366 DK. C. CHREE: ANALYSIS OF RESULTS FROM THE KEW MAGNETOGRAPHS 
Declination. 
§ 22. A remark applicable to most if not all of the diurnal inequalities is that turning 
points, whether maxima or minima, which occur near noon are much less variable in 
the time of their appearance than those which occur early or late in the day. A 
particularly good instance of this is afforded by the chief maximum in D. It will be 
seen in Table XI. that the largest hourly value appears at 1 p.m. in 11 out of the 12 
months. The uniformity in the time of appearance of the maximum is perhaps even 
better shown in the curves in fig. 2, which represent the D inequality for December, 
March and June. In the 6 months, October to March, the D inequality shows two 
distinct maxima and minima, and in every month of the year, with the exception of 
September, Table XL shows at least a suggestion of a second maximum and minimum. 
There is in all months a well marked morning minimum which, except in January 
and Decemher, is the chief minimum of the day. Its time of occurrence shows a 
pronounced seasonal change, varying from 7 a.m. in summer to 9 a.w. in vfinter. 
This is well brought out in fig. 2, which also shows the rapid swing from east to west 
between 9 a.m. and 1 p.m. so characteristic of the declination needle. It would 
require a very large numl;er of years’ records, and possibly the employment of 
greater sensitiveness, to settle defi 2 iitely the times of occurrence of the second 
maximum and minimum, and to place their occurrence or non-occurrence in summer 
in a position of certainty. 
In the mean inequality for the year, we have the somewhat curious phenomenon 
of a maximum and minimum presenting themselves at adjacent hours, viz., 1 a.m. 
and midnight. As this occurs in the inequalities for the two sub-groups of years, 
as well as in that for the whole period, it is presumably a natural phenomenon. 
It will be noticed that though the amplitudes of the mean inequalities for the 
year are widely diflTerent for the two groups of years, the hours of occurrence of the 
maxima and minima are alike. A minute comparison of the figures shows, however, 
a slight tendency for definite features of the inequality to be later in the day in the 
case of the second group of years (sun-spot maximum). More definite evidence in 
this point is adduced later (see § 46). 
The month of the year in which the amplitude of the inequality is least is 
unmistakably December, but the ranges for January, February and November are 
also very small. There is a very rapid increase of range in March, and correspond¬ 
ingly rapid decrease in October, whilst in the six months April to September there is 
comparatively little change. The sum of the 24 hourly differences, however, is 
decidedly less for April and September than for the four mid-summer fnonths. The 
range appears slightly larger in May and August than in June and July, so that 
the annual variation of the range seemingly presents two nearly equal maxima, 
respectively in early and late summer, with an intermediate inconspicuous minimum 
at midsummer, and a very prominent minimum at midwinter. 
