8o 
Mr. Christie on the mutual action of 
nets are in its vicinity, the excess which we have mentioned 
would be thus gradually diminished, and consequently also the 
value of a. 
The forces with which the magnets, revolving at dif- 
ferent distances with the same angular velocity urged the disc, 
are proportional to the mean values of « in Table II. and to 
deduce the relative forces with which the magnets would urge 
the disc when revolving at different distances with the same 
linear velocity, for instance, that at the distance 4’ 2 inches, 
the values of u must be increased in the inverse ratio of the 
respective distances, since the forces, cceteris paribus , are pro- 
tional to the velocities. This reduction is made in the fol- 
lowing Table. 
Table III. 
Distance of the axes of *» 
the magnets from the > = 
axis of rotation - J 
Inches. 
4-2 
Inches. 
37 
Inches. 
3-2 
Inches. 
2-7 
Inches. 
2-2 
Inches. 
I *7 
Force with which the *j 
magnets, revolving with L _ 
the same linear velocity f 
would urge the disc -» 
j 680-5 
1360-3 
2006-4 
2275-9 
2120-8 
1540-7 
So that the distance at which the magnets would produce the 
maximum effect by revolving with the same linear velocity 
would be very nearly 2-44 inches. 
The distance from the axis at which the magnets must re- 
volve, in order that the magnetism may be developed with the 
greatest intensity, is less than this ; since, in estimating this 
intensity, the length of the lever, at the extremity of which 
the magnets act, must be taken into account. We shall 
obtain, at least approximately, the relative intensities of the 
nduced magnetism when the magnets revolved at different 
