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Page:Popular Science Monthly Volume 38.djvu/91

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THE HISTORY OF A STAR.

those farther away will be less metallic. Bit by bit, in the case of the interior bodies, we shall have these permanent gases coming back again, and more carbon will be added to their superficial layers; those bodies also must condense before the central one.

If we consider the conditions of the outer condensations, they must be particularly rich in permanent gases. We shall, therefore, get in the case the outer bodies excessively small density, and probably associated with that only the very sparse presence of these metals which have been alone allowed to penetrate toward the center, because their vapors can condense.

Our sun must ultimately go through the stage in which its absorption will be due no longer to hydrogen, or to iron, but to carbon, chiefly by virtue of the process which has been referred to; and eventually, as its radiant energy gets less and less, as it gets cooler and dimmer, the last speck of blood-red sunlight will be put out by an excess of carbon vapors in its atmosphere.

That is what must have happened to our own earth. It is a very interesting question indeed to attempt to determine at what period of the sun's history a solid crust was formed on the planet on which we dwell. It looks very much as if the consolidation of the earth may have preceded the highest point of temperature of the sun—that is to say, that the earth may have reached a condition closely resembling its present one at the time the sun occupied the apex of the temperature curve to which reference has been made.

In any case the high density of the earth, compared with the density of its crust (the enormous quantity of silicon and oxygen and carbon near the crust having an entirely different specific gravity from the specific gravity of the earth taken as a whole), seems to follow as a matter of course from these considerations.

I trust it will be seen that the hypothesis we have been considering supplies us with an orderly progression of meteoritic dust through heat conditions produced by collisions till finally a cool mass is produced; that this orderly progression brings about all the known phenomena of the heavens on its way, and simply and sufficiently explains them. But, though much of the mystery is gone, all the majesty is left—indeed, to my mind it is vastly increased. It seems as if the working out of the meteoritic idea will entirely justify Kant's conviction that the physical side of the science of the universe would in the future reach the same degree of perfection to which Newton had in his time brought the mathematical side.—Nineteenth Century.

[Note. In the foregoing remarkable paper the well-known astronomical author and authority, Prof. Lockyer, demonstrates, by a process of observation and reasoning which carries conviction with it at almost every step, the evolution of all the numberless kinds of matter, from the most primary form or substance recognizable by our senses, assisted