theory. In Sir William Tilden's recent book entitled "Chemical Discovery
and Invention in the Twentieth Century," I read that Mendeleef,
"disregarding conventional views," supposed the ether to have a molecular
or atomic structure, and in time all physicists must come to recognise that
the Electron is not, as so many suppose at present, an atom of electricity,
but an atom of ether carrying a definite unit charge of electricity.

Long before the discovery of radium led to the recognition of the electron
as the common constituent of all the bodies previously described as
chemical elements, the minute particles of matter in question had been
identified with the cathode rays observed in Sir William Crookes' vacuum
tubes. When an electric current is passed through a tube from which the air
(or other gas it may contain) has been almost entirely exhausted, a
luminous glow pervades the tube manifestly emanating from the cathode or
negative pole of the circuit. This effect was studied by Sir William
Crookes very profoundly. Among other characteristics it was found that, if
a minute windmill was set up in the tube before it was exhausted, the
cathode ray caused the vanes to revolve, thus suggesting the idea that they
consisted of actual particles driven against the vanes; the ray being thus
evidently something more than a mere luminous effect. Here was a mechanical
energy to be explained, and at the first glance it seemed difficult to
reconcile the facts observed with the idea creeping into favour, that the
particles, already invested with the name "electron," were atoms of
electricity pure and simple. Electricity was found, or certain eminent
physicists thought they had found, that electricity _per se_ had inertia.
So the windmills in the Crookes' vacuum tubes were supposed to be moved by
the impact of electric atoms.

Then in the progress of ordinary research the discovery of radium by Madame
Curie in the year 1902 put an entirely new face upon the subject of