136 Dr. Young's Experiments and Inquiries 



and Chladni, principally on the motion of rods, nothing has 

 been attempted on the subject. For the present purpose, the 

 motion of the chord may be simplified, by tying a long fine 

 thread to any part of it, and fixing this thread in a direction 

 perpendicular to that of the chord, without drawing it so 

 tight as to increase the tension: by these means, the vibra- 

 tions are confined nearly to one plane, which scarcely ever 

 happens when the chord vibrates at liberty. If the chord be 

 now inflected in the middle, it will be found, by comparison 

 with an object which marked its quiescent position, to make 

 equal excursions on each side of the axis ; and the figure which 

 it apparently occupies will be terminated by two lines, the more 

 luminous as they are nearer the ends, Plate VI. Fig. 49. But, 

 if the chord be inflected near one of its extremities, Fig. 50, it 

 will proceed but a very small distance on the opposite side of 

 the axis, and will there form a very bright line, indicating its 

 longer continuance in that place; yet it will return on the 

 former side nearly to the point from whence it was let go, but 

 will be there very faintly visible, on account of its short delay. 

 In the middle of the chord, the excursions on each side the axis 

 are always equal; and, beyond the middle, the same circum- 

 stances take place as in the half where it was inflected, but on 

 the opposite side of the axis ; and this appearance continues 

 unaltered in its proportions, as long as the chord vibrates at all : 

 fully confirming the non-existence of the harmonic curve, and 

 the accuracy of the construction of Euler and De la Grange. 

 At the same time, as M. Bernoulli has justly observed, since 

 every figure may be infinitely approximated, by considering its 

 ordinates as composed of the ordinates of an infinite number of 

 trochoids of different magnitudes, it may be demonstrated, that 



