330 CARNEGIE INSTITUTION OF WASHINGTON. 



Solar Radiation and Terrestrial Magnetism. L. A. Bauer. Terr. Mag., vol. 20 (Dec. 1915). 



This paper was presented at the special meeting on atmospheric physics of 

 section B of the American Association for the Advancement of Science, at San 

 Francisco, August 5, 1915. Doubtless the chief instruments of research from 

 which we may expect definite knowledge respecting certain salient physical 

 characteristics of the highest levels of the atmosphere are the self-recording 

 instruments installed at magnetic observatories for the purpose of registering 

 the countless fluctuations to which the Earth's sensitive magnetic field is 

 continually subject. The paper, in the first paragraphs, shows the role which 

 certain terrestrial-magnetic phenomena may play in opening up to us the 

 possible electrical conditions which must obtain in atmospheric regions 100 

 kilometers and more above the surface, as shown bj^ the researches of Schuster, 

 Birkeland, Stoermer, and Chapman. 



Special attention is next paid to the conclusions rlerived from refined mag- 

 netic observations made during periods of increased or decreased solar radia- 

 tion, as, for example, during times of total solar eclipses, or from a concomitant 

 study of magnetic variations and of variations in the solar constant, as shown 

 by Abbot's observations. The bearing of a certain class of magnetic disturb- 

 ances, usually recorded only at observatories in the daylight zone, on the ques- 

 tion of the magnitude and duration of variations in the solar radiation, is 

 discussed in this connection, and it is indicated how magnetic instrmnents may 

 effectively supplement other appliances in the detection and measurement of 

 solar radiations of various kinds. 



In continuation of the author's investigations, described on pages 323 and 

 324 of the Annual Report for 1914, an account is then given of the results of a 

 reexamination of the question as to possible changes in the Earth's magnetism 

 which correspond to changes in solar radiation. The solar data used for this 

 purpose are Abbot's values of the solar constant observed at Mount Wilson, 

 California, in 1913, and courteously supplied by him in manuscript in advance 

 of publication. The magnetic data are those furnished by courtesy of the 

 Superintendent of the Coast and Geodetic Survey and apply to the 1913 

 observations at the stations: Vieques (Porto Rico), Cheltenham (Maryland), 

 Tucson (Arizona), Sitka (Alaska), and Honolulu (Hawaii). Furthermore, 

 there are utilized the 1913 published data for the magnetic observatories at 

 Pola, Potsdam, and Del Ebro. 



The provisional results for 1913 confirm those for 1911 and 1912. Thus it is 

 found that a 1 per cent decrease in the solar-constant values for 1913 would 

 correspond to an increase in the "local magnetic constant" of 0.002 per cent 

 of its value. 



It is next shown that, as far as may be concluded from the available data 

 for 1913, in about 82 per cent of the cases decreased solar radiation is accom- 

 panied by decreased range in the diurnal variation of the Earth's magnetism. 

 A 1 per cent decrease in the solar constant corresponds to a decrease of about 

 1 per cent in the range of the diurnal magnetic variation. 



The proportional magnetic changes associated apparently with a 10 per cent 

 change in the solar constant are of the same general order of magnitude and of 

 the same general sense as those which have occurred during certain total solar 

 eclipses. 



The daily non-cyclic changes in the Earth's magnetism, as found on mag- 

 netically-quiet days by previous investigators, furnish an additional check on 

 the foregoing results, their quantities harmonizing completely both as regards 

 sign and magnitude with those given here. It is found that on consecutive 

 quiet days the magnetic constant is, on the average, larger on the second day 

 than on the first, the increase being equal to that which would be caused by 



