nown, we will endeavour to group the chief
of them round a few essential ideas, and will seek to state precisely
the data they afford us for the solution of this grave problem.

It was the study of the conductivity of gases which at the very first
furnished the most important information, and allowed us to penetrate
more deeply than had till then been possible into the inmost
constitution of matter, and thus to, as it were, catch in the act the
actions that matter can exercise on the ether, or, reciprocally, those
it may receive from it.

It might, perhaps, have been foreseen that such a study would prove
remarkably fruitful. The examination of the phenomena of electrolysis
had, in fact, led to results of the highest importance on the
constitution of liquids, and the gaseous media which presented
themselves as particularly simple in all their properties ought, it
would seem, to have supplied from the very first a field of
investigation easy to work and highly productive.

This, however, was not at all the case. Experimental complications
springing up at every step obscured the problem. One generally found
one's self in the presence of violent disruptive discharges with a
train of accessory phenomena, due, for instance, to the use of
metallic electrodes, and made evident by the complex appearance of
aigrettes and effluves; or else one had to deal with heated gases
difficult to handle, which were confined in receptacles whose walls
played a troublesome part and succeeded in veiling the simplicity of
the fundamental facts. Notwithstanding, therefore, the efforts of a
great number of seekers, no general idea disengaged itself out of a
mass of often contradictory information.

Many physicists, in France particularly, discarded the study of
questions which seemed so confused, and it must even be frankly
acknowledged that some among them had a really unfounded distrust of
certain results which should have been considered proved, but which
had the misfortune to be in contradiction with the theories in current
use. All the classic ideas relating to electrical phenomena led to the
consideration that there existed a perfect symmetry between the two
electricities, positive and negative. In the passing of electricity
through gases there is manifested, on the contrary, an evident
dissymmetry. The anode and the cathode are immediately distinguished
in a tube of rarefied gas by their peculiar appearance; and the
conductivity does