388 DE. C. CHEEE: ANALYSIS OF EESULTS FROM THE KEW MAGNETOGEAPHS 
§ 33. The mode of variation of the c coefficients throughout the year is of 
importance, as its comparison with other phenomena seems one of the most promising 
methods of investigating the source of diurnal inequality. To facilitate inter¬ 
comparisons, I have expressed each monthly value of a “ c ” as a percentage of the 
mean value for the 12 months. The results appear in Tables XXIV. and XXY. The 
tables give also percentage values for the three seasons; these are based on the 
seasonal diurnal inequalities, 100 representing in their case the arithmetic mean 
of the values for the three seasons. The mode of annual variation of the c’s is also 
shown graphically in figs. 16 and 17. 
It will be readily seen, either from the tables or the curves, that the mode of 
variation of corresponding c coefficients is fairly similar in all the elements. The 
coefficient has an annual variation very similar to that shown by the range of the 
diurnal inequality (see Table XVIII.). There is the same very pronounced minimum 
at midwinter, with at least a suggestion of two nearly equal maxima in summer. 
The annual variation in c, is fairly similar to that in c^, but the existence of a 
secondary minimum in summer is usually indicated more clearly. In Cg the summer 
minimum is prominent, and in it is in some cases the chief minimum of the year. 
The two maxima in Cg and are very prominent, and the interval between their 
occurrence is so much greater than in c, or that they fall approximately at the 
equinoxes. This question is further dealt with in § 37. 
Table XXIV.—Variation of Fourier Coefficients throughout the Year. 
Kew, 11 Years. 
1 
Declination. 
Horizontal force. 
f’l- 
C2. 
O- 
Ci. 
Cl. 
C-2. 
O- 
O- 
January . 
56 
46 
52 
90 
29 
69 
70 
102 
F eljruary. 
75 
56 
66 
92 
48 
63 
91 
105 
March. 
99 
110 
136 
175 
89 
100 
133 
133 1 
April. 
116 
131 
150 
128 
131 
138 
135 
122 1 
May. 
130 
144 
122 
56 
153 
111 
74 
95 
June. 
144 
135 
95 
17 
150 
114 
88 
50 
July. 
136 
132 
101 
66 
151 
123 
85 
41 
August. 
133 
141 
130 
64 
148 
113 
123 
110 
September. 
118 
119 
131 
175 
128 
106 
153 
169 
October. 
89 
88 
111 
165 
101 
107 
126 
134 
November. 
61 
56 
68 
112 
55 
98 
81 
92 
December. 
44 
42 
38 
59 
16 
56 
40 
47 
Winter. 
59 
50 
56 
92 
37 
73 
73 
87 
Equinox. 
105 
111 
131 
166 
112 
110 
133 
141 
Summer. 
135 
138 
113 
42 
151 
117 
94 
73 
