198 



Dr. C. Chree. On the Relationship between [Feb. 8, 



" An Inquiry into the Nature of the Eelationship between Sun- 

 spot Frequency aud Terrestrial Magnetism." By C. Chree, 

 Sc.D., LL.D., F.RS. Eeceived February 8 — Eead March 3, 

 1904. 



(Abstract.) 



§ 1. The formula' 



E = d + bS (1), 



where E is some magnetic quantity such as the amplitude of the 

 diurnal oscillation of the needle, a and b constants, and S sunspot 

 frequency (after Wolf and Wolfer), was first applied by Wolf to the 

 mean declination range throughout the year. 



In a recent paper,* mainly devoted to other subjects, I applied 

 it to the ranges, and the sum of the 24 hourly differences from the 

 mean for the day, in the mean monthly and annual diurnal inequalities 

 of declination, inclination, horizontal force, and vertical force at Kew. 

 Some analogous results were also given for Wilhelmshaven, Potsdam, 

 and Pare St. Maur. 



The present paper is entirely devoted to the connection between 

 sunspot frequency and terrestrial magnetism. It deals with data from 

 Milan (1836—1901), Greenwich (1841— 96), Pawlowsh and Katharinen- 

 burg (1890—1900), Batavia (1887—98), and Mauritius (1875—90). 

 It aims at ascertaining wherein the results in my previous paper are 

 peculiar to the station or period (chiefly 1890 — 1900) dealt with. 



It investigates what differences may exist between the sunspot 

 connection on ordinary days and on magnetically quiet days, and 

 what differences arise when one applies (1) to the mean of the 

 differences between the absolutely highest and lowest daily readings, 

 instead of to the range of the mean diurnal inequality. It also 

 considers various measures of the magnetically disturbed character of 

 the year, and their relation to sunspot frequency. 



§ 2. The inquiry into the influence of the period selected on the 

 values of a and b in (1) is based on the above-mentioned Milan and 

 Greenwich results, due respectively to Signor Eajna and Mr. Ellis. 

 In both cases, unfortunately, there is a want of strict homogeneity in 

 the earlier data. The Greenwich data suggest a slight progressive 

 increase in bja during the last 60 years in the case both of declination 

 and horizontal force ; but this is not confirmed by the Milan results. 

 The values, however, obtained from bja in the case of the declination 

 range at Milan from the two periods 1837 — 50 and 1854—67 are, the 

 one 28 per cent, below, the other 12 per cent, above the value obtained 

 by Eajna for the period 1836 — 94. In more recent years there is less 

 apparent irregularity in the magnetic and sunspot relation. This 



* ' Phil. Trans.,' A, vol. 202, p. 335. 



