The next act recorded is, that "God divided the light from the darkness." This is one of those passages which we are very apt to pass over as unimportant, without giving ourselves any trouble to ascertain what they mean, or asking if they may not give valuable information, or supply some important hints. It is evident, however, that in these words some act of the Creator is implied, but when we inquire what that act was, the answer does not lie immediately on the surface. Darkness is simply the absence of light. It cannot therefore be said that God divided the light from the darkness in the same sense in which it is said that "a shepherd divideth his sheep from the goats". Between light and darkness that division exists in the very nature of things, and it could not therefore be said to be made by a definite act. Nor again, is there any sharp well-defined boundary set between light and darkness, so that we can say, "Here light begins, here darkness ends." The very opposite is the case, the one blends imperceptibly into the other. This then cannot be the meaning of the words. But the next verse guides us to the real meaning. "And God called the light Day, and the darkness He called Night." The division of light from darkness then is the alternation of night and day. When God divided the light from the darkness He made provision for that alternation. But we know that that alternation is the result of the earth's rotation upon its axis, so that the dividing the light from the darkness evidently implies the communication to the accumulated mass of the motion of rotation.
It does not clearly appear in the account of the first day, whether this alternation of day and night took effect immediately. Certainly the introduction of it here does not prove that it did so follow. For there was no way in which the fact of the earth's rotation could be directly communicated to those for whom the narrative was primarily intended. They were ignorant of the spherical form of the earth, and so could not have attached any idea whatever to a statement that it revolved about its axis.
The only way then in which Moses could speak of that rotation was in connexion with some phenomenon resulting from it. The only such phenomenon with which the Jews were acquainted was the alternation of day and night. There was therefore no way in which Moses could record the fact except with reference to this ultimate effect. It does not follow that that effect was immediate. Beside the rotation of the earth, another condition is required. The light must come from a single source, and so when the act is recorded by which that condition is effected, the division of light and darkness is again noticed. The sun and the moon are set in the firmament of heaven to divide the light from the darkness. But that division was potentially effected when the motion of rotation was given.
The third defect noticed in the Nebular Hypothesis was, that it did not account for this motion of rotation. This defect, then, like the two preceding ones, is supplied by the Mosaic Record, and the hypothesis thus supplemented becomes complete. It is capable of giving a satisfactory account of the phenomena to which it applies. But as it is only a theory, and only points out a way in which the universe might have been constructed, it does not in itself exclude the possibility that some other plan might in fact have been adopted, and we have now to examine into the reasons for supposing that it was the method which was actually employed. These divide themselves into two classes:—those which render it probable that similar processes are now in progress; and those which render it probable that the solar system has passed through such a process.
It has already been pointed out that the great nebulae in Orion and Argo seem to represent the condition of our system on the first appearance of light, and that changes are strongly suspected to be taking place in both; but we cannot expect to trace any single nebula through the stages of its development, since that development must occupy untold ages. All we can do is to inquire if there are other nebulas which seem to be in more advanced stages. It must at once be recognized, that if this be one of the processes now going on, it is not the only one. There are many nebulas "which have assumed forms for which the law of gravitation, as we know it, will not enable us to account—such as the Ring Nebula in Lyra, the Dumb-bell Nebula in Vulpecula, or the double Horseshoe in Scutum Sobieski. But some nebulas can be found which arrange themselves so as to illustrate the stages through which we may suppose our world to have passed. These are chiefly to be found among the planetary nebulse, which in a small telescope exhibit a faint circular disc, but in larger instruments frequently show considerable varieties of structure. Some of them present the appearance of a condensation of light in the centre, which gradually fades off; in others there is a bright ring surrounding the central spot, but separated from it by a darker space. The Nebula Andromeda 49647, [Footnote: The numbers are those given by Sir J. Hersohel.] as seen in Mr. Lassel's four-foot reflector appears as a luminous spot, surrounded by two luminous rings, which, in the more powerful instrument of Lord Bosse, combine into a spiral. Its spectrum is gaseous, with one line indicating some element unknown to us. In another nebula, Draco 4373, there is a double spectrum, the one gaseous, indicating the presence of hydrogen, nitrogen, and barium; the other, apparently from the nucleus, continuous, and so representing a solid or fluid mass, but so faint that the lines belonging to particular elements cannot be distinguished. [Footnote: Hugging, Philosophical Transactions, 1864.] Bridanus 846, and Andromeda 116, are probably similar nebulee occupying different positions with reference to us. They both give a continuous spectrum. The one in Bridanus is described as "an eleventh magnitude star, standing in the centre of a circular nebula, itself placed centrally on a larger and fainter circle of hazy light." [Footnote: Lassell, quoted in Webb's "Celestial Objects," p. 227.] The nebula in Andromeda assumes a lenticular form; that in Bridanus would probably present the same appearance if we saw it edge-ways. The former has probably increased in brilliancy in the course of centuries. Mr. Webb remarks of it, "It is so plain to the naked eye that it is strange the ancients scarcely mention it." [Footnote: Webb's "Celestial Objects," p. 180.] In these two nebulas we may perhaps see the mass ready to break up into separate worlds, the lenticular form being a natural result of extremely rapid rotation. Prom the fact that Andromeda 116 gives a continuous spectrum, Dr. Huggins inclines to the belief that it is an unresolved star cluster. But the reasons which led Sir W. Herschel to conclude that the nebula in Orion was gaseous, (a conclusion which, though for a time discredited by the supposed resolution of the nebula in Lord Kosse's telescope, was ultimately found to be correct), are equally applicable here. In general a certain proportion exists between the telescopic power requisite to render a star cluster visible as a nebulous spot, and that which will resolve it into stars; but this nebula, like that in Orion, though visible to the naked eye, cannot be resolved by the most powerful instruments yet made. And the nebula in Draco 4373, seems to present an intermediate stage between the purely gaseous nebula and this one. The faint continuous spectrum is probably the result of incipient central condensation. This nebula, if recent observations by Mr. Gill, of Aberdeen, are confirmed [Footnote: Popular Science Review, 1871, p. 426.], is much nearer to us than any of the fixed stars.
"We come now to the reasons derived from the Solar System itself, and of these there are several, some of them of considerable weight. The first is to be found in the uniform direction of almost all the motions of the system. They are from west to east. The sun rotates upon his axis, the planets revolve about the sun and rotate upon their axes, and the satellites, with one exception, revolve about their primaries, and, so far as is known, rotate upon their axes in the same direction, from west to east, and the motions take place very nearly in the same plane—the ecliptic. This seems to point to the conclusion that these motions have a common origin, as would be the case if all these bodies at one time existed as a single mass which revolved in the same direction. The one exception is to be found in the satellites of Uranus, whose motion is retrograde. But there are certain phenomena, which lead to the conclusion, that, on the outskirts of our system, there has at some time or other been an action of a disturbing force, of which, except from these results, we know nothing."
[Footnote: Bode's "Law of Planetary Distances," What holds good as far as Uranus, breaks down in the case of Neptune. Both Leverrier and Adams were to some extent misled by this law. The new planet should according to their calculations, based on this law, have been of greater magnitude and at a greater distance than Neptune.
The polar axis of Uranus, instead of being nearly perpendicular to the ecliptic, as in the case of all the other planets (except Venus), is nearly coincident with it. Venus occupies an intermediate position, the inclination of its equator to its orbit being 49 degrees 58'.]
There is also strong reason for believing that the sun is still a nebulous star, that the whole of the original nebula is not yet gathered up in the vast globe which at ordinary times is all that we can see. This aspect of the case, however, will come more fully under our notice when we come to the work of the fourth day. The figure of the earth, which is that naturally assumed by a plastic mass revolving about its axis, and the traces which it retains of a former state of intense heat, are both in accordance with this theory.
When these facts are duly weighed, there seems to be a reasonable probability that this process is the one which was actually employed in the formation of the solar system. The remarkable manner in which the theory adapts itself to the Mosaic account, and the fact that that account records special interferences of the Creator exactly at the points where the theory shows that such interferences would be necessary, give rise to a very strong presumption in its favour. We have in it also a clear illustration of the combination of general laws of nature with special interferences of Creative Power—the law of gravitation was called into action, and the work would proceed steadily under that law for a considerable period, till matters were ripe for a farther stage in the progress, and then the special interference would take place, in this instance the imparting the motion of rotation, and the work would again proceed under the natural law. All this while, however, the work would be one, and performed by one power, the only difference being in the direct or indirect action of that power.