produced in Gases by Rontgen Rays Sfc. 



433 



by a copper wire to the insulated terminal of the electrometer. 

 Suitable means were taken to protect this connecting wire 

 from inductive effects (see fig. 9) . 



Fig-. 9. 



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[From 'Nature,' Feb. 11, 1897.] 



The Rontgen lamp was placed in a lead cylinder connected 

 to the case of the electrometer. The rays passed into the 

 cylinder of aluminium through a window in the lead cylinder 

 2 centim. broad and 4 centim. long. This window could be 

 screened or unscreened at will. 



The course of the experiment was the same with each 

 insulated conductor. The conductor was charged first 

 positively, then negatively ; the Rontgen rays were then 

 caused to shine on it through the aluminium cylinder sur- 

 rounding it and the electrometer-readings taken at fixed 

 intervals, until a steady reading on the electrometer was 

 obtained. The point at which the electrometer-readino- 

 remained steady with the rays acting we shall call the rays- 

 zero. 



Finally, the insulated conductor was discharged by metallic 

 connexion in the electrometer and re-insulated ; the rays 

 were again caused to shine on it till the deviation from the 

 metallic zero reached the rays-zero and there remained steady. 



This deviation from the metallic zero was not stopped by 

 placing an aluminium screen over the window of the lead 

 cylinder surrounding the Rontgen lamp ; on the other hand, 

 it was stopped if a lead screen was used. 



In the following table, column II. gives the potential- 

 differences of the rays-zero from the metallic zero for twelve 



