Radium and the Electron Theory. 411 
This theory has been much developed by Drude, and has been 
supported by the calculations of Lorenz. It seems to bring 
the electrical one in metals into close touch with con- 
duction in gases; for in both cases we suppose a movement 
of small particles endowed with velocity. These particles 
have a greater free path in rarefied gases than they have 
between the molecules of a metal; and their action is much 
modified by the X-rays. This modification is usually attri- 
buted to a species of ionization due toa physical connexion 
between the energy emitted by the X-rays and the trans- 
formation of energy witnessed in the rare fied gus. A Geissler 
tube, for instance, ‘which will not permit the passage of an 
electric current, W ‘hen the degree of exhaustion is beyond the 
point of breaking down with the electromotive force employed, 
is made conducting when the X-rays fall upon it. 
We mention this fact in order to give a sign nificance to our 
experiments with radium. This remarkab ie substance also, 
in common with the X-rays, can affect by what we call 
ionization the conduction of electricity through gases. The 
X-rays and certain emanations of radiumalso can pass through 
thin sheets of metals, especially sheets of aluminium. We 
are therefore for the first time in the history of electricity in 
a condition to test the question, whether radiant energy 
exhibiting light and passing through a metal can affect the 
passage Be a Current of electricity. 
One immediately is reminded, in this connexion, of 
Faraday’s attempt to discover w hether or dinary light is 
modified in passing through an electrolyte which is sub- 
mitted to the action of a Gureent of electricity. He thought 
that there might be a state of tension which could be detected 
by polarized light; and he therefore passed a beam of 
polarized light in ie direction of the current and also at right 
angles to this direction. 
The result of the experiment was negative; absolutely 
no effect was observed.  f*araday’s custom of publishing 
both positive and negative results has its adv antages, 
especially in the early days of a science ; and especially when 
it shows us the working of a great mind groping in a region 
not yet submitted to calculation. Lesser inde must, how 
ever, use caution in publishing negative results ; for one 
must have a due regard for brevity of publication and the 
limits of experimentation. 
Can we not, however, imagine Faraday continuing his 
efforts to discover some connexion between the passage of 
light through an electrolyte or a conductor and the passage 
of a current of electricity, if he could penetrate such a con- 
ductor by light? In ier words, might he not have been 
tempted, if he had had command of the X- -rays or radium, to 
