for Measuring Ionization. 



I'll 



be multiplied in order to give the " rate of leak " of the 

 standard. 



Experiment II. Balance-point and sensitiveness. — In this 

 experiment some uranium oxide was placed in the vessel X 

 and the balance-point obtained for different sensitivenesses 

 of the electrometer. The results expressed in Table I. show 

 that the balance-point is practically independent of the sensi- 

 tiveness of the electrometer. The observations were made 

 on different days and not always under exactly the same 

 conditions, which will account for any considerable variation 

 of the balance-point. 



Table I. 



Sensitiveness. 



Balance-point. 



P.D. between plates. 



0-408 



33-8 



51 volts. 



•444 



33-5 



51 „ 



•690 



32-5 



41 „ 



•690 



33-8 



51 „ 



•480 



34-8 



52 „ 



•688 



34-1 



52 „ 



•760 



34-0 



52 „ 



•454 



340 



51 „ 



•454 



26-8 



11 „ 



•840 



343 



51 „ 



•840 



27-5 



11 „ 



•220 



34-6 



51 „ 



•150 



343 



51 „ 



Experiment III. Decay-curve of the excited activity col- 

 lected from the atmosphere. — In this experiment the active 

 matter present in the atmosphere was collected on a copper 

 wire about 300 feet long suspended 20 feet above the earth. 



The active deposit on the wire was rubbed off onto a piece 

 of cloth and placed in the vessel X. Headings of the activity 

 were made at different times by both the balarfbe and the 

 " rate of leak " method, and the results are expressed in 

 Table II. 



An examination of these shows that the activity does not 

 decay to half value in about 40 to 45 minutes, which is the 

 usual rate, but is much longer, thus undoubtedly showing the 

 presence of some thorium-excited activity as well. 



Experiment IV. Test of the penetrating power of Rbntgen 

 rags. — This experiment was made with the completed instru- 

 ment, and will serve to illustrate its action. 



