84 Mr. Christie on the mutual action of 
After having made these experiments, I ascertained what 
would be the effect produced when the magnets revolved 
under the separated ring alone, and likewise under the re- 
maining disc alone : first, when the axes of the magnets were 
at the distance 3-7 inches from the axis of rotation, that is, 
remaining as in the foregoing experiments : secondly, when 
they revolved at the distance 3-2 inches from the axis, that 
is, having their axes under the inner edge of the ring, or the 
edge of the remaining disc. 
Table VI. 
The distance of the axes of the magnets from the axis of rotation. 
3 *7 inches 
3-2 inches. 
The magnets revolving under 
The magnets revolving under 
The ring alone. 
The disc alone. 
The ring alone. 
The disc alone. 
a. — 268'0 
a. ~ I 20 - 0 
a 160-5 
a = 283-5 
The sum of the values of a, corresponding to the distance 
3-7 inches, is rather greater than the value of a when the 
magnets revolved at the same distance under the disc and 
ring together ; so that it would appear that no increase in the 
magnetism takes place in consequence of the proximity of the 
two masses. That the sum of the value of a, corresponding 
to the ring and disc separately, exceeds that of a. corresponding 
to the ring and disc together, Table V. probably arises from 
a circumstance which affected slightly all the results. Al- 
though the direct communication between the disc and the 
currents of air, arising from the rotation of the magnets, was 
cut off by a screen of paper stretched on a frame, with sides 
considerably raised ; yet a slight current of air was produced 
