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V. § 54.] MODE OF PERCUSSION. 109
nature of the striking object, and on the material of the string. It is clear that a node can never be formed at the point of percussion. Therefore no partial-tone requiring for its production a node in that place can exist in the resulting sound. If, for instance, we excite the string exactly at its middle point, the forms of vibration with an even number of ventral segments, all of which have a node at the centre of the string, are excluded, and only the odd partial-tones, i.e. the 1st, 3rd, 5th, and so on, are heard. In this manner we can always prevent the formation of any assigned partial-tone, by choosing a suitable point of percussion. On the other hand, a vibration-form is in the most favourable position for development when the middle point of one of its ventral segments coincides with the point of percussion. The more nearly it occupies this position the louder will be the corresponding partial-tone, while the further it recedes from this position towards that in which one of its nodes falls on the point of percussion, the weaker will the partial-tone become.
The form and material of the hammer, or other object with which the string is struck, have also a great influence in modifying the quality of the sound produced. Sharpness of edge and hardness of substance tend to develope high and powerful overtones, a rounded form and soft elastic substance