Residual Ionization in Gases. 



421 



were made was about 21° C. and the temperature on the lake 

 from 0° C. to —10° C. The manner in which the electro- 

 meter behaved is illustrated by the diagram shown in fig. 2, 

 which represents the readings in volts taken with air on a 

 particular day from about 9 o'clock a.m. until after 6 o'clock 

 in the evening. 



Fig. 2. 



10 u u l 



4 5 6 7 



TIME- O'CLOCK 



After this portion of the investigation had been completed 

 a set of readings was taken in the laboratory with each of 

 the gases under natural ionization and then with them tra- 

 versed consecutively by streams of alpha, beta, and gamma 

 rays of moderate intensity. Measurements with the beta rays 

 were made by placing in the chamber which usually con- 

 tained the metallic sodium a small capsule containing some 

 uranium oxide. The back and walls of this capsule were 

 made of thick zinc, and the face consisted of a sheet of 

 aluminium thick enough to cut off all alpha radiation. 



The arrangement is shown in fig. 3, and from the diagram 

 it Avill be seen that the effect of the rays on the gas in the 



