172 Prof. Maxwell on the Theory of Molecular Vortices 
element will be urged in the direction of —z, transversely to the 
direction of the current and of the lines of force; that is, an 
ascending current in a field of force magnetized towards the north 
would tend to move west. 
To illustrate the action of the molecular vor- Fig. 6. 
tices, let sm be the direction of magnetic force ~ n 
in the field, and let C be the section of an 
ascending magnetic current perpendicular to 
the paper. The lines of force due to this current ,, 
will be circles drawn in the opposite direction 
from that of the hands of a watch ; that is, in the 
direction nwse. At e the lines of force will be 
the sum of those of the field and of the current, 8 
and at w they will be the difference of the two 
sets of lines; so that the vortices on the east side of the current 
will be more powerful than those on the west side. Both sets 
of vortices have their equatorial parts turned towards C, so that 
they tend to expand towards C, but those on the east side have 
the greatest effect, so that the resultant effect on the current is to 
urge it towards the west. 
The fourth term, 
1 (de 
+m {Fe oat or +uyg, . . + (10) 
may be interpreted in the same way, and indicates that a current 
g in the direction of y, that is, to the north, placed in a magnetic 
field in which the lines are vertically upwards in the direction of 
z, will be urged towards the east. 
The fifth term, 
dp, 
Fa tue ho athe a 
merely implies that the element will be urged in the direction in 
which the hydrostatic pressure p, diminishes. 
We may now write down the expressions for the components 
of the resultant force on an element of the medium per unit of 
volume, thus: 
ie 4 d, . 
X=am+ ws (%)—wOrt+pyg—S3, . . (12) 
Losi d 
Y=@m+ Sa ay Hw + mar — 7 :  % hae 
gpg d, 
Z=ym+ 3- wo (v*)— pag +mBp — 2. wore (lp 
The first term of each expression refers to the force acting on 
magnetic poles. 
