Charge on 

 electroscope 



Magne 



+ 



off 



+ 



on 



- 



off 



— 



on 



and the emission of slowly moving cathode rays, etc. 51 

 Distance of polonium from electroscope 4 cm. 



Leak in five minutes 

 in scale divisions of 

 micrometer eye-piece 



70 

 2-5 

 5 

 5 



Distance of polonium from electroscope 5 cm. (this ivas 

 a different tube). 



50 + off 



1 + on 



1 - off 



1 — on 



Thus we see that when the electroscope is charged with 

 positive electricity there is a large leak which is practically 

 stopped by a magnetic field, while when the charge is negative 

 there is very little leak. This shows that the polonium gives 

 out streams of negative electricity, we have however as yet 

 no indication of any emission of positive. I was never able to 

 get an increase in the negative charge of the electroscope, this 

 I attribute to the velocity of the cathode rays given out by the 

 polonium being so low that they are not able to make their 

 way against the repulsion exerted by the negatively electrified 

 electroscope. In order to be sure that the effect was due 

 to the polonium I had the polonium disc mounted on swivels 

 so that by tapping the disc could be made to rotate about a 

 vertical axis and the face on which the polonium is deposited 

 made to face towards or away from the electroscope. When the 

 polonium-coated face of the disc was towards the electroscope, the 

 leak, when the latter was charged positively, was 45 divisions 

 when the magnet was off, six divisions when the magnet was on; 

 when the electroscope was charged negatively the leak was seven 

 divisions when the magnet was off, three when it was on ; the disc 

 was then tapped until it turned through 180 degrees, the polonium- 

 coated face now facing down the tube E, and away from the 

 electroscope, the leak when the electroscope was positively charged 

 was now only three when the magnet was off, and it was too small 

 to detect when the magnet was on. When the electroscope was 

 negatively charged the leak was one with the magnet off, zero 

 with it on. This shows that the leak observed is due to the 

 polonium. There is however a considerable leak when the disc 

 is so placed that rays proceeding normally from the disc could not 



