Darken a room, and let the light be admitted therein only by a small hole; then, if the weather be fine, you will see on the wall, which is facing the hole, a picture of all those exterior objects which are opposite thereto, with all their colours, though these will be but faintly seen. The image of the objects that are stationary, as trees, houses, &c. will appear fixed; while the images of those that are in motion, will be seen to move. The image of every object will appear inverted, because the rays cross each other in passing through the small hole. If the sun shine on the hole, we shall see a luminous ray proceed in a strait line, and terminate on the wall. If the eye be placed in this ray, it will be in a right line with the hole and the sun: it is the same with every other object which is painted on the wall. The images of the objects exhibited on the same plane, are smaller in proportion as the objects are further from the hole. Many and important are the inferences which may be deduced from the foregoing experiment, among which are the following: 1. That light flows in a right line. 2. That a luminous point may be seen from all those places to which a strait line can be drawn from the point, without meeting with any obstacle; and consequently, 3. That a luminous point, by some unknown power, sends forth rays of light in all directions, and is the center of a sphere of light, which extends indefinitely on all sides; and if we conceive some of these rays to be intercepted by a plane, then is the luminous point the summit of a pyramid, whose body is formed by the rays, and its base by the intercepting plane. The image of the surface of an object, which is painted on the wall, is also the base of a pyramid of light, the apex of which is the hole; the rays which form this pyramid, by crossing at the hole, form another, similar and opposite to this, of which the hole is also the summit, and the surface of the object the base. 4. That an object is visible, because all its points are radiant points. 5. That the particles of light are indefinitely small; for the rays, which proceed from the points of all the objects opposite to the hole, pass through it, though extremely small, without embarrassing or confounding each other. 6. That every ray of light carries with it the image of the object from which it was emitted.