It is only in modern times that science has taken the advanced step, and led philosophy into the beautiful avenues of Nature, where, amid the infinite, she gazes at the universe, listens to the music of the spheres, and beholds the golden wealth of the infinite displayed on every side. It is thus that philosophy has become inspired with a desire to account for everything, and finds that Nature has written her own history in the hills and in the rocks, in the depths of the sea, and in the stars of heaven, leaving nothing for man to do except to read the record, and accept its truthful teachings. In fact, the material universe may be regarded as an outspoken revelation of the infinite. The elementary substances which compose the earth and its atmosphere are essentially the same, and are not numerous, so far as ascertained. The leading vital principle is oxygen, which constitutes at least one half of all known matter. The earth's crust is estimated to be about fifty miles thick. This estimate is based on the fact that in penetrating the earth, the heat uniformly increases at a rate which would fuse all mineral substances at that depth. Hence, the interior of the earth is believed to be a region of molten substances, fiery billows that roll impatient of restraint, and escape here and there in the form of volcanic eruptions. Volcanoes are, therefore, but the outposts of gigantic central forces, and earthquakes but the spasmodic trials of their strength. It would seem, go where we will, that "fiery billows" literally roll beneath our feet. What Nature's ultimate designs are, it is impossible to predict. But it is pretty certain that her internal fires are working out some mystical problem. A scientific German has recently ascertained that the surface of the earth is gradually becoming hotter, and that in five hundred millions of years it will attain to such a degree of heat as to destroy human life. And yet there are other scientists equally wise, perhaps, who assert that the earth's crust is gradually cooling and contracting, and therefore radiating less heat, the final result of which will be the destruction of all life and a return of the glacial period.