250 
magnet to shut out all light except from the pinhole, and to hold rigidly 
the insulating glass tubes, which firmly held the rods containing the points. 
An opening was cut in the upper side of this auxiliary tube and a suitable 
Fig. 8 
cap provided, so that one could easily open it to adjust the points, or to 
observe the nature of the discharge. The inside of all portions of the 
tube and the inside of the hollow cores were painted a dead black. 
