Yet an explanation and a source of this statement is not far to seek, and instead of proving ignorance it indicates that the author of the _Quæstio_ knew his Alfraganus well. The passage is evidently slightly corrupt, but the clue to its meaning lies in the word “eccentricity.” In two other places of the _Quæstio_ the moon’s eccentric “orbis” is alluded to,[635] but if we translate this as “orbit” we shall be introducing modern ideas which meant nothing to Dante or his contemporaries. According to Alfraganus and Ptolemy the moon’s orb or sphere[636] was eccentric, but this was not the main cause of her varying distance from Earth. It was the revolution of her epicycle round its centre C, which caused her to move continually from apogee M to perigee P; and as the whole epicycle was meanwhile revolving on the deferent round C, and these two periods were not quite equal, the moon was as often in the perigee of her epicycle when it was south as when it was north. But besides this, the deferent, being eccentric to Earth, had also a perigee and apogee; and Alfraganus says that _the perigee of the eccentric is always in the south_. “Saturnus, Jupiter, atque Mars eccentricorum suorum absidas summas et imas habent declinatas a zodiaco, illas ad boream, hasce ad austrum, secundum eandem semper deflexus mensuram: _quedadmodum res in Luna obtinet_.”[637] ------------------------------------------------------------------------ [635] _Qu._ vii. 4, 6, and xxiii. 52. [636] “Orbis” and “sphæra” are used indifferently by Alfraganus to indicate the celestial spheres: thus, in ch. xii. he says “_Orbes_, qui stellarum omnes motus complectantur, numero esse octo,” and on the next page, “unamquamque harum _sphærarum_ octo.” [637] “The upper and lower apsides of the eccentrics of Saturn, Jupiter, and Mars, have a certain declination from the zodiac, the former to the north, the latter to the south, the amount always remaining constant: _and it is just the same with the moon_.” _El. Ast._ xviii. par. 6. ------------------------------------------------------------------------ The upper and lower apsides are defined in chapter xii. as the positions of apogee and perigee respectively.[638] In this quotation the word “declinatas” also supplies us with the meaning of Dante’s “declinatio,” which need not be changed for “elevatio.” He is using it in the astronomical sense of position north or south, like Alfraganus and modern astronomers, and it refers here to the “declinet” of five lines earlier. “Luna ... tantum _declinet_ per zodiacum ab æquinoctiali _versus polum antarcticum_ quantum versus arcticum.”[639] ------------------------------------------------------------------------ [638] In the edition of Golius ch. vii. par. 5, the position of greatest distance is called the perigee, of least the apogee, but this mistake is corrected in the next paragraph.