the large ones, since both the one and the other find everywhere an easy passage, from the very moment that no obstacle intervenes to thwart their movements? Movement from low to high, horizontal movement to and fro, in virtue of the reciprocal percussion of the atoms, movement downwards, in virtue of their weight, will be all equal, for in whatever sense the atom moves, it must have a movement as rapid as the thought, till the moment when it is repelled, in virtue of some external cause, or of its own proper weight, by the shock of some object which resists it.
“Again, even in the compound bodies, one atom does not move more rapidly than another. In fact, if one only looks at the continued movement of an atom which takes place in an indivisible moment of time, the briefest possible, they all have a movement equally rapid. At the same time, an atom has not, in any moment perceptible to the intelligence, a continued movement in the same direction; but rather a series of oscillating movements from which there results, in the last analysis, a continued movement perceptible to the senses. If then, one were to suppose, in virtue of a reasoning on things invisible, that, in the intervals of time accessible to thought, the atoms have a continued movement one would deceive one’s self, for that which is conceived by the thought is true as well as that which is directly perceived.
“Let us now return to the study of the affections, and of the sensations; for this will be the best method of proving that the soul is a bodily substance composed of slight particles, diffused over all the members of the body, and presenting a great analogy to a sort of spirit, having an admixture of heat, resembling at one time one, and at another time the other of those two principles. There exists in it a special part, endowed with an extreme mobility, in consequence of the exceeding slightness of the elements which compose it, and