Source : Webster's Revised Unabridged Dictionary (1913)

Crookes tube \Crookes" tube`\ (kr??ks" t?b`). (Phys.)
   A vacuum tube in which the exhaustion is carried to a very
   high degree, with the production of a distinct class of
   effects; -- so called from W. Crookes who introduced it.

Source : WordNet®

Crookes tube
     n : the original gas-discharge cathode-ray tube