Oct. 4, 1021 proceedings: phii.osophicai, society 309 



the time when the Earth's north magnetic pole, for example, 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 degrees. These correlations support the 

 assumptions of various investigators that the Earth's electric charge and re- 

 sultant field may be very intimately related to an electric radiation from the 

 Sun. 



A more complete summary will appear in the current volume of Terrestrial 

 Magnetism and Atmospheric Electricity. The paper was discussed by Messrs. 

 C. A. Briggs, White, and Humphreys. 



The third paper, on New relations between terrestrial magnetism, terrestrial 

 electricity, and solar activity was presented by L. A. Bauer and was illustrated. 



Connections between sun-spot activity, disturbances of the Earth's magne- 

 tism, earth-currents, and polar lights have been worked out by various in- 

 vestigators. The recent severe magnetic disturbances and earth-currents 

 which accompanied a week ago the remarkable sunspot activity and brilliant 

 display of polar lights have drawn renewed attention to the relationships 

 between these four classes of natural phenomena. 



The present paper shows that there is a fifth natural phenomenon — atmos- 

 pheric electricity — with which an interesting and suggestive relationship with 

 solar activity is exhibited. Owing to the many disturbances to which the 

 atmospheric-electric elements are subject, as for example during cloudy and 

 rainy weather, it has been difficult to establish the existence of definite varia- 

 tions of the chief atmospheric-electric elements during the well-known sun- 

 spot cycle of somewhat over 11 years than in the case of magnetic effects, 

 earth currents, and polar lights. The new results found are based upon 

 atmospheric electric data obtained chiefly at four European observatories 

 between 189rS and 1910, the combined data, in the case of the potential grad- 

 ient, thus covering about two sun-spot cycles. Recent observations on board 

 the Carnegie indicate a decrease in the electric potential -gradient since 1017, 

 when sun-spot activity was at a maximum. 



The following chief facts have resulted : 



(1) The Earth's average intensity of magnetism, as well as the strength of 

 the normal electric currents circulating in the Earth's crust, suffers a diminu- 

 tion during increased solar activity, i.e., the currents induced in the Earth 

 during periods of increased solar activity are in general reversed in direction 

 to the normal currents, the strength of these superposed currents increasing 

 with increased solar activity. The diurnal range of the strength of the 

 normal earth currents, as in the case of the diurnal range of the Earth's 

 magnetic elements, increases with increased sun-spot activity. 



(2) The atmospheric potential gradient, or the deduced negative charge on 

 the surface of the Earth, increases with increased solar activity, the range in 

 the variation between minimum and maximum sun-spot activity being about 

 20 per cent. The electric conductivity of the atmosphere, on the other hand, 

 shows but little, if any, systematic variation during the sun-spot cycle. Ac- 

 cordingly, since the vertical conduction current of atmospheric electricity is 

 derived from the product of the potential-gradient and the electric conductiv- 

 ity, it is found that this vertical current increases in strength with increased 

 solar activity. It would thus appear that atmospheric electricity, like ter- 

 restrial magnetism, is controlled by cosmic factors. The results derived 

 here may have an important bearing upon theories of atmospheric electricity. 



(3) Instead of using for short periods, as for example a month, the sun- 



