Mr Lahy, A slicing electrometer. 



107 



These plates were connected to the ends of a battery, CD, the 

 middle of which was earthed. The silvered quartz fibre, EF, 

 is stretched parallel to and equidistant from the two plates A, B; 

 this position of the string relative to A and B is attained by the 

 lateral movement of its points of support, E, F; while its tension, 

 which has to be kept very constant, is controlled by the screw S. 



Fig. 1. 



The terminals of the middle cell M, of the battery G, D, were 

 connected to the potentiometer Rr, the middle of which was 

 earthed, while the connection to the fibre could be moved from R 

 to r, i.e. its potential varied from —1 volt to 1 volt by steps of 1/50 

 of a volt. 



As the fibre was not highly insulated, tests could not be made 

 with it isolated, so that the results given later, it should be pointed 

 out, were got with the potential of the fibre maintained. 



The motion of the middle of the fibre was observed by means 

 of a microscope with a Zeiss achromatic objective A, and micro- 

 meter eye-piece No. 3. The tube length was such as to give 

 a magnification of 100. A slight illumination gave a sharp image 

 of the black silvered fibre on a bright ground. 



