Discussion of Atmospheric-Electric Observations 

 CONDUCTIVITY. IONIC CONTENT. AND AIR-EARTH CURRENT-DENSITY. 



411 



Turning now to the conductivity, ionic content, and air-earth current-density, the results 

 recorded by other observers correspond frequently to all sorts of different times of the year 

 and periods of the day, especially in the case of ocean values. Tables 86-89 show a collec- 

 tion of land values, while Tables 90 and 91 show a collection of ocean values. The means 

 of these values are collected in Table 93, and the corresponding quantities from Table 85 

 have been added for comparison. 



The observations for v+ and y_, and for i, other than those of the present cruise, are too 

 few in number to afford means for the table. 



It will be seen that the present values of the ionic content are shghtly higher than the 

 means from other observers on the ocean and the mean of the land values. A glance at 

 Tables 86 and 90 will, however, show that the means for other ocean observers and for land 

 observations are means of relatively small numbers of widely differing quantities. On the 

 other hand, as already stated, there is a remarkable constancy in the values of the ionic 

 numbers as obtained throughout the present cruise. 



The very close agreement will be noted between the values of X^. and X_ for the 

 Carnegie's fourth cruise and those of former observers on the ocean. 



It is of interest to compare the present values of X+ and X _ with the values obtained by 

 former observers on the Carnegie and Galilee. We can do this only for the Pacific Ocean, 

 since, as already stated, the fourth cruise values for the Atlantic Ocean are probably 

 abnormal. The Pacific-Ocean values of X+ and X _ as obtained on the fonner cruises of the 

 Carnegie and Galilee are contained in Table 91. They vary somewhat, but the mean values 

 X^ = 1.46X10"^ E.S.U., and X_ = 1.22X10"'' e.s.u. are in remarkable agreement with 

 the corresponding values 1.46X10"* e.s.u. and 1.24X10"'' e.s.u. given in Table 85 as 

 the mean Pacific-Ocean values for the Carnegie's fourth cruise. 



Practically the only ocean value of the air-earth current-density with which to 

 compare the present results is the value 7.7 X 10"^ e.s.u. obtained by Johnston' on the third 

 cruiseof the Carne^rie. The lattervaluewas,however,obtained in the North Atlantic Ocean. 



The value of the air-earth current-density for the Carnegie's fourth cruise is con- 

 siderably greater than the average land value ; a rather curious circumstance with reference 

 to the land values must, however, be noted. The mean of 8 land values of the potential- 

 gradient as obtained from Table 92 is 151 volts per meter, and the mean of 24 land values of 

 X+-|-X_ as obtained from Table 87 is 2.4X10"* e.s.u.; we should thus expect the mean 

 air-earth current-density to lie in the neighborhood of 2.4X10"*X 1.51/300, i.e., 12X10"^ 

 E.s.u. On the other hand, the mean of 11 land detenninations obtained in different 

 localities gives the value 6. 5X 10"^ e.s.u., recorded in Table 93. The discrepancy between 

 6.5 and 12 is so large, however, as to suggest that at any rate some of the means for X+, X_, 

 X, and i as obtained from Tables 87, 88, and 92, are not truly representative of average 



'See page 373. 



