But next, the atmosphere of Jupiter is probably of very great density. Dr. Huggins states that he has observed in the spectrum of Jupiter "three or four strong lines, one of them coincident with a strong line in the earth's atmosphere." [Footnote: Lecture at Manchester, November 16, 1870.] Strong lines mark increased density in the absorbent medium, and lines hitherto unobserved indicate new elements. It is therefore probable that the atmosphere of Jupiter is not only much more dense than that of the earth, but also contains some elements—which are absent from the latter. When with this fact we connect the very great extent of the atmosphere, it will be evident that the pressure at the surface of the planet will be enormous, and from this we can form an estimate of the intensity of the forces which must be at work in the interior of the planet, to project jets of vapour through such an atmosphere to so great a height.
The link which connects Jupiter with the earth, in the second stage of its existence, is the mention by Moses of the "waters which were above the firmament." Viewed in the light of the present condition of the earth such a notice seems unaccountable. But if the earth at that time were in a condition similar to that in which Jupiter appears to be now, the water in the atmosphere or above the firmament would be a very important element in any description that might be given of it. It is in fact most probable that all the water (in the strict sense of the word) then in existence would be in a state of vapour, and that the waters which were under the firmament were the molten materials which afterwards formed rocks and ores, since, as has been already noticed, the word is the only one which could be employed to describe fluids in general.
We may now try to form some idea of the probable state of the earth at this period. Its centre would be occupied by a fused mass, in which were blended all the more intractable solid constituents of the present world. This would be surrounded by an atmosphere of very great height and density, containing not only all the present constituents of air, but also all, or nearly all, the water, and all the more volatile of the metals and other elements. Carbonic acid, to a very large extent, would probably be present, and a very considerable proportion of the oxygen which now exists in combination with various bases, and forms by weight so large a proportion of the solid crust of the world.
Owing to the intense heat, chemical combinations would readily be formed between the ingredients of the fused mass and the other elements which existed in the form of vapour, and thus the earliest of the vast variety of existing minerals would be elaborated. The volumes of steam which floated in the upper regions of the atmosphere would rapidly part with their heat by radiation into space, and would descend towards the surface of the earth in the form of rain. At first probably, and for a long time, they would not reach the surface, but as they approached it would be again converted into vapour, and re-ascend to pass again and again through the same process. But by this means the intense heat of the nucleus would be gradually conveyed away, till the cooling reached a point at which some of the superficial materials would assume a solid form. It is by no means certain what is the true primary rock—for a long time it was almost universally assumed to be granite, since granite is uniformly found underlying the oldest sedimentary rocks that are known. But as these rocks have been forced from their original position and tilted up, the underlying stratum may probably be of later date than the upper ones, since it was the elevating agent. So that we can have no certain knowledge on this point, since the earliest sedimentary strata, wherever they retain their original position, must be at a depth far below the reach of man. If, however, Sir C. Kyell's view of the conditions requisite for the formation of granite are correct, these conditions [Footnote: Student's Geology, chap. xxxi.]—heat, moisture, and enormous pressure—would all be present at the surface of the nucleus. Some kind of solid floor must have been formed before the next stage could be reached, at which it would be possible for water to exist in a fluid state. This, however, would be possible at a much higher temperature than at present, owing to the enormous atmospheric pressure. It is possible now, by artificial means, to raise water, nearly if not quite, to a red heat, without the formation of steam, and the pressure of the atmosphere in the case supposed would, in all probability, be much greater than any which we can now apply under the conditions necessary for heating the water.
It is probable that at this point the close of the second day must be placed: but the indications of the narrative do not enable us to fix it with any degree of certainty. As, however, from this point a new series of processes would commence, and those processes are in intimate connexion with the first of the two developments ascribed to the third day, the period when water could first maintain a fluid form on the earth's surface, seems to present the most probable line of demarcation.
SECTION 6. THE THIRD DAY.
"And God said, Let the waters under the Heaven be gathered together in one place, and let the dry land appear; and it was so.
"And God called the dry land Earth, and the gathering together of the waters called He Seas, and God saw that it was good.
"And God said, Let the earth sprout sprouts, the herb seeding seed, and the fruit-tree yielding fruit after his kind, whose seed is in it, [Footnote: "It" seems preferable to "itself" here. The same Hebrew word stands for both, but if the "fruit-tree" be taken as the antecedent, which it must be if we translate "itself," there seems no meaning in the statement. If we read "it," the pronoun will refer to the fruit—"the tree whose seed is in its fruit"—which gives an intelligible sense.] upon the earth, and it was so.
"And the earth caused to go forth sprouts, the herb seeding seed, and the fruit-tree yielding fruit whose seed is in it, after his kind, and God saw that it was good. And there was evening, and there was morning, a third day."