applied to Magnetic Phenomena. 173 
The second term to the action on bodies capable of magnetism 
by induction. 7 
The third and fourth terms to the force acting on electric 
currents. 
And the fifth to the effect of simple pressure. 
Before going further in the general investigation, we shall 
consider equations (12, 13, 14,) in particular cases, corresponding 
to those simplified cases of the actual phenomena which we seek 
to obtain in order to determine their laws by experiment. 
We have found that the quantities p, g, and r represent the 
resolved parts of an electric current in the three coordinate 
directions. Let us suppose in the first instance that there is no 
electric current, or that p, g, and rvanish. We have then by (9), 
dy dB da dy dB da _ s 
perce > ge ae ae ap ne 
whence we learn that 
eer eyed. 6 el suits Met we) eh e@lO) 
is an exact differential of ¢, so that 
tO oy hea beashesen eV 
oe he’ ay dee 
p is proportional to the density of the vortices, and represents the 
“ capacity for magnetic induction” in the medium. It is equal 
to 1 in air, or in whatever medium the experiments were made 
which determined the powers of the magnets, the strengths of 
the electric currents, &c. 
Let us suppose constant, then 
1/d d iy, ) 
m= 5 (7, (ue) + 5 (HB) + oe (on) 
_ 1 (ad , a , dd 
= (Ss + dy? + dz? ° ° ° ° e (18) 
represents the amount of imaginary magnetic matter in unit of 
volume. That there may be no resultant force on that unit of 
volume arising from the action represented by the first term of 
equations (12, 13, 14), we must have m=0, or 
FD IEE 2.6) 3 nn ag EE 
da® * ay? * dz? 
Now it may be shown that equation (19), if true within a given 
space, implies that the forces acting within that space are such 
as would result from a distribution of centres of force beyond 
that space, attracting or repelling inversely as the square of the 
distance. 
