xo8 Mr. Christie on the mutual action of 
carried the ring : they were placed on their flat sides at the 
distance -34 inch from each other, with their poles of the 
same name adjacent, precisely as they were in the preceding 
case ; and when the index on the scale between their south 
poles pointed in the magnetic meridian, there was no torsion 
in the wire. The suspending wire, if produced, would have 
bisected the line equidistant from the axes of the magnets, 
and passed through the axis of rotation. The ring was 
firmly fixed on the top of the frame, G H, so as to revolve 
horizontally in its own plane, about its centre, under the 
magnets ; and the same precautions as before were taken in 
order to determine accurately the distance between K and M, 
corresponding to the zero of distance between the middle 
section of the ring and the axes of the magnets. I have 
before stated that the weight suspended in the preceding 
experiments was 32-56 ounces : in the present case, the 
weight of the magnets, scale, &c. suspended by the same 
wire was 33-47 5 ounces, so that the tension was rather more 
than before ; but this difference was unavoidable, as the 
weight of the magnets alone is nearly equal to that of the 
ring. 
The effects produced at different distances by the rotation 
of the ring being measured by the deviation of the magnets 
from the meridian, in order to compare these effects with 
those observed when the magnets revolved under the ring, 
it was necessary to determine the degree of torsion equivalent 
to any deviation of this compound needle. For this purpose 
the suspending wire was twisted 2, 4, 6 circles by making 
the magnets describe 2, 4, 6 circles, first in the direction of 
screwing, then in the contrary direction, noting the corres- 
