produced by the Point Discharge. 471 



traces of their presence were obtained from the various deposits 

 produced by them. 



It was noticed that with slight deposits the activity was less 

 than was the case with denser deposits, while, in one case, on 

 accidentally wiping off the deposit, very little activity was found at 

 all, which suggested that the deposit was in some way responsible 

 for this radio-activity. 



In all cases in this series it was noticed that when the disc 

 was at the negative terminal during the discharge it would, on 

 being fixed in the testing vessel, only cause a leak of positive 

 electricity, while when reversed and made the positive terminal 

 for the discharge, it would only leak negative when connected up 

 in the testing vessel, the maximum deflections after reaching the 

 stationary state at the end of half-an-hour being respectively 

 between 82 and 85 when the disc leaked negative, and 78 to 80 

 when it leaked positive electricity. 



With a view to testing the theory as regards the deposits, 

 a series of experiments were made in which the discharge passed 

 between the points and the disc in the open air, they being fixed 

 up on the window-sill in the same positions as before. Very slight 

 deposits indeed were obtained by this treatment, and on testing in 

 the cylinder the effects produced were extremely small, the observed 

 deflections at the end of the half-an-hour being respectively 7 for 

 a negative leak, and 6 for a positive leak, the different metals 

 behaving equally well, no difference being observable in the various 

 deflections obtained. 



In one of these experiments with an aluminium disc a fall of 

 snow occurred during the discharge, but practically no difference 

 could be observed in the deflection yielded by this disc when in 

 the cylinder. 



A wooden box was next procured having a capacity of 55 litres, 

 and its walls covered with paraffin wax to close up any small cracks 

 present ; insulated uprights of ebonite being fixed in position to 

 carry the points, and the brass electrode, to which the discs 

 were screwed, and connecting wires from both were led out 

 through wax plugs in the side. Soft wax was placed round 

 the edges, and the box sealed by screwing the cover down upon 

 this wax. 



After the box had been closed for some 16 hours, giving any 

 dust particles in the air inside time to settle down, the discharge 

 was passed for an hour, the box opened, and the disc blown upon 

 and connected up in the test cylinder, when it was found that, 

 after half-an-hour, the deflection was only 3 divisions. The same 

 effect was noticed for all the metals, whether they were connected 

 to either terminal of the machine, and no deposit whatever could 

 be observed upon any of the discs. 



