Indeed, everything runs, flies, falls, rolls, rushes through the void, but at such respective distances that it all appears to be at rest. If we wanted to place in a frame, the size of Paris, the stars whose distances have been measured up to the present time, the nearest star would be placed at two kilometres from the Sun, from which the Earth would be distant one centimetre, Jupiter at five centimetres, and Neptune at thirty centimetres. The 61st of Cygnus would be at four kilometres, Sirius at ten kilometres, the polar star at twenty-seven kilometres, etc.; and the immense majority of the stars would remain outside the department of the Seine. Well, to give to all these projectiles their relative motions, the Earth would take a year to run through its orbit of a centimetre radius, Jupiter twelve years to run through his of five centimetres, and Neptune one hundred and sixty-five years. The proper motions of the Sun and stars would be of the same nature; that is to say, all would appear to be at rest, even under the microscope. Urania reigns with calmness and serenity in the immensity of the universe. So the constitution of the sidereal universe is just like that of the bodies which we call material. All bodies, organic or inorganic, man, animal, plant, stone, iron, bronze, are composed of molecules which are in perpetual motion, and which do not touch one another. Each one of these atoms is infinitely small, and invisible not only to the eye, not only to the microscope, but even to thought; since it is possible that these atoms may be centres of force. It has been calculated that in the head of a pin there are not less than eight sextillions of atoms,--that is, eight thousand milliards of milliards,--and that in one centimetre of cubic air there are not less than a sextillion of molecules. All these atoms, all these molecules, are in motion under the influence of the forces which govern them; and as compared with their dimensions, great distances separate them. We may even believe that there is in principle but one kind of atoms, and that it is the number of primitive atoms, essentially simple and homogeneous, their modes of arrangement, and their motions, which constitute the diversity of molecules; a molecule of gold, of iron, would not differ from a molecule of sulphur, of oxygen, of hydrogen, etc., except in the number, the disposition, and the motion of the primitive atoms which compose it: each molecule would be a system, a microcosm.