That is a fact against which the misleading testimony of the senses can no longer prevail. The Earth, which was believed to be the stable basis of creation, is itself not sustained by anything material, but by invisible force. The void extends above and below, right and left, and to infinity in every direction. It is sustained by solar attraction and by its own movement. The same applies to all worlds, to all heavenly bodies, to everything which composes the universe, to the intimate constitution of bodies as well as the sidereal total. The Earth, the planets, the suns, the stars, the stellar systems, are the mobile atoms of the grand organism of the universe. The Milky Way is a dust in which every grain is a sun. * * * * * From the infinitely great, let us now descend to the infinitely small The substances which appear to us most solid and hard are composed of molecules which do not touch each other. Every one of these molecules is invisible to the naked eye and is itself made up of still smaller atoms which do not touch either. A bar of iron, for example, is composed of molecules which do not touch, which are in perpetual vibration, which separate under the influence of heat and close up under the influence of cold. Exposed to the Sun, the temperature of that bar reaches about 60 degrees centigrade; cooled by the ice of winter, it descends a few degrees below zero. Now, the length of that bar varies between the first condition and the second, and its molecules can be further separated by heating them to a higher temperature: they can thus be so far separated from each other that they exercise no further mutual attraction. When that happens, the bar melts and forms first a liquid and then a gas. * * * * * The Eiffel Tower is a little higher in summer than in winter and in the afternoon than the morning, on account of the variation produced by solar heat. The difference in height can attain 6 inches. * * * * * The smallness of molecules surpasses anything one can imagine. In the gold-beating industry gold-leaf has been obtained so thin that a quarter of a million leaves go to the inch. Each gold-leaf, therefore, has only a thickness of a 1/10,000 of a millimetre. Now, it is composed of molecules a considerable number of which is required to fill up that thickness. Two hundred of them arranged in a line and separated by intervals equal to their own diameters would just fill up the thickness of a gold-leaf. In experiments made on the action of oil upon the surface of water for calming the waves, it has been found possible to cover 400 square yards on the Lake of Geneva with 20 c.cm. of oil, which reduces the layer of oil also to 1/200,000 of a millimetre. Supposing that under these conditions the molecules of oil are in contact and in a single layer, they would at the most have that diameter.