238
XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
would be easily intelligible without necessitating any split-
ting up of the discharge into partial discharges. This would
still be a continuous discharge in the sense in which we have
used the word.
II. DO THE CATHODE RAYS INDICATE THE PATH
OF THE CURRENT ?
As is well known, the cathode rays spread outwards in
straight lines, approximately perpendicular to the cathode
and without reference to the position of the anode. Accord-
ing to the density of the gas, they proceed in the medium for
a few millimetres, centimetres, or even up to lengths of the
order of a metre. In air they are blue, but at low densities
their luminosity is exceedingly feeble; they are then most
noticeable on account of the phosphorescence which they
excite when they strike the glass. If a magnet is brought
near the tube they appear bent, much as an elastic wire
attached to the cathode and traversed by a current would
become bent under the influence of the magnet. This is
universally regarded as an electromagnetic action, and, ex-
cepting that passing doubts were expressed, the view that
used to be held by physicists was as follows: The cathode
rays indicate the path of the current, and their blue light
arises from the glowing or phosphorescence of the gas-particles
under the action of the current. As a fuller knowledge of
the facts was attained this view appeared less probable, and
more recent experimenters express themselves very reservedly
as to the relation between the cathode rays and the actual
process of discharge.¹ Under these circumstances it appeared
advisable to obtain by experiment a decisive answer to the
question-Does the current travel along the cathode rays
before it turns towards the anode ? If this question was to
be answered in the negative it would become clear that the
path of the current could not be recognised by the naked eye,
and a fresh question would arise, namely, What is the path
1 See, e.g. W. Spottiswoode and J. Fletcher Moulton, Phil. Trans. 171,
p. 649, 1880.