52(5 



HOURLY values of potential in volts, November 22 to 25, 1902. 



This series shows a, minimum on each day about noon, and a maximum in the early morning hours, the 

 time of the maximum for the mean of the three days being 4 a.m. 



During the summer months, when the sun is always above the horizon, there is evidence of a daily 

 variation, the maximum being when the sun is low, the minimum in the middle of the day. 



Mr. BERXACCHI remarks in a note added to the observations of November 15, 1902: "There seems 

 little doubt that atmospheric electricity is a maximum at midnight and a minimum at noon." 



For the rest of the year the data are insufficient to establish any regular daily variation. There is one 

 series of 2-hourly observations extending from noon on October 7 till noon on October 10, 1903. There 

 was considerable disturbance due to drifting snow, and the observations were made with the collector at a 

 height of 12 feet ; the insulation in the high-level observations is not above suspicion. This series is, 

 therefore, of little value for the purpose of studying the daily variation. 



Annual Variation. 



The fact that the observations were not taken at the same hours daily throughout the year makes it 

 difficult to decide upon the best mode of treating the observations for the purpose of determining whether 

 there is any regular annual variation. In the three tables which follow are given the mean potential at 

 the point of observation (5 feet above the ground) for each month, the mean for each month being in the 

 first table that of the forenoon observations (taken between 9.30 and 11 a.m.) of all the available days ; 

 in obtaining the values given in the second table the mean of the available values for each day was 

 calculated, and the mean for the month is the mean of these means ; in the last table the mean of all the 

 available observations for each month is given. In all cases observations taken during snow or drift, as 

 well as all giving negative or zero or abnormally high potentials (exceeding 300 volts) have been 

 excluded. The period covered is from March, 1902, to April, 1903, inclusive.* 



Under March and April arc given the means of the observations of both 1M2 and 1'JUJJ. 



