of Radium on the Electric Spark, 383 



part of the jar by means of an external magnet. The spark- 

 gap was about 6 cms. long. The results are as follows : — 



j 

 Pressure in ems. of Effect of radium. 



mercury. 



n 

 51 



40 



28 >~o effect. 



Visible discharge (spark and brush) stopped. 



Discharge (all brush) stopped. 



Dischai-ge (all brush) concentrated but not extinguished. 



The action of the radium is therefore less marked as the 

 pros-ure is reduced. This may be due to the reduction of 

 the voltage required to maintain the current. 



A very much weaker sample of the salt enclosed in a glass 

 capsule showed quite an appreciable effect when the discharge 

 was in a fairly sensitive condition. Thus the action cannot 

 be due to the u rays, since these would be absorbed by the 

 glass. It must be due to either the ft or <y rays. Since the 

 latter are supposed to be identical with Rontgen rays, 

 the influence of these on the spark was tried, but they brought 

 about no stoppage of the discharge. The ionizing powers of 

 the Rontgen rays and of the rays from the radium on the 

 air in the spark-gap were of altogether different orders. 

 Thus the radium at 50 cms. readily extinguished the spark, 

 a Rontgen-ray tube 25 cms. away had no effect : but if the 

 gap was replaced by the knob of a charged electroscope, 

 the latter was completely discharged in less than 1 sec. when 

 the tube was working, while with the radium complete 

 discharge took 5 min. to accomplish. 



The result obtained cannot therefore be ascribed to the 

 y rays, nor does it depend directly on the number of ions 

 produced by the ionizing agent, but rather is a special action 

 o£ the ft rays. 



The negative result obtained with Rontgen rays also 

 precludes the following explanation : — The ions in the 

 discharge are produced in two ways, directly by the field and 

 by collision of ions already present with neutral atoms if the 

 field is sufficiently intense. If the ionizing agent, rays of 

 any kind, produces sufficient ions, the voltage between the 

 electrodes may be so reduced that the second method of 

 formation is impossible, and the final result may be a decrease 

 in the current which passes. The effect would then be more 

 marked as the external agent produces more ions, but, as is 

 <een, this is not the case. 



It remains only to show directly that the effects observed 

 are due to the ft rays. The radium was enclosed in a lead 



