670 Dr. A. S. Eve on the Effect of 



smouldering Joss sticks, made by Chun Lun Hing of Macao, 

 gave a steady supply o£ smoke. In all experiments with 

 this, it was found that the ionization current decreased in the 

 low potential testing vessel A, and increased in the high 

 potential testing vessel B, whether the radium was present 

 or absent. 



Thus, with a large Joss stick, with radium under a funnel 

 which replaced V, the readings obtained in divisions a minute 

 were : — 



Elect. A (low pot.). Elect. B (high pot.). 



Ra, no smoke 152 IS 



Ra, with smoke ... 12 28 



Smoke, no Ra very small. 27 



The fact that the smoke particles in a moderately dense 

 cloud are sometimes charged to the extent of several tens of 

 thousands per cm. 3 explains Owens' experiment. It appears 

 that while some of the small ions may combine together, 

 others will neutralize smoke particles already charged, and 

 again others will give a charge to neutral particles ; nor 

 must the possibility of multiple-charged particles be ignored. 

 Similar effects wdl occur with uncharged dust, or smoke, 

 but the disappearance of the small ions will not be so rapid. 



I have made many experiments to determine if the y rays 

 of radium increased or decreased the number of positive and 

 negative smoke ions. Sometimes there was a small increase, 

 sometimes the reverse ; the number of particles neutralized 

 nearly balances those freshly charged. As the smoke passes 

 from the funnel to B in about one second, the almost total 

 disappearance of small ions is rapidly brought about. 



The advantage of a large electrode, as in B, is not so great 

 as was at first expected, because the velocity of the air 

 current is twice as great past the electrode of B as past the 

 electrode of A. 



Some experiments were made with testing vessel and 

 electroscope A. It will be remembered that the length of 

 the electrode is 8 cm., the diameter 2 mm., and that it is 

 within a cylinder of diameter 3 cm. 



Leaf. Voltage on Leaf. No Smoke. Smoke. 



Div./min. Div./min. 



heavy 1500 18 74 



„ 1200 14 40 



„ 1000 14 28 



lighter 840 15 10 



700 15 5 



600 11 2 



The velocity of the air current was 100 to 120 cm. per 

 second ; and the air was ionized by y rays as usual. 



