“…The light source consisted of a pyrex bulb, 22 cm in diameter, containing a titanium anode and a cathode in the form of a thin-walled titanium cylinder, 12 mm in diameter and 50 mm in length. This discharge tube, very similar to the one previously used by Glad [2], was filled with helium at 6-15 torr and connected to a 10 pF condenser through a rotating switch. When the discharge operated at 1 500 to 1 800 volts, a great number of sparks appeared inside the cathode, and a luminous layer became visible along the walls.…”