356 CARNEGIE INSTITUTION OF WASHINGTON. 



general way, when this pole is farthest from the Sun, The actual times of 

 maximum and minimum, however, appear to depend upon the positions of 

 both magnetic poles and the fact that their longitude difference is not 180°. 

 These correlations appear to support the assumptions of various investigators 

 that the Earth's electric charge and resultant field may be very intimately 

 related to an electric radiation from the Sun. 



Although the Carnegie has obtained more diurnal-variation data regarding 

 the potential gradient than for other elements, reductions of the available 

 data for positive ionic content (ri+),and conductivity due to positive ions (X+), 

 and the positive vertical current-density (i+) have also been made. For 

 example, the mean curves from 37 practically complete series for n+ show for 

 the Atlantic, Pacific, and Indian Oceans a consistent diurnal variation with 

 local time, day values being in general above and night values below the 

 mean-of-day value. This is in agreement with the results given in Volume 

 III of the "Researches of the Department of Terrestrial Magnetism" (1. c.) 

 and in the Director's annual report for 1917 (1. c). 



Observations for the diurnal variation of X+ were not begun until 1918; 

 consequently, fewer series are available than for the other elements. How- 

 ever, reductions based on 20 series indicate for each ocean a diurnal variation 

 of X+ similar to though somewhat less regular than that found forn+. The 

 range of this variation is of the order of 10 per cent of the mean-of-day value. 



Since the diurnal-variation observations for X+ were not begun until 1918, 

 the number of series which provide data for both potential gradient and X+ 

 are necessarily Umited, Nevertheless, from 19 such series we have some 

 interesting preliminary evidence regarding the probable diurnal variation of 

 i+, the product of practically simultaneous values X+ and potential gradient. 

 Since the potential gradient has, over the ocean, a well-defined variation 

 according to universal time, and X+ only a weak variation on a local-time basis, 

 we should expect the diurnal variation of 1+ to resemble most nearly that of 

 the potential-gradient. This, in fact, is what we find, and while the limited 

 data available will not justify complete confidence in the result, it is signifi- 

 cant that the separate mean curves for the three oceans are in good agree- 

 ment with each other, both as to the mean-of-day values of i+ and in showing 

 a well-marked diurnal variation, whose chief component progresses roughly 

 according to universal time. The results, so far as they go, give no evidence 

 whatever which would indicate an automatic adjustment between potential 

 gradient and conductivity, such as to maintain a practically constant vertical- 

 current density. 



Briefly summarized, the reductions of the data available to date from diur- 

 nal-variation observations made aboard the Carnegie indicate the following 

 preliminary' results : 



(a) For the potential gradient, a marked diurnal variation whose chief component over 

 the major portion of the Earth is a wave of 24-hour period which occurs approximately 

 simultaneously in all localities. 



(6) For n+ and \+ a weak diurnal variation according to local time, both quantities 

 being, on the average, greater during the day than during the night. 



(c) For i-\-, the product of X+and potential gradient, a well-defined diurnal variation 

 which is approximately similar to that noted under (a) for the potential gradient. 



The full publication of the observational data and discussion of results 

 will be deferred until after the completion of the present cruise of the Carnegie. 



