HANDBOOK OF ACOUSTICS - online book

A complete view of Acoustical Science & its bearings on music, for musicians & music students.

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HAND-BOOK OF ACOUSTICS.
attached to a weight. On bowing the fork, the string is set vibrating in one, two, three, or more segments, according to its degree of tension.
The two ends of a stretched string being at rest, it is evident that the number of ventral segments, into which it can break up, must be a whole number; it cannot break up into a certain number of ventral segments and a fraction of a segment. Any point of the string capable of being a node, can be made such, by lightly touch­ing that point, so as to keep it at rest, and bowing or plucking at the middle of the corresponding ventral segment. Thus, if the string of the Sonometer be lightly touched at the centre, and bowed about
of its length from the end, it will break up into two (or possibly six) ventral segments, with a node in the centre. Again, if the string be lightly touched atof its length from the end, and bowed about the middle of this third, it will vibrate in three segments (the other § dividing into two) separated by two nodes. That the larger part of the string, in this experiment, does divide into two segments separated by a node, may be shown, by placing riders on the string, before it is bowed, one in the centre of this part, where the node occurs, and one in the middle of each of the two ventral segments. When the string is now lightly touched atof its length from the end, and bowed as before, the riders in the middle of the ventral segments will be thrown off, but that at the node will keep its place (fig. 48). This experiment may be repeated
with a larger number of nodes. Thus, suppose four nodes are required. Divide the string into five equal parts, as there will evidently be that number of segments, and at each of the four points of division, place a coloured rider, with a white one equidistant between each pair, and also between the last one and the end. Remove the coloured rider nearest the other end and lightly touch the point where it stood, with the finger. Draw the bow gently across the string, midway between this point and the end, and the white riders will fall off, while the coloured ones will remain at rest (fig. 49).