I am not ignorant that the mind is most powerfully drawn by the phenomena of crystallization, chemistry, and physics generally to the acknowledgment of centres of force. I feel myself constrained, for the present, hypothetically to admit them, and cannot do without them; but I feel great difficulty in the conception of atoms of matter which in solids, fluids, and vapours are supposed to be more or less apart from each other, with intervening space not occupied by atoms, and perceive great contradictions in the conclusions which flow from such a view.
If we must assume at all, as indeed in a branch of knowledge like the present we can hardly help it, then the safest course appears to be to assume as little as possible; and in that respect the atoms of Boscovich appear to me to have a great advantage over the more usual notion. His atoms, if I understand aright, are mere centres of forces or powers, not particles of matter in which the powers themselves reside. If in the ordinary view of atoms, we call the particle of matter away from the powers a, and the system of powers or forces in and around it m, then in Boscovich’s theory a disappears, and is a mere mathematical point, while in the usual notion it is a little, unchangeable, impenetrable piece of matter, and m is an atmosphere of force grouped around it.
In many of the hypothetical uses made of atoms, as in crystallography, chemistry, magnetism, &c., this difference in the assumption makes little or no alteration in the results; but in other cases, as of electric conductors, the nature of light, the manner in which bodies combine to produce compounds, the effect of forces, as heat or electricity, upon matter, the difference will be very great.
Thus, referring back to potassium, in which as a metal the atoms must, as we have seen, be, according to the usual view, very far apart from each other, how can we for a moment imagine that its conducting property belongs to it any otherwise than as a consequence of the properties of the space, or, as I have called it above, the m? So also its other properties in regard to light, or magnetism, or solidity, or hardness, or specific gravity, must belong to it, in consequence of the properties or forces of the m, not those of the a, which, without the forces, is conceived of as having no powers. But then, surely, the m is the matter of the potassium, for where is there the least ground (except in a gratuitous assumption) for imagining a difference in kind between the nature of that space midway between the centres of two contiguous atoms, and any other spot between these centres? A difference in degree or even in the nature of the power consistent with the laws of continuity I can admit, but the difference between a supposed little hard particle and the powers around it, I cannot imagine.
To my mind, therefore, the a or nucleus vanishes, and the substance consist of the powers or m; and indeed what notion can we form of the nucleus independent of its powers? All our perception and knowledge of the atom, and even our fancy, is limited to ideas of its powers; what thought remains on which to hang the imagination of an a independent of the acknowledged forces? As mind just entering on the subject may consider it difficult to think of the powers of matter independent of a separate something to be called the matter, but it is certainly far more difficult, and indeed impossible to think of or imagine that matter independent of the powers. Now, the powers we know and recognise in every phenomena of the creation, the abstract matter in one; why, then, assume the existence of that of which we are ignorant, which we cannot conceive, and for which there is no philosophical necessity?
Before concluding these speculations, I will refer to a few of the important differences between the assumption of atoms consisting merely of centres of force like those of Boscovich, and that other assumption of molecules of something specially material, having powers attached in and around them.
With the latter atoms a mass of matter consists of atoms and intervening space; with the former atoms matter is everywhere present, and there is no intervening space unoccupied by it. In gases the atoms touch each other just as truly as in solids. In this respect the atoms of water touch each other, whether that substance be in the form of ice, water, or steam; no mere intervening space is present. Doubtless, the centres of force vary in their distance one from another, but that which is truly the matter of one atom touches the matter of its neighbours.
Hence matter will be continuous throughout, and in considering we have not to suppose a distinction between its atoms and any intervening space. The powers around the centres give these centres the properties of atoms of matter; and these powers again, when many centres by their conjoint forces are grouped into a mass, give to every part of that mass the properties of matter. In such a view all the contradiction resulting from the consideration of electric insulation and conduction disappears.
The atoms may be conceived of as highly elastic, instead of being supposed excessively hard and unalterable in form; the mere compression of a bladder of air between the hands can alter their size a little, and the experiments of Cagniard la Tour carry on this change in size until the difference in bulk at one time and another may be made several hundred times. Such is also the case when a solid or a fluid body is converted into vapour.