FROM ORDINARY DAYS OF THE ELEVEN YEARS 1890 TO 1900. 
2 HI 
and afternoon maximum is less for Y than for H, and, speaking generally, the 
preponderance in changes by day over those by night is greater in V. A further 
notable difference is that the season in which the double maximum and minimum are 
most in evidence is summer for Y, but winter for H. Also the secondary maximum 
in the forenoon is in Y most prominent at sunspot maximum, while in H it is most 
prominent at sunspot minimum. In winter the changes during the night hours are 
exceedingly slow in Y as in H ; but while the fall to the forenoon minimum is the 
conspicuous feature in H, it is the rise after the morning minimum that stands out in 
Y. The minimum amplitude occurs as distinctly in December and January for V as 
for H. In Y the lower value is found in December, both in sunspot maximum and 
minimum, especially the latter, again a difference from what we found in H. The 
smallness of the amplitude in Y in December at sunspot minimum was, however, in 
considerable measure due to one year, 1890. During the last three months of that 
year the changes apparent in the Y curves, regular and irregular alike, became so 
small that some defect in the magnetograph was suspected at the time, and the Y 
data in the tables published in the Annual Report of the Kew Committee were 
confined to the first nine months of the year. There was, however, nothing but the 
smallness of the movements to suggest instrumental defect, and as the movements 
rapidly increased in 1891, without anything being done to the instrument, and the 
scale value determination showed nothing abnormal, the phenomenon was presumably 
real, and not of instrumental origin. As regards the month when the Y inequality 
is largest, the decision depends upon what we accept as the criterion of amplitude. 
May comes distinctly first if we take the range, but if we take the A.D. July comes 
first in the case of the eleven years, and still more so in the case of the sunspot 
maximum group of years. August falls markedly short of the other summer months, 
and is inferior even to April. 
Table XII. shows that in Y, as in H, 1890 and 1900 were the years when the 
amplitude of the inequality was least; 1893, however, the year of sunspot maximum, 
was not the year of largest amplitude in Y, being exceeded by 1892 and 1894, which 
were also much more disturbed. The difference in amplitude between years of many 
and few sunspots is less conspicuous in Table XII. than in Table VIII., and, as will be 
seen more clearly later, the parallelism between the amplitude of the inequality range 
and the development of sunspots was not so close in A as in H. A\ hether this last 
is a real natural phenomenon, independent of the lesser reliability of the A data in 
respect especially of temperature correction, is perhaps open to some doubt. 
§ 9. If we write the first of equations (2), p. 198, in the form 
T AT = H AH + V AY, 
and remember that at Kew V = 2‘4H roughly, while the range of the diurnal 
inequality in V is about three-fourths that in H, we see at once that so far as diurnal 
changes are concerned, the influence of Y on T very considerably exceeds that of IT. 
2 H 
VOL. CCXVI.—A. 
