102 
Mr. Christie on the mutual action of 
indeed that no wire, on the torsion of which any sensible 
effect could be produced, would do so, the preceding experi- 
ments could not be made use of as strictly comparative with 
others in which the ring should revolve under the mag- 
nets. It therefore became necessary to make a different 
adjustment of the magnets, in the first instance, under the 
copper. 
The magnets used in the preceding experiments were now 
placed horizontally, and parallel to each other, on their flat 
sides, on the top of the frame G H, with their poles of the 
same name adjacent, and their nearest sides at the distance 
*34 inch from each other. The copper ring remained sus- 
pended by the same wire as in the preceding experiments, 
and being lowered until its under surface just touched, with- 
out resting upon two brass nuts, fixing the magnets to the 
frame, the distance between K and M was ascertained to be 
9' 575 inches : so that the distance from the under surface of 
the magnets to the under surface of the ring being *59 inch, 
the thickness of the ring -24 inch, and that of the magnets 
■36 inch, the distance between K and M would have been 
10*105, could the middle horizontal section of the ring have 
coincided with the axes of the magnets ; which distance was 
therefore in this case to be considered as zero, on the scale 
measuring the distances between the middle horizontal sec- 
tion of the ring, in any case, and the horizontal plane passing 
through the axes of the magnets. 
I have before mentioned, that, from the formula a=\ i . 
\p + c j * 
I had found p , or the distance of the poles of the magnets from 
their extremities, to be -256 inch, which, as I was not aware 
