Endnotes

  1. For about 300 years the observatory of Paris had ceased to be an observing station, and had been perpetuated only as the central administrative bureau of French astronomy. Astronomical observations were made under far more satisfactory conditions upon mountain summits in a pure atmosphere, free from disturbing influences. Observers were in direct and constant communication by telephone with the central office, whose instruments were used only to verify certain discoveries or to satisfy the curiosity of savants detained in Paris by their sedentary occupation. ↩

  2. It is needless to remind the reader that the language of the twenty-fifth century is here translated into that of the nineteenth. ↩

  3. St. Matthew, xxiv and xvi; St. Mark, xiii; St. Luke, xvii and xxi. ↩

  4. In the nineteenth century, researches in natural history had revealed the fact that secular vertical oscillations, vary with the locality, were taking place in the earth’s crust, and had proved that, from prehistoric times, the soil of western and southern France had been slowly sinking and the sea slowly gaining upon the land. One after another, the islands of Jersey, of Minquiers, of Chaussey, of Écrehou, of Cezembre, of Mont-Saint-Michel, had been detached from the continent by the sea; the cities of Is, Helion, Tommen, Portzmeûr, Harbour, Saint Louis, Monny, Bourgneuf, La Feillette, Paluel and Nazado had been buried beneath its waves, and the Armorican peninsula had slowly retreated before the advancing waters. The hour of this invasion by the sea had struck, from century to century, also for Herbavilla; to the west of Nantes; for Saint-Denis-Chef-de-Caux, to the north of Havre; for Saint-Etienne-de-Paluel and for Gardoine, to the north of Dol; for Tolente, to the west of Brest; more than eighty habitable cities of Holland had been submerged in the eleventh century, etc., etc. In other regions the reverse had taken place, and the sea had retired; but to the north and west of Paris this double action of the subsidence of the land and the wearing away of the shores had, in less than seven thousand years, made Paris accessible to ships of the greatest tonnage. ↩

  5. Of all terrestrial substances water has the greatest specific heat. It cools more slowly than any other. Its specific heat is four times greater than that of air. When the temperature of a kilogram of water falls one degree, it raises the temperature of four kilograms of air one degree. But water is seven hundred and seventy times heavier than air, so that if we compare two equal volumes of water and air, we find that a cubic meter of water, in losing one degree of temperature, raises the temperature of seven hundred and seventy times four, or 3080 cubic meters of air by the same amount. This is the explanation of the influence of the sea in modifying the climate of continents. The heat of summer is stored in the ocean and is slowly given out in winter. This explains why islands and seashores have no extremes of climate. The heat of summer is tempered by the breezes, and the cold of winter is alleviated by the heat stored in the water. ↩

  6. 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. ↩