working hypothesis, which, in the present state of our knowledge, may
be regarded as a necessary help to be retained only so long as it
proves useful. In experimental research early hypotheses have
necessarily to be modified, or adjusted, or perhaps entirely
abandoned, in deference to more accurate observations. Dumas said,
truly, that hypotheses were like crutches, which we throw away when we
are able to walk without them.

RADIANT MATTER AND "RADIANT ELECTRODE MATTER."

In recording my investigations on the subject of radiant matter and
the state of gaseous residues in high vacua under electrical strain, I
must refer to certain attacks on the views I have propounded. The most
important of these questionings are contained in a volume of "Physical
Memoirs," selected and translated from foreign sources under the
direction of the Physical Society (vol. i., part 2). This volume
contains two memoirs, one by Hittorff on the "Conduction of
Electricity in Gases," and the other by Puluj on "Radiant Electrode
Matter and the So-called Fourth State." Dr. Puluj's paper concerns me
most, as the author has set himself vigorously to the task of opposing
my conclusions. Apart from my desire to keep controversial matter out
of an address of this sort, time would not permit me to discuss the
points raised by my critic; I will, therefore, only observe in passing
that Dr. Puluj has no authority for linking my theory of a fourth
state of matter with the highly transcendental doctrine of four
dimensional space.

Reference has already been made to the mistaken supposition that I
have pronounced the thickness of the dark space in a highly exhausted
tube through which an induction spark is passed to be identical with
the natural mean free path of the molecules of gas at that exhaustion.
I could quote numerous passages from my writings to show that what I
meant and said was the mean free path as amplified and modified by the
electrification.[2] In this view I am supported by Prof. Schuster,[3]
who, in a passage quoted below, distinctly admits that the mean free
path of an electrified molecule may differ from that of one in its
ordinary state.

[Footnote 2: "The thickness of the dark space surrounding the negative
pole is the measure of the mean length of the path of the gaseous
molecules between successive collisions. The electrified molecules are
projected from the negative pole with enormous velocity, varying,
however, with the degree