DIURNAL VARIATIONS OF TERRESTRIAL MAGNETISM. 
0 ^ 
*j 0 
Table J. —Comparison of the External and Internal Lunar Diurnal Magnetic 
Variation Fields. 
The unit is 10 7 C.G.S. 
External. 
Internal. 
m. 
E,„' 1 
P n _i 11 
f 
a 
n. 
E J\ 
T n 
Mil • 
1 n 
I m n ' 
calculated. 
calculated.. 
Mean Solstice, ^ ( 
Summer 
+ Winte 
>r). 
1 
1 
2 
22-2 
0 
101 
7-9 
0 
124 
2-8 
0 
-23 
2-6 
-21 
2 
3 
4-9 
83 
2-7 
112 
1-8 
-29 
2-5 
- 20 
3 
4 
0-33 
106 
0-12 
125 
2-7 
- 19 
2-5 
-20 
4 
5 
0-0120 
121 
0-0044 
173 
2-7 
-52 
2-7 
-22 
Equinox, Spring and Autumn. 
1 
•7 
20-5 
81 
11-0 
110 
1-9 
-29 
2-6 
-21 
0 
3 
5-5 
73 
3-7 
104 
1-5 
-29 
2-5 
-20 
3 
4 
0-43 
83 
0-16 
97 
2-7 
- 14 
2 • 5 
-20 
4 
5 
0-022 
100 
0-011 
117 
2-0 
- 17 
2-7 
— 22 
Solstitial Inequality, (Summer—Winter). 
1 
1 
41-9 
72 
17-7 
103 
2-4 
-31 
2-8 
- 13 
0 
•) 
14-8 
77 
7-8 
83 
1-9 
6 
2-3 
- 15 
0 
O 
3 
1-11 
94 
0-59 
106 
1-9 
- 12 
2-3 
- 16 
4 
4 
0-017 
110 
0-006 
93 
2-8 
+ 17 
2-4 
- 18 
The numbers in Table I, relating to the solar diurnal magnetic variation, are 
remarkable for the almost unbroken uniformity (neglecting the uncertain values for 
Q'h+ 2 ) with which they indicate that the external magnetic field is about 2'5 times 
as great — reckoning by the surface values of the potentials—as the internal 
field, and that the latter is in advance of the former, in phase, by about 20 degrees. 
The differences between the values for the various harmonic terms, of different 
degrees and periods, are much less noteworthy than the accordance exhibited : the 
differences, moreover, appear to be in part real (§ 17). If the sixteen values of 
for the annual harmonics Q ra „ +1 are treated as if their differences were altogether 
accidental, the probable error of the mean, 2‘55, is found to be only 0‘06. It may also 
be noticed that the nearly constant value 2‘5 corresponds to very different values of 
AV/A/, B,//B m n , for the various values of m i and that these different ratios are 
actually observed. 
The general result that the external field is about 2\ times as great as the internal 
field, at the earth’s surface, lies between the conclusions of Schuster (E m ”/I„” — 4, 
approximately) and Fritsche (E ot b /I,/ = l'o, approximately); van Bemmelen obtained 
f 2 
