398 Mr. Christie on the magnetism of 
Taking a mean of the two values, we shall have, 
.058009 = .058 very nearly. 
The equations (5) and (6) therefore become. 
Tan. & = 
3 sin. 2 X .058 X (3 cos. 2 X + I) 
cos. 70® 15' 51 — 3 cos. 2 ^ + .058 X 3 sin. 2 a 
g I 3 sin. 2 X-—. 058 X (3 cos. 2 A -f- 1) 
‘ ' cos. 70® 15' * 51—3 cos. 2 A + .058 X 3 sin. 2 x 
From Table B, we shall in the same manner obtain 
2toR^ 
(5a)> 
( 6 .)- 
F r 
46.0278 = 46 very nearly ; 
.054571, when x = o, and ^ = .060986, when a=9o; 
so that the mean value of yj is 0.57778 or .058 nearly, the 
same as before. 
The equations (5) and (6) in this case become, 
3 sin. 2x4 .058 X (3 cos. 2 A+ i) 
cos. 70° 15' 47 — 3 cos. 2A + .058 X 3 sin. 2X 
T'ap ^ L X 3 sin. 2 x — .058 x (3 cos. 2 x + 1) 
’ t cos. 70® 15' 47— 3 cos. 2X — . .058 X 3 sin. 2X 
We will first compare the situations of the points where 
the deviation due to rotation vanishes, as deduced from these 
equations, with the situation as determined by actual obser- 
vation. 
When the deviation due to rotation vanishes 6^ = 6 = 6^; 
we shall therefore have from equations (5^) and (6j 
3 sin. 2 X 3 cos. 2 X + I 
51 — 3 cos. 2 X 3 sin. 2 X ’ 
whence cos. 2 x = — .2800000 and x = 53“ 07' 48''. 
The equations (5^) and (6 J give 
3 sin. 2 X 3 cos. 2x4-1 
47 — 3 cos. 2 X 3 sin. 2 X ’ 
whence cos. 2 x = — .2753623 and x = 52° 59' 30". 
Now I have uniformly found, in repeated observations 
which I have made at different distances, that when the centre 
