THE memory of Urania and the celestial journey on which she had borne me away, the truths she had made me realize, Spero's history, his trials in his pursuit of the absolute, his apparition, his story of another world, still haunted me, and kept the same problems (partly solved, partly veiled in the uncertainty of our knowledge) incessantly before my mind. I felt that I had gradually risen to a perception of the truth, and that the visible universe was really but an appearance, which we must pass through in order to reach reality.

The testimony of our senses is but an illusion. The Earth is not what it seems to be. Nature is not what we think. In the physical universe itself, where is the fixed point upon which material creation is in equilibrium?

The natural and direct impression given by the observation of Nature is that we inhabit a solid, stable Earth, fixed in the centre of the universe. It took long centuries of study and a great deal of boldness to free ourselves from that natural conviction, and to realize that the world we are on is isolated in space, without any support whatever, in rapid motion on itself and around the Sun. But to the ages before scientific analysis, to primitive peoples, and even to-day to three quarters of the human race, our feet are resting on a solid Earth which is fixed at the base of the universe, and whose foundations are supposed to extend into the depths of the infinite.

And yet from the time when it was first realized that it is the same Sun which rises and sets every day; that it is the same Moon, the same stars, the same constellations which revolve about us, those very facts forced one to admit with absolute certainty that there must be empty space underneath the Earth, to let the stars of the firmament pass from their setting to their rising. This first recognition was a turning-point. The admission of the Earth's isolation in space was astronomy's first triumph. It was the first step, and indeed the most difficult one. Think of it! To give up the foundations of the Earth! Such an idea would never have sprung from any brain without the study of the stars, or indeed without the transparency of the atmosphere. Under a perpetually cloudy sky, human thoughts would have remained fixed on terrestrial ground like the oyster to the rock.

The Earth once isolated in space, the first step was taken. Before this revolution, whose philosophical bearing equals its scientific value, all manner of shapes had been imagined for our sublunary dwelling-place. In the first place, the Earth was thought to be an island emerging from a boundless ocean, the island having infinite roots. Then the Earth, with its seas, was supposed to be a flat, circular disk, all around which rested the vault of the firmament. Later, cubic, cylindrical, polyhedric forms, etc., were imagined. But still the progress of navigation tended to reveal its spherical nature, and when its isolation, with its incontestable proofs, was recognized, this sphericity was admitted as a natural corollary of that isolation and of the circular motion of the celestial spheres around the supposed central globe.

The terrestrial globe being from that time recognized as isolated, to move it was no longer difficult. Formerly, when the sky was looked upon as a dome crowning the massive and unlimited Earth, the very idea of supposing it to be in motion would have been not only absurd but untenable. But from the time that we could see it in our minds, placed like a globe in the centre of celestial motion, the idea of imagining that perhaps this globe could revolve on itself, so as to avoid obliging the whole sky and the immense universe to perform this daily task, might come naturally into a thinker's mind; and indeed we see the hypothesis of the daily rotation of the terrestrial sphere coming to light in ancient civilizations, among the Greeks, the Egyptians, the Indians, etc. It is sufficient to read a few chapters of Ptolemy, Plutarch, or Surya-Siddhanta for an account of these conjectures. But this new hypothesis, although it had been prepared for by the first one, was none the less bold, and contrary to the feelings inspired by the direct contemplation of Nature. Thoughtful mankind was obliged to wait until the sixteenth century, or, to speak more correctly, until the seventeenth century, to learn our planet's true position in the universe, and to know by supported proofs that it has a double movement,—daily about itself, and yearly about the Sun. From that time only, from the time of Copernicus, Galileo, Kepler, and Newton, has real astronomy existed.

And yet again, that was but a beginning, for the great remodeller of the world's system, Copernicus himself, had no suspicion of the Earth's other motions, or of the distances of the stars. It is only in our own century that the first measurements of the distances of the stars could be made, and it is only in our day that sidereal discoveries have afforded us the necessary data by which we might endeavor to account for the forces which maintain the equilibrium of creation.

The ancient idea of endless roots attributed to the Earth, evidently left much to be desired to minds anxious to go to the bottom of things. It is absolutely impossible for us to conceive of a material pillar, as thick and as wide as you like (of the diameter of the Earth, for example), sinking down into the infinite; just as one cannot admit the real existence of a stick which should have but one end. No matter how far our mind goes down towards the base of such a material pillar, there is a point where it can see the end of it. The difficulty had been obviated by materializing the celestial sphere and putting the Earth inside it, occupying all its lower portion. But in the first place it became difficult to adjust the motion of the stars, and on the other hand this material universe itself, enclosed in an immense crystal globe, was held up by nothing, since the infinite must extend all around, beneath it, as well as above. Investigating minds were at first obliged to free themselves from the vulgar idea of weight.

Isolated in space like a child's balloon floating in the air, and more absolutely too, for the balloon is carried by aerial waves, while worlds gravitate in the void, the Earth is a toy for the invisible cosmic forces which it obeys,—a real soap-bubble, sensitive to the faintest breath. Besides, we can easily judge of it by looking at the same time at the whole of the eleven principal motions of the Earth, by which it is moved. Perhaps they will help us to find that "fixed point" which our philosophical ambition asks for. Thrown around the Sun at a distance of 37,000,000 leagues, and making at this distance its annual revolution around the luminous star, it consequently moves at the rate of 643,000 leagues per day; that is, 26,800 leagues an hour, or 29,450 metres per second. This speed is eleven hundred times more rapid than an express train going at the rate of a hundred kilometres an hour. It is a ball, going with a rapidity seventy-five times greater than that of a bomb, always hurrying on, but never reaching its goal. In 365 days, 6 hours, 9 minutes, and 10 seconds, the terrestrial projectile has returned to the same point of its orbit relative to the Sun, and continues its flight. The Sun, on its part, is moving in space, following a line oblique to the plane of the Earth's annual motion,—a line drawn towards the constellation of Hercules. The result is, that instead of describing an exact circle, the Earth describes a spiral, and has never passed over the same road twice in its existence. To its motion of annual revolution around the Sun there is added perpetually, as a second motion, that of the Sun itself, which draws it, with all the solar system, into an oblique descent towards the constellation of Hercules. During all this time our little globe pirouettes around itself every twenty-four hours, and gives us the daily succession of days and nights,—diurnal rotation: third motion.

It does not turn upright upon itself, like a top, which would be vertical on a table, but is inclined, as everybody knows, by 23° 27'. This inclination, too, is not always the same; it varies from year to year, from age to age, oscillating slowly by secular periods. That is a fourth kind of motion.

The orbit in which our planet yearly travels around the Sun is not circular, but elliptical. This ellipse itself also varies from year to year, and from century to century; sometimes it approaches the circumference of a circle, sometimes it lengthens out to a great eccentricity. It is like an elastic ring, which can be bent more or less out of shape. Fifth complication in the Earth's motion.

This ellipse itself is not fixed in space, but revolves in its own plane in a period of 21,000 years. The perihelion, which at the beginning of our era was at 65 degrees of longitude, starting from the vernal equinox, is now at 101 degrees. This secular displacement of the line of the apsides brings a sixth complication to the motion of our abiding-place.

Here is a seventh. We said just now that our globe's axis of rotation is inclined, and everybody knows that the imaginary prolongation of this axis points towards the polar star. This axis itself is not fixed. It revolves in 25,765 years, keeping its inclination of 22 to 24 degrees, so that its prolongation describes a circle of 44 to 48 degrees in diameter—according to the epoch—on the celestial sphere around the pole of the ecliptic. It is in consequence of this displacement of the pole that Vega, in twelve thousand years, will again become the polar star, as she was fourteen thousand years ago. Seventh kind of movement.

An eighth motion, due to the action of the Moon on the equatorial swelling of the Earth, that of nutation, causes the pole of the equator to describe a small ellipse in eighteen years and eight months.

A ninth, due also to the attraction of our satellite, incessantly changes the position of the globe's centre of gravity and the Earth's place in space. When the Moon is in front of us, she accelerates the speed of the globe; when she is behind, she retards us, on the contrary, like a check-rein,—a monthly complication which is added to all the others.

When the Earth passes between the Sun and Jupiter, the attraction of the latter, in spite of its distance of 155,000,000 leagues, makes it deviate by 2 m. 10 sec. from its absolute orbit. The attraction of Venus makes it deviate 1 m. 25 sec. the other way. Saturn and Mars also act upon it, but more feebly. These are exterior disturbances, which make up a tenth kind of correction to add to the motion of our celestial barque.

The whole of the planets weigh about one seven hundredth part of the weight of the Sun; the centre of gravity around which the Earth annually turns is not in the very centre of the Sun, but far from the centre, and often even outside of the solar globe. Now, absolutely speaking, the Earth does not turn around the Sun; but the two heavenly bodies, Sun and Earth, turn about their common centre of gravity. Thus the centre of our planet's annual motion is constantly changing place, and we may add this eleventh complication to the others. We might even add many others to these; but the preceding ones are enough to make the degree of lightness and delicacy of our floating island appreciated, subject, as we have seen, to all the fluctuations of celestial influences. Mathematical analysis goes very far beyond this summary statement. It has found that the Moon alone, which seems to turn so peacefully about us, has more than sixty distinct motions.

The expression is therefore not exaggerated: our planet is but the plaything of the cosmic forces which accompany it in the meadows of the sky, and it is the same with everything existing in the universe. Matter is meekly obedient to force.

Where, then, is the fixed point which we desire for our support?

Our planet, then, formerly supposed to be at the base of the universe, is in fact kept up at a distance by the Sun, which makes the Earth gravitate about it with a speed corresponding to that distance. This speed, caused by the solar mass itself, keeps our planet at the same mean distance from the central star. A lesser speed would make the weight predominate, and would lead to the Earth's falling into the Sun; a greater speed, on the contrary, would progressively and infinitely send our planet away from its life-giving focus. But at the speed resulting from gravitation, our wandering home remains suspended in permanent stability, just as the Moon is upheld in space by the force of the Earth's gravity, which makes it circulate about the Earth with the speed requisite to maintain it constantly at the same mean distance. The Earth and the Moon thus form a planetary couple in space which sustain each other in perpetual equilibrium under the supreme domination of solar attraction. If the Earth existed alone in the universe, it would be forever motionless in the void, wherever it had been placed, with no power to descend or rise or change its position in any way whatsoever; these very expressions—to rise, descend, left or right—having no absolute sense whatever. If this same Earth, while existing alone, had received any impetus whatever, had been thrown with any speed in any direction, it would have whirled away forever in a straight line in that direction, never being able to stop or to slacken its pace or change its motion. It would have been the same thing if the Moon had existed alone with it; they would both have turned about their common centre of gravity, fulfilling their destiny in the same place in space, flying together, following the direction in which they had been thrown. The Sun existing and being the centre of its system, the Earth, all the planets and their satellites, are dependent upon it, and to it their destiny is irrevocably bound.

Is the fixed point that we are seeking, the solid base which we seem to need to insure the stability of the universe, to be found in that colossal and heavy globe, the Sun?

Assuredly not, since the Sun itself is not in repose, for it is bearing us and all its system away towards the constellation of Hercules.

Does our Sun gravitate around an immense sun whose attraction extends to it and controls its destinies as it controls that of the planets? Do investigations in sidereal astronomy lead us to believe that a star of such magnitude can exist in a direction situated at right angles with our course towards Hercules? No; our Sun is influenced by sidereal attraction, but no one star appears to overpower all the others and reign sovereign over our central star.

Although it may be perfectly admissible, or rather certain, that the sun nearest to ours, the star Alpha Centauri, and our own Sun feel their mutual attraction; although this star may be situated at about 90 degrees from our tangent towards Hercules, and, more than that, in the plane of the principal stars, passing by Perseus, Capella, Vega, Aldebaran, and the Southern Cross; and although the proper motion of this neighboring sun may be turned sensibly in the opposite direction from ours,—yet we could not consider these two systems as forming one couple analogous to that of the double stars; in the first place, because all the known double-star systems are composed of stars much nearer to each other, and then because in the immensity of the orbit described, according to this hypothesis, the attraction of the neighboring stars could not be considered as remaining without influence; and lastly, because the actual rates of speed with which these two suns are moved are much less great than those which would result from their mutual attraction.

The little constellation of Perseus, especially, might very well exert a more powerful action than that of the Pleiades, or than any other group of stars, and be the fixed point, the centre of gravity, of the motions of our Sun, of Alpha Centauri, and the neighboring stars, inasmuch as the cluster of Perseus is not only at right angles with the tangent of our movement towards Hercules, but also in the great circle of the principal stars and precisely at the intersection of this circle with the Milky Way. But here another factor comes in, of more importance than all the preceding ones,—this Milky Way, with its eighteen millions of suns, of which it would assuredly be audacious to seek the centre of gravity.

But what is the whole entire Milky Way, after all, compared with the milliards of stars which our mind contemplates in the bosom of the sidereal universe? Is not this Milky Way itself moving like an archipelago of floating islands? Is not every resolvable nebula, each cluster of stars, a Milky Way in motion under the action of the gravitation of other universes, which call to it and appeal to it through the infinite night?

Our thoughts are transported from star to star, from system to system, from region to region, in the presence of unfathomable grandeurs, in sight of celestial motions whose speed we are but just beginning properly to value, but which already surpasses all conception. The proper annual motion of the sun Alpha Centauri exceeds 188 millions of leagues per year. The proper motion of the 61st of Cygnus (second sun in the order of distances) is equivalent to 370 millions of leagues per year, or about one million of leagues per day. The star Alpha Cygni comes to us in a direct line at a speed of 500 millions of leagues per year. The proper motion of the star 1830 of Groombridge's Catalogue rises to 2,590 millions of leagues per year, which represents seven millions of leagues per day, 115,000 kilometres per hour, or 320,000 metres per second! These are minimum estimates, inasmuch as we certainly do not see perpendicularly, but obliquely, the stellar displacements thus measured.

What projectiles! They are suns thousands and millions of times heavier than the Earth, launched through the unfathomable void with giddy rates of speed, revolving in immensity under the influence of the gravitation of all the stars of the universe. And these millions and thousand millions of suns, planets, clusters of stars, nebulÆ, worlds in their infancy, worlds near their end, rush with equal velocity towards goals of which they are ignorant, with an energy and intensity of action before which gunpowder and dynamite are like the breath of sleeping babes.

And thus everything hurries on through all eternity perhaps, without being able ever to reach the unexisting limits of infinity.... Motion, activity, light, life everywhere. Happily so, without doubt. If all these innumerable suns, planets, earths, moons, comets, were fixed and immovable, petrified kings in their eternal tombs, how much more formidable, but also more mournful, would be the aspect of such a universe! Can you imagine the whole creation stopped, benumbed, mummified? Is not such an idea unbearable? Is there not something funereal about it?

What causes these motions? What maintains them? What regulates them? Universal gravitation, invisible force, which the visible universe (what we call matter) obeys. A body attracted from infinity by the Earth would attain a velocity of 11,300 metres per second; just as a body thrown from the Earth with that speed would never fall again. A body attracted by the Sun from the infinite would attain a speed of 608,000 metres; and a body thrown by the Sun with that swiftness would never return to its point of departure. Clusters of stars may give us velocities much more remarkable still, but which are explained by the theory of gravitation. A glance at a map of the proper motions of the stars is enough to make one understand the variety and grandeur of these motions.

Thus the stars, the suns, the planets, the worlds, the shooting-stars, the meteoric stones, in short all the bodies which constitute this vast universe, rest, not on solid bases, as the childish and primitive conception of our fathers seemed to require, but upon invisible and immaterial forces which govern their motions. These milliards of celestial bodies have their respective movements for the purpose of stability, and mutually lean upon each other across the void which separates them. The mind which could eliminate time and space would see the Earth, the planets, the Sun, the stars, rain down from a limitless sky in all imaginable directions, like the drops carried away by the whirlwinds of a gigantic tempest, and drawn, not by a common basis, but by the attraction of each and all; each one of these cosmic drops, each one of these worlds, each one of these suns, is whirled away at a speed so rapid that the flight of cannon-balls is but rest in comparison: it is not one hundred, nor five hundred, nor a thousand metres per second,—it is ten thousand, twenty, fifty, a hundred, and even two or three hundred thousand metres per second!

How is it that there are no meetings in the midst of all this motion? Perhaps there may be some,—the "temporary stars," which appear to rise again from their ashes, would seem to indicate it. But as a matter of fact, it would be difficult for meetings to occur, because space is immense, relatively to the celestial bodies, and because the motion by which each body is animated entirely prevents it from submitting passively to the attraction of another body and falling upon it; it keeps its own motion, which cannot be destroyed, and glides around the focus which attracts it, as a butterfly would obey the attraction of a flame without burning itself in it. Besides, absolutely speaking, these motions are not "rapid."

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.

But whatever may be the idea that one conceives of the inner constitution of bodies, the truth is now recognized and indisputable that the fixed point for which our imagination has been seeking, exists nowhere. Archimedes can vainly call for a point of support, that he may lift the world. Worlds, like atoms, rest on the invisible, on immaterial force; everything moves, urged on by attraction, and as if in search of that fixed point which flies as it is pursued, and which does not exist, since in the infinite the centre is everywhere and nowhere. So-called positive minds, which assert with so much assurance that "Matter reigns alone, with its properties," and who smile disdainfully at the researches of thinkers, should first tell us what they mean by that famous word "matter." If they did not stop at the surface of things, if they even suspected that appearances hid intangible realities, they would doubtless be a little more modest.

To us, who seek the truth with no jealousy of system, it seems that the essence of matter remains as mysterious as the essence of force; the visible universe not being in the least what it appears to be to our senses. In fact, that visible universe is composed of invisible atoms; it rests upon the void, and the forces which govern it are in themselves immaterial and invisible. It would be less bold to think that matter does not exist, that all is dynamism, than to pretend to affirm the existence of an exclusively material universe. As to the material support of the world, it disappeared—a somewhat interesting observation—precisely with the conquest of Mechanics, which proclaim the triumph of the invisible. The fixed point vanishes in the universal balance of powers, in the ideal harmony of ether vibrations; the more one seeks it, the less one finds it; and the last effort of our thought has for a last support, for supreme reality, the Infinite.