Dictionary.net

• The dark space within the negative-pole glow at the cathode of a vacuum tube, observed only when the pressure is low enough to give a striated discharge; - called also Crookes layer.

2010 - New Age Dictionary Database
By Oddity Software

• The dark space within the negative-pole glow at the cathode of a vacuum tube, observed only when the pressure is low enough to give a striated discharge; - called also Crookes layer.

1913 - Webster's Revised Unabridged Dictionary
By Noah Webster.