Formerly people were troubled, not without reason, concerning the solidity of the foundations of the world, for before the isolation of our planet in space and its movement round the Sun had been demonstrated it seemed indispensable to give to the Earth an unshakable foundation and an unlimited route. But since the heavenly bodies rise and set and pass under our feet this foundation had to be given up, apart from the fact that it did not satisfy the most far-seeing minds. It is quite impossible for us to conceive a material pile, however solid or thick, even as thick as the Earth’s diameter and rooted in infinite space, just as one cannot imagine the real existence of a stick which has only one end. However far the mind can descend towards the base of that material pillar, the end must come at last, since only empty space can be without end, and then that terrestrial pillar serves no purpose at all since it is itself without a support. Besides, travellers succeeded one day in voyaging all round the globe, and nowhere was this imaginary pillar discovered.
The modern conception of force in contrast with the ancient idea of matter has a philosophical import without precedent in the whole history of the science. It teaches, proves to us, and convinces us that the visible, palpable, material universe rests on the invisible and the immaterial, on imponderable force.
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.
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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.
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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.
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