In the first place, the gravity of all bodies, which is daily experienced, evinces, that the repulsive forces which we discover in the smaller distances, is by no means indefinitely extended ; but in the greater dis tances, gives place to a force of attraction : and the _laws of Kepler, in astronomy, happily reduced by Newton under the single law of general gravity, suffi-, ciently spew, that this attraction, if it does not ex tend- ad infinitum, must,- at least,- pass as • far as •the utmost limits of the planetary and cometary system. The curve, expressing the law of forces, has there fore another arc STY, which, to all sense, is the same with that hyperbola of the third order, of which the ordinates are reciprocally in the duplicate ratio of the distances or abscissa. But it is evident that there must be some place E, where this curve cuts the axis, and in which the transition is made from attraction to repulsion.
The phenomena of vapour arising from water; and. of air produced from fixed substances, exhibit tows two other limits of the same kind : For in these there is at first no :epulsion,.but rather an •attraction and coherence. Nevertheless their expansion and elastic. force are afterwards sufficient manifestations, that a repulsive force exists among their particles. We • therefore, first, a transition from the primary repul sion to attraction ; then to repulsion again ; • and last ly, to the general attraction of gravity. But indeed there appears to be many such limits and transitions; for without them the numerous effervescences and fermentations in which the particles approach and re cede so variously, and the phenomena especially of soft bodies, are not otherwise to be explained.
The whole form of the curve of forces being now elicited, by direct reasoning, from the phenomena, it remains to determine the constitution of the primary elements of matter, as deduced from those forces ; and this being done, the theory, as proposed in the be ginning of this account of it, may be legitimately ap plied to mechanical and physical science.
Seeing that the, repulsive force, in lessening the distance, increases in infinitum, it is evident, that no particle of matter can be contiguous to, or in contact with, another. The first elements of matter must therefore be altogether simple, and composed of no contiguous parts. .They must be also inextended. , 'We need not therefore be perplexed with the ques _ tions, whether any division of a real being can be car ried gd infinitum? or, whether the number of distinct and separable parts of matter be finite or infinite ? or any of the numberless difficulties which arise from the supposed continued extension of body, and which philosophers have hitherto been so much puzzled to explain : For if the first elements of matter are points altogether inextended, indivisible, and separated by some interval, the number in any given mass must ne cessarily be finite. The density of a body may be in definitely increased as well as diminished ; since the distance between the particles may be indefinitely di minished ; but upon the supposition of solid and ex tended elements, there is an evident limit to the increase of density, even when the particles come into contact.
With the simplicity and inextension of the primary particles, we should also admit their homogeneity. The arch of the curve expressing impenetrability, and the exterior arc exhibiting gravity, are always the same; for all bodies are equally impenetrable, and for their quantity of matter are equally heavy. It is therefore exceedingly improbable, that there should be any variety in the other parts of the curve among different particles ; or that it should be dif ferent in different directions from the same particle. Besides, such a variety is unnecessary, since it can; as we shall soon see, be sufficiently provided for, from the variety in the number and position of the points composing the sensible particles of matter.
The objections to this doctrine, which are urged by the Leibnitzians, derived from the principle of indiscerniblei, and of the sufficient reason, (See LEIBNITZ,) Boscovich removes, by expressing his conviction, that the infinite mind of the Divinity can perceive the individUation of obkcts altogether simi• lar ; and, with respect to the sufficient reason, he con tends for its falsity, as being founded on the princi ple necessity, maintained by Leibnitz ; and 'as the argument from induction, derived from the won derful variety we find in nature, where not two leaves in a forest are exactly the same, he says, all this va riety may be completely produced by the various ar rangement of the points of matter, seeing their num ber is so great. This he illustrates, by supposing an immense library of books in various languages, the letters in which were formed by small round points, placed so near each other, that the interval could only be discovered by the help of the microscope. Now any person, ignorant of languages, and of this kind of writing, begin diligently to examine this col lection•lie would first find out of the vast multitude of words, a certain number which occurred often in some of the books, and in others never appeared ; and collecting these together, he might form diction aries of the several languages. But dpon further inves tigation, it would be found, that•the whole of these words were expressed by the help of only twenty-four different letters ; and here he must stop, unless he could procure farther assistance : But suppose him provided with a microscope, he would at 'length dis cover, that by the various arrangements of single points, were formed the whole of the letters, words, langua ges, and books, on various subjects, that composed this great collection. Just so, says Boscovich, Is it in • chemistry, where the farther we push our analysis, the more nearly do we arrive at elements, simple and homogeneous. And thus we have detailed the whole of the proofs which Boscovich has given for his sys• tem : but before going farther, it will not be impro per to follow him also in refuting some of the objec tions which have been, or may be, proposed against its general reception.