224 
DR. C. C1IREE: ’ DISCUSSION OF KEW MAGNETIC DATA 
The arrest in the afternoon fall of I, it will be seen, is more prominent at sunspot 
minimum than at sunspot maximum. 
According to Table XIY., the December diurnal inequality in I has a decidedly 
smaller range than the January inequality, but the values of the A.D. for the two 
months are equal. In this case the August diurnal inequality markedly exceeds 
that for May, and is practically equal in amplitude to the June and July inequalities. 
The diminished amplitude of the May inequality in I is associated with the corre¬ 
sponding enhanced amplitude of the inequality in V. So far as amplitude is 
concerned, one would naturally group May with April, September and October. 
In amplitude March shows a closer approach to February than to x\pril; in type 
it stands about equidistant from the two adjacent months. 
§11. The graphical presentation of N and W diurnal inequalities, as given in 
Tables XYI. and XVII., is limited to the mean diurnal inequalities for the year from 
the eleven years and the groups of years of sunspot maximum and minimum. These 
are shown in the six uppermost curves of fig. 7. 
If we take the mean diurnal inequality for the year, the range in H is only about 
three-fifths that in D, while cos D is three times sin D. It follows from the last of 
equations (2) that the influence of the D diurnal changes on W will largely exceed 
that of the IT changes. Hence the diurnal inequality in W must show a fairly close 
approach in type to that in D. In the case of N the H diurnal changes exert more 
influence than the D changes, but the preponderance is less. As a matter of fact, 
however, there is a very close resemblance between the diurnal inequalities in H and 
N. The inequality in D if reversed has a considerable resemblance to that in H, and 
the contributions from H and D to the N diurnal inequality have opposite signs, so 
numerically they assist one another. 
It is pretty obvious, comparing figs. 1 to 7, that if we measured east-west changes 
positive to the east, instead of to the west, and I changes positive from instead of 
towards the vertical, the diurnal inequality curves for the year in all the six elements 
considered here, and in D as well, would agree in having as one of their most 
prominent features a principal minimum occurring within an hour or two of noon. 
According to Table XVI., the diurnal inequality in N is least in December, January 
coming next. June and July show the largest ranges, but there is little variation in 
that respect from April to September. August shows the largest A.D., April 
coming next. The six months April to September agree in having the maximum or 
principal maximum in the afternoon, while the other six months have it between 5 
and 7 a.m. 
Thus the phenomena in N rather favour the sub-division of the year into two 
seasons, each of six months. In March and October, however, while the forenoon 
maximum is the larger, it but very slightly exceeds the afternoon maximum, 
and the grouping of these months with the four midwinter months would be 
unsatisfactory. 
