216 
DR. C. CHREE: MAGNETIC DECLINATION 
§ 12. Fig. 1 shows the mean diurnal inequalities for the year from the 11-year 
period for the ordinary and the disturbed days, with, for comparison, the corre¬ 
sponding inequality derived in A from quiet days. The difference between the 
ordinary and quiet day curves, though not large, is systematic. 
0 2 4 o 10 /W?i 2 4 Q> <5 10 12 
Fig. 
years of sunspot maximum and minimum, and between the inequalities in ordinary 
and quiet days for the year as a whole and the three seasons. The ordinates 
represent the excess in the westerly declination in years of sunspot maximum (or in 
ordinary days) over the declination at the same hour in years of sunspot minimum 
(or in quiet days). The difference curves for sunspot maximum and minimum are of 
the same general type as ordinary inequality curves; but the difference curves for 
ordinary and quiet days are of a totally distinct character. These latter curves are 
double peaked in equinox and summer, but show only one distinct maximum and 
minimum in winter. 
Fig. 3 gives difference curves in the case of the mean diurnal inequality for the 
whole year from disturbed, ordinary, and quiet day curves. The difference curves 
involving the disturbed days display a remarkably sudden rise and fall and are 
comparatively flat topped from 5 a.m. to 5 p.m. Disturbed and quiet days difference 
curves (not reproduced here) for winter, equinox, and summer all show this rapid rise 
and fall, and they are all fairly symmetrical with reference to the ordinate for noon. 
The summer curve has two well-marked maxima, with a secondary minimum near 
noon; even in the equinox the depression near noon is distinctly visible. 
