146 



OCEAN ATMOSPHERIC -ELECTRIC RESULTS 



regular manner, with a daily range of 2 to 5 x 10-7 esu 

 In mean curves representing several days. When indi- 

 vidual days are examined, as found in the table in sec- 

 tion VI, the daily minimum may be as low as 5 x 10-7 

 esu and the maximum as high as 15 x 10-7 gsu, thus 



Table 1. Daily means of air-earth current density and 



daily ranges for four groups of data containing forty 



diurnal-variation series of measurements from 



cruise VII: first group, Atlantic data; other 



groups, Pacific data 



Month 

 and 

 year 



Average 



longitude 



east 



No. 



of 



days 



Range of 

 current 

 density 



in 10-7esu 



Average 



current 



density 



in 10-7esu 



giving a range of 10 x 10-7 esu. This not unusual range 

 through the day must be borne in mind when decision is 

 made as to whether certain values of air-earth current 

 density are unusually low or not. 



Similarly, daily average current -density values vary 

 over a considerable range. This may be seen from table 

 2, where mean daily values of conductivity, potential- 

 gradient, and air-earth current density are tabulated for 

 the twenty-seven diurnal-variation series found in the 

 table in section VI. Included in the table, in the last col- 

 umn, are maximum and minimum values of current den- 

 sity for each day, illustrating the large diurnal range 

 mentioned in the preceding paragraph. 



In table 2 there are two days with conspicuously low 

 mean values of air-earth current density, namely, Au- 

 gust 17-18 and 24-25, 1928, with values of 4.8 and 4.5 x 

 10-7 esu, respectively. These days are part of a period 

 of sixteen days between August 10 and 25, for which the 

 brief day-to-day observations also showed consistently 

 low values of current density, the latter being computed 

 from unusually low values of conductivity and more or 

 less ordinary values of potential-gradient. This dis- 

 turbed period is one of three which will be discussed in 

 detail later. 



Besides the two lowest daily mean values of current 

 density just mentioned, there are two other low values of 



Table 2. Daily mean values of conductivity, potential-gradient, and air-earth current density for 

 diurnal-variation series of cruise Vn from July 30, 1928 to November 5, 1929 



*Air-earth current density computed assuming X+ = 1.10X-. 

 ^Except two low values 2.6 and 2.7. "^Except two low values 4.: 

 3.7. ^October 21-22 has only 18 hourly values. 



bLow values throughout day. 

 and 5.0. ^Except one low value of 



