A short examination will, moreover, suffice to show of what this mechanical model is formed which is presented to us as constituting the essence of matter. This can be nothing else than the sensations, since we are incapable of perceiving or imagining anything else. It is the sensations of sight, of touch, and even of the muscular sense. Motion is a fact seen by the eye, felt by the hand; it enters into us by the perception we have of the solid masses visible to the naked eye which exist in our field of observation, of their movements and their equilibrium and the displacement we ourselves effect with our bodies. Here is the sensory origin, very humble and very gross, of all the mechanics of the atoms. Here is the stuff of which our lofty conception is formed. Our mind can, it is true, by a work of purification, strip movement of most of its concrete qualities, separate it even from the perception of the object in motion, and make of it a something or other ideal and diagrammatic; but there will still remain a residuum of visual, tactile, and muscular sensations, and consequently it is still nothing else than a subjective state, bound to the structure of our organs. We are, for the rest, so wrapped up in sensations that none of our boldest conceptions can break through the circle. But it is not the notion of movement alone which proceeds from sensation. There is also that of exteriority, of space, of position, and, by opposition, that of external or psychological events. Without declaring it to be certain, I will remind you that it is infinitely probable that these notions are derived from our muscular experience. Free motion, arrested motion, the effort, the speed, and the direction of motion, such are the sensorial elements, which, in all probability, constitute the foundation of our ideas on space and its properties. And those are so many subjective notions which we have no right to treat as objects belonging to the outer world. What is more remarkable, also, is that even the ideas of object, of body, and of matter, are derived from visual and tactile sensations which have been illegitimately set up as entities. We have come, in fact, to consider matter as a being separate from sensations, superior to our sensations, distinct from the properties which enable us to know it, and binding together these properties, as it were, in a sheaf. Here again is a conception at the base of visualisation and muscularisation; it consists in referring to the visual and other sensations, raised for the occasion to the dignity of external and permanent causes, the other sensations which are considered as the effects of the first named upon our organs of sense. It demands a great effort to clear our minds of these familiar conceptions which, it is plain are nothing but naive realism. Yes! the mechanical conception of the universe is nothing but naive realism.