the particles of magnetic bodies , &c. 1 1 1 
agreement such, that there can be no doubt, that the forces 
are the same at the same distances in the two cases. The 
mean value of a at the distance -756 inch when the magnets 
revolved was 181 1 *7 ; but it is to be observed that the value 
of a in the present instance, 1777-3, should not be compared 
with this, but with 1763-75, that value of a which is half the 
arc of torsion when the ring comes to rest, previously to 
turning in the contrary direction to that of the rotation of the 
magnets, since in the present case the rotation of the ring 
was continued until it balanced steadily the directive force of 
the magnets. This consideration greatly diminishes the 
difference in the two cases, and will account also in some 
measure for the values of M and e 2 being different in Table VI. 
and Table IX.; but I must likewise state that the observa- 
tions, when the ring revolved under the magnets, were liable 
to errors which did not affect those in the reverse form of 
the experiment, although I took great care to determine 
correctly the direction of the index to the magnets when the 
force of rotation balanced the directive force. 
The comparison between the values of a contained in the 
preceding table, and those computed for the several values 
of c from the formula ( 5 ), making M = 46-63 and a a =-5491 , 
is made in the following table ; and their agreement is such, 
that there can be no doubt, that the effects produced on the 
magnets by the rotation of the ring at different distances are 
correctly represented by this formula. 
