. A text-book of physiology : for medical students and physicians . kind may be due to the nature of the impulse givento the air by the sounding body,—single pulses, for instance, or aseries of such pulses or shocks following at a slow or irregularrhythm, or as is more frequently the case, they may result from amixture of very short and different rhythmical vibrations. Asthe case of musical sounds is far the simpler, the theory of theaction of the cochlea has been based chiefly upon the resultsobtained from a study of these forms of waves. Classification and Properties of Musical Sounds.—Music
. A text-book of physiology : for medical students and physicians . kind may be due to the nature of the impulse givento the air by the sounding body,—single pulses, for instance, or aseries of such pulses or shocks following at a slow or irregularrhythm, or as is more frequently the case, they may result from amixture of very short and different rhythmical vibrations. Asthe case of musical sounds is far the simpler, the theory of theaction of the cochlea has been based chiefly upon the resultsobtained from a study of these forms of waves. Classification and Properties of Musical Sounds.—Musicalsounds exhibit three fundamental properties, each of which may bereferred to a difference in the physical stimulus. They vary, inthe first place, in pitch, and this difference finds its explanation inthe rapidity of vibration of the sounding body and the sound wavesproduced by it. The more rapid the rate, the shorter will be thewaves and the higher will be the pitch of the musical note. Notesof the same pitch may, however, vary in loudness or intensity, and. Fig. 173.—To illustrate the conception of differences in pitch and in amplitude or intensity:In A three pendular or sinus curves of the same period or pitch, but with different B three pendular or sinus curves of the same amplitude, but with different periods (after-Auerbach). this difference is referable to the amplitude of the vibrations (seeFig. 173). A given tuning-fork emits always a note of the samepitch, but the loudness of the note may vary according to the amp-litude of the vibrations. The vibrations of the tympanic mem-brane and of the perilymph in the internal ear vary in rate and in-tensity with the sounding body; so that we may say that the stimu-lation of the hair-cells in the cochlea gives us auditory sensations EAR AS AN ORGAN FOR SOUND SENSATIONS. 395 that vary in pitch with the rate of excitation and in intensity withthe amplitude of the vibratory movement. A third property ofmusical
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