59 6 



Tables 748 and 749 



TABLE 748. — Elements and Constants of Atmospheric Electricity 



(Prepared by O. H. Gish, Department of Terrestrial Magnetism, Carnegie Institution of Washington, 1930.) 



The elements of atmospheric electricity show variations, both regular and irregular. Over 

 land the irregular variations are very pronounced and the regular variations differ notably 

 from place to place, in marked contrast to the corresponding characteristics over the ocean. 

 Therefore, and because of the wider and more uniform geographical distribution of ocean 

 observations, it seems best to give the greater weight to the ocean data when attempting 

 to arrive at values characterizing world-wide conditions. Because of the wide variation 

 from place to place in the means from land stations, due to local factors, a general mean of 

 these is of questionable significance. Hence it seems better to indicate the extremes of station 

 means in the case of elements for which the data are sufficiently abundant. 



Certain disparities which will be found between these and other published tables [see 

 references (2) and (21)] arise largely from the inclusion of more recent data. The references 

 to authorities have been selected with a view to being helpful in following up the literature 

 rather than to assigning due credit for the original investigations. 



Of the atmospheric-electric elements the potential gradient has been the most extensively 

 observed. The sign of the average gradient is everywhere such as to drive positive ions 

 toward the earth. The periodic variations in this element are of great interest because of 

 their apparent relation with cosmic phenomena. Thus the potential gradient apparently 

 increases with increase in the Wolfer sun-spot numbers, varies throughout the year, the 

 maxima in monthly means occur everywhere, with few exceptions, at the time of northern 

 winter, and the corresponding minima occur at the time of northern summer. The diurnal 

 variation observed over the oceans is everywhere in phase when considered on a common- 

 time basis, except for a minor phase-shift that depends upon the season. This diurnal 

 variation derived from observations made on the Carnegie during 1915 to 1921 is given by 

 the Fourier expression 1 AP/P = 0.15 sin (0 + 186 ) + 0.03 sin (2d -+- 237 ) where 6 is 

 reckoned at 15 per hour beginning at o h Greenwich mean civil time. 



No general expression that will approximately characterize the diurnal variation over land 

 can b given. There variations determined by local factors are apparently superimposed 

 upon a variati a of the same world-wide character as that found to prevail over the oceans 

 [see reference (5)]. 



1 From revised calculations in unpublished manuscript of the Department of Terrestrial Magnetism. 



TABLE 749.— Atmospheric-Electric Data 



Smithsonian Tables 



