403 
iron arising from its rotation. 
then suppose such poles to exist in the iron plate, in the dia- 
meter in the direction of the dip, and that the rotation causes 
the line joining them to describe in the iron an angle ^ from 
this diameter. The whole effect being now produced by the 
action of these poles, F being equal to o in the equations (s) 
and (3), we shall, on this supposition, have. 
3 sin. (X + vj/) . COS. X — sin. 4 
lan. (p — I 
- + 3 sin. (X + t}') • sin. X — cos. 4 
2 / P 
3 sin. (X — • cos. X + sin. 4 / 
Tan. (p^ 
m RJ 
^77 
-f 3 sin. (x — ■ 4 ') . sin. X — cos. 4 ' 
(2'). 
(3'). 
Tan. (p = ^ 
— ^ + 3sm.*x— I 
2/ p 
These equations being reduced, give, 
Tan. 0 ' = 
( 4 ')- 
cos J 
3 sin. 2 X + tan. 4 ' (3 cos. 2 X + i) 
m R^ 
Tan. 0'=z 
Tan. d = 
— (3 cos. 2 X— i) +tan 4 / . 3 sin. 2 X 
/ p cos. 4^ 
I 3 sin. 2 X — tan. 4 (3 cos. 2 x + i ) 
cos. ^ R^ , , \ * 1 • 
_ (3 cos. 2X— 1) — tan.4.3 sin. 2X 
/'/.cos. 4 ^ 
1 3 sin. 2 X 
cos. S' VI R^ 
T7 
— (3 cos. 2 X — l) 
(S'). 
( 6 '). 
( 7 '), 
which will be precisely the same as ths equations (5), (6), (7), 
if tan. 4/ 
2/> 
Fr 
andy' p cos. \jy = ~ 
The numerical values which we should obtain for 6' and 
from these equations, would, in all cases, be exactly the same 
as those which we have already obtained from the equations 
(5) and (6) : so that the agreement between the observations 
and the results from this theory would not be greater than 
in the former case. 
In the explanation of the phaenomena which take place on 
MDCccxxv. 3 G 
