goes, the solid bodies which we see, but which differ materially from them in the thinness of their substance. In fact it is not impossible but that there may be in space some secretions of this kind, and an aptitude to form surfaces without depth, and of an extreme thinness; or else that from the solids there may emanate some particles which preserve the connection, the disposition, and the motion which they had in the body. I give the name of images to these representations; and, indeed, their movement through the vacuum taking place, without meeting any obstacle or hindrance, perfects all imaginable extent in an inconceivable moment of time; for it is the meeting of obstacles, or the absence of obstacles, which produces the rapidity or the slowness of their motion. At all events, a body in motion does not find itself, at any moment imaginable, in two places at the same time; that is quite inconceivable. From whatever point of infinity it arrives at some appreciable moment, and whatever may be the spot in its course in which we perceive its motion, it has evidently quitted that spot at the moment of our thought; for this motion which, as we have admitted up to this point, encounters no obstacle to its rapidity, is wholly in the same condition as that the rapidity of which is diminished by the shock of some resistance.
“It is useful, also, to retain this principle, and to know that the images have an incomparable thinness; which fact indeed is in no respect contradicted by sensible appearances. From which it follows that their rapidity also is incomparable; for they find everywhere an easy passage, and besides, their infinite smallness causes them to experience no shock, or at all events to experience but a very slight one, while an infinite multitude of elements very soon encounter some resistance.
“One must not forget that the production of images is simultaneous with the thought; for from the surface of the bodies images of this kind are continually flowing off