109 
the particles of magnetic bodies , &c. 
ponding deviations of the index on the compound needle ; 
and the mean of the deviations in opposite directions being 
taken, the ratio of the torsion to the sine of the deviation was 
obtained : the following are the results. 
No. of turns 
of the wire. 
Deviation of the index 
to the magnets. 
Mean 
deviation. 
Arc of 
torsion. 
Torsion 
Sin. deviation. 
Screwing. 
Unscrewing. 
2 
4 
6 
0 / 
6 05 E 
12 30 
18 55 
O / 
6 20 W 
12 30 
18 45 
O / 
6 12^ 
12 30 
18 50 
O / 
7*3 48 
1427 30 
2141 10 
6600-465 
6595-386 
6634-320 
. . , r Torsion 
Mean value of sin< deviation 
6610-057 
The ring was made to revolve with the same velocity as 
before, viz. 5 revolutions in a second ; first in the direction 
of screwing ; and this velocity was carefully maintained until 
the needle became steady in its direction, when the devia- 
tion marked by the index was noted : the same was done in 
the direction of unscrewing ; and the mean of these deviations 
was taken as the deviation due to the rotation of the ring. 
When the distance between the middle section of the ring 
and the axes of the magnets exceeded 2 inches, the deviation 
was so small, that the errors to which the observation of it 
was liable, 2' or s', bore too great a proportion to the whole 
for me to place much/ reliance on the observations, and I, 
consequently, have not noted the deviation at the distance 
2-756 inches. 
In the following table are contained the observed deviations, 
the torsion equivalent to the force urging the magnets during 
rotation, and likewise the values of M and e 9 obtained from 
