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72 RESONANCE. 111. § 37.
produced by two or by three wires. Having, as in the previous case, raised one of the dampers without striking the note, twitch one of the corresponding wires sharply with the finger-nail, and then wait a few seconds. The vibrations will, during this interval, have communicated themselves to the other string or strings belonging to the note pressed down: if, now, the first wire be stopped by applying the tip of the finger to the point where it was at first twitched, the same note, due to transmitted vibrations, will continue to be sustained by the remaining wire or wires.
A more instructive method of studying resonance is to take two unison tuning-forks, strike one of them, and hold it a short distance from the other. The second fork will then commence sounding by resonance, and will continue to produce its note though the first fork be brought to silence. It is essential to the success of this experiment that the two forks should be rigorously in unison. If the pitch of one of them be lowered by causing a small pellet of wax to adhere to the end of one of its prongs, the effect of resonance will no longer be produced, even though the alteration of pitch be too small to be recognised by the ear. Further, the phenomenon generally requires a certain length of time to develope itself; for, if the silent fork be only momentarily