respecting Sound and Light. 149 



Fig. 40. A vibration represented by a curve of which the 

 ordinates are the sines of circular arcs increasing uniformly, 

 corresponding with the motion of a cycloidal pendulum, com- 

 bined with similar subordinate vibrations in the ratios of 3, 5, 

 and 7. 



Plate VL 



Figs. 41 and 4,3. Two different positions of a major third, 

 composed of similar vibrations, as represented by figures of 

 sines. 



Fig. 43. A contracted representation of a series of vibrations. 

 A, a simple uniform sound. B, the beating of two equal sounds 

 nearly in unison, as derived from rectilinear figures. C, the 

 beats of two equal sounds, derived from figures of sines. D, a 

 musical consonance, making by its frequent beats a fundamental 

 harmonic. E, the imperfect beats of two unequal sounds. 



Fig. 44. Various forms of the orbit of a musical chord, when 

 inflected, and when struck. 



Fig. 45. Forms of the orbit, when the sound is produced by 

 means of a bow. 



Fig. 46. Epitrochoidal curves, formed by combining a simple 

 rotation or vibration with other subordinate rotations or vibra- 

 tions. 



Figs. 47 and 48. The successive forms of a tended chord, 

 when inflected and let go, according to the construction of 

 De la Grange and Euler. 



Fig. 49. The appearance of a vibrating chord which had been 

 inflected in the middle, the strongest lines representing the 

 most luminous parts. 



Fig. 50. The appearance of a vibrating chord, when inflected 

 at any other point than the middle. 



