82 
DR. C. CHREE: SOME PHENOMENA OF SUNSPOTS AND OP 
Taking the numerical sums of the percentage figures from the large and small spot 
area groups separately, we find 
(H sums)/(D sums) = 179 from days of large spot area, 
„ „ = 1'63 „ „ „ small „ „ . 
This makes the phenomenon some 70 per cent, larger in H than in D, and so more 
than justifies our anticipations. 
§ 8. In the majority of the earlier investigations use was made of 10-day groups 
selected by reference to the size of the absolute daily range. In the investigations 
now to he described it was decided to employ 5-day groups, and to make the 
Greenwich projected sunspot area the criterion for selection. It had become obvious 
that the number of days preceding and following the representative day 
must be largely increased, if one wished to ascertain the true nature of the 
phenomenon, and it was obvious that the arithmetical operations would thus become 
exceedingly heavy, even with 5-day groups. Experience had also shown that the 
5 days of largest spot area in a month were not infrequently consecutive, while this was 
hardly ever the case for the 10 days of largest area. Thus 5 appeared a more natural 
number than 10, while the fact that the majority of the 5 days often occurred in a 
sequence led to a marked economy of time in entering the data in the several columns. 
The main reason for preferring the spot area as the criterion for grouping the days 
was that it promised to facilitate the comparison of results from difterent stations, and 
the comparison of results from difierent elements at the same station. The numerical 
results for the sunspot areas for the groups of days of the present investigation will 
obviously serve for any similar investigation dealing with the same period of years. 
One slight drawback to sunspot areas as the criterion of selection is the absence 
of spot areas for a few days in the Greenwich publications. In these cases the day 
for which information was lacking was disregarded when selecting the 5 days of large 
(or small) spot area; but when it occurred in any column (other, of course, than n) it 
had assigned to it the arithmetic mean of the areas for the two adjacent days. 
There were a few days for which Kew H ranges were lacking. The gaps were 
filled up by reference to the Falmouth curves, with the exception of one occasion when 
the traces at both Kew and Falmouth got off the sheet. The range for that day was 
taken as if the curve stopped at the edge of the sheet. Judging by the appearance 
of the curves, the consequent underestimate of the range was not serious. 
It was decided to take 15 days before and 15 after each selected day. Thus, calling 
the representative day n, there were 31 columns of figures extending from day 
76 — 15 to day 76-1-15. 
There was one month in 1890 and one in 1900 when the days showing measureable 
sunspot areas numbered less than 5. These two months were omitted, leaving in all 
130. The investigation relating to the 5 days a month of largest spot area thus in¬ 
cluded the treatment of 130 x 31 x 5, or 20150, H ranges and as many sunspot areas. 
