126 Mr. 0. Heaviside on the 



(7) ; but that does not necessitate the closure of the magnetic 

 induction, which is necessary to avoid having unipolar magnets. 

 Hence 



div.B = (10) 



is required to meet facts, in addition to (4), (5), (6)_, (7). 

 There is no magnetic conduction-current with dissipation of 

 energy, analogous to the electric conduction-current. 



As regards the meanings of e and h, in the light of dynamics 

 they define themselves in the equation of activity ; that is, so 

 far as the mere measure of impressed forces is concerned, 

 apart from physical causation. Thus e is the amount of 

 energy taken in by the electromagnetic field per second per 

 unit volume per unit electric current, and li is similarly 

 related to magnetic current. Under e has to be included the 

 recognized voltaic and thermoelectric forces. But besides 

 them, it has to include the impressed electric force due to 

 motion in a magnetic field, or VvB if v is the vector velocity, 

 necessitating a mechanical force VFB. It has also to in- 

 clude intrinsic electrization, the state which is set up in solid 

 dielectrics under the continued application of electric force. 



Thus J = ce/47T 



connects the intensity of intrinsic electrization J with the 

 corresponding e. 



I can only find two kinds of h. First, due to motion in an 

 electric field, viz. 4ttVDv, necessitating a mechanical force 

 47rYDG ; and, secondly, much more importantly, intrinsic 

 magnetization I, connected with the corresponding h thus, 



As regards potentials, there are, to match the two electric 

 potentials A and P, two magnetic potentials, say Z and 12 ; 

 Q, being the single-valued scalar magnetic potential, and Z 

 the vector potential of the magnetic current, some of whose 

 properties in relation to dielectric and conductive displacement 

 I have worked out in the paper referred to before. 



As regards the general equations of disturbances, like Max- 

 well's (7), chapter xx. vol. ii., they are far more a hindrance 

 than an assistance in general investigations. But when we 

 come to a special investigation, and need to know the forms 

 of the functions involved, then we may eliminate either E or 

 H between (6) and (7), and use the suitable coordinates. 



We may make use of the above equations at the start, in 

 passing to the question of the propagation of disturbances 

 along a wire, after which the investigation will be wholly 

 scalar. Put e = in (7) ; then we see that we cannot alter 



