attending subordinate facts has diluted the evidence of the principal and unquestionable ones, since the same general forms of expression are, and must be used in both cases.
It may be observed of natural philosophy, that in the parts where the ideas are simple, clear, and of the visible kind, or adequately expounded by such, and the method of investigation and computation mathematical, as in mechanics, hydrostatics, pneumatics, optics, and astronomy, the doubts and diversities of opinion which arise, are inconsiderable. But in the theories of chemistry, of manual arts and trades, of medicine, and, in general, of the powers and mutual actions of the small parts of matter, the uncertainties and perplexities are as great as in any part of science. For the small parts of matter, with their actions, are too minute to be the objects of sight; and we are as yet neither possessed of a detail of the phænomena sufficiently copious and regular, whereon to ground an investigation; nor of a method of investigation, subtle enough to arrive at the subtlety of nature even in the biggest component particles, much less in the particles of the smaller orders; and how far the number of orders may go, is impossible to say. I see no contradiction in supposing it infinite, and a great difficulty in stopping at any particular size.
Suppose the number of orders of particles infinite, or at least very great; and that particles of all orders are perpetually flying off from all bodies with great velocity. First, This may occasion the gravitation of the great bodies of the universe to each other, by the impulse of the smaller corpuscles upon particles of sizes equal to each other in the greater bodies, the impulses of the larger corpuscles, and upon particles, of unequal size, being evanescent in respect of the foregoing impulses. But where particles approach near to one another, and the corpuscles bear some finite ratio to the particles so as not to pervade them freely, before they come to particles of equal size to each other, but affect them in proportion to their surfaces, not solid content, and I suppose from many other causes, attractions of other kinds may arise; and if one or both of the contiguous particles send out many corpuscles with great force; also if these corpuscles effervesce together in the intermediate space, and gain new forces thence, &c. repulsive powers may rise. If it be reasonable to suppose many orders of particles, it is also reasonable to suppose, that their powers and properties are somewhat analogous to one another; and that those of the larger particles arise from, and are compounded of, those of the next less in size, and so on; just as the whole gravity of the moon is compounded of the gravity of all its parts. But these are all very gross and uncertain conjectures.
In the mean time, it seems proper to use the words magnetism,
