Page:Popular Science Monthly Volume 9.djvu/416

392 witnessed with profound interest by physicians and physiologists. In 1860 he came to Paris, and astonished many of the members of our learned societies. He exhibited not only the whole of his own larynx, but also the interior of his trachea down to the bifurcation—a sight well calculated to cause astonishment when one sees it for the first time. The vocal organ cannot be examined with the same facility in all persons, and some practice is needed for experimenting successfully. Dr. Mandl and Dr. Krishaber possess an extraordinary power of controlling the various movements of the larynx. After repeated experiments we now fully understand the functions of the vocal organs in speaking and in singing. The studies of Helmholtz upon the formation of sounds have thrown new light upon the phenomena of voice.

The notes of an organ, when heard beneath the arched roof of a cathedral, produce a profound impression. Inasmuch as no other kind of music so closely resembles the human voice, we can fancy ourselves communing with the thoughts and feelings of the human soul. We naturally compare the organ to man's vocal apparatus. The organ has a bellows, we have lungs; in the organ is a "sound-board" the trachea performs the same function; the vibrating tongue of the organ has its counterpart in our vocal cords; and the pharynx and the mouth answer to the resonating cavities of the organ. Yet the natural instrument is immensely superior to the artificial one. In the organ there must be a number of pipes to produce the different sounds; in the natural instrument there is only one pipe for both speech and song, but it is a wonderful pipe, being susceptible of endless modifications. It has a double vibrating spring and a resonator. The glottis is the vibrating spring or tongue, and, according as the air-passage is more or less narrowed, and the vocal cords more or less tense and vibrant, the sounds emitted are either grave or sharp. The mouth forms the resonator; the cavity of the mouth is susceptible of almost endless modifications, producing an infinite diversity of sounds.

Our various senses are each affected by a special order of impressions; the organ of hearing takes note of sounds, which are propagated by concussions of the air, by vibrations. When these vibrations are continuous, regular, isochronous, they constitute a musical sound; when irregular, the result is noise. Sounds possess very definite characters, as intensity, pitch, timbre. Intensity depends upon the amplitude of the vibrations, which travel in the form of concentric spheres from the starting-point, as the waves caused by a pebble dropped into water are diffused in the form of concentric circles. Amplitude is always the result of the force of the primary shock. The pitch of a sound is determined by the number of vibrations occurring in the space of one second: when the vibrations are few, the sound is grave; when very numerous, it is sharp. In a word, the shorter the duration of each vibration, the higher the pitch of the sound. Timbre means quality of voice. We distinguish voices