in an insensible manner indeed, because they are immediately replaced. They preserve for a long time the same disposition, and the same arrangement that the atoms do in the solid body, although, notwithstanding, their form may be sometimes altered. The direct production of images in space is equally instantaneous, because these images are only light substances destitute of depth.
“But there are other manners in which natures of this kind are produced; for there is nothing in all this which at all contradicts the senses, if one only considers in what way the senses are exercised, and if one is inclined to explain the relation which is established between external objects and ourselves. Also, one must admit that something passes from external objects into us in order to produce in us sight and the knowledge of forms; for it is difficult to conceive that external objects can affect us through the medium of the air which is between us and them, or by means of rays, whatever emissions proceed from us to them, so as to give us an impression of their form and colour. This phenomenon, on the contrary, is perfectly explained, if we admit that certain images of the same colour, of the same shape, and of a proportionate magnitude pass from these objects to us, and so arrive at being seen and comprehended. These images are animated by an exceeding rapidity, and, as on the other side, the solid object forming a compact mass, and comprising a vast quantity of atoms, emits always the same quantity of particles, the vision is continued, and only produces in us one single perception which preserves always the same relation to the object. Every conception, every sensible perception which bears upon the form or the other attributes of these images, is only the same form of the solid perceived directly, either in virtue of a sort of actual and continued condensation of the image, or in consequence of the traces which it has left in us.
“Error and false judgments always depend upon