Page:Popular Science Monthly Volume 64.djvu/266

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HERE is no physical faculty which so distinguishes man from the lower animals, and marks him more conspicuously in the image of his Maker than the power of articulate speech. That there is some means of communication among the lower animals, we can not doubt, but that faculty of articulate speech which enables us to communicate to our fellowmen not only our ordinary desires and wishes, but even the most delicate shades of our inmost thought, that faculty belongs distinctively to the human race.

This subject may be treated from various standpoints, but we will here limit ourselves to a strictly physical consideration, explaining first the general anatomy of the parts essential in the production of the voice, and afterwards the manner in which these are used in the formation of song and speech.

Before discussing the subject of the voice, we must have some conception of sound in order to understand more fully how the voice is produced and how it is modified by the various parts concerned in the faculty of speech. All sounds are due to the vibration of the surrounding air, which conveys to the ear the vibrations produced by the sound-producing object. Perhaps one of the simplest methods of producing sound is by means of the tuning fork. When this is struck the prongs are made to vibrate, and these in turn set up in the air vibrations which are carried to the drum of the ear, and thence transmitted to the brain as sound.

In sound we have three important qualities, pitch, loudness and timbre. The pitch depends upon the number of vibrations which the sounding body makes in a given time. When these vibrations are repeated less than eighteen times per second they produce no musical tone to the ear. When a boy strikes a stick against a paling fence we have simply a rattle. If, however, this could be done so rapidly as to make more than eighteen beats to the second, then the ear would cease to recognize each individual stroke and would perceive a musical tone. The more rapid the vibrations the higher the tone, until the limit of human hearing is reached, which is about 48,000 vibrations to the second.

The second quality of sound, which we may call 'loudness,' is due to the range of the vibrations made by the sound-producing body. If