170 ~~ Prof. Maxwell on the Theory of Molecular Vortices 
on A will be to pull it more powerfully towards D than towards 
C; that is, A will tend to move to the north. 
Let B in fig. 2 represent a south pole. The lines of force 
belonging to B will tend towards B, and we shall find that the 
lines of force are rendered stronger towards E than towards F, 
so that the effect in this case is to urge B towards the south. 
It appears therefore that, on the hypothesis of molecular vor- 
tices, our first term gives a mechanical explanation of the force 
acting on a north or south pole in the magnetic field. 
We now proceed to examine the second term, 
| aeti 
Sg sp (a? + 8? + 97). 
Here «?+ 87+? is the square of the intensity at any part of 
the field, and w is the magnetic inductive capacity at the same 
place. Any body therefore placed in the field will be urged 
towards places of stronger magnetic intensity with a force depend- 
ing partly on its own capacity for magnetic induction, and partly 
on the rate at which the square of the intensity increases. 
If the body be placed in a fluid medium, then the medium, as 
well as the body, will be urged towards places of greater intensity, 
so that its hydrostatic pressure will be increased in that direc- 
tion. The resultant effect on a body placed in the medium will 
be the difference of the actions on the body and on the portion 
of the medium which it displaces, so that the body will tend to 
or from places of greatest magnetic intensity, according as it has 
a greater or less capacity for magnetic induction than the sur- 
rounding medium. 
In fig. 4 the lines of force are represented as converging and 
becoming more powerful towards the right, so that the magnetic 
tension at B is stronger than at A, and the body AB will be 
urged to the nght. If the capacity for magnetic induction is 
greater in the body than in the surrounding medium , it will move 
to the right, but if less it will move to the left. 
Fig. 4, Fig. 5. 
D 
A B 
Cc 
We may suppose in this case that the lines of force are con- 
verging to a magnetic pole, either north or south, on the right 
hand. 
In fig. 5 the lines of force are represented as vertical, and be- 
