3. This supposed, he easily gives an account, why the Nile yearly overflows about the end of June: For, as at that time there falls much rain in Æthiopia, it must needs be, that the Nile, whose source is in that Country, should then overflow, when those rains begin, and subside, when they cease.
There are besides, in this Book, two other Tracts. In the first, M. Vossins endeavours to maintain the Doctrine, he had deliver'd in his Book De Lumine, and to shew, that the Soul of Animals is nothing but Fire, that there are no invisible Atoms; nor so much as any Pores, even in the Skin of man. Here he treats also of Refractions, and alledges the Examples of several persons, who have then seen the Sun by the means of Refraction, when really He was under the Horizon.
In the second, He discourses of some points of the Mechanicks; and relates among other things, that the Arrows and battering Rams (Aries) of the Antients did as much execution, as our Muskets and Canons; and then, that the Vehemence of the percussion depends as much upon the Length of the percutient Body, as upon the velocity of the Motion. He adds, that the Length of a Canon ought not to exceed 13 foot, and that a greater length is not onely useless, but hinders also the effect of the Gun, not because the Bullet is thrown out of the Gun, before all the powder is fired (as some believe;) but because the Bullet is then beaten back into the Gun by the Air, re-entring into it with impetuosity, when the flame is extinct.
III. LE DISCERNEMENT DU CORPS ET DE L'AME, par M. de Cordemoy.
This French Treatise (but very lately come to the Publisher's hands) examines the different Operations of the Soul and Body, and the Secret of their Union, pretending to discover to every one, what he is, and what is transacting within him. It consists of six Discourses.
1. In the first, the Author examines the Notions, we have in general of Bodies and Matter; of Quantity; of Qualities; of Place; of Rest; of Motion; of Vacuity; of Forms: to shew what is to be understood by these Terms, which cause all the perplexity that is in the ordinary Physicks. He begins with taking notice, that hitherto Philosophers have had no distinct notions of Bodies and Matter, from the want whereof he conceives, that almost all the Errors in Common Physiology have
* It sounds hard, To say, An extended substance is indivisible. sprung. To rectify which, he defines Bodies to be * Extended Substances, and Matter an Aggregate of Bodies. Whence he inferrs, that Bodies are Indivisible and Matter divisible; a Body being nothing but one and the same substance, whose different extremities are inseparable, because they are the extremities of one and the same Extension, and, in a word, of one and the same Substance; but Matter being nothing but an Association or Collection of Bodies, 'tis evident, (saith he) it must be divisible. This doctrine he so much insists upon, that he conceives, Nature cannot subsist, if a Body in the sence he takes it, be divisible; and that Motion and Rest cannot be explicated without it. As for Quantity, he makes that to be nothing but More or Less Bodies; not allowing, that each Body should be a Quantity, though it be a part of Quantity; no more than an Unite is a Number, though it make part of a Number: so that Quantity and Extension are two distinct things with him, the first belonging properly to Matter, the last to a Body. Touching Vacuity, he conceives, that the Bodies, which compose a mass, are not every where so near one another, as not to leave some interval in several places. Neither does he think it necessary, that those intervals should be fill'd up; nor unconceivable, that there should be no Body between two Bodies; which touch not one another. And when 'tis said, that those intervals cannot be conceived without Extension, and that consequently there are Bodies that replenish them, he frankly pronounces that not to be true; and affirms, that though it may be said, that between two Bodies, which touch not one another, other Bodies may be placed of so or so many feet, &c: yet ought it not to be inferred, that therefore they are there, but onely, that they are thus placed, that there may be put between them so many Bodies, as joyned together would compose an Extension of so many feet. So that one conceives onely, that Bodies may be placed there, but not that they are there: and as we can have an Idea of many Bodies, though none of them be in being; so we can conceive, that some Bodies may be put between others, where really there are none. And when 'tis alledged, that if all the Bodies, that fill a vessel full, were destroyed, the sides of the vessel would be closed together; He professes, he understands not that ratiocination, nor can conceive, what one Body does to the subsistence of another, more than to sustain themselves mutually, when they are thrust by the neighbouring ones: and therefore sees not, why the sides of the vessel should close, if nothing did thrust them together; but understands clearly, that two Bodies may well subsist so far from one another, that one might place a great many Bodies between them, or none at all, and yet they neither approach to, not recoil from one another.
2. In the Second, he examines the Changes, which he knows in Matter, and makes it his business to explicate all those that respect Quantity, Qualities and Forms, by Local Motion, esteeming that needs no other.
3. In the third, he explains the Motion of Artificial Engins, and that of Natural ones, by one and the same Cause; endeavouring among other things to shew, that the Body of an Animal is moved after the same manner with a Watch. That cause of motion he makes the Materia Subtilis; and the finer or subtiler that is, the better and fitter he conceives it to be to preserve Motion.