Trowbridge and Rollins — Radium and Electron Theory. TT 



Art. XII. — Radium and the Electron Theory; by John 

 Trowbridge and William Rollins. 



The mechanism of electric conduction through metals con- 

 tinues to be one of the greatest mysteries of electricity ; and 

 there is no plausible explanation of it unless we accept the 

 theory of electrons. This theory, as is well known, supposes 

 the existence of small bodies called electrons, which move 

 between the molecules of the metals during the passage of an 

 electric current. It has been much developed by Drude.* 



The theory seems to bring the electrical conduction in metals 

 into close touch with conduction in gases ; for in both cases 

 we suppose a movement of small particles. These particles 

 have a greater free-path in rarified gases than they have 

 between the molecules of a metal, and their action is much 

 modified by the X-rays. This modification is usually attributed 

 to a species of ionization due to a physical connection 

 between the energy emitted by the X-rays and the trans- 

 formation of energy witnessed in the rarified gas. A Geissler 

 tube, for instance, which will not permit the passage of an 

 electric current, when 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 significance to our 

 experiments with radium. This remarkable substance, also, in 

 common witli the X-rays can affect by what we call ionization, 

 the conduction of electricity through gases. The X-rays and 

 certain emanations of radium can also pass through thin sheets 

 of metal, 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 of a current of 

 electricity. 



In this connection one is immediately reminded of Faraday's 

 attempt to discover whether ordinary light is modified in pass- 

 ing through an electrolyte which is submitted to the action of 

 a current 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 the direc- 

 tion of the current and also at right angles to this direction. 

 The result of the experiment was negative ; absolutely no 

 effect was observed. Faraday's custom of publishing both 

 positive and negative results has its advantages, especially in 

 the early days of a science ; and particularly when it shows us 



* Ann. derPhysik., No. 1, 1900. 



