“O ineffabile Sapienza che a così ordinasti, quanto è povera la nostra mente a Te comprendere! E voi, a cui utilità e diletto io scrivo, in quanta cecità vivete, non levando gli occhi suso a queste cose, tenendoli fissi nel fango della vostra stoltezza.”[389]
It is interesting to compare this passage with the parallel passages in Alfraganus and Ristoro. The astronomer is concise and clear; the monk is diffuse and apt to repeat himself; the poet is quaintly picturesque. Both the Italians evidently draw the main facts from the Arab, and all use the illustration of a mill-stone to explain the horizontal motion of the heavens at the pole: here are the three corresponding passages:—
“Coelumque molæ trusatilis instar gyrum vertitur.”[390]
“Lì si volgera il cielo attorno con tutte le sue stelle, in modo di macina.”[391]
“Conviene che Maria veggia ... esso sole ‘girare il mondo’ ... come una mola.”[392]
Dante alone uses the figure of a wheel to illustrate the vertical motion at the equator; he perhaps takes from Ristoro the idea of the spiral. For the latter describes the path of the sun as a “via tortuosa, la quale i savi chiamano spira;”[393] but he explains it as like a string wound round a stick, Dante like the screw of a press. Dante is dealing only with the sun, and does not enter into details about the visibility of the zodiacal signs like the other two authors; but on the other hand he goes south to the other pole, which apparently does not interest the others, perhaps because the southern hemisphere was thought to be uninhabited. But the poet has added life to his description by supposing both poles inhabited, placing there his imaginary, mysteriously-named cities of “Maria” and “Lucia.” On the equator, where Ristoro has the mythical city of Arym, whose wise and prosperous citizens enjoy a perfect climate, Dante, relying more on the classics, lets his barbarous Garamantes run about naked most of the year, under the fierce equatorial sun.
Needless to say, his little homily in conclusion is all his own; it is more interesting to find that he alone mentions the opposite movements of the Sun, to right and left respectively in the north and south hemispheres,[394] and the fact that every part of the earth receives the same amount of sunlight in a year. This may have been suggested by someone else, but one would like to think he arrived at it independently, when thinking over the facts.
In the light of this treatise, which describes so truthfully the path of the sun, and its effect on the seasons in different latitudes, we may explain two rather puzzling passages in the Divine Comedy.
One is at the beginning of the tenth canto of the Paradiso, where Dante wishes his readers to realize the position of the sun when he entered it with Beatrice, and the great importance of this position. “Lift your eyes with me, reader,” he says, “to that place in the lofty heavens where the one motion meets the other, and see how the oblique circle which carries the planets branches off from that point.” The reader is now familiar with the “two chief motions,” and knows that one is the diurnal, from east to west, the other the planetary periodical motions in the opposite direction; they meet at the equinoxes, where the ecliptic cuts the equator. It is the spring equinox which Dante is speaking of, for a little further on he says that the sun, situated in the place above-mentioned, was circling in those spirals which bring him to us earlier every day (lines 31-33). Now if the path of the planets were not thus oblique, he continues, much virtue in heaven would be lost, and almost every earthly power dead. Even if the obliquity were merely less or more, the universal order of both heaven and earth would suffer greatly. But why this should be so he leaves his readers to think out for themselves, having a greater matter in hand which demands all his attention.
It is easy to see that if the sun always moved in the equator, without departing from it either north or south, he would rise every day to the same height in the sky, and there would be no change of seasons anywhere on the earth; he would always be overhead at noon to Dante’s Garamantes, living on the equator, and always just on the horizon, day and night, to the people of “Maria” and “Lucia” at the Poles. If the ecliptic made a greater angle with the equator the seasons would be more marked, and the sun would rise higher in summer in high latitudes. If the angle were less, the reverse would be the case. Moreover if sun and moon and all the planets followed the same track, they would be constantly eclipsing one another.