respecting Sound and Light. 137 



all these constituent curves would revert to their initial state, in 

 the same time that a similar chord bent into a trochoidal curve 

 would perform a single vibration ; and this is in some respects 

 a convenient and compendious method of considering the pro- 

 blem. But, when a chord vibrates freely, it never remains long 

 in motion, without a very evident departure from the plane of 

 the vibration ; and, whether from the original obliquity of the 

 impulse, or from an interference with the reflected vibrations of 

 the air, or from the inequability of its own weight or flexibility, 

 or from the immediate resistance of the particles of air in con- 

 tact with it, it is thrown into a very evident rotatory motion, 

 more or less simple and uniform according to circumstances. 

 Some specimens of the figures of the orbits of chords are 

 exhibited in Plate VI. Fig. 44. At the middle of the chord, its 

 orbit has always two equal halves, but seldom at any other 

 point. The curves of Fig. 46, are described by combining 

 together various circular motions, supposed to be performed in 

 aliquot parts of the primitive orbit : and some of them approach 

 nearly to the figures actually observed. When the chord is of 

 unequal thickness, or when it is loosely tended and forcibly 

 inflected, the apsides and double points of the orbits have a very 

 evident rotatory motion. The compound rotations seem to 

 demonstrate to the eye the existence of secondary vibrations, 

 and to account for the acute harmonic sounds which generally 

 attend the fundamental sound. There is one fact respecting 

 these secondary notes, which seems intirely to have escaped 

 observation. If a chord be inflected at one-half, one-third, or 

 any other aliquot part of its length, and then suddenly left at 

 liberty, the harmonic note which would be produced by divid- 

 ing the chord at that point is intirely lost, and is not to be dis- 



MDCCC T 



