E2AInt4
Axiom (Physical interlude) — Part II
Latin
Cum corpus motum alteri quiescenti quod dimovere nequit, impingit, reflectitur ut moveri pergat et angulus lineæ motus reflectionis cum plano corporis quiescentis cui impegit, æqualis erit angulo quem linea motus incidentiæ cum eodem plano efficit. Atque hæc de corporibus simplicissimis quæ scilicet solo motu et quiete, celeritate et tarditate ab invicem distinguuntur : jam ad composita ascendamus.
English (Elwes 1883)
--When a body in motion impinges on another body at rest, which it is unable to move, it recoils, in order to continue its motion, and the angle made by the line of motion in the recoil and the plane of the body at rest, whereon the moving body has impinged, will be equal to the angle formed by the line of motion of incidence and the same plane.
So far we have been speaking only of the most simple bodies, which are only distinguished one from the other by motion and rest, quickness and slowness. We now pass on to compound bodies.
Definition.--When any given bodies of the same or different magnitude are compelled by other bodies to remain in contact, or if they be moved at the same or different rates of speed, so that their mutual movements should preserve among themselves a certain fixed relation, we say that such bodies are in union, and that together they compose one body or individual, which is distinguished from other bodies by the fact of this union.
Modern English
When a body in motion strikes another body at rest that it cannot move, it rebounds so as to continue its motion, and the angle of the line of reflected motion with the plane of the body at rest that was struck equals the angle formed by the line of incident motion with that same plane.
So much for the simplest bodies, which are distinguished from one another only by motion and rest, speed and slowness. Now let us move to composite ones.