WE

CHAPTER XXXVIII.

THE SUN COOLING OFF.

E are not driven to the necessity of summoning exaggerated and imaginary agencies to the destruction of the earth. There are hostile powers reserved for the final conflict that will not be content with directing toward us merely "Quaker guns."

The sun, we say, affords us thirty-nine fortieths of all the warmth which we enjoy, and we feel quite unconcerned about the alleged slow cooling of the earth. To the sun we owe the numberless activities of the organic and inorganic worlds, and we feel quite independent of the waning temperature of this dying ember which we call the earth.

The amount of heat dispensed by our solar orb is truly something the contemplation of which overpowers the imagination. The rays which fall upon a common burningglass, converged to a focus, speedily ignite a piece of wood. The heat which is received by a space of ten yards square is sufficient, as Ericsson states, to drive a nine-horse power engine. The amount of heat which falls upon half a Swedish square mile is sufficient to actuate 64,800 engines, each of 100 horse power. The total amount of heat received annually by the earth would melt a layer of ice one hundred feet thick. As the solar heat is radiated equally in all directions, it is easily calculated that the total emission of heat from the sun is 2300 millions of times the whole amount which reaches our earth.

Such an enormous expenditure of heat is sufficient to re

duce the temperature of the sun two and one fifth degrees annually. During the human period of 6000 years, the temperature would have been reduced more than 19,000 degrees. At such a rate of cooling it is obvious that the sun must speedily cease to warm our planet sufficiently to sustain vegetable and animal life. But it is certain that the sun's high temperature has been maintained during almost countless ages anterior to the commencement of the human era. Those Titanic reptiles which could luxuriate only under tropical warmth flourished a hundred thousand years before the world was prepared for man; and those rank, umbrageous ferns, whose forms we trace upon the roof-shales of a coal mine, existed before the reptile horde, and purified the air for their respiration.

What unseen cause has perpetuated, for a million of years, those solar fires? Kepler asserted that the firmament is as full of comets as the sea is of fishes, and Newton conjectured that these comets are the fuel-carriers of the sun. Alas! we only know that the wandering comet, though flying in tantalizing proximity to the sun, but accelerates its speed and hurries onward, as virtue hastens past the vortex of ruin. Is it a chemical action which maintains the solar heat? The most efficient chemical action for this purpose is combustion. Now, if the sun were a solid mass of coal, its combustion would only suffice for the brief space of forty-six centuries to replenish the solar system with its vivifying influence. Is it the effect of the sun's rotation on his axis? Such rotation could generate no heat without the resistance of another body. Even if that other body were present, a calculation based upon the sun's mass and his rate of rotation shows that the heat generated could only supply the expenditure for the space of one hundred and eighty-three years.

There exists, nevertheless, a means of recuperation to the

S

solar energy. It is not an exhaustless resource, but it prolongs materially the period of the sun's activity. Though no comet has been known to fall into the sun, it is now generally admitted that cosmical matter is raining down upon the sun from every direction.

Besides the planetary and cometary bodies which revolve about the sun, it is now demonstrated that the interplanetary spaces are occupied by smaller masses of matter, from the size of a meteorite to particles of cosmical dust. These all are flowing about the sun in a circling stream, but forever approaching nearer and nearer, until they are gradually drawn into the solar fires. The showers of meteoric hail which pelt our earth at certain periods of the year are merely cosmical bodies that have been diverted from their path by the proximity of the earth in certain parts of her orbit. That faint cone of light which streams upward from the setting or the rising sun, near the time of the equinoxes, is but a zone of planetary dust illuminated by the sun's rays-a shower of matter descending upon the solar orb, and rendered visible to us, like the rain sent down from a summer cloud and projected upon the clear heavens beyond.

Arrested motion becomes heat. The blacksmith's hammer warms the cold iron. A meteorite falling through the earth's atmosphere develops so much friction as to generate heat sufficient to dissipate the body into vapor. One of these cosmical bodies falling upon the sun must, by the concussion, produce about 7000 times as much heat s would be generated by an equal mass of coal. It is thus that the enormously high temperature of our sun is maintained.

But the very mention of this source of recuperation of exhausted solar energy suggests a limit to the process. For how many ages can the cosmical matter within the

limits of the solar system be rained down upon the sun without complete exhaustion? The space inclosed by the orbit of Neptune is not infinite. The supply of cosmical. matter is but a finite quantity. Time enough will drain the bounds of the solar system of all its wandering particles of planetary dust. What then will be the fate of the sun?

The conviction can not be resisted that the processes going forward before our eyes aim directly at the final extinction of the solar fire. Helmholtz says: "The inexorable laws of mechanics show that the store of heat in the sun must be finally exhausted." What a conception overshadows and overpowers the mind! We are forced to contemplate the slow waning of that beneficent orb whose vivid light and cheering warmth animate and vivify the circuit of the solar system. For ages past unbounded gifts have been wasted through all the expanding fields of space-wasted, I say, since less than half a billionth of his rays have fallen upon our planet. The treasury of life and motion from age to age is running lower and lower. The great sun which, stricken with the pangs of dissolution, has bravely looked down with steady and undimmed eye upon our earth ever since organization first bloomed upon it, is nevertheless a dying existence. The pelting rain of cosmical matter descending upon his surface can only retard, for a limited time, the encroachments of the mortal rigors, as friction may perpetuate, for a few brief moments, the vital warmth of a dying man. The time is coming when the July sun will shine with a paler light than he now gives us at the winter solstice. The nations of men, if they still exist, will have emigrated from the temperate to the equatorial regions. New diseases will have diminished their numbers. Polar frost will have crept stealthily and steadily from Behring's Straits to the

Gulf of Mexico. Continental glaciers will again have brooded over the land. The prairie blossom will have perished beneath a mantle of snow as limitless as now the prairie expanse. The fluent rivers will have been chained to their rocky banks. The ruins of great cities will be bemoaned by wintry winds howling past in rage at the presence of unending frost. If yet a narrow belt remains where sickly verdure maintains the desperate conflict with the powers of cold, it is a dwarfed and arctic vegetation. The magnolia has given place to the birch. The cypress has been supplanted by the lichen-covered fir. The emerald has departed from the shivering leaf, and even the hardy violet is pale unto death. All things have assumed a faded and leaden hue. The Mongolian is not known from the Caucasian. Even the sooty negro, if he be not extinct, blanched from the want of light and heat, can only be recognized by his features. Pale, thin, and feeble, the shivering remnant of humanity have gathered themselves together into compact communities for economy of vital warmth. Forests are consumed to thaw the soil. Temples, costly structures—the patient rearing of the golden ages of the race-are pulled down to eke out the scanty supply of fuel. Men return to caves, whence they came in the beginning. Nature has become their enemy. Science and art are forgotten. The page which narrates the glory of the nineteenth century is like the narrative which tells us of the labors of the men upon the plains of Shinar. Year by year the populations become less-year by year the dread empire of frost is extended. Forests have been consumed; cities have been burned; navies have rotted in the deserted, ice-locked harbors; men have immured themselves in gloomy caverns till they have almost lost the forms of humanity.