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122                     HAND-BOOK OF ACOUSTICS.
Fig. 61
simplest is with three nodes, fig. 61, B. The tones, corresponding to these divisions, rise very rapidly in pitch, thus :
The Harmonicon is an example of an instrument, in which the lateral vibrations of rods free at both ends are utilized; but the most important member of this class is the Tuning-fork. This in­strument, generally constructed of steel, may be considered as derived from a straight bar, such as that depicted at the lower part of fig. 62, by folding it in two, at the middle. The tone of the bent
Fig. 62.
bar will be somewhat flatter than the original straight one, and the nodes, which in the straight bar were near the two ends, will have approached very close together in the bent one. Fig. 62 shows by the short marks, this gradual approach of the nodes, as the bar is more and more bent; and fig. 63, by its thin and dotted lines, represents the two extreme positions of the fork, while sounding its fundamental. When the prongs are at their extreme outward position b m, the portion between the nodes p and q rises; when thev are closest together, at «./, this same portion descends. Thus