applied to Magnetic Phenomena. 169 
where « is the intensity of the magnetic force, and m is the 
amount of magnetic matter pointing north in unit of volume. 
The physical interpretation of this term is, that the force 
urging a north pole in the positive direction of # is the product 
of the intensity of the magnetic force resolved in that direction, 
and the strength of the north pole of the magnet. 
Let the parallel limes from left to right in fig. 1 represent a 
field of magnetic force such as that of the earth, sv being the 
direction from south to north. The vortices, according to our 
hypothesis, will be in the direction shown by the arrows in fig. 3, 
that is, in a plane perpendicular to the lines of force, and revolv- 
ing in the direction of the hands of a watch when observed from 
s looking towards n. The parts of the vortices above the plane 
of the paper will be moving towards e, and the parts below that 
plane towards w. . 
We shall always mark by an arrow-head the direction in which 
we must look in order to see the vortices rotating in the direc- 
tion of the hands of a watch. The arrow-head will then indicate 
the northward direction in the magnetic field, that is, the direc- 
tion in which that end of a magnet which points to the north 
would set itself in the field. 
Now let A be the end 
of a magnet which points Big) 
north. Since it repels the i a 
north ends of other mag- —————_+_|__7 > 
nets, the lines of force will pemCN IY 4 Su 
be directed from A out- § CS ee m 
wards in all directions. | Bt 
On the north side the line ‘ ) a ca 
AD will be in the same e a 
direction with the lines of 
the magnetic field, and the Fig. 2. 
velocity of the vortices will a 
be increased. On the south Ne ee ag 
side the line A C will be in 2 MG WS ee 
the opposite direction, and MS ie Oe Vee 
the velocity of the vortices Oss h es 
will be diminished, so that 
the lines of force are more 
powerful on the north side 
of Athan on the southside. 
We have seen that the 
mechanical effect of the 
vortices is to produce a 
tension along their axes, 
so that the resultant effect 
VEY 
