If the current traversing the conductor is constant, the magnetic field around it is stable and static, unless other influences come in to modify it.  The cutting off of the current is followed by instability of the field whereby it can and must produce dynamic effects.  I say must because the field represents stored energy, and in disappearing must give out that energy.  To throw light on this part of the subject is one of the objects of the present paper.  Cutting off the current supply in the case assumed leaves the developed magnetic lines or strains unsupported.  They at once shorten their paths or circuits, collapsing upon the conductor as it were, and continuing this action, cut the section of the conductor, and apparently disappear in magnetic closed circuits of infinitesimal diameter but of great strength of polarization.  It appears to me that we must either be prepared to give up the idea of lines of force or take the position that the magnetic circuits precipitate themselves in shortening their circuits and disappearing upon and cut the conductor.  It was Hughes who put forward the idea that an iron bar in losing its apparent magnetism really short-circuits the lines in itself as innumerable strongly magnetized closed circuits among the molecules.  In becoming magnetic once more these short circuits are opened or extended into the air by some source of energy applied to strain the lines, such as a current in a conductor around the bar.

May not this idea be extended, then, to include the magnetic medium, the ether itself?  Does it contain intensely polarized closed circuits of magnetism which are ready to be stretched or extended under certain conditions by the application of energy, which energy is returned by the collapse of the extended circuits?  This is doubtless but a crude expression of the real condition of things, for the lines are only symbols for a condition of strain in a medium which cannot be represented in thought, as we know nothing of its real nature.  There is one point in this connection which I must emphasize.  The strained lines, Fig. 1, are indications of stored energy in the ether, and the lines cannot disappear without giving out that energy.  Ordinarily, it makes its appearance as the extra current, and adds itself so as to prolong the current which extended the lines when an attempt is made to cut off such current.  Were it conceivable that the current could be cut off and the wire put on open circuit while the lines still remained open or strained, the energy must still escape when the field disappears.  It would then produce such a high potential as to be able to discharge from the ends of the conductor, and if the conductor were of some section, part of the energy would be expended in setting up local currents in it.  The field could not disappear without an outlet for the energy it represents.  But we cannot cut off a current in a wire so as to leave the wire on open circuit