[Margin: Averroes’s system.]

[I.] How doubtful and inconstant Averroes was in [his] system of the heaven is clear from [his commentary] on 2 On the Heaven, comment 35, and on Metaphysics 12, comment 45, and in the commentaries on the Almagest; for there, as to the order of the Planets, you would not know whether he subscribes to Ptolemy or rather to others—though he inclines to the order of Ptolemy. Yet he contends, with many arguments, to overthrow the Eccentrics and Epicycles, and in their place to substitute the ancient concentrics; and he promises, in that text 35, that—if God should prolong his life—he would treat of that theory of the celestial motions which was cultivated in Aristotle’s time, and which he reckons agreeable to Physical principles; but (Metaphysics 12, comment 45), recognizing himself worn out by old age, he despairs of this matter, and exhorts posterity to it, and hopes there will not be lacking [one] who may undertake this task. Nor much after did Alpetragius arise, who applied [his] mind to this. And his work is entitled The Theory of the Planets, Proved by Physical Reasons—because he otherwise suspected that Ptolemy’s hypotheses are indeed not theoretically impossible, but repugnant to Physical principles, and impede themselves; granted that, as to the numbers of the motions and the periods of the times, he follows Ptolemy to a hair’s breadth. But he himself too, at the end of this work, confesses that many other particulars regarding the motion of the Planets, which are in Ptolemy’s Almagest, were passed over by him, because he now saw himself worn out by old age.

[Margin: Alpetragius’s system and hypotheses.]

[II.] First, then, Alpetragius teaches that there is given a Ninth sphere, which is moved by the most perfect motion of the prime mobile alone, by one Intelligence, in the space of 24 hours, from East through the Meridian toward the West; and that the same Intelligence impresses on the eight lower spheres its motion, but uniformly-difformly more and more remiss [slowed]; and therefore that the sphere of the Fixed [stars] is moved somewhat more slowly toward the West, and is not wholly revolved to the same Meridian in 24 hours, but in a somewhat greater little-appendage of time; and that yet more slowly is moved the sphere of Saturn, and more slowly than this the sphere of Jupiter, and more slowly than this [the sphere] of Mars, and [more slowly] than Mars, Venus, and [more slowly] than Venus, the Sun, and [more slowly] than the Sun, Mercury, and [more slowly] than Mercury, the Moon—because, on account of the imperfect participation of that impetus, they are more sluggish. And hence [he thinks that] the observers, deceived, supposed the Fixed [stars] and Planets to have a proper motion contrary to the motion of the prime mobile; whereas in reality they are not moved by a contrary motion, but by [a motion] the same in kind, yet slower—and slower, the more they are distant from the—

[…continues on p. 286 (PDF 321): “…sphere of the prime mobile.” Then ¶III (Alpetragius on Venus above the Sun, Mercury below; the Arabic laulabina), ¶IV (Delphinus), ¶V (Amici) — ending Chapter VI; then Chapter VII opens, on the homocentric system of Turriano [Della Torre] and Fracastoro.]

(printed p. 286 — Chapter VI concludes with Alpetragius, Delphinus, and Amici; these systems being obsolete, no diagram is given. Chapter VII then opens, on the homocentric system of Turriano [Della Torre] and Fracastoro, recounting Fracastoro’s epistle and Turriano’s deathbed request and treating the seven orbs of the starry sphere.)

…[are distant from the] sphere of the prime mobile.

[III.] Secondly, he establishes (ch. 8, 9, & 11) that Venus is to be placed above the Sun, but Mercury below, because it [Venus] is revolved more quickly to the same meridian than the Sun, and is therefore nearer to the supreme sphere. And in the same place he affirms that Venus and Mercury have their own light from themselves, and therefore, although Mercury comes between our eye and the Sun, it nevertheless does not obscure any part of the Sun. Further, the slowness and velocity of the motions, all [their] inequality, and the stations and retrogressions, he ascribes to the motion of the poles of each sphere, [the poles] describing various little circles around the poles of the world or of the Ecliptic. But from his Theory it follows that the Planets always preserve the same distance from the center of the world; nor, however, does he bring a cause why they appear now smaller, now larger than themselves. And the Planets describe a certain sphere—in Arabic laulabina [a helix/spiral]—but on the same spherical surface.

[Margin: John Anthony Delphinus’s system.]

[IV.] John Anthony Delphinus, of Casale Maggiore, of the Franciscan order, in his book On the celestial globes and motions (from ch. 30), besides the Empyrean, posits a ninth sphere, or crystalline heaven, to which he attributes the office of the prime Mobile; but he will have each sphere to have its own Intelligences moving [it] toward the West through spiral lines. As to the order of the Planets, he follows Ptolemy, but uses concentrics; and the cause why the Planets seem to have a diverse magnitude he attributes to a diverse density and opacity of the air—on account of which, by refraction, the apparent disc of the stars is amplified—and to a diverse disposition of the eyes.

[Margin: Giovanni Battista Amici’s system.]

[V.] But Giovanni Battista Amici (in the opusculum On the motions of the celestial bodies, according to the Peripatetic principles, without Eccentrics and Epicycles) defends the counter-revolving [spheres] of Aristotle, and uses homocentrics; and the cause of the diverse apparent magnitude in the same Planet he refers partly to the sight and the fallacy of instruments, partly to the diverse temperament of the air. But in the eighth sphere he admits a proper motion toward the East, and indeed an unequal one. And therefore he posits ten spheres, of which the tenth is the Prime Mobile, the ninth and eighth for the motion of the Fixed [stars]—equal of itself, but per accidens unequal on account of the “titubation” [wobble] or trepidation—exactly as the Alfonsines posited (whose order, too, in placing the Planets, he follows); nor among the superior Planets does he acknowledge others than Saturn, Jupiter, [and] Mars. But the systems of these [authors] are so obsolete that it is not worthwhile to delineate a peculiar figure for explaining them; but let it suffice to have indicated their hypotheses.