350 CARNEGIE INSTITUTION OF WASHINGTON. 



current of atmospheric electricity is derived from the product of the poten- 

 tial gradient and the electric conductivity, it is found that this vertical cur- 

 rent also increases in strength with increased solar activity. It would thus 

 appear that atmospheric electricity, like terrestrial magnetism, is controlled 

 by cosmic factors. The results derived here may have an important bearing 

 upon theories of atmospheric electricity. 



e. The diurnal range of the electric potential-gradient, as deduced from the 

 observations on the electrically calm days made at the Observatorio del 

 Ebro, Tortosa, Spain, 1910-1919, is found to increase with solar activity; the 

 minimum occurred in 1911 and the maximum in 1917, whereas the sun-spot 

 minimum occurred in 1912 and the maximum in 1917. The range between 

 minimum and maximum diurnal range is about 25 per cent. (It appears 

 probalile that the fact just stated for the potential-gradient will also be found 

 true for the vertical conduction-current.) 



New measures of solar activity and the "Earth-effect. "^ Louis A. Bauer. 



Various measures (sun-spot frequencies, sun-spot areas, faculse, promi- 

 nences, flocculi, etc.) have been used, with greater or less success, by previous 

 investigators of the relations between solar activity and geophysical phe- 

 nomena, especially as regards the Earth's magnetic fluctuations. When the 

 comparisons are made for intervals of a year, for example with the aid of an- 

 nual means, a striking parallelism is, in general, exhibited between solar 

 activity and activity of the Earth's magnetism. If, however, comparisons 

 are attempted for shorter intervals, a month, a week, or a day, then the dis- 

 cordances between the solar curve and the magnetic curve are so pronounced 

 as to have led several eminent investigators to express doubt as to a direct 

 relationship between the two sets of phenomena. 



The measures of solar activity most frequently employed in such compari- 

 sons are the well-known Wolf-Wolfer relative sun-spot numbers, as they are 

 the most readily available systematic data. The author in his investigations, 

 extending over a period of about 20 years, has tried every measure of solar 

 activity available. As the combined result to date it is found that, in general, 

 the most successful measure of that kind of solar activity, of special interest 

 here, is a quantity indicative of the amount of variahility of sun-spottedness 

 during a given period. For example, instead of taking the sun-spot numbers 

 direct for comparison with magnetic or electric fluctuations, take the 

 range {R) in the sun-spot numbers per month, or, still better, the average 

 departure (D) of the daily sun-spot numbers from their monthly mean, irre- 

 spective of sign. Such R and D measures of solar activity are also being 

 derived from the published Greenwich areas of sun-spots and faculse, in order 

 to see whether any further improvement may be made. At times our new 

 measures may be usefully supplemented with the aid of prominence-data. 



It is also of interest to mention here the following significant result: The 

 D and R measures of solar activity derived first from the Wolfer sun-spot 

 numbers for 1919 and 1920, and second from the series of solar-constant values, 

 obtained by the Smithsonian Institution at Calama, Chile, for the same two 

 years show a very satisfactory general agreement, especially after the first 

 half of 1919, when observational methods for determining the solar-constant 

 values had been improved. 



Various slides were exhibited showing close relationships between the new 

 measures of solar activity, terrestrial magnetism, earth-currents, polar lights, 

 and atmospheric electricity, not only year by year, but also month by month, 



'Abstract of paper presented before the American Astronomical Society, Middletown, Con- 

 necticut, August 30, 1921. See also Terr. Mag., vol. 26, 113-115 (September 1921). 



