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V. § 69.] COALESCENCE OF PARTIAL-TONES. 137 |
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approximately simple tones [§ 48]. If therefore we allow a number of such sounds, coinciding in pitch with the fundamental-tone and individual overtones of one and the same clang, to be simultaneously produced, the effect on the ear ought, if Helmholtz's theory is true, to be that of a single musical sound, not that of a group of separate notes. To try, the experiment in its simplest shape, take two mounted forks forming the interval of an Octave, and cause them to utter their respective tones together. For a short time we are able to distinguish the two notes as coming from separate instruments, but soon they blend into one sound, to which we assign the pitch of the loiver fork, and a quality more brilliant than that of either. So strong is the illusion, that we can hardly believe the higher fork to be really still contributing its note, until we ascertain that placing a finger on its prongs at once changes the timbre, by reducing it to the dull, uninteresting quality of a simple tone. The character of a clang consisting of only one overtone and the fundamental may be shown to admit of many different shades of quality by suitably varying the relative intensities of the two fork-tones in this experiment. If we add a fork a Fifth above the higher of the first two, and therefore yielding the third partial-tone of the clang of which they form |
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