AT KEW OBSERVATORY, 1890 TO 1900. 
219 
Diurnal Inequality. Fourier Coefficients. 
jjj 13. The diurnal inequality was analysed in the usual way in a series 
c x sin (t + a i) +c 2 sin (2£ + a 2 ) + ..., 
where t is time counted from midnight (G.M.T.), one hour being taken as equiva¬ 
lent to 15°. Thus c x , c 2 , c 3 , c 4 , denote the amplitudes, a l5 a 2 , a 3 , and a 4 the phase 
angles of the terms whose periods are respectively 24, 12, 8, and G hours. The 
object of such an analysis is to provide a ready means of tracing affinities and 
differences between different stations at the same season, and between different 
seasons at the same station. The most instructive way of presenting the facts is 
probably to show side by side the corresponding results for the different types of 
years and for the different kinds of days. 
Table VII. contrasts the amplitudes of the 24- and 12-hour terms from ordinary 
and disturbed days for each month of the year. Similar complete results were 
calculated for the 8- and 6-hour terms, but only those for ordinary days from the 
11-year period are included. A complete set of seasonal values are, however, given 
Table VII.—Diurnal Inequality. Fourier Coefficients. Amplitudes. 
♦ 
Cl- 
C 2 . 
C3 • 
c 4 . 
Ordinary days. 
Disturbed 
days. 
Ordinary days. 
Disturbed 
days. 
Ordinary 
days. 
Ordinary 
days. 
Sun¬ 
spot 
mini¬ 
mum. 
11 
years. 
Sun¬ 
spot 
maxi¬ 
mum. 
11 
years. 
Sun¬ 
spot 
mini¬ 
mum. 
11 
years. 
Sun¬ 
spot 
maxi¬ 
mum. 
11 
years. 
11 
years. 
11 
years. 
January . 
1-44 
1-79 
/ 
2-17 
/ 
4-27 
1 
0-66 
0-86 
1-03 
/ 
1-27 
/ 
0-41 
0-27 
February . . . 
1-73 
2-41 
3-17 
4-49 
0-84 
I'll 
1-35 
1-25 
0-57 
0-30 
March.... 
2-25 
3-05 
3-73 
6-26 
1-65 
1-98 
2-32 
2-29 
1-11 
0'45 
April .... 
2-61 
3-35 
4-06 
7-03 
2-08 
2-48 
2'91 
2-87 
1-17 
0'39 
May .... 
2-81 
3-57 
4-36 
6-73 
2-00 
2-38 
2-75 
1-79 
0-87 
0-17 
June .... 
3-19 
3-83 
4-62 
5-89 
2-18 
2-39 
2-81 
0-05 
0-74 
0-05 
July .... 
2-97 
3-72 
4-45 
5-01 
1-95 
2-30 
2-61 
2-09 
0'77 
0-11 
August . . . 
3-06 
3-64 
4-15 
4-47 
2-14 
2-43 
2-79 
2-94 
1-05 
0-18 
September . . 
2-74 
3-35 
3-94 
5-42 
1-74 
2-02 
2-27 
2'58 
1-04 
0-35 
October . 
2-09 
2-69 
3-39 
4-55 
1-42 
1-69 
1-92 
2-38 
0-92 
0-48 
November . . 
1-44 
1-94 
2-28 
4-90 
0-88 
1-06 
1-30 
1-71 
0-51 
0-32 
December. 
1-14 
1 -61 
2-06 
4-17 
0-75 
0-81 
0-94 
1-35 
0-35 
0-20 
Arithmetic 1 
means . J 
2-29 
2-91 
3-53 
5-27 
1-52 
o 
1-79 
2-08 
1-88 
0-79 
0-27 
2 f 2 
