. A text-book of physiology : for medical students and physicians . l sum of the ordinatesabove and below the lines of rest. If the movements are so timedthat e in curve B is synchronous with d° in curve A, then theresulting compound wave form is illustrated by C. If, how-ever, curve B is supposed to be in a different phase, so that eis synchronous with d, then a form of wave illustrated by D will beobtained. In this way a great variety of forms of compound wavesmay be supposed to be produced by the union of a series of simplewaves of different periods of vibration. That compound waves dif-fer
. A text-book of physiology : for medical students and physicians . l sum of the ordinatesabove and below the lines of rest. If the movements are so timedthat e in curve B is synchronous with d° in curve A, then theresulting compound wave form is illustrated by C. If, how-ever, curve B is supposed to be in a different phase, so that eis synchronous with d, then a form of wave illustrated by D will beobtained. In this way a great variety of forms of compound wavesmay be supposed to be produced by the union of a series of simplewaves of different periods of vibration. That compound waves dif-fer from simple ones in being composed of several series of vibrationsis indicated directly by our sensations. When we listen to the noteof a tuning-fork we hear only a single tone; when two or moretuning-forks are sounded together the trained ear can detect the tonedue to each fork, and similarly when a single note is sounded bythe human voice, a violin, or any other instrument that has a char-acteristic quality the trained ear can detect a series of higher tones,. Fig. 175.—Schema by Helmholtz to illustrate the formation of a compound wavefrom two pendular waves: A and B, pendular vibrations, B being the octave of A. Ifsuperposed so that e coincides with d° and the ordinates are added algebraically, the non-pendular curve C is produced. If superposed so that e coincides with d the non-pendularcurve D is produced. the upper partial tones, or harmonics, or overtones, which indicatethat the note is really compound, and not simple. The formationof these overtones is due to the fact that the sounding body may beconsidered as vibrating not only as a whole, but also in its aliquot EAR AS AN ORGAN FOR SOUND SENSATIONS. 397 parts, as is represented in Fig. 176, illustrating the vibrations of astring. When the string is plucked, it vibrates as a whole (a), giv-ing large waves which produce what is called the fundamental tone,but at the same time each half (6), third (c), fourth (d), e
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