LIBER II · CAPUT 97
CONCERNING THE CAUSE OF THE FLOWING AND EBBING OF THE SEA
Latine · Mayhoff 1906
Et de aquarum natura complura dicta sunt, sed aestus maris accedere ac reciprocare maxime mirum, pluribus quidem modis, verum causa in sole lunaque. bis inter duos exortus lunae adfluunt bisque remeant vicenis quaternisque semper horis, et primum attollente se cum ea mundo intumescentes, mox a meridiano caeli fastigio vergente in occasum residentes, rursusque ab occasu subter ad caeli ima et meridiano contraria accedente inundantes, hinc, donec iterum exoriatur, se resorbentes nec umquam eodem tempore quo pridie reflui, velut anhelantes sidere avido trahente secum haustu maria et adsidue aliunde quam pridie exoriente, paribus tamen intervallis reciproci senisque semper horis, non cuiusque diei aut noctis aut loci, sed aequinoctialibus ideoque inaequales vulgarium horarum spatio, utcumque plures in eos aut diei aut noctis illarum mensurae cadant, et aequinoctio tantum pares ubique. ingens argumentum plenumque lucis ac vocis etiam diurnae, hebetes esse qui negent subtermeare sidera ac rursus eadem exsurgere, similemque terris, immo vero naturae universae, et inde faciem in isdem ortus occasusque operibus, non aliter sub terra manifesto sideris cursu 5 aliove effectu quam cum praeter oculos nostros feratur.
Multiplex etiamnum lunaris differentia, primumque septenis diebus. quippe modici a nova ad dividuam aestus, pleniores ab ea exundant plenaque maxime fervent. inde mitescunt, pares ad septimam primis, iterumque alio latere dividua augentur. in coitu solis pares plenae. eadem in aquilonia et a terris longius recedente mitiores quam cum in austros digressa propiore nisu vim suam exercet. per octonos quosque annos ad principia motus et paria incrementa centesimo lunae revocantur ambitu. augent ea cuncta solis annuis causis, duobus aequinoctiis maxime tumentes et autumnali amplius quam verno, inanes vero bruma et magis solstitio. nec tamen in ipsis quos dixi temporum articulis, sed paucis post diebus, sicuti neque in plena aut novissima, sed postea, nec statim ut lunam mundus ostendat occultetve aut media plaga declinet, verum fere duabus horis aequinoctialibus serius, tardiore semper ad terras omnium, quae geruntur in caelo, effectu cadente quam visu, sicuti fulguris et tonitrus et fulminum.
Omnes autem aestus in oceano maiora integunt spatia nudantque quam in reliquo mari, sive quia in totum universitate animosius quam parte est, sive quia magnitude aperta sideris vim laxe grassantis efficacius sentit, eandem angustiis arcentibus. qua de causa nec lacus nec amnes similiter moventur. — (octogenis cubitis supra Britanniam intumescere aestus Pytheas Massiliensis auctor est.) — et interiora autem maria terris clauduntur ut portu; quibusdam tamen in locis spatiosior laxitas dicioni paret, utpote cum plura exempla sint in tranquillo mari nulloque velorum pulsu tertio die ex Italia pervectorum Vticam aestu fervente. circa litora autem magis quam in alto deprehenduntur hi motus, quoniam et in corpore extrema pulsum venarum, id est spiritus, magis sentiunt. in plerisque tamen aestuariis propter dispares siderum in quoque tractu exortus diversi existunt aestus, tempore, non ratione discordes, sicut in Syrtibus.
Et quorundam tamen privata natura est, velut Tauromenitani euripi saepius et in Euboea septies die ac nocte reciprocantis. idem aestus triduo in mense consistit, septima, octava nonaque luna. Gadibus qui est delubro Herculis proximus fons, inclusus ad putei modum, alias simul cum oceano augetur minuiturque, alias utrumque contrariis temporibus; eodem in loco alter oceani motibus consentit. in ripa Baetis oppidum est, cuius putei crescente aestu minuuntur, augescunt decedente, mediis temporum immobiles. eadem natura Hispali oppido uni puteo, ceteris vulgaris. et Pontus semper extra meat in Propontidem, introrsus in Pontum numquam refluo mari.
English · Bostock & Riley 1855–57
Much has been said about the nature of waters; but the most wonderful circumstance is the alternate flowing and ebbing of the tides, which exists, indeed, under various forms, but is caused by the sun and the moon. The tide flows twice and ebbs twice between each two risings of the moon, always in the space of twenty-four hours. First, the moon rising with the stars swells out the tide, and after some time, having gained the summit of the heavens, she declines from the meridian and sets, and the tide subsides. Again, after she has set, and moves in the heavens under the earth, as she approaches the meridian on the opposite side, the tide flows in; after which it recedes until she again rises to us. But the tide of the next day is never at the same time with that of the preceding; as if the planet was in attendance, greedily drinking up the sea, and continually rising in a different place from what she did the day before. The intervals are, however, equal, being always of six hours; not indeed in respect of any particular day or night or place, but equinoctial hours, and therefore they are unequal as estimated by the length of common hours, since a greater number of them fall on some certain days or nights, and they are never equal everywhere except at the equinox. This is a great, most clear, and even divine proof of the dullness of those, who deny that the stars go below the earth and rise up again, and that nature presents the same face in the same states of their rising and setting; for the course of the stars is equally obvious in the one case as in the other, producing the same effect as when it is manifest to the sight.
There is a difference in the tides, depending on the moon, of a complicated nature, and, first, as to the period of seven days. For the tides are of moderate height from the new moon to the first quarter; from this time they increase, and are the highest at the full: they then decrease. On the seventh day they are equal to what they were at the first quarter, and they again increase from the time that she is at first quarter on the other side. At her conjunction with the sun they are equally high as at the full. When the moon is in the northern hemisphere, and recedes further from the earth, the tides are lower than when, going towards the south, she exercises her influence at a less distance. After an interval of eight years, and the hundredth revolution of the moon, the periods and the heights of the tides return into the same order as at first, this planet always acting upon them; and all these effects are likewise increased by the annual changes of the sun, the tides rising up higher at the equinoxes, and more so at the autumnal than at the vernal; while they are lower about the winter solstice, and still more so at the summer solstice; not indeed precisely at the points of time which I have mentioned, but a few days after; for example, not exactly at the full nor at the new moon, but after them; and not immediately when the moon becomes visible or invisible, or has advanced to the middle of her course, but generally about two hours later than the equinoctial hours; the effect of what is going on in the heavens being felt after a short interval; as we observe with respect to lightning, thunder, and thunderbolts.
But the tides of the ocean cover greater spaces and produce greater inundations than the tides of the other seas; whether it be that the whole of the universe taken together is more full of life than its individual parts, or that the large open space feels more sensibly the power of the planet, as it moves freely about, than when restrained within narrow bounds. On which account neither lakes nor rivers are moved in the same manner. Pytheas of Massilia informs us, that in Britain the tide rises 80 cubits. Inland seas are enclosed as in a harbour, but, in some parts of them, there is a more free space which obeys the influence. Among many other examples, the force of the tide will carry us in three days from Italy to Utica, when the sea is tranquil and there is no impulse from the sails. But these motions are more felt about the shores than in the deep parts of the seas, as in the body the extremities of the veins feel the pulse, which is the vital spirit, more than the other parts. And in most estuaries, on account of the unequal rising of the stars in each tract, the tides differ from each other, but this respects the period, not the nature of them; as is the case in the Syrtes.
There are, however, some tides which are of a peculiar nature, as in the Tauromenian Euripus, where the ebb and flow is more frequent than in other places, and in Eubœa, where it takes place seven times during the day and the night. The tides intermit three times during each month, being the 7th, 8th and 9th day of the moon. At Gades, which is very near the temple of Hercules, there is a spring enclosed like a well, which sometimes rises and falls with the ocean, and, at other times, in both respects contrary to it. In the same place there is another well, which always agrees with the ocean. On the shores of the Bætis, there is a town where the wells become lower when the tide rises, and fill again when it ebbs; while at other times they remain stationary. The same thing occurs in one well in the town of Hispalis, while there is nothing peculiar in the other wells. The Euxine always flows into the Propontis, the water never flowing back into the Euxine.