182 DE. C. CHREE: AN ENQUIRY INTO THE NATURE OF THE RELATIONSHIP 



On examining the tables, I found that the mean D ranges in 1881 and 1882 years 

 of fairly large sun-spot frequency showed a remarkable depression, being only about 

 half those in 1880 and 1883, and in the preface I found the following editorial 

 reference to some readjustment of the declination magnetograph in December, 1882 : 

 "In the latter part of the year 1882 the effect of torsion on the magnetograph is 

 very pronounced." As the phenomenal smallness of the range seems to have ceased 

 with the readjustment, and as the Milan and Greenwich records show no parallel to 

 the reduction of the ranges in 1881 and 1882, I have omitted these years entirely 

 from the calculations. 



The Mauritius publication gives in special detail the mean value for each month 

 and year of the absolute daily ranges. These ranges seem based entirely on hourly 

 readings, and so are not absolutely equivalent to the Katharinenburg ranges dealt 

 with in Table XIII. 



As the variation in these daily ranges throughout the year has exceptional features, 

 I give particulars in Table XXIV. There is a resemblance to phenomena at Batavia. 

 In D the variation in the range, though much less conspicuous than in Northern 

 Europe, is well marked ; the vahies for the three midwinter months May, June, 

 and July are well below the average. In H the variation is small, and somewhat 

 irregular ; on the whole, the range is smallest in winter, from May to August, but 

 the next lowest values appear in February and December. 



There is a distinct reduction in the V range near midwinter, but a very similar 

 reduction occurs at midsummer. 



TABLE XXIV. Mauritius (Units 1' for I), ly for H and V). 

 Monthly Means of Absolute Daily Ranges. 



