His later ideas as to the nature of these physical lines of force are perhaps most fully explained in a letter to Richard Phillips, Esq., written in May, 1846, and published in Experimental Researches, III., p. 447. Some extracts from this letter are given below.
You are aware of the speculation which I sometime since uttered respecting that view of the nature of matter which considers its ultimate atoms as centers of force, and not as so many little bodies surrounded by forces, the bodies being considered in the abstract as independent of the forces and capable of existing without them. In the latter view, these little particles have a definite form and a certain limited size; in the former view such is not the case, for that which represents size may be considered as extending to any distance to which the lines of force of the particles extend: the particle indeed is supposed to exist only by these forces, and where they are it is. The consideration of matter under this view gradually led me to look at the lines of force as being perhaps the seat of the vibrations of radiant phenomena. ............. The ether is assumed as pervading all bodies as well as space: In the view now set forth, it is the forces of the atomic centres which pervade (and make) all bodies, and also penetrate all space. As regards space, the difference is, that the ether presents successive parts or centres of action, and the present supposition only lines of action; as regards matter, the difference is, that the ether lies between the particles and so carries on the vibrations, whilst as respects the supposition, it is by the lines of force between the centres of the particles that the vibration is continued.
Again, in Experimental Researches II, p. 291, Faraday presents his theory of the nature of matter in much the same manner as above. At the conclusion of this discussion, he says:
The view now stated of the constitution of matter would seem to involve necessarily the conclusion that matter fills all space, or, at least, all space to which gravitation extends (including the sun and its system); for gravitation is a property of matter dependent on a certain force, and it is this force which constitutes the matter. In that view, matter is not merely mutually penetrable, but each atom extends, so to say, throughout the whole of the solar system, yet always retaining its own centre of force.
We see from the above that Faraday's later electrical theory was based upon a concept of the nature of matter which is no longer regarded as tenable, but which necessarily profoundly modified his views on electrical phenomena. It did away at once with all distinction between matter and the ether, unless those parts of space in which the centers of force were less numerous than in other parts could be regarded as a separate medium. Any question as to the number of electrical fluids, or whether there was any electrical fluid at all, could have little significance. The atoms of bodies were merely centers from which innumerable contractile filaments which he called lines of force radiated in all directions and throughout all space. From his reasoning, these filaments
