A string may vibrate transversely as a whole, or as independent segments. Such segments will be aliquot parts of the whole string and separated from each other by points of no motion, called nodes or nodal points. The tone produced by the vibrations of the whole length of a string is called its fundamental tone. The tones produced by the vibrations of the segments of a string are called its overtones or harmonics. (a.) The fact that a string may thus vibrate in segments, with the further fact that string, or other sounding body, can hardly be made to vibrate as a whole without vibrating in segments at the same time, furnishes a means of explaining quality or timbre of sound.