diaphragm finally is made known to the brain and is interpretable therein.

The human ear can appreciate and interpret sound waves at frequencies from 32 to about 32,000 vibrations per second.  Below the lesser-number, the tendency is to appreciate the separate vibrations as separate sounds.  Above the higher number, the vibrations are inaudible to the human ear.  The most acute perception of sound differences lies at about 3,000 vibrations per second.  It may be that the range of hearing of organisms other than man lies far above the range with which human beings are familiar.  Some trained musicians are able to discriminate between two sounds as differing one from the other when the difference in frequency is less than one-thousandth of either number.  Other ears are unable to detect a difference in two sounds when they differ by as much as one full step of the chromatic scale.  Whatever faculty an individual may possess as to tone discrimination, it can be improved by training and practice.

CHAPTER II

ELECTRICAL REPRODUCTION OF SPEECH

The art of telephony in its present form has for its problem so to relate two diaphragms and an electrical system that one diaphragm will respond to all the fundamental and harmonic vibrations beating upon it and cause the other to vibrate in exact consonance, producing just such vibrations, which beat upon an ear.

The art does not do all this today; it falls short of it in every phase.  Many of the harmonics are lost in one or another stage of the process; new harmonics are inserted by the operations of the system itself and much of the volume originally available fails to reappear.  The art, however, has been able to change commercial and social affairs in a profound degree.