MUSICAL SOUNDS FROM VIBRATION OF AIR. 247 



string. At the nodes C and 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 

 a-vibrating in the same room, the string A B will be set 

 a-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 sym- 

 pathetic 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 sepa- 

 rate 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. 



The production of musical sounds by the vibrations of 

 a column of air in a pipe is familiar to every person, but 

 the extraordinary mechanism by which it is effected is 

 known principally to philosophers. A column of air in a 



