Bar us — Displacement Interferometer. 



67 



The cylinder Tck is either of very thin aluminum tubing, or 

 preferably of gilt paper. The wires yy pass through small 

 holes at the top ends. To secure adequate damping, thin cir- 

 cular rings of mica or of paper, BB, surround the ends, and 

 the front one carries the light mirror w, which reflects one of 



Fig. 2. 



Fig. 2. Cylindrical electrometer, vertical section. Side view. 



the component beams of the interferometer, as indicated at the 

 glass window p. If liquid damping is desired, in the case of 

 a heavy cylinder, wires ending in a vane may be dropped from 

 one of these disks with the vane in a box of oil below. This 



