Bifilae or Horizontal Force Magnetometer. 
xxxm 
Table 11. — Values of v, Jc, and q, in 1843. 
Periods to which the Values apply. 
V. 
h. 
d. h. d. h. 
Jan. 1 — April 27 4 
69 6 
00001248 
Sc. Div. 
1-98 
April 28 2— Nov. 8 22 
69 46 
0-0001205 
2-05 
Nov. 9 0— Nov. 10 6 
55 18 
0-0002263 
110 
Nov. 10 8— Dec. 31 
68 18 
0-0001300 
1-90 
The values of h are given at the foot of each page of the magnetical observa- 
tions. 
40. During considerable disturbances the collimator scale, which contains too 
small an angle, goes out of the field of the reading telescope, and it has been found 
necessary to turn the arms of the torsion circle until it again appears ; without this, 
it has happened that the greater part of a disturbance could not have been observed. 
As there was some doubt that turning the arms of the torsion circle after adjust- 
ment might affect the instrument injuriously, experiments were made in the end of 
1842, during periods of slight change, which shewed, after turning the arms of the 
torsion circle a few degrees in either direction, that on recurring to the original value 
of v the scale readings were unaltered. 
41. In turning the arms of the torsion circle the value of the scale divisions and 
the unit of force are changed, it is necessary therefore to reduce the observations to 
a common unit and zero ; let ft be the small angle through which the arms of the 
o 2 
torsion circle are turned, if = v + ft, m X = F, Wy=G, (34.) The equation of equi- 
librium originally, u = 90°, is 
F = G sin v, (1.) 
for the new value of v, u = 90 + a u = 90 + a if where a v = the angular value of the 
scale reading at any instant from the zero reading 
F = G si n ( ?/ + _ (2 ) 
cos A v' 
Subtracting (1.) from (2.), and dividing by (1.), 
F-F aF 
F 
sin v — sm v cos v , 
. 1 . a v 
sm v 
sin v 
If n be the number of scale divisions from the zero or scale reading for u = 90°, 
when v'=v + ft ; and N be the number of scale divisions corrected for temperature 
from the zero corresponding to the same force when /3=0, then 
XT sin v — sin v cos v , . , 
N = + n V tq 
a cos v 
cos V 
MAG. AND MET. OBS. 1843 
