Source : Webster's Revised Unabridged Dictionary (1913)

Plucker tube \Pl["u]ck"er tube\ [So named after Julius
   Pl["u]cker, a German physicist.] (Physics)
   (a) A vacuum tube, used in spectrum analysis, in which the
       part through which the discharge takes place is a
       capillary tube, thus producing intense incandescence of
       the contained gases.
   (b) Crookes tube.

Geissler tube \Geis"sler tube`\ (Elec.)
   A glass tube provided with platinum electrodes, and
   containing some gas under very low tension, which becomes
   luminous when an electrical discharge is passed through it;
   -- so called from the name of a noted maker in germany. It is
   called also {Pl["u]cker tube}, from the German physicist who
   devised it.