McClelland and Kennedy — The Large Ions in the Atmosphere. 83 



9 and 10 p.m. the values on the same days were between 16,000 and 41,000. 

 This increase in the evening was found on all occasions on which such 

 observations were taken in that particular type of weather. 



Many observations of ^V were made during the night. In general 

 they showed no striMng difference from the values obtained during the 

 day-time. 



The table contains many instances of very great changes in the value of 

 N in a short time. The variable natm-e of N is further emphasized by the 

 diagram (fig. 8), which gives the values of N, taken at half-hour intervals 

 during a prolonged period when the number was not specially unsteady. 



Half -Hour Intervals. 

 Fig. 8. 



On several occasions, long-continued series of observations were made 

 alternately on the number of positive and negative ions. Tliese failed to 

 show any appreciable difference between the numbers of positive and 

 negative at any time. 



The values of N obtained by us are, on the whole, much greater than 

 those found by Pollock in Sydney. In his investigation a series of 117 

 observations gave 5,500 as the maximum, and 600 as the minimum value 

 of y, the mean for the positive ions being 1,914 and for the negative 2,228. 

 The values obtained by Lange'^'in give an average of about 10,000. 



Beproduction of tlie Ions. ■ 



With a view of ascertaining the natm-e and process of fonnation of the 

 large ions, experiments were made on the reproduction of these ions in air 

 which had been pre^dously freed from them. For this purpose a cylindrical 

 gas-holder with a water-seal was employed. Its capacity was about 450,000 



