But one thing was lacking to complete the triumph of the new theory—an explanation of the force which held the planets in their orbits and balanced the universe. That explanation came in Newton's great law of gravitation, by which it is made know that "Every portion of matter in the universe attracts every other portion with a force varying directly as the product of the masses acted upon, and inversely as the square of the distance between them."[[9]]
The explanation of the Copernican system was now complete, and everywhere triumphant. Meantime larger and more powerful telescopes were being invented which constantly extended man's knowledge of the immensity of the universe. It is estimated that the unaided eye can see from five to eight thousand of the fixed stars; but with the aid of our modern telescopes, though no very reliable computation has yet been made, it is estimated that between thirty and fifty millions are visible;[[10]] and it only requires the invention of larger or more perfect telescopes to increase the number of God's creations to our already astonished vision!
It could only be expected that the facts discovered by our exact scientists would set in motion those of a speculative turn of mind. Among those most noted for outstripping the plodding scientists and plunging into speculation were Kant[[11]] and Johann Heinrich Lambert.[[12]] The former taking the now well-known construction of the planetary system as the basis of his speculation advanced the idea that the whole stellar universe was constructed on the same plan. That is, as the planets of our solar system revolved about a common centre, and are kept from falling into each other or into the sun by the centrifugal force generated by their revolutions in their orbits, "so Kant supposed the stars to be kept apart by a revolution around some common centre."[[13]]
At that time but little, if anything, was known positively about the proper motion of the stars; and the objection was made to his theory that the stars were found to occupy not only the same position from year to year, but from age to age, and therefore could not be moving about a centre. To this the philosopher replied that the motion of the stars was so slow, their distances from us so immense, and the time of their revolutions so long that the movement was imperceptible to us, but he doubted not that "future generations by combining their observations with those of their predecessors, would find that there actually was a motion among the stars."[[14]]
Lambert, the contemporary and a correspondent of Kant's, supposed "the universe to be arranged in a system of different orders. The smallest systems which we know are those made up of a planet with its satellites circulating around it as a center. The next system in order of magnitude is a solar system, in which a number of smaller systems are each carried round the sun. Each individual star which we see is a sun, and has its retinue of planets revolving round it, so that there are as many solar systems as stars. These systems are not, however, scattered at random, but are divided up into greater systems which appear in our telescopes as clusters of stars. An immense number of these clusters make up our galaxy, and form the visible universe as seen in our telescopes. There may be yet greater systems, each made up of galaxies, and so on indefinitely, only their distance is so immense as to elude our observation. Each of the smaller systems visible to us has its central body, the mass of which is much greater than that of those which revolve around it. This feature Lambert supposed to extend to other systems. As the planets are larger than their satellites, and the sun larger than its planets, so he supposed each stellar cluster to have a great central body round which each solar system revolved. As these central bodies are invisible to us, he supposed them to be opaque and dark. All the systems from the smallest to the greatest, were supposed to be bound together by the one universal law of gravitation."[[15]]
This of course in Lambert was speculative conjecture, based on the few facts that astronomers had discovered up to his day. There was no evidence, astronomers said, of the existence of the opaque centers referred to by Lambert, and they relegate the sublime ideas of the philosopher to the realm of pure speculation.
Later the German astronomer Madler[[16]] attempted to show from an examination he made of the motion of the stars that the whole steller universe was revolving around the star Alcyone, in the constellation of Pleiades. No more weight, however, has been given by astronomers to the conjectures of Madler than to those of Kant or Lambert. The ideas of all three have been held to be mere baseless speculation.[[17]] There is this to say, however, in favor of the theories of Kant, Lambert and Madler, and against the astronomers who condemn their conjectures: the stars which, in the days of the two former, at least, were generally supposed to be stationary and hence called fixed stars, are now known to have "a proper motion," by which astronomers mean "not an absolute motion, but only a motion relative to our system. As the sun moves, he carries the earth and all the planets with him; and if we observe a star at perfect rest while we ourselves are thus moving, the star will appear to move in the opposite direction. * * * Hence from the motion of a single star it is impossible to decide how much of this apparent motion is due to the motion of our system, and how much to the real motion of the star. If, however, we should observe a great number of stars on all sides of us, and find them all apparently moving in the same direction, it would be natural to conclude that it was really our system which was moving and not the stars. When Herschel averaged the proper motions of the stars in different regions of the heavens he found that this was actually the case. In general the stars moved from the direction of the constellation Hercules, and toward the opposite point of the celestial sphere, near the constellation Argues. This would show that, relatively to the general mass of the stars, our sun was moving in the direction of the constellation Hercules."[[18]]
As our sun is conceded to be one of the stars—one of the smaller ones, too, of the great galaxy that spans the heavens—if it be in motion, the inference that other stars are also in motion is not unreasonable. Indeed they are known to be in motion, but their appears to be, so far as the observations of astronomers enable them to determine, no regularity in that movement more than the general movement noted from the direction of Hercules. "So far as they have yet been observed," says Newcomb, "and indeed so far as they can be observed for many centuries to come, these motions take place in perfectly straight lines. If each star is moving in some orbit, the orbit is so immense that no curvature can be perceived in the short arc which has been described since accurate determinations of the position of the stars began to be made. * * * The stars in all parts of the heavens move in all directions, with all sorts of velocities. It is true that by averaging the proper motions, as it were, we can trace a certain law in them; but this law indicates, not a particular kind of orbit, but only an apparent proper motion, common to all the stars, which is probably due to a real motion of our sun and solar system."[[19]]
The assertion of the fact on the part of our exact masters in working astronomy that there is a motion among the stars, places under the speculations of Kant, Lambert and Madler the groundwork of a great probability in respect to their main idea, which I understand to be, that as the planets move around the sun in regular order, influenced by unvarying law, so the stars that make up the visible universe move around one or more centres. These centres are yet unknown. Madler may have been mistaken in pointing to Alcyone as that centre, but who shall say that one does not exist?
Meantime we need not follow this matter further. Enough has been said to show that the false geocentric theory has been displaced by the heliocentric doctrine, which has been demonstrated to be true. The earth is no longer looked upon as the centre of the universe, with the sun, the moon and stars especially created to revolve about it, to give it light by day and preserve it from total darkness in the night. The burning of Bruno, the imprisonment of Galileo by the Catholics, the condemnation of the works of Kepler by the Protestants of Germany, could not save the erroneous geocentric theory. It went down as all error in the end must go down. The earth instead of being the immovable centre of the universe is relegated to its true place—it is one of a number of planets, one of the smaller ones—that revolve around the sun. With all its islands and continents; its rivers, lakes and mighty oceans; its mountains and valleys; its towns, cities, and all the tribes of men, together with all their hopes and fears and petty ambitions—all is but a moat in God's sunbeam—a single grain of sand on the seashore! Our solar system itself, magnificent as it is in its greatness, is nevertheless insignificant in comparison with the visible universe of which it is only so small a part.