49 ^ Christie on the magnetism developed in 
horizontally parallel to each other, and having their poles of 
the same name contiguous. These produced quick rotation 
in a heavy disk of copper 6 inches in diameter, and suspended 
by a wire, No. 20. 
A bar magnet 4 inches long, and having both its ends 
south poles, was made to revolve rapidly under a copper 
disk. The disk revolved in the same direction as the 
magnets. 
The two bar magnets before mentioned were adjusted to the 
axis of rotation, so that their upper ends were at the distance 
of 5 inches from each other, and their lower ends 1.8 inch 
apart. They were first made to revolve rapidly under the 
copper disk with poles of the same name nearest to the disk, 
and then with poles of a contrary name : the times in which 
the several rotations of the disk took place were as nearly as 
possible the same in the two cases. 
No. of 
Revolutions. 
Poles of the same name 
nearest to the disk. 
Poles of a contrary name 
nearest to the disk. 
Screw.* 
Unscrew.* 
Screw. 
Unscrew. 
Time. 
Time. 
Time. 
Time. 
I 
1 5 sec. 
15 sec. 
15 sec. 
15.4 
2 
21 
21 
21 
21.5 
3 
26 
26 
26 
26.3 
4 
30 
30 
30 
30.0 
In the first three, I could only remark the time to the 
nearest second, having no assistance. Should the times 
agree precisely, which I have very little doubt they would be 
found to do, the result would, I think, be singular. It would 
* These expressions refer to the direction witli respect to the spectator in which 
the rotation was performed. 
