solid materials for the construction of new theories of
electricity and matter.

For a long time it was noticed that the phenomena in a Geissler tube
changed their aspect considerably, when the gas pressure became very
weak, without, however, a complete vacuum being formed. From the
cathode there is shot forth normally and in a straight line a flood
within the tube, dark but capable of impressing a photographic plate,
of developing the fluorescence of various substances (particularly the
glass walls of the tube), and of producing calorific and mechanical
effects. These are the cathode rays, so named in 1883 by E. Wiedemann,
and their name, which was unknown to a great number of physicists till
barely twelve years ago, has become popular at the present day.

About 1869, Hittorf made an already very complete study of them and
put in evidence their principal properties; but it was the researches
of Sir W. Crookes in especial which drew attention to them. The
celebrated physicist foresaw that the phenomena which were thus
produced in rarefied gases were, in spite of their very great
complication, more simple than those presented by matter under the
conditions in which it is generally met with.

He devised a celebrated theory no longer admissible in its entirety,
because it is not in complete accord with the facts, which was,
however, very interesting, and contained, in germ, certain of our
present ideas. In the opinion of Crookes, in a tube in which the gas
has been rarefied we are in presence of a special state of matter. The
number of the gas molecules has become small enough for their
independence to be almost absolute, and they are able in this
so-called radiant state to traverse long spaces without departing
from a straight line. The cathode rays are due to a kind of molecular
bombardment of the walls of the tubes, and of the screens which can be
introduced into them; and it is the molecules, electrified by their
contact with the cathode and then forcibly repelled by electrostatic
action, which produce, by their movement and their _vis viva_, all the
phenomena observed. Moreover, these electrified molecules animated
with extremely rapid velocities correspond, according to the theory
verified in the celebrated experiment of Rowland on convection
currents, to a true electric current, and can be deviated by a magnet.

Notwithstanding the success of Crookes' experiments, many physicists--
the Germans especially--did n