go Mr. Christie on tlie mutual action of 
by a glass cover over the screen, between the magnets and 
the disc. 
Table VIII. 
The magnets revolving with their axes at the distance yz inches from the 
axis of rotation. 
Under the ring, diameters 
4'4 and 8’4 inches, with 
disc, diameter 4*4 inches. 
Under the ring,diameters 
4-4 and 8-4 inches, 
alone. 
Under the disc 
diameter 4*4 inches 
alone. 
6 
Time. 
Time. 
oc 
Time. 
a 
fti • ^ 1 
« 0 ^ 
— 0 ir ^ ^ 
W M ^ 
V. H £ V, * 
° « 0 ° 2 
H 5 0 ,2 -a T- 
Values of and a. — 
360 
720 
1080 
1440 
= 2 0. 
sec. 
82*0 
I23’0 
165-5 
226-5 
264-0 
819*0 
806-1 
777-9 
757 -i 
754-5 
sec. 
84*5 
127-0 
170-5 
265-5 
785-0 
770-2 
752-4 
732-5 
265-0 
18-0 
Mean values of a, 
782-9 
760-0 
i8-o 
The sum of the mean values of when the magnets 
revolved under the ring alone, and under the disc alone, is 
here as nearly as can possibly be expected equal to the value 
of a when they revolved under the ring and disc together. If 
we attribute the whole difference to error in determining the 
value of a, when the magnets revolved under the disc alone, 
which however I have no reason for thinking should be done, 
the value of a would still in this case be only 23. Increasing 
this in proportion to the values of a in Table VII. the mag¬ 
netism developed in the uncut disc, diameter 8*4 inches, that 
in the ring alone, diameters 8-4 and 4-4 inches, and that in 
the disc alone, diameter 4-4 inches, would very nearly be 
represented respectively by 1517, 880, and 26. 
That the magnetism destroyed by the removal of a portion 
