200 On Sunspot Frequency and Terrestrial Magnetism. [Feb. 8 r 



a and b, and the corresponding value of b/a for Greenwich and some- 

 other stations. Here, as in Table I, the data relate to the mean 

 diurnal inequality. The units are the same as in Table I. 



§ 5. For comparison with Table I, I give in Table III results 

 applicable to the mean value for the year of the absolute daily ranges 

 (taken from individual days irrespective of the hours of occurrence of 

 the maximum and minimum). The units are as before : — 



Table III. 



Place. 



Declination. 



Horizontal 

 force. 



Vertical 

 force. 



a. 



10 4 6. 





a. 



10 3 6. 



10 4 6/a. 



a. 







11 -3 



1130 



100 



45 -2 



636 



141 



17 -6 



520 295 



Katharinenburg. 



8 -00 



652 



82 



30 -7 



366 



119 



14 -6 



248 \ 171 





5 -53 



255 



46 



30 -4 



186 



61 



16 "2 



84 52 



1 



The large increase in the values of both a and b as compared to- 

 Table I will be noted. Except at Mauritius, the values of b/a for 

 declination and horizontal force are considerably greater in Table III 

 than in Table I. There seems, in fact, a general tendency for b/a to 

 increase as we pass from a quantity, such as the range of a diurnal 

 inequality, which is comparatively independent of disturbances, to a 

 quantity such as the mean absolute daily range, which is largely 

 dependent on disturbances. Formula (1) becomes, however, less and 

 less strictly applicable, the more disturbed the magnetic quantity to- 

 which it is applied. When we consider quantities such as the mean 

 of the 12 monthly ranges (maximum and minimum for the month), or 

 the annual range (maximum and minimum for the year), we find large 

 differences between observed values and those calculated from (1). In. 

 all the stations considered, 1893, though a year of absolute sunspot 

 maximum, was much less disturbed than 1892. At Pawlowsk and 

 Katharinenburg 1893 might fairly be termed a quiet year, while 1892' 

 and 1894 were largely and persistently disturbed. 



In the case of ranges from mean diurnal inequalities for the year, 

 the agreement between observed and calculated values is about equally 

 good at Pawlowsk, Katharinenburg, Batavia, and Kew. In the ease- 

 of declination, the mean difference between observed and calculated 

 values is about 4 per cent, of the mean value of the range during the 

 period dealt with. On the whole, the agreement is distinctly less good 

 in the case of vertical force than in the case of declination, inclination 

 or horizontal force. 



