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. [Sidenote: * _It sounds hard, To say, An _extended_ substance is _indivisible_._] 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 {307} 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