IVehnelt Cathode-Ray Tube Magnetometer. 383 



photographic plate held near the top of the tube in a simple 

 form of plateholder and shutter. The holder, which rests on 

 a brass ring waxed to the inside of the tube, is a disk of 



TO PUMP 



Fk>\ 1. 



S— Standard Coil, to Battery. 



H — Heating Circuit, to Battery. 



DIS— Discharge Circuit, to High Potential Battery. 



