AT KEW OBSERVATORY, 1890 TO 1900. 
215 
In the case of the ordinary days a double daily period is always clearly apparent 
in winter; but this tends to disappear in the equinoctial months, especially in years 
of sunspot maximum, and it is not recognisable in summer, even in the years of sun¬ 
spot minimum. 
§ 11. Table VI. gives the range of the diurnal inequality on ordinary days—still 
from hourly readings—for each individual month of the eleven years. It is instruc¬ 
tive to compare the monthly means in Table VI. with the corresponding ranges in 
Table VI.—Diurnal Inequality Ranges from Ordinary Days. 
S 
>> 
c3 
g 
March. 
April. 
May. 
J une. 
July. 
August. 
September. 
O 
o 
o 
O 
November. 
<D 
<D 
O 
o 
M 
Yearly 
means. 
1890 
/ 
4-40 
5-11 
7-94 
' 
9-66 
/ 
8-56 
/ 
9-10 
8-82 
9-44 
8-61 
6-93 
/ 
5-28 
f 
3-94 
/ 
7-32 
1891 
4-27 
5-07 
8-36 
10-35 
11-37 
9-99 
11-23 
10-85 
9-69 
9-13 
6-83 
4-64 
8-48 
1892 
6-02 
8-09 
10-79 
11-88 
11-96 
12-15 
11 • 92 
12-67 
10-60 
9-99 
6-01 
6-10 
9-85 
1893 
5-90 
7-99 
11-84 
14-40 
13-31 
13-87 
13-05 
14-36 
12-09 
9-97 
6-66 
5-39 
10-74 
1894 
5-70 
7-67 
10-47 
12-97 
12-43 
11-92 
12-11 
12-90 
11-22 
8-87 
6-26 
5-06 
9-80 
1895 
5-60 
7-40 
9-56 
12-57 
12-73 
14-11 
12-66 
10-71 
9-85 
7-78 
6-16 
5-38 
9-54 
1896 
6-24 
7 ■ 55 
10-11 
11*30 
9-79 
10-06 
10-52 
10-90 
9-89 
6 • 76 
4-68 
4-21 
8-50 
1897 
4- 54 
5-39 
8-88 
10-23 
9-88 
9-68 
9-62 
10-27 
8-52 
6-48 
5-36 
4-22 
7-76 
1898 
4-58 
5-49 
7-83 
9-02 
9-90 
10-15 
9-64 
9-84 
8-33 
7-08 
4-99 
4-22- 
7-59 
1899 
4-16 
4-73 
7-54 
9-46 
9-40 
9-88 
8-53 
9-72 
9-16 
6-71 
4-49 
3-80 
7-30 
1900 
4-14 
4-61 
7-15 
8-64 
8-44 
9-40 
9-15 
9-52 
7-66 
6 - 52 
3-53 
3-25 
6-83 
i 
Monthly 1 
means J 
5 - 05 
6-28 
9-13 
10-95 
10-71 
10-94 
10-66 
11-02 
9-60 
OO 
5-48 
4-56 
8 ■ 52 
1 
Tables III. and V. The observational data are exactly the same, and at first sight it 
may appear strange that the mean ranges in Table VI. are as a rule not equal to but 
greater than the ranges in Table III. This is due simply to the fact that the hours 
of maxima and minima vary slightly from year to year. The greater this variation 
the more does the mean in Table VI. exceed that in Table III. On the average of 
the 12 months the mean range in Table VI. is almost exactly 1 per cent, greater than 
that in Table III., but the ratio of the two ranges is notably largest in winter, varying 
from D03 in January to 1 '00 in April, June and August. 
If we compare the arithmetic mean of the 132 ranges of Table VI. with the range 
in the mean diurnal inequality for the year in Table V. from the 11-year period, we 
find that the former is 6 per cent, the larger. This shows that the variability with 
the season of the year in the hours of maximum and minimum is greater than is the 
variability for the same month of the year in different years. 
