“This end is all the more certain, because not only the aqueous vapor is diminishing, but also the oxygen and nitrogen, in brief, the entire atmosphere. Little by little the oxygen becomes fixed in the various oxides which are constantly forming on the earth’s surface; this is the case also with the nitrogen, which disappears in the soil and vegetation, never wholly regaining a gaseous state; and the atmosphere penetrates by its weight into the land and sea, descending into subterranean depths. Little by little, from century to century, it grows less. Once, as for example in the early primary period, it was of vast extent; the earth was almost wholly covered by water, only the first granite upheaval broke the surface of the universal ocean, and the atmosphere was saturated with a quantity of aqueous vapor immeasurably greater than that it now holds. This is the explanation of the high temperature of those bygone days, when the tropical plants of our time, the tree ferns, such as the calamites, the equisetaceæ, the sigillaria and the lepidodendrons flourished as luxuriously at the poles as at the equator. Today, both the atmosphere and aqueous vapor have considerably diminished in amount. In the future they are destined to disappear. Jupiter, which is still in its primary period, possesses an immense atmosphere full of vapors. The moon does not appear to have any at all, so that the temperature is always below the freezing point, even in the sunlight, and the atmosphere of Mars is sensibly rarer than ours. “As to the time which must elapse before this reign of cold caused by the diminution of the aqueous atmosphere which surrounds the globe, I also would adopt the period of 10,000,000 years, as estimated by the speaker who preceded me. Such, ladies, are the stages of world-life which nature seems to have marked out, at least for the planetary system to which we belong. I conclude, therefore, that the fate of the earth will be the same as that of the moon, and that when it loses the airy garment which now guarantees it against the loss of the heat received from the sun, it will perish with cold.” At this point the chancellor of the Columbian academy, who had come that very day from Bogota by an electric air-ship to participate in the discussion, requested permission to speak. It was known that he had founded on the very equator itself, at an enormous altitude, an observatory overlooking the entire planet, from which one might see both the celestial poles at the same time, and which he had named in honor of a French astronomer who had devoted his whole life to making known his favorite science and to establishing its great philosophical importance. He was received with marked sympathy and attention.