be false.'

He then tosses the atomic theory from horn to horn of his dilemmas. What
do we know, he asks, of the atom apart from its force? You imagine a
nucleus which may be called a, and surround it by forces which may
be called m; 'to my mind the a or nucleus vanishes, and the substance
consists in the powers of m. And indeed what notion can we form of the
nucleus independent of its powers? What thought remains on which to hang
the imagination of an a independent of the acknowledged forces?' Like
Boscovich, he abolishes the atom, and puts a 'centre of force' in its
place.

With his usual courage and sincerity he pushes his view to its utmost
consequences. 'This view of the constitution of matter,' he continues,
'would seem to involve necessarily the conclusion that matter fills
all space, or at least all space to which gravitation extends; 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;[1] but each atom extends, so to say,
throughout the whole of the solar system, yet always retaining its own
centre of force.'

It is the operation of a mind filled with thoughts of this profound,
strange, and subtle character that we have to take into account in
dealing with Faraday's later researches. A similar cast of thought
pervades a letter addressed by Faraday to Mr. Richard Phillips, and
published in the 'Philosophical Magazine' for May, 1846. It is entitled
'Thoughts on Ray-vibrations,' and it contains one of the most singular
speculations that ever emanated from a scientific mind. It must be
remembered here, that though Faraday lived amid such speculations he did
not rate them highly, and that he was prepared at any moment to change
them or let them go. They spurred him on, but they did not hamper him.
His theoretic notions were fluent; and when minds less plastic than his
own attempted to render those fluxional images rigid, he rebelled. He
warns Phillips moreover, that from first to last, 'he merely threw out
as matter for speculation the vague impressions of his mind; for he gave
nothing as the result of sufficient consideration, or as the settled
conviction, or even probable conclusion at which he had arrived.'

The gist of this communication is that gravitating force acts in lines
across space, and that the vibrations of light and radiant heat consist
in the tremors of these lines of force.