78 
Mr. Christie on the mutual action of 
The values of a deduced from the different values of 0, for 
the same distance of the magnets, agree with each other as 
nearly as could be expected, excepting in two cases, those 
corresponding to 9 360°, at the distances 3 2 inches and 2-7 
inches, which are so much greater than the other values of a 
at those distances, that I am disposed to think the observations 
from which they are deduced inaccurate. A slight impulse 
given to the disc when it was released at zero, would dimi- 
nish most sensibly the time of the first revolution, and con- 
sequently increase the corresponding value of a ; and as it was 
difficult to avoid this in all cases, the inaccuracy in the obser- 
vation might possibly arise from this cause. I was not aware 
of the incongruity in these values of a until it was too late to 
repeat the observations, having cut the disc and moved the 
apparatus before I made the computations. 
Not only in these, but in all the observations which I have 
made, and from which I have computed the values of a, I have 
almost invariably found, that the values of u decrease as those 
of 9 , from which they are deduced, increase : in 169 observa- 
tions there are only 14. exceptions, and in these, in general, 
the differences are so small, that they most probably arose 
from small errors in the observations. It would appear then, 
that in all the experiments there must have been some circum- 
stance which has a tendency to diminish the value of u as that 
of 6 increased. It at first occurred to me that this might be 
a small deviation from the received law, in the connection be- 
tween the force exerted by the wire and its torsion ; but this 
I found was not the case, as the results which I obtained by 
comparing the deviations of a magnetized needle with the 
torsion of the wire, were extremely uniform. If the force 
