CirAXGE OF ELA8TIC COXSTAXÏS OF FFlUlO.MACiXETICS. 



_a.^3^E_a 



line cop23er wires, which 

 pressed the axis of the 

 mirror lightly upon the 

 plane vertical side of 

 the carriage. To the 

 lower ends of these rods, 

 a flexible silk cord was 

 attached ; a pulley p 

 hanging in this cord was 

 pulled vertically down- 

 ward by a weight. The 

 friction-wheel q served 

 to adjust the distance 

 between the two vertical 

 wires. Instead of bung- 

 ing the weight directly, 

 a system of pulleys gh 

 was used in order to 

 avoid any injurious 

 shock accompanying the 

 loading and unloading 

 of the wires. When the 

 elongations of the two 



wires due to tension were 



exactly equal, there was 

 of course no rotation of tlie axis of the mirror. If, however, the 

 compensation were disturbed in any way, the rotation could be 

 observed in the usual manner by means of a vertical scale and a 

 telescope. 



To increase the .sensitiveness of the arrangement, a wire about 



