326 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



graph circuits, 1 and consists of a disc of silver, suspended by a quartz 

 fibre, so as to hang near a small coil of a few turns of wire, with the 

 axis of which the plane of the disc makes an angle of 45°, as is shown 

 in Fig. 2. The disc is at M ; and the coil, which in 

 this experiment consisted of five turns of wire wound Q 



on a vulcanite tube, is shown at C, Fig. 2. The ter- 

 minals from the coil are connected to binding posts 

 by which the coil is put into the wavemeter circuit. 

 The front of the disc M carries a small mirror, ena- 

 bling the deflections of the disc to be measured by 

 means of a telescope and scale. 



Figure 1. Wavemeter circuit and 

 Hertz oscillator. 



G 



QO ]Q 



The mounting of the instrument is shown in Fig. 3. 

 The disc is suspended in the vertical vulcanite tube, 

 which stands on a base provided with leveling screws ; 

 the support of the coil is inserted in the side of the 

 vertical tube, and is arranged to be moved in and q 



out by a micrometer screw. This delicate motion 

 of the coil in or out brings the coil nearer to or farther from the 

 suspended silver disc so as to vary the sensitiveness of the instru- 

 ment to make it suitable for measuring small or large oscillating 

 currents. 



i Phys. Review, 1904, 19, 196; 1905, 20, 220; 1905, 21, 367; 1906, 22, 159; 

 1907, 24, 152. 



