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XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
speed which is very easily measurable. And in every actual
electromagnetic effect the ponderable substratum of the
current is set in motion; which is not the case with the
deflection of the discharge.¹ Hence this deflection corresponds
much more nearly to Hall's phenomenon. But this analogy
again is seen to be defective when we recollect that the
cathode rays are not to be regarded as the path of the current.
Lastly, it is known that the battery-discharge can be ex-
tinguished by bringing a powerful magnet near it; and after
the magnet is removed the discharge immediately starts off again.
This shows that the action of the magnet upon the discharge
cannot be purely electromagnetic.
The action of the magnet,
which prevents the current from starting, certainly cannot be
an action upon the current itself; it can only be an action
upon the medium through which the current has to pass. On
account of these difficulties, and the fact that the cathode rays
do not react upon the magnet, it seems to me probable that
the analogy between the deflection of the cathode rays and
the electromagnetic action is quite superficial. Without
attempting any explanation for the present, we may say that
the magnet acts upon the medium, and that in the magnetised
medium the cathode rays are not propagated in the same way
as in the unmagnetised medium. This statement is in accord-
ance with the above-mentioned fact, and avoids the diffi-
culties. It makes no comparison with the deflection of a wire
carrying a current, but rather suggests an analogy with the
rotation of the plane of polarisation of light in a magnetised
medium.
2. E. Wiedemann and Goldstein have expressed the
opinion that the discharge consists of an ether-disturbance, of
itself invisible, and only converted into light by imparting its
energy to the gas-particles. This view seems to me to be
based upon convincing arguments. I should, however, like to
see the word 'discharge' replaced by 'cathode rays': the two
things are quite distinct, although the physicists referred to
do not observe the distinction. If we consider carefully the
following experiment, it will be difficult to resist the view that
the cathode rays themselves are invisible, and that they only
produce light by their absorption in the gas. The tube
1 See Goldstein, Wied. Ann. 12, p. 262, 1881.