Faraday for a long period used the lines of force merely as 'a representative idea.' He seemed for a time averse to going further in expression than the lines themselves, however much further he may have gone in idea. That he believed them to exist at all times round a magnet, and irrespective of the existence of magnetic matter, such as iron filings, external to the magnet, is certain.
No doubt the space round every magnet presented itself to his imagination as traversed by loops of magnetic power; but he was chary in speaking of the physical substratum of those loops. Indeed it may be doubted whether the physical theory of lines of force presented itself with any distinctness to his own mind.
The possible complicity of the luminiferous ether in magnetic phenomena was certainly in his thoughts. 'How the magnetic force,' he writes, 'is transferred through bodies or through space we know not; whether the result is merely action at a distance, as in the case of gravity; or by some intermediate agency, as in the case of light, heat, the electric current, and (as I believe) static electric action.
The idea of magnetic fluids, as applied by some, or of Magnetic centres of action, does not include that of the latter kind of transmission, but the idea of lines of force does.' And he continues thus:--'I am more inclined to the notion that in the transmission of the [magnetic] force there is such an action [an intermediate agency] external to the magnet, than that the effects are merely attraction and repulsion at a distance. Such an affection may be a function of the ether; for it is not at all unlikely that, if there be an ether, it should have other uses than simply the conveyance of radiations.'
When he speaks of the magnet in certain cases, 'revolving amongst its own forces,' he appears to have some conception of this kind in view.
A great part of the investigation completed in October, 1851, was taken up with the motions of wires round the poles of a magnet and the converse. He carried an insulated wire along the axis of a bar magnet from its pole to its equator, where it issued from the magnet, and was bent up so as to connect its two ends. A complete circuit, no part of which was in contact with the magnet, was thus obtained.
He found that when the magnet and the external wire were rotated together no current was produced; whereas, when either of them was rotated and the other left at rest currents were evolved. He then abandoned the axial wire, and allowed the magnet itself to take its place; the result was the same. It was the relative motion of the magnet and the loop that was effectual in producing a current.
The lines of force have their roots in the magnet, and though they may expand into infinite space, they eventually return to the magnet.
Now these lines may be intersected close to the magnet or at a distance from it. Faraday finds distance to be perfectly immaterial so long as the number of lines intersected is the same.
