Many readers will regard this climate quite bearable, inasmuch, as in our own day regions may be cited whose mean temperature is much lower, yet which are nevertheless habitable, as, for example, Verchnoiansk, whose mean annual temperature is –19.3°. But in these regions there is a summer during which the ice melts; and if in January the temperature falls to –60°, and even lower, in July they enjoy a temperature of fifteen and twenty degrees above zero. But at the stage which we have now reached in the history of the world, this mean temperature of the equatorial zone was constant, and it was impossible for ice ever to melt again. As for the other latitudes, they had been totally uninhabitable for thousands of years, in spite of every effort made to live in them. In the latitudes of Paris, Nice, Rome, Naples, Algiers and Tunis, all protective atmospheric action had ceased, and the oblique rays of the sun had proved insufficient to warm the soil which was frozen to a great depth, like a veritable block of ice. The world’s population had gradually diminished from ten milliards to nine, to eight, and then to seven, one-half the surface of the globe being then habitable. As the habitable zone became more and more restricted to the equator, the population had still further diminished, as had also the mean length of human life, and the day came when only a few hundred millions remained, scattered in groups along the equator, and maintaining life only by the artifices of a laborious and scientific industry. Later still, toward the end, only two groups of a few hundred human beings were left, occupying the last surviving centers of industry. From all the rest of the globe the human race had slowly but inexorably disappeared—dried up, exhausted, degenerated, from century to century, through the lack of an assimilable atmosphere and sufficient food. Its last remnants seemed to have lapsed back into barbarism, vegetating like the Esquimaux of the north. These two ancient centers of civilization, themselves yielding to decay, had survived only at the cost of a constant struggle between industrial genius and implacable nature. Even here, between the tropics and the equator, the two remaining groups of human beings which still contrived to exist in face of a thousand hardships which yearly became more insupportable, did so only by subsisting, so to speak, on what their predecessors had left behind. These two ocean valleys, one of which was near the bottom of what is now the Pacific ocean, the other to the south of the present island of Ceylon, had formerly been the sites of two immense cities of glass—iron and glass having been, for a long time, the materials chiefly employed in building construction. They resembled vast winter-gardens, without upper stories, with transparent ceilings of immense height. Here were to be found the last plants, except those cultivated in the subterranean galleries leading to rivers flowing under ground.