252 
DR. C. CHREE: DISCUSSION OF KEW MAGNETIC DATA 
Before leaving the subject, attention may be called to the remarkable difference 
between the phenomena exhibited in the case of 04 by the different elements. In D 
the ordinary day phase angle substantially exceeded the quiet day angle throughout 
the whole year, the excess being greatest in the equinoctial and least in the summer 
months. The excess in the mean diurnal inequality for the year represented about 
29lr minutes* of time. In H the ordinary day phase angle slightly exceeded the 
quiet day angle in summer, but fell notably short of it in winter, and in the diurnal 
inequality for the whole year was inferior to an extent representing about 6 minutes 
of time. In V the ordinary day phase angle substantially exceeded the quiet day 
angle throughout the year, the excess being greatest in the equinoctial and least in 
the winter months. In the mean diurnal inequality for the year the excess represented 
about 72 minutes of time. 
Wolf’s Formula. 
§ 23. If R denote the range of the mean diurnal inequality for the year, and S the 
sunspot frequency (after Wolf and Wolfek), the formula 
R = a+b S = a{l+(b/a)8}, .. . (l) 
with a and b constants, was found by Prof. Wolf to represent closely the variation of 
the declination range with sunspot frequency. It lias been applied by myself to the 
ranges of the other magnetic elements, and to the individual months or seasons of the 
year as well as to the whole year. In the case of the quiet day inequalities, the 
formula applied fairly to all the magnetic elements, being as closely true of H as 
of D. The value of b/a was, however, not the same for the different elements. Also, 
when the 12 months were treated separately, bja fluctuated from month to month, 
being greatest in winter and least in summer. 
The formula has now been applied in the case of both H and V to the diurnal 
inequalities from ordinary days, for the year, the seasons, and the individual 12 months. 
The results appear in Table XXXIII. ; ly is the unit in the case of a and b, and in the 
mean (numerical) difference between the values calculated by aid of the formula and 
those actually observed. While a and b are given respectively to 2 and to 4 places 
of decimals, so as to show the exact values employed in the calculated ranges, the 
last figure possesses little if any physical significance. Two sets of results are given for 
the year and the seasons. In the first set the values assigned to a and b are arithmetic 
means from the individual months included. The corresponding value given for b/a 
is derived from these mean values of a and b, and is not the arithmetic mean of the 
values of b/a for the individual months. The second set of figures refers to the diurnal 
inequalities calculated for the year and seasons. 
* There is a mistake in the description of Table XII. of my previous paper dealing with the declination. 
The data in it refer not to the seasonal inequalities, but to arithmetic means from the individual months 
comprised in the season. 
