Page:Popular Science Monthly Volume 10.djvu/726

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in such abundance and under such conditions that it cannot be stored away in the motion of the masses. It is then, probably for the first time, that heat becomes a wave-force, and is radiated into space as light and radiant heat—not, however, lost, for that is impossible, but moving ever onward and outward to the day and the place of its final reclamation.

Our own solar system has already progressed far in this stage of aggregation. All the planets and satellites have become crusted over, and have ceased almost entirely to radiate heat. But the sun, the great central body, the one which should last of all become cold, is still in active combustion or chemical combination. Immense quantities of light and heat are still radiating from its surface—so immense that the little fraction which our earth catches as it flies through space gives us all the motion, and life, and beauty, which we enjoy. But the sun is not even now the glowing orb that once it was, as the rock-records of our globe testify. Its bright radiance is slowly but surely fading. Those huge, black incrustations, often twice as large as the whole surface of the earth, that float awhile on its photosphere, and then are suddenly broken up—they were not always there. And, if they have grown upon it, the uncomfortable conviction arises that they will continue to grow and darken more and more its life-giving face. Old age is certainly being written on the solar brow. It may be millions of years hence—for time is not one of the economies of Nature—but the period will surely come when light and heat will all have departed from the sun, as they once ceased to be radiated from the earth and the planets and the numerous stars that have gone out within the records of astronomy. A pall of darkness will gradually overspread the universe as one by one the stars of the firmament shall fade away and sink into gloomy, lifeless sleep. A day in the mighty calendar of creation has passed, and a night has followed, cold and dark as the tomb of expiring Nature.

But is there no awakening, no morrow to this night of the universe? Is the contest over, and never to be renewed? For answer, let us seek out in this case, as we did once before, the condition and movements of the great contending forces. Those of attraction have now in each world expended their utmost possible energy, and are holding all the forms of matter combined and compacted in a cold and rigid embrace. The forces of repulsion have entirely abandoned the contest, and are either vibrating through the unknown realms of space, or are locked up in the swift and complicated motions of the heavenly bodies. It is probable that by far the greater part of the repulsive forces thus exists in the form of motion. It has been estimated, no doubt with a near approximation to truth, that, if by any means the earth could be suddenly arrested in its rapid course, its mass would thereby be raised to the enormous temperature of 23,360° Fahr.—a heat sufficient to vaporize and dissipate every known sub-