5o8 Mr, Christie on the magnetism developed in 
but the approximation is evidently towards the inverse 
square. 
With regard to the forces with which different disks are 
urged at the same distance, they appear to be very accu- 
rately proportional to the weights of the disks when their 
distances from the magnets are small ; but as the distances 
are increased, the forces appear to increase in a greater ratio 
than that of the weights of the disks. 
Distance 
.6 
1. 1 
1 .6 
2.1 
2.6 
Torsion 
Weight 
— 1.372 
.483 
.194 
. 100 
.049 
Disk A. 
Torsion 
Weight 
• 
00 
0 
.633 
.286 
.134 
.067 
Disk B. 
As it was only by a rough estimate, that I considered the 
velocity with which the magnets revolved under the disk A, 
was double in one case of what it was in the other, I would 
not, from these observations, pretend to determine the ratio 
of the forces as depending upon the velocities, but I should 
have little doubt that they are proportional. 
From these experiments it appears, that the time in which 
the disk begins to return, by the torsion of the wire, is the 
same at all distances ; and from another experiment it ap- 
peared to be independent of the velocity of rotation. This 
ought to be the case, the force accelerating the disk ^being 
constant ; and the retarding force, the torsion, varying as 
the distance from a fixed point. 
I fear that I have trespassed too long on your time by 
this account of the experiments which I have made, but had 
no idea of rendering it so long when I began. I shall be 
happy if any of these experiments throw any light upon the 
