Page:The System of Nature.djvu/38

 which either accompany or follow them. Thus, when we see a man run away, we judge him to be interiorly actuated by the passion of fear.

Motion, whether visible or concealed, is styled ACQUIRED, when it is impressed on one body by another; either by a cause to which we are a stranger, or by an exterior agent which our senses enable us to discover. Thus we call that acquired motion, which the wind gives to the sails of a ship. That motion which is excited in a body, that contains within itself the causes of those changes we see it undergo, is called SPONTANEOUS. Then it is said, this body acts or moves by its own peculiar energies. Of this kind is the motion of the man who walks, who talks, who thinks. Nevertheless, if we examine the matter a little closer, we shall be convinced, that, strictly speaking, there is no such thing as spontaneous motion in any of the various bodies of Nature; seeing they are perpetually acting one upon the other; that all their changes are to be attributed to the causes, either visible or concealed, by which they are moved. The will of man is secretly moved or determined by some exterior cause that produces a change in him: we believe he moves of himself, because we neither see the cause that determined him, the mode in which it acted, nor the organ that it put in motion.

That is called SIMPLE MOTION, which is excited in a body by a single cause. COMPOUND MOTION, that which is produced by two or more different causes; whether these causes are equal or unequal, conspiring differently, acting together or in succession, known or unknown.

Let the motion of beings be of whatsoever nature