Dante and the early astronomers

by M. A. Orr

It is only through the spiritual teaching which Beatrice symbolizes that the human race can rise above all that is comprised within the heaven of the smallest sphere. And it is taught by Beatrice herself when, in the heaven of Mercury, she discourses on the mysteries of the creation and redemption. The angels, the souls of men, and the spheres, were created directly by God, she says, and are therefore immortal, but the elements, water, fire, air, earth, and all things that are formed out of them, also the souls or living principles of all animals and plants, were created through intermediate instruments and are mortal. These intermediate instruments are the heavenly bodies. Pure or inchoate matter was created at the beginning by God, and a power infused into the stars to give it form.[620]

Dante follows the classics and agrees with his contemporaries in arranging the four elements in four spheres, which are below the celestial spheres. The sphere of Fire is immediately within that of the moon, below this comes Air, then Water, and lastly the solid sphere of Earth. The contrast between Fire which constantly tends to rise towards the moon, and Earth which sinks towards the centre of the universe, is a favourite thought with him;[621] and lightning striking the earth is described as fleeing its proper place.[622] Aristotle seems to have regarded the four elements as flowing into one another, so that these lowly spheres beneath the moon were not sharply divided, but his mediæval disciples, following the Greek idea to its logical conclusion, conceived them with boundaries as definite as those of the celestial spheres. “Exhalations” could pass from one to another, but each particle of every element tended always to revert to its own place, which was distinct from the others.

And here they encountered a serious difficulty. If the sphere of water is naturally higher than that of earth, how comes it that in one quarter of the globe land rises above the ocean? It was recognised as necessary that this should happen in some part of the world, in order for an opportunity to be given for the elements to combine and to form all those substances and all those living creatures, including man, for which this earth was prepared; it was also agreed that the celestial spheres were the agency by which the Creator had first chosen to “let the dry land appear,” and by which it was maintained above the ocean; but the exact nature of this force and the way in which it acted was a question sometimes discussed. Albertus Magnus was of opinion that the rays of the sun and the stars, which had more power in the temperate and tropic zones than in the arctic, had here dried up the ocean, and he quotes Albumassar’s statement that this proves the existence of land on the southern side of the equator also. Ristoro, on the other hand, believed that the waters had been drawn up and rolled back from the habitable earth, and he attributes the elevating force to the stars of the north, bringing in his favourite theory that in this hemisphere they are far more numerous, and the constellations, from their upright position, are far more powerful than in the south.

He compares this lifting force of the stars to the attractive power of a magnet over iron, and argues that it must be the waters which are drawn away from the earth, not the earth which is lifted above the water, because the starry influence in its downward course would meet first the sphere of water, and moreover it is lighter and easier to move than Earth. He also thinks that the presence of springs on mountain tops is to be explained by the fact that the ocean is preserved at a higher level, hence water percolating through the porous land, as through a sponge, is forced up to its utmost height.

It does not seem as if Dante had paid much attention to this problem when he was writing the Convivio, for although he calls the habitable part of the earth “the uncovered land,” “la terra discoperta” (Conv. III. v. 73), he speaks of Earth and ocean as if they formed a globe together, “Questa terra ... col mare è centro del cielo,”[623] in the manner of Alfraganus, “Inter sapientes convenit, terram unà cum aqua globosam esse.”[624] But if we may believe that Dante is the author of the Quæstio de Aqua et Terra—a belief shared by many experts—he became greatly interested in the problem later on. According to the introduction and the final colophon, he attended a discussion on the subject and joined in it himself, when in Mantua, and afterwards in Verona less than two years before his death he wrote and read in public a Latin treatise in which his arguments and conclusions are set forth.

He seems to have had in mind Ristoro’s book, and while refuting some of the conclusions agrees with others. As a thirteenth century scholar he admits, as a matter of course, that the centre of the earth is the centre of the Universe and the goal towards which all heavy things tend; that earth as the heaviest element ought to be everywhere nearest this centre, while water ought to occupy the nobler place above it, that is, nearer to the most noble sphere of all which envelops all the others (the Empyrean). He also reasons, in true Dantesque and true mediæval fashion that there must be some place in the universe where all the elements may meet and mingle so that all potential forms of matter may be realized; otherwise the Mover of heaven, in whom all these forms (Plato’s Ideas) actually exist, would fail to give complete expression to his goodness, which is impossible.[625]

The author of the Quæstio denies, however, that this was accomplished by the removal of part of the sphere of water from the underlying earth. The ocean cannot have been drawn away and heaped up, he says, for water would always flow down again, being fluid and naturally seeking its own level; nor can the sphere of water be eccentric to that of Earth so that the latter emerges from it in one part. The reason for this is interesting since it implies a curious and apparently novel theory of gravity. Aristotle’s theory was that all heavy things tend by a natural law towards the centre of the universe, and therefore necessarily range themselves in spheres round it; the writer might therefore have made short work of Water’s eccentric sphere by stating briefly that it could not exist; instead of this, however, he suggests a new law of gravity, apparently invented on the spur of the moment, according to which everything which has weight tends towards the centre of its own circumference. If then earth and water had two separate centres, they would fall naturally in different directions, or as he puts it “to different downs.” Yet we know that the law of gravity is the same for both, and therefore their spheres must be concentric. The centre of the universe must be also the centre of the sea.[626] It had apparently been urged (perhaps in the discussion at Mantua) that since water follows the moon in the tides, its sphere may also imitate hers in being eccentric, but although Dante takes for granted that a connection between moon and tides is proved (and indeed it had been noted by the Greeks),[627] he replies that imitation in one particular need not imply imitation in all. Again, if the sphere of earth emerged from the sphere of water in the way proposed, the outline of the emergent earth must be circular, instead of which it is that of a half-moon, or nearly so, its width from east to west being much greater than its length from north to south.

Dante has been blamed for assigning this shape to the emergent earth, but the comparison of Earth’s habitable quadrant with the illuminated quadrant of the moon is perfectly just, as we saw with Ristoro,[628] from whom Dante is perhaps quoting here. The qualifying “vel quasi”[629] is added because the truly habitable regions did not extend over the whole quadrant, but stopped short at the arctic circle.

The existence of springs on mountain tops is explained by the fact that water rises thither not in the form of water but of vapour. Another upholder of Ristoro’s theory that Water was rolled away from Earth seems to have brought forward as evidence that sailors can see distant land from the mast which is invisible from the deck, and that therefore it evidently lies below the ocean; but this is confuted by the true and well known explanation that it is the convex shape of the sea which hides the distant land. Our author adds to his other arguments, in the curiously casual way so characteristic of his age, the ordinary observation which would be the first to occur to us, and quite sufficient in itself, viz. that instead of seeing a great wall of ocean rising above our sea-coasts, we invariably see the coast rising above the sea.

His own idea is that though the sphere of Water in general rises above Earth, in one part of the northern hemisphere Earth has been drawn up above the ocean. Earth must be subject to an uplifting influence, as well as to the downward drag of gravity, just as man is susceptible to the influence of reason as well as to the sway of his lower passions. This uplifting influence is not inherent in Earth herself, an upward impulse would be contrary to her own nature; nor can it be in water, or air, or fire, since all these are homogeneous bodies, and their virtue is evenly distributed, so that they could not cause a local and partial effect. It must be therefore in one of the heavens, and it remains for us to enquire which.