1770. According to Newton, matter consists of hard, impenetrable particles, endowed with vis inertiæ, gravitation, and chemical attraction for other particles; vis inertiæ being that force by which a body, if in motion, requires a certain degree of force to arrest or retard it, or to put it into motion if at rest. Gravitation causes all masses to attract each other reciprocally, with a force exactly proportioned to their vis inertiæ; so that these forces are reciprocally measures of each other. It is usual to make gravitation its own measure, by estimating it to be as the weight of the mass; while weight is only the reciprocal attraction of gravitation between the body tried, and the earth. ([64].)
1771. These properties being conceded as belonging to matter, and the measure of its quantity, the next question is, of what does massive matter consist? As to the ratio of weight to bulk, which is designated as “specific gravity,” we see an immense disparity between solids. Potassium, for instance, weighs three-fourths of its bulk of water, while platinum weighs twenty-one times its bulk in that fluid. The density of gaseous hydrogen is to that of platina not more than 1 to 25,000, and yet it may be rarified to the one-hundredth part of its normal spissitude, while apparently filling the same space. Thus the same space may be filled successively by different portions of matter, yet the quantity of matter in the space, in the first case, may be to the quantity contained in the second, as 2,500,000 to 1. Newton’s definition of material particles was as follows:
1772. “It seems probable to me that God, in the beginning, formed matter in solid, massy, hard, impenetrable, movable particles, of such sizes and figures, and with such other properties, and in such proportion to space, as most conduced to the end for which he formed them; and that those primitive particles, being solids, are incomparably harder than any porous bodies compounded of them; even so very hard as never to wear or break in pieces; no mundane power being able to divide what God himself intended to be indivisible.”
1773. Boscovitch, observing that all that was essential to material atoms was attraction and repulsion, the latter being the substitute of Newton’s impenetrability, suggested an hypothesis which dispensed with the atom, and assumed only the forces of attraction and repulsion; alternating, as it appears to me, in a way more original than warrantable. This idea of atoms has been modified by an accomplished mathematician, Exley, of Bristol, England. I quote here Exley’s view:
1774. “The reader has only to allow that each atom of matter consists of an indefinitely extensive sphere of attraction, resting on a very small concentric sphere of repulsion, the force being everywhere, from the centre, inversely as the square of the distance, repulsive near the centre, and then attractive. Now that part which regards the attraction has already obtained the consent of all the followers of Newton; and much more than the other part, which respects repulsion, has been already received in the principles of our present philosophy.
1775. It may be here asked—Are we absolutely to exclude solid atoms? I confess I can find no use for them. It is true, Sir Isaac Newton thought that the atoms of matter consisted of minute solids.
1776. But this hypothesis, however convenient and consonant with our prejudices, is not absolutely necessary to the explanation of natural phenomena; for, it may be conceived, according to the theory of Boscovitch, that matter consists not of solid particles, but of mere mathematical centres, of forces attractive and repulsive, whose relations to space were ordained, and whose actions are regulated and maintained by the Creator of the universe. Both hypotheses, however, agree in one great principle, viz.: that the properties of bodies depend upon forces emanating from immovable points (whether substantial or not is of little importance) of their masses.
1777. The atoms of matter constituted as in the theory now proposed possess all the individuality, indivisibility, and indestructibility, which the learned and illustrious Newton ascribes to his small solids, and they answer all the ends he has mentioned; the central points, indeed, will be utterly impenetrable by each other, since the repulsion there is infinite; and if at those centres we suppose small solids to be placed, they can answer no farther end than is accomplished by this immensely great repulsive force; for from what we know of matter, we must suppose them to be indefinitely small, if we introduce such solids; and hence they will occupy the place where the repulsion is infinitely great; such solids would be found only an obstacle, and an incumbrance to the free actions of matter; since, however small we imagine them to be, their magnitude will be infinite if compared with a mathematical point, the centre of an atom, which is devoid altogether of magnitude. It may be added, that if any reader wish to retain these solids at the centres of the atoms, it will not materially affect the conclusions, provided he allow us to have them as small as we please; and so much, if he intend to philosophize, he must grant, whatever course he may determine to pursue.”
1778. These efforts to define matter derive interest from the following attempt of Farraday to sustain a view inconsistent with that of Newton, by practical illustration: