282 DR. CHARLES CHREE: SOME PHENOMENA OF 



The corresponding disturbed days' data present irregularities which are presumably 

 due to the paucity of days. The figures strongly suggest that during the 11 years 

 October and April were less disturbed, but November more disturbed than usual ; 

 February seems also a little outstanding as compared to March. 



The 1 1 years contained few very large disturbances. The largest and smallest D 

 ranges included in the list,-455y (85''6) and 55y (10''3), both belong to March. The 

 former may have been surpassed on February 14, 1892, when the limit of registration 

 was exceeded. The 10' 4 3 range was exceptional. On 5 of the 12 months no range 

 under 1 OOy was included, and few ranges less than this occurred in the remaining 

 7 months. 



The H and V figures in Table V. go beyond those for D in representing October 

 and April as abnormally quiet, and December and January present very small ranges, 

 especially in V, as compared to the summer months. Table V. certainly suggests 

 that tin disturbed days the seasonal variation in the absolute ranges is much larger 

 in V and even in H than in D, but this wants confirmation from a more extended 

 enquiry. 



As regards the absolute size of the ranges in the three elements, the mean value 

 for D is the largest in every month, except July, and that for V is invariably the 

 least. The inference, however, that D is the most disturbed element would be 

 incorrect. It must be remembered that the regular diurnal inequality is greater in D 

 than in the other elements on undisturbed days. The ranges in the mean diurnal 

 inequalities for the year from the quiet days of 1890 to 1900 were 42'0y (7''90) in 

 D, and only 26 "2y in H, and 17'9y in V. Thus, relative to the ranges of the regular 

 diurnal inequality, the absolute ranges for H and V are not less but larger than the 

 ranges in D. Further, Table V. is derived from days in which the criterion of 

 disturbance was the character of the D curve alone. A good many days were 

 included amongst the 209 which would have been excluded if the criterion had been 

 disturbance in H or in V. 



A remarkable example of this is afforded by December 21, 1897. The range in D 

 was 103y (19''4), and that in H 86y, but the V trace to the eye appeared practically 

 a straight line. Under such circumstances one is very apt to miss the absolute 

 maximum and minimum, and the true absolute range may have slightly exceeded 

 the value 2y found by measurement. But, for all practical purposes, the inclusion of 

 this day amongst the disturbed simply tended to reduce the inequality range in V by 

 some 7 per cent. This was an extreme case the next smallest absolute range for V 

 being lly ; still amongst the 209 days there were an appreciable number, especially 

 in the winter months, which, so far as V was concerned, were essentially quiet days. 



Comparing the results from the whole number of disturbed days with those from 

 the 10 days a month of largest range, we see that the uniformity secured in the latter 

 case in the number of days, whilst reducing the variability amongst the days of each 

 month, increased on the whole the differences between the different months. The 



