BETWEEN SUN-SPOT FREQUENCY AND TERRESTRIAL MAGNETISM. 183 



37. Table XXV. gives the values of a, b, and b/a applicable to the monthly 

 means of the absolute daily ranges at Mauritius. The method of groups was 

 employed, the groups being as follows : 



The seasonal and yearly values of a and b are arithmetic means from the included 

 months, and these means are employed in calculating b/a. 



The values of b in Table XXV. fluctuate somewhat erratically from month to 

 month even for D, where 14 years' data are utilised. The exceptional features 

 presented by the September and October data in V had better be regarded pro- 

 visionally as accidental. 



In D and V we have b largest in winter and least at the equinox, a very remarkable 

 feature. 



Comparing Tables XXV. and XIII., we see that whilst the mean values of a for 

 the year are fairly similar, the values of b and of b/a at Mauritius are roughly only 

 from a half to a third of the corresponding values at Katharinenburg. 



TABLE XXV. Mauritius (Units 1' for D, ly for H and V). 

 Monthly Means of Absolute Daily llanges. 



