6. Besides its annual motion around the sun, which produces the seasons; its rotary movement upon itself in twenty-four hours, which produces day and night, - the Earth has a third movement, which is completed in about twenty-five thousand years (or, more exactly, 25,868 years), which produces the phenomenon designated in astronomy “the precession of the equinoxes” (Chap. V, n° 11).52
This movement, which it would be impossible to explain in a few words without figures and without a geometrical demonstration, is described by a waved curve very nearly circular, which has been compared to the movement of a dying spinning-top, in consequence of which the axis of the Earth, changing in inclination, described a double cone, of which the summit is at the center of the Earth, and the bases embrace the surface circumscribed by the polar circles; that is to say, an amplitude of twenty-three and a half degrees of radius.
7. The equinox is the time when the sun enters the equinoctial points, - viz., March 21 and Sept. 22; the former being called the vernal or spring equinox, and the latter the autumnal: therefore the sun is exactly on the equator twice a year.
But, in consequence of the gradual change in the obliquity of the axis, the obliquity of the ecliptic is brought about. The time of the equinox is found each year to have advanced a few minutes (twenty-five minutes seven seconds). It is this advance which is called the precession of the equinoxes from the Latin proecedere, to march before,” derived from proe, signifying “before,” and cedere, signifying “to go away.”
These few minutes, after a long time, make years. The result is that the equinox of the springtime, which now arrives in March, will arrive in a given time in February, then in January, then in December; and then the month of December will have the temperature of March, and March that of June, and so on in succession, until, returning to the month of March, it will be found as at present, which will be 25,868 years from now. Then it will recommence the same revolution indefinitely. *
* The procession of the equinoxes leads to another change, that which has been brought to pass in the signs of the Zodiac. The earth going around the sun in a year, according as it advances, the sun finds itself every month opposite a new constellation; these are twelve in number; viz., Taurus, Aries, Pisces, Aquarius, Capricorn, Sagittarius, Scorpio, Libra, Virgo, Leo, Cancer, Gemini. These are the signs of the Zodiac they form a circle in the plan of the terrestrial equator. According to the month of the birth of an individual, they say that he was born under such a sign: whence the prognostications of astrology. But, in consequence of the precession of the equinoxes, it happens that the months do not correspond to constellations as they did two thousand years ago. For instance, a person born in July is not now born in the sign Leo, but in that of cancer: thus falls the superstition attaching to signs (chap. V, n° 12).
8. It results from this conical movement of the axis that the poles of the Earth do not constantly regard the same points in the heavens; that the polar star is not always the same; that the poles are gradually more or less inclined toward the sun, and receive from it more or less direct rays. Whence it follows that Iceland and Lapland, for example, which are under the polar circle, will, in a given time, be able to receive the solar rays as though they were in the latitude of Spain or Italy; and that, in the extreme opposite position, Spain and Italy will have the temperature of Iceland and Lapland; so in succession at every renewed period of 25,000 years. *
* The gradual displacement of the isothermal lines, a phenomenon recognized by science in such a positive way as the displacement of the sea, is a material fact that supports this theory.
9. The consequences of this movement have not yet been determined upon with precision, because only a very small part of its revolution has been observed. We have only then to offer a few presumptions, some of which are, however, highly probable.
The consequence of this are:
1st- The heat and the cold alternating at the poles, and consequently the fusion of polar ice during half of the period of 25,000 years, and their new formation during another similar period; whence it must result that the poles are not destined to abide in everlasting sterility, but will enjoy in their turn the blessing of fertility.
2nd- The gradual displacement of the sea, which encroaches little by little upon the land, whilst it leaves bare other lands in order to abandon them again, and lie upon its former bed. This periodical movement indefinitely renewed would cover the whole Earth with water once every 25,000 years.
The slowness with which the seas thus operate renders it almost imperceptible to each generation; but after a few centuries it is very marked. It can cause no sudden inundation, because men retreat from it from age to age by measure as the sea advances, and they advance upon that land from which the sea retreats. It is to this cause that some wise men attribute the retreat of the sea upon certain shores, and its invasion upon others.
10. The slow, gradual, and periodical displacement of the sea is a fact proved by experience, attested by numerous examples at all points of the globe. In this manner it keeps in repair the productive forces of the Earth. This long immersion is a time of repose, during which the submerged Earth recuperates the vital principals exhausted by a no shorter period of production. The immense deposits of organic matter brought by the waters from age to age are natural composts periodically renewed; and generations succeed generations without perceiving these changes. *
* Among the most recent facts proving the displacement of the sea, one can cite the following: In the Gulf of Gascogne, between the old Souillac and the tower of Cordova, when the sea is calm, one discovers in the water’s depths pieces of wall. These are the remains of the great and ancient city of Noviomagus, invaded by the water A.D. 580. The rock of Cordova, which then joined the shore, is now twelve kilometers from it. By La Manche, upon the Havre side, the sea gains every day upon the earth, and undermines the cliffs of St. Andres, which are gradually crumbling. Two kilometers from the shore, between St. Andres and Cape Hague, exists the bank of L’Eclat, in olden time dry ground and united to terra firma. Ancient documents state that upon this ground where one can sail upon the water today was the village of St. Denis-chef-de-Caux. The sea having invaded the land during the fourteenth century, the church was engulfed in 1378. It is pretended that in a calm tide the remains of it can be seen in the waters. Upon nearly the whole extent of the coast of Holland the sea has been restrained only by dikes, which give way from time to time. The ancient Lake Fleno, united with the sea in 1255, forms today the Gulf of Zuyder-Zee. This eruption of the ocean submerged many villages. Judging from this, Paris and, indeed, all of France, will some day be again occupied by the sea, as it has already been many times, as geological observations prove. The mountainous regions will then form islands like Jersey, Guernsey, and England, formerly contiguous to the continent. The countries now traversed by railroads will then be sailed over. Ships will stop at Montmartre, at Mount Valerian, on the shore of St. Cloud and Meudon. The woods and forests through which we now promenade will be buried under water, covered again with earth, and inhabited by fish instead of birds. The biblical deluge cannot have been caused in this way, since the invasion of the waters was sudden and their sojourn short; otherwise, it would have lasted many thousand years, would still exist without men knowing of its occurrence.