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. 



ca]_> jjrovidicd. S(i (lia( oiio could easily ojk'u it to adjust the points, or to 

 obser\'e the nature of the discharge. The inside of all portions of the 

 tube and the inside of the hollow cores \yvve ]iainted a dead bh|clv. 



