slowly and steadily surging from the sea. The sea, robbed of half his dominions, has ever since been raging around the borders of the land. At last he will again reclaim his own, and the universal empire will be Neptune's.

It is vain to hope that elevatory forces can permanently avert the disappearance of the land. We discover here another argument against the vague belief entertained by some, that the human fauna is to be succeeded by a higher one, as it has itself succeeded the lower. Should it be supposed that the ultimate submergence predicted is sufficiently remote to permit the interposition of a superior race of intelligences, I recall to mind the evidences that the lands are wasting and deteriorating; the river-beds are deepening, and diminishing the sources of irrigation; and all the populated regions of the earth are slowly approaching the desert condition of that ancient continent drained by the Colorado. Each continental surface in the geological succession is the exclusive gift to a single great fauna. A single race witnesses the disappearance of the freshness and fertility of the land. A new race would demand a thorough renovation, like that which immediately preceded the advent of man. Such a revolution the senescent forces are unable to inaugurate.

WE

CHAPTER XXXVII.

THE REIGN OF UNIVERSAL WINTER.

E open now another volume of geological records.
From this we glean another prophecy.

I have stated that the energies of the earth's internal fires are waning. There is a chain of effects which, when we trace them backward, conduct us to an ancient molten condition of the world. At a period comparatively recent, it was still so warm that tropical vegetation flourished within the arctic circle. At a remoter period, neither animal nor plant could endure the temperature which prevailed, nor the warfare which fire and water were waging with each other. We retain the solid monuments of a terrestrial condition which carries us still deeper into the heart of eternity; when the whole orb was a glowing ocean of incandescent lava, while yet the waters of the earth hung in invisible vapor upon the outskirts of the atmosphere, like a concealed foe meditating a secret attack upon a powerful enemy,

Few who have studied the physics of the globe, and fewer still who have deciphered geological records, doubt that such were once the temperature and conditions of our planet. From that state to this, it has passed by the simple process of cooling. We trace the footsteps of this progress at every stage. Through Azoic, Eozoic, Paleozoic, Mesozoic, and Cenozoic Ages, heat has been gradually wasted in space-the solid crust has been thickening-the surface conditions have been changing. The average temperature of to-day, instead of being a state that is destined

to perpetuity, is but a passing phase; and when we shall have passed away with the other transient existences around us, some succeeding intelligence, gifted with the power to travel from sphere to sphere, will note the world in an altered condition.

I step here upon ground which has been somewhat contested. It was long since alleged that if our world be still in process of refrigeration, a sensible reduction in temperature ought to have taken place in 2000 years. But no such reduction has been satisfactorily established, though it will be confessed that we scarcely have exact observations on temperature which are more than two hundred years old. It was also alleged that since a reduction of temperature must be accompanied by a reduction of volume, the rate of the earth's rotation upon its axis must have been accelerated. But Laplace has demonstrated from ancient observations on eclipses that the mean day has not been diminishedth of a second since the time of Hipparchus, or during an interval of 2500 years. These negative results have been opposed to the theory of Cordier in reference to the former high temperature of the earth, and it has, till recently, been customary to speak of the thermal, no less than the astronomical conditions of our planet as constant. Poisson, an eminent French mathematician, proved, as was supposed, that the heat escaping from the earth in the latitude of Paris was only sufficient to elevate the temperature of a column of water eighteen inches high the trifling amount of one degree and a half. Vogt, a celebrated German geologist, affirms that the existing temperature of the surface of the earth is but one twelfth of a degree higher than it would be if the earth were completely cooled to the core. According to the later researches of Pouillet, the heat communicated to the surface of the earth from the central fire is but one fortieth the amount received from

the sun; while, according to Fourier's celebrated computation, the heat radiated from the earth's surface is only sufficient to melt a layer of ice ten feet thick in one hundred years.

The most conservative of these results may be regarded as showing that our earth is actually losing heat to a perceptible and measurable extent. Neither is the amount of heat escaping at Paris to be taken as the measure of the reduction of the temperature of the mass of the earth in general. There are three hundred active volcanoes in existence, from the craters of which enormous quantities of heat are permitted to waste. The ocean, too, carries off vastly larger quantities than the land. The floor of the ocean is generally overlaid by a stratum of ice-cold water setting southward from the polar regions. This cold stream is overlaid by a warmer one moving northward from the tropics. Water being a better conductor of heat than atmospheric air, this cold stratum must necessarily abstract terrestrial heat with vastly greater rapidity than the average atmosphere of the temperate zone. Many observations indicate that the temperature of the solid crust beneath the waters of the ocean is much higher than that of continental surfaces, and hence imparts its warmth in larger quantities. Throughout all that part of the Frozen Ocean north of Europe and Asia, the temperature is found to increase at considerable depths, contrary to the well-known laws of hydrostatics. [See Appendix, Note X.] The same phenomenon has been observed on the coast of Australia, in the Adriatic, and Lago Maggiore. Horner asserts that in the deep soundings of the Gulf Stream, off the coast of the United States, the lead, when drawn up, "used to be hotter than boiling water."

These facts, with others, seem to demonstrate that our planet is wasting its warmth many times faster than the

calculations of the mathematicians would indicate. It seems inevitable, therefore, that the earth should have expended sufficient heat in 2500 years to effect a sensible reduction in the length of the day.

Thanks to the mathematicians, they have again come to our aid. The tide-wave is a protuberance of the oceanwaters raised by the moon, and following the moon around the earth from east to west. This motion is contrary to the earth's diurnal rotation, and the friction of the tidal waters against the shore and the standing waters must necessarily tend to retard the rotary motion of the earth. Now it has been calculated that this retardation must have amounted to one sixteenth of a second in 2500 years. If, therefore, no counteracting tendency has been experienced, the sidereal day is one sixteenth of a second longer than it was in the time of Hipparchus. But Laplace has shown that the sidereal day has not varied in length. It follows, therefore, that the shrinkage of the earth from loss of heat has tended to accelerate its rotation to the extent of one sixteenth of a second in twenty-five centuries. Such an acceleration corresponds to a shortening of the diameter about sixty feet, and a reduction of the temperature of the whole mass of the earth one fourteenth of a degree.

When the earth was in its youth, just emerging from a molten state, the loss of heat and consequent contraction must necessarily have been rapid. During this period the sidereal day underwent a much more rapid shortening than at present. In the distant future, on the contrary, the loss of heat will become diminished to an extreme extent, and, as a consequence, the retardation caused by the tide-wave will gain the ascendency, and the day will eventually be lengthened to such an extent that the earth will always turn the same side toward the sun, as the moon always turns the same side toward the earth. The historic period