D it will remain perfectly at rest, while at _m_ or _n_ in the middle of the loops it will be thrown off or violently agitated. The acute sounds given out by each of the vibrating portions are called _harmonic sounds_, and they accompany the fundamental sound of the string in the very same manner as we have already seen that the eye sees the accidental or harmonic colours while it is affected with the fundamental colour. The subdivision of the string, and consequently the production of harmonic sounds, may be effected without touching the string at all, and by means of a sympathetic action conveyed by the air. If a string A B, for example, Fig. 40, is at rest, and if a shorter string A´´ C, one third of its length, fixed at the two points A´´ and C, is set vibrating in the same room, the string A B will be set vibrating in three loops like A´´ B´´, giving out the same harmonic sounds as the small string A´´ C. It is owing to this property of sounding bodies that singers with great power of voice are able to break into pieces a large tumbler glass, by singing close to it its proper fundamental note; and it is from the same sympathetic communication of vibrations that two pendulum clocks fixed to the same wall, or two watches lying upon the same table, will take the same rate of going, though they would not agree with one another if placed in separate apartments. Mr. Ellicott even observed that the pendulum of the one clock will stop that of the other, and that the stopped pendulum will, after a certain time, resume its vibrations, and in its turn stop the vibrations of the other pendulum.