234 
DR. C. CHREE: MAGNETIC DECLINATION 
element which takes part in the annual variation—is in all cases less for the ordinary 
than for the quiet days. P 2 , on the contrary, distinctly increases as we pass from 
quiet to ordinary days, and sometimes in a larger proportion than M. The import¬ 
ance of the 6-month term as compared to the 12-month term is thus, in general, 
notably greater for the ordinary than the quiet days. It seems specially great for 
the disturbed days. 
Pj and P 2 both rise with increase in sunspot frequency, but P x increases less 
relatively than M, and Pi/M falls notably. 
We thus see that, relative to the mean value of the element, the term whose period 
is 12 months is most conspicuous on quiet days and when sunspots are few. 
Coming to the phase, as I have pointed out before, 0 1 and 0 2 for quiet days both 
increase with sunspot frequency, i.e. the times of occurrence of the maxima are 
earlier for both the 12-month and 6-month terms in years of sunspot maximum than 
in years of sunspot minimum. The value of 0 1 for ordinary days exhibits the same 
phenomenon, but to an enhanced degree. Taking the 24 differences, the inequality 
range, and c 1; the mean difference in time was only 3'4 days in the case of the quiet 
days, whereas for the ordinary days the mean difference in time from the 24 differ¬ 
ences and (q is 8'9 days. Ordinary days show, however, a diminution in 0 2 , or a 
retardation of phase in the 6-month term, as we pass from sunspot minimum to 
sunspot maximum. 
Comparing ordinary and quiet day phases, we find that 0 X is greater for the former, 
except in years of sunspot minimum. Taking a mean from the 11-year data for the 
24 differences, the inequality range, and c u the maximum in the 12-month term 
occurs 3T days earlier for the ordinary than the quiet days. The advance of phase is 
still more notable in the cases of C] from disturbed days, and of the absolute range 
from all days. The results for the influence of disturbance on 0 2 appear somewhat 
contradictory. 
Sunspot Relationships. 
§ 25. In the previous part of the paper there have been a number of references to 
sunspot frequency, but all with the object of illustrating the differences that exist 
between the phenomena of different years. The remainder of the paper is exclusively 
devoted to a study of the sunspot relationship, but from a somewhat different point 
of view. 
In A, I investigated whether the average sunspot frequency after Wolfer was less 
for the Astronomer Royal’s quiet days than for days as a whole. The quiet days 
are practically free from magnetic disturbance, thus, if disturbance is intimately 
connected with the simultaneous sunspot frequency, one would expect the mean 
sunspot frequency from the quiet days of a month to be notably less than that from 
the month as a whole. The comparison was made for the ] 1 years 1890 to 1900 
(A, pp, 433, 434), and showed that if any real difference existed between sunspot 
