In order to explain my view on the natural causes of light and colors, let us conceive of a large balloon compressed from without by an almost infinite force, and filled with a fluid matter whose motion is so rapid that not only does it tum with great speed about a common center but also that each part of it in order to expend all its motion,.e., to move as much as it has force to, is also required to tum on the center of an infinity of tiny vortexes and to flow between them, and all this with extraordinary rapidity.