442 
MR, 0. HEAVISIDE OH THE FORCES, STRESSES, AND 
making the first circuital law become 
curl (H — h 0 — h) = J = C + I) + qy>.(89) 
Maxwell’s other connection to form the equations of propagation is made through 
his vector-potential A and scalar potential 'F. Finding this method not practically 
workable, and also not sufficiently general, I have introduced instead a companion 
equation to (89) in the form 
— curl (E — e 0 — e) = G = K + B + q^,.(90) 
where e 0 expresses intrinsic force, and e is the motional electric force given by 
e = VqB, 
(91) 
which is one of the terms in Maxwell’s equation of electromotive force. As for e 0 , 
it includes not merely the force of intrinsic electrification, the analogue of intrinsic 
magnetisation, but also the sources of energy, voltaic force, thermoelectric force, &c. 
(89) and (90) are thus the working equations, with (88) and (91) in case the 
medium moves; along with the linear relations before mentioned, and the definitions 
of energy and waste of energy per unit volume. The fictitious K and cr are useful in 
symmetrizing the equations, if for no other purpose. 
Another way of writing the two equations of curl is by removing the e and h 
terms to the right side. Let 
curl h = j, j + j = j 0 , 
— curl e = g, G -f- g = G 0 . 
Then (89) and (90) may be written 
curl (H — h 0 ) = J 0 = C + D + q/. + j, 
curl (E — e 0 ) = G, ; = K + B + qrr + g. 
(93) 
So far as circuitality of the current goes, the change is needless, and stiil further 
complicates the make-up of the true current, supposed now to be J 0 . On the other 
hand, it is a simplification on the left side, deriving the current from the force of the 
flux or of the field more simply. 
A question to be settled is whether J or J 0 should be the true current. There 
seems only one crucial test, viz., to find whether e (1 J or e 0 J 0 is the rate of supply of 
energy to the electromagnetic system by an intrinsic force e 0 . This requires, however, 
a full and rigorous examination of all the fluxes of energy concerned. 
