[WRIGHT] VARIATIONS IN THE CONDUCTIVITY OF AIR lOl 



This difference in the drop in conductivity is well illustrated by 

 the results obtained with the lead cylinder No. 1. With this cylinder 

 in the steady state, as the nmnbers in Table X shew, the conductivity 

 when measured in the laboratory corresponded to the generation of 

 22.5 ions per c.c. per sec. With the same cylinder freshly cleaned 

 and filled with well filtered air the conductivity, as measured in the 

 same room in the laboratoiy always corresponded to the generation of 

 approximately 15.3 ions per c.c. per second. In the measurements on 

 the surface of the lake water, however, the conductivity corresponded 

 to the generation of 13.9 ions per c.c. per second when the cylinder 

 was in the steady state, while, as will be seen from the results recorded 

 in the next section, it corresponded to the generation of only 8.5 ions 

 per c.c. per second when the cylinder had been freshly cleaned and filled 

 with filtered air. 



This difference in the values obtained for the drop in conductivity 

 with the lead cylinder in the two conditions can no doubt be traced to 

 differences in the secondary radiation elicited in the walls of the vessels 

 by the penetrating radiation from the earth. 



It is clear that the surface of the lead after being freshly cleaned 

 must have gradually become covered with a deposit through oxidation 

 and other causes, and it is reasonable to conclude that the presence of 

 this deposit would produce such a modification in the intensity of the 

 secondary radiation as to bring about the results described. 



3. — Measurements made in different localities and with different 

 receivers freshly cleaned. 



The preliminary measurements just described made it abundantly 

 evident that the lake water acted as a very efficient screen for the earth's 

 radiation, a maximum decrease in the value of " q," of as much as 

 9 ions being recorded in the last series of observations. A careful 

 set of measurements was therefore undertaken, having for its object a 

 determination of the relative decrease in the values of " q " over water 

 from those obtained in the laboratory, when freslily cleaned receivers 

 of lead, zinc and aluminium were used in turn as the containing vessels. 

 In the case of the lead cylinder the conductivity was measured at a 

 larger number of points to determine if possible in what way the ioniza- 

 tion was influenced by external conditions such as a change of soil. 



The results, which are in many cases the mean of a number of 

 observed values obtained on different occasions and differing but slightly 

 from one another, are given in Table XI. 



