232 
DR. C. CHREE: DISCUSSION OF KEW MAGNETIC DATA 
Mr. It. B. Sangster # is the approach which the diagram makes in the early afternoon 
hours to a straight line. This feature is prominent in the summer diagram between 
noon and 4 or 5 p.m. It is also fairly shown in the equinoctial diagram and in the 
diagrams for the year, especially that from sunspot maximum, hut hardly in 
the winter diagram. 
§ 14. Fig. 12 shows ordinary less quiet day difference curves, i.e., the ordinate 
represents the algebraic excess of the ordinary day over the corresponding quiet day 
value in the diurnal inequality. All the curves refer to the mean diurnal inequality 
for the year. In the case of V, T and I there is only one curve, which corresponds 
to the whole eleven years. In the case of H, N and W there are three curves, 
representing the sunspot maximum and minimum groups of years in addition 
to the whole eleven years. The results were not smooth enough to justify drawing 
curves of continuous curvature. The scale, which is the same for all the force curves, 
is much more open than in the corresponding ordinary day curves. 
In each case the ordinary less quiet day difference curve shows a considerable 
resemblance in type to the corresponding disturbed less quiet day difference curve 
given in a previous paper, but its amplitude is very much less. 
In the case of the H difference curves in fig. 12 the amplitude is so small that a 
longer period than eleven years would have been needed to bring out the character 
fully during the night hours. There is a distinct minimum in the curve near noon— 
signifying that the principal daily minimum is more developed in the ordinary than 
in the quiet day curve—but that is perhaps the only unmistakable feature. The 
irregularities in the sunspot maximum and minimum curves are too great to 
warrant deductions as to differences between them. 
The N, and still more the W, difference curves have a decidedly larger amplitude 
and are less irregular, especially the 11-year curves. The N difference curve has 
its mid-day minimum well developed, like the ordinary N curve, but it has a relatively 
better developed night maximum, and there seems to be no secondary maximum and 
minimum. 
The W difference curve differs markedly from both the ordinary and quiet day 
curves. There is no morning minimum near 8 a.m., as in the ordinary day curve, and 
instead of a sharply defined maximum in the early afternoon, there is a wide plateau 
for some four hours on either side of noon. The largest ordinate appears at 4 p.m., 
i.e., from two to three hours later than in the ordinary day curve. Whether the 
saddle near 1 p.m., which is more apparent in the sunspot maximum and minimum 
than in the 11-year curves, is a real or an accidental feature is open to some doubt. 
The V and T difference curves closely resemble one another, as might have been 
inferred from the fact that the difference between ordinary and quiet day inequalities 
is much larger for Y than for H. The two curves, while quite unlike the ordinary 
day Y and T curves, closely resemble the disturbed less quiet day V difference 
* ‘ Roy. Soc. Proc.,’ A, vol. 83, p. 428 
