76 
Mr. Christie on the mutual action of 
assistance in making the experiments I could only note the 
time to the nearest second. 
The numbers in the first column of the following table 
indicate the torsion of the suspending wire in circles, or the 
number of revolutions performed by the disc from rest ; and 
in the following columns, are set down, the times in which 
these revolutions were performed when the magnets re- 
volved at the several distances indicated above the respective 
columns. 
Table I. 
Distance of the axes of the "1 
magnets from the axis of f — 
rotation - - . •* 
Inches 
4-2 
Inches 
3-7 
Inches 
3-2 
Inches 
2-7 
Inches 
2-2 
Indies 
1-7 
Time. 
Time. 
Time. 
Time. 
Time. 
Time. 
D In W r 
^ o a (i 
+-> o 
EJ , 
OUT? 3 
u O 
r* "C U U s» J 4 
O 2 .S3 ^ ^ r 
•h £ nj J 
C ° 6 
h.So" 7 
& £ o J L 8 
sec. 
9 i- 5 
139-0 
I 9°'S 
sec. 
67-5 
99 ' 0 
125-0 
152-0 
180-5 
222-0 
sec. 
58-0 
87-0 
109-0 
130-0 
151-0 
173-0 
199-5 
237-0 
sec. 
59-0 
88-o 
1 1 1 -o 
I 34‘° 
158-0 
180-0 
213-0 
sec. 
70-5 
103-5 
132-5 
161-5 
! 94‘5 
246-5 
sec. 
96-0 
147-0 
206-5 
Disc beginning to f Arc ~~ 
revolve in direction * 
0 0° 
3 238 
A 0 0 
6 152 -5 
Q 0 ° 
8 107 
(?) O 
7268 -5 
z-O 0 
6 52 
G 0 
3 121 
opposite to that ofS 
the magnets - 
sec. 
267-0 
sec. 
269-5 
sec* 
270-5 
sec. 
269-5 
sec. 
272*5 
sec. 
270*0 
In order to deduce from these times, the force with which 
the disc was urged by the magnets revolving at different 
distances from the centre, let us suppose that this force is 
equivalent to a certain force acting at the distance 1 from the 
centre of rotation, and that this latter force would balance a 
torsion a° of the wire, or that it is equal to mu,m being a 
constant to be deduced from the experiments : also let t be 
the time in which the index on the scale describes an angle 
