PARAMAGNETIC AND DIAM'AONETIC FORCES. 245 
every other particle; in magnetism also we have attraction, 
but we have always, at the same time, repulsion, the final 
effect being due to the difference of these two forces. A 
body may be intensely acted on by a magnet, and still no 
motion of translation will follow, if the repulsion be equal 
to the attraction. Previous to magnetization, a dipping 
needle, when its center of gravity is supported, stands 
accurately level; but, after magnetization, one end of it, 
in our latitude, is pulled toward the north pole of the 
earth. The needle, however, being suspended from the 
arm of a fine balance, its weight is found unaltered by its 
magnetization. In like manner, when the needle is per- 
mitted to float upon a liquid, and thus to follow the attrac- 
tion of the north magnetic pole of the earth, there is no 
motion of the mass toward that pole. The reason is known 
to be, that although the marked end of the needle is 
attracted by the north pole, the unmarked end is repelled 
by an equal force, the two equal and opposite forces 
neutralizing each other. 
When the pole of an ordinary magnet is brought to act 
upon the swimming needle, the latter is attracted the 
reason being that the attracted end of the needle being 
nearer to the pole of the magnet than the repelled 
end, the force of attraction is the more powerful of 
the two. In the case of the earth, its pole is so 
distant that the length of the needle is practically zero. 
In like manner, when a piece of iron is presented to a 
magnet, the nearer parts are attracted, while the more dis- 
tant parts are repelled; and because the attracted portions 
are nearer to the magnet than the repelled ones, we have a 
balance in favor of attraction. Here, then, is the special 
characteristic of the magnetic force, which distinguishes it 
from that of gravitation. The latter is a simple uupolar 
force, while the former is duplex or polar. Were gravita- 
tion like magnetism, a stone would no more fall to the 
ground than a piece of iron toward the north magnetic 
pole: and thus, however rich in consequences the supposi- 
tion of Kepler and others may have been, it is clear that a 
force like that of magnetism would not be able to trans- 
act the business of the universe. 
The object of this discourse is to inquire whether 
the force of diamagnetism, which manifests itself as a 
repulsion of certain bodies by the poles of a magnet, is to 
