BETWEEN SUN-SPOT FREQUENCY AND TERRESTEIAL MAGNETISM. 185 



TABLE XXVII. Mauritius (Units 1' for I), l y for H and V). 



Observed Less Calculated Values. 



Summary. 



40. A slight progressive decrease in a and increase in b in the sun-spot formula 

 (1) is suggested by the Greenwich D and H data from 1841 to 1896, but this does 

 not meet with support from Signor RAJNA'S analysis of D ranges at Milan from 1836 

 to 1894. In both cases there is an element of uncertainty, arising from want ot 

 homogeneousness in the data. 



According to RAJNA'S earlier data, values of a, and to a lesser extent values of b, 

 calculated from periods as long as 14 years may differ very sensibly from those 

 calculated from longer periods, but differences of this kind seem to have diminished 

 since observations became more homogeneous and are probably ascribable in part to 

 observational uncertainties. 



VOL. CCIII. A. 2 B 



