f 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.

Conversion from Sound Waves to Vibration of Diaphragm. However
produced, by the voice or otherwise, sounds to be transmitted by
telephone consist of vibrations of the air. These vibrations, upon
reaching a diaphragm, cause it to move. The greatest amplitude of
motion of a diaphragm is, or is wished to be, at its center, and its
edge ordinarily is fixed