Vibration- Curves of String and Bridge. 447 



diameter was 0'92 mm., and it was illuminated at 5 or 6 cms. 

 from the centre. In the original plates the string's motion 

 was magnified 14- and the bridge's vertical motion 1425 times. 

 Thus on the reduced prints, though both magnifications are 

 changed, their ratio 1069 remains constant and gives the mag- 

 nification o£ the bridge's motion relative to that of the string. 



Fig. 1. — Plan of Optical Arrangements. 

 A R N l 



Fig. 2.— Detail of Optical Lever and Bridge. 

 O. L 



t^M 



For the horizontal motion of the bridge in the direction 

 parallel to the length of the string a special form of optical 

 lever was adopted. A plan of the entire optical arrange- 

 ments is shown in fig. 1^ and an enlarged detail of the 

 optical lever and bridge in fig. 2. Consider first the light 

 which falls on the optical lever. It starts from the arc 



