iJ20 
DR. C. CHREE: MAGNETIC DECLINATION 
in Table VIII., including data for quiet days. The great difference between different 
years and between days of different type cannot be brought too clearly home to 
those combining data from different stations for theoretical purposes. It will be 
noticed that c 1 increases regularly as we pass from years of sunspot minimum 
through average years to years of sunspot maximum, or as we pass from quiet 
Table VIII.—Diurnal Inequality. Fourier Coefficients. Amplitudes. 
Season. 
Quiet days. 
Ordinary days. 
Disturbed 
days. 
Sunspot 
minimum. 
11 years. 
Sunspot 
maximum. 
Sunspot 
minimum. 
11 years. 
Sunspot 
maximum. 
11 years. 
r 
Year 
/ 
1-80 
/ 
2-32 
2-86 
/ 
2-21 
/ 
2-84 
/ 
3-47 
/ 
5; 07 
Winter. 
0-99 
1-39 
1-83 
1-43 
1-93 
2-42 
4-36 
Cl ^ 
Equinox . 
1-98 
2-48 
2-99 
2-41 
3-10 
3-76 
5'70 
l 
Summer . 
2-56 
3-19 
3-85 
2-98 
3-67 
4-38 
5'46 
r 
Year 
1-54 
1-79 
2-11 
1 -51 
1-76 
2-04 
1-76 
, J 
Winter. 
0-75 
0-91 
1-12 
0-78 
0-96 
1-15 
1-34 
Equinox . 
1-74 
2-01 
2-34 
1-71 
2-02 
2-33 
2-50 
l 
Summer . 
2-16 
2-50 
2-95 
2-06 
2-37 
2-73 
1-71 
r 
Year . . 
0-79 
0-89 
1-01 
0-72 
0-78 
0-89 
0'80 
c <1 
Winter. 
0-44 
0-50 
0-58 
0-42 
0-45 
O - 55 
0-44 
1 
Equinox . 
1-06 
1-17 
1-33 
0-97 
1-05 
1-16 
0-63 
l 
Summer . 
0-90 
1-01 
1-14 
0-77 
0-85 
0-97 
1-38 
r 
Year . . 
0-28 
0-28 
0-29 
0-27 
0-29 
0-28 
0-50 
Winter. . 
0-25 
0-26 
0-30 
0-27 
0-27 
0-30 
0-43 
c < 
C 4 < 
Equinox . 
0-45 
0-47 
0-46 
0-42 
0-41 
0-42 
1-15 
L 
Summer . 
0-15 
0-12 
0-11 
0-11 
0-11 
Oil 
0'64 
days through ordinary to disturbed days. But c 2 , whilst increasing with sunspot 
frequency, seems practically no larger in ordinary or even in disturbed days than 
in quiet days. 
The influence of disturbance on c 3 seems very small. The values of c 4 seem almost 
independent of sunspot frequency, and those derived from ordinary and from quiet 
days are nearly equal. 
The fact that c 2 , c 3 and c 4 are so nearly the same for ordinary and quiet days may 
seem at first sight to imply that the ordinary and quiet day difference curve is 
necessarily almost a pure sine curve of 24-hour period. This conclusion, however, 
does not necessarily follow unless the phase angles are nearly the same in the two 
cases. 
