Contracting still more, the rarer gases, aided by centrifugal force, would be left behind as a ring that would ultimately be separated, like Saturn’s ring, from the retreating body. There would naturally be some places in this ring denser than others; these would gradually absorb all the ring into a planet, and still revolve about the central mass, and still rotate on its own axis, throwing off rings from itself.
Thus the planet Neptune would be left behind in the first sun-ring, to make its one moon; the planet Uranus left in the next sun-ring; and so on down to Mercury. The outer planets would cool off first, become habitable, and, as the sun contracted and they radiated their own heat, become refrigerated and left behind by the retreating sun. The four great classes of facts confirmatory of this hypothesis are as follows: 1st. All the planets move in the same direction and nearly in the same plane, as if thrown off from one equator; 2d. The motions of the satellites about their primaries are mostly in the same direction as that of their primaries about the sun; 3d. The rotation of most of these bodies on their axes, and also of the sun, is in the same direction as the motion of the planets about the sun; 4th. The orbits of the planets, excluding asteroids, and their satellites, have but a comparatively small eccentricity; 5th. Certain nebulae are observable which are not yet condensed into solids, but are still bright gas.”[1]
The nebular hypothesis above stated was advanced by astronomers early in the eighteenth century, and later established by Laplace on a mathematical basis, who at the same time advocated the theory as materialistic. It is accepted quite generally by astronomers at the present day, though in a greatly modified form; for there are many difficulties in the way of a full belief of the theory. Sir Robert Ball in a late work says of Herschel’s belief of the transmutation of nebulae into stars; “To establish this theory it would be necessary to watch the actual condensation of one single nebula from the primitive gaseous condition down to the stellar points. It may easily be conceived that such a process would require a vast lapse of time, perhaps enormously greater than the period between the invention of the telescope and the present moment. It may at all events be confidently asserted that this condensation of a nebula into a star is a process which has never been witnessed.” Concerning the theory of Laplace he tells us that it is “almost incapable of receiving any direct testimony;” and gives as the verdict of science, the words of Newcomb; “At the present time the nebular hypothesis is only indicated by the general tendencies of the laws of nature.”
According to this theory,—if all the planets are of the same substance as the earth on which we live, and of the greater sun from which they have ages since been separated,—there must once have been material heavy as rock and earth after condensation, filling the space around our sun in every direction for 3,000 millions of miles. If we could learn how this material of fire-mist originated we could better understand the mystery of world-making. A theory that would explain the formation of our own solar system should explain the formation of all the suns in space, a state of fire-mist for one implying the same for all. Let us consider whether there may not be other explanations of the phenomena in question fully as credible as the one given, and quite as consistent with all the known laws of nature.
CHAPTER I.
EXPANSION AND CONTRACTION.
1st. Expansion. It is supposed by the nebular hypothesis that the planets were all formed from rings of condensing vapor thrown off from a contracting sun which once filled space to, and beyond, Neptune’s distance. Let us imagine them again expanded to a like dimension, or even greater, reaching half way to the next nearest sun, Alpha Centauri, whose distance from our sun is computed as about twenty trillions of miles. Assuming this to be the true distance there could be placed between the two stars fifteen septillions of suns, each with a diameter of 800 thousand miles. Were it possible to expand the earth a million and a quarter times its present size, that is as large as the sun now is, it would then be but one fifteen-septillionth the size necessary to fill the space between the sun and Alpha Centauri. What we know of earth, air, water, rocks, and the metals would not lead us to suppose that these substances could be increased by expansion even a million of times. Could there be such an expansion they would then exist as mere atomic particles of dust incapable of holding heat with the outside element space 300° below zero. Nearly all known substances expand on being heated, though not often to any great extent; as, for example, iron and the metals. But anything that is greatly expanded cools rapidly. Then may we suppose that earth to-day could be expanded into a body large enough to fill the great space it must once have occupied in the state of fire-mist claimed for it? or, if thus expanded, that it would take one year, or even one day, to cool such a body?
We have seen thus how improbable it is that the earth could be expanded to fill the space it must once have occupied according to the nebular theory; and as we imagine the denser any volume is the more it will expand can we suppose the other planets, with a volume thousands of times greater than that of earth but a density not averaging one-fourth as much, will expand to a greater degree? Were they all ground to the finest dust, even like the atoms we detect floating in the sunbeams, they would no more than fill a globe, with the sun for its centre, whose circumference reached out to Neptune.
2d. Contraction. It is thought by many that the sun obtains its heat by the contraction of its diameter, and that at the rate of two hundred and twenty feet per year, or four miles a century. Before contraction, then, both the sun and the earth must have been much larger and consequently nearer each other than they are as seen to-day. If the sun’s diameter contracts four miles during a century, to increase its size so as to carry it out to Neptune, 3,000 millions of miles distant, would take 1500 million centuries. But that the sun thus receives its heat is a supposition; for how can any one tell that it contracts each century two miles on its radius, when a second represents four hundred and fifty miles, and two miles would be but one-two hundred and fiftieth part of a second?
Should the earth be cooling by expending more heat than it receives, as some claim, it should contract from the loss of heat as well as the sun. But if earth does thus contract it must be smaller than formerly, the sun must have less hold upon it, and with a varying gravitation, must lose its delicate balance.[2] Yet what proof have we that earth is to-day smaller than it was two thousand years ago?
Further, we find that the more a body contracts the faster it revolves. The sun now revolves in twenty-five days, but when eight million times larger and extended out as far as earth, it must have revolved very slowly; hence with a slow revolution, and at the same time having only four cubic rods of hard substance out of every thirty-three millions of cubic rods, or one cubic mile,—for earth has contracted to one eight-millionth part of the size it then was,—why did not the rocky substance settle to the sun’s centre instead of being thrown off to form earth, especially as the sun’s gravitation was so great at its surface?