228
XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
felt compelled to assume a discontinuity, were not convinced
by Hittorf, although they were willing to admit that the
current might be made up of hundreds of thousands, or even
millions, of separate discharges per second. Among these
were E. Wiedemann,' Goldstein, and Warren de la Rue.³ The
latter had also described experiments by which he had
demonstrated the discontinuity of an apparently continuous
discharge otherwise than with a rotating mirror; but this
demonstration could only be carried out under special condi-
tions, and these conditions appeared to be just those under
which the rotating mirror would have proved discontinuity.
The point in question may therefore be regarded as still
an open one. The question is not whether an apparently
continuous discharge may under certain circumstances be
shown to be discontinuous; there is no doubt that this would
have to be answered in the affirmative. The question should
rather be put in the following form:-Can we establish the
existence of a discharge which is undoubtedly a cathode
discharge, but in which, nevertheless, no trace of discontinuity
can be detected, even by the most delicate methods?
The discharge, which was tested by the following methods,
was produced in a tube of length 340 mm., and clear width
20 mm., between a steel plate (serving as the cathode) 18 mm.
in diameter and a steel wire. It took place in air under such
a pressure that the blue glow-light extended to a distance of
50 to 60 mm. from the cathode; furthermore, from six to
nine positive red striæ were formed in the tube. The
current used lay between 1 and 0 of that sent by a
Daniell cell through a Siemens unit, and was regulated by
introducing a large liquid resistance. Only in the method
which will last be described was a stronger current necessary,
and this was to 3 Dan./S.U. In this case it was found
advisable to use a somewhat wider and shorter tube, so that
only one positive stria was visible, and this only indistinctly.
But at the same time there could be no doubt that the
discharge was of the nature of a cathode discharge. Of course
the discharges investigated showed none of the ordinary
1 Wied. Ann. 10, p. 245, 1880.
2 Loc. cit. 12, p. 101, 1881.
3 Ann. de Chim. et de Phys., series 5, 24, p. 461, 1881; and Phil. Trans.
169, p. 225, 1878.