As we continue our weekly readings of Sulayman al-Mahri’s Mir’at al-salak (Mirror of Travellers; see our previous post), wondering about the relation between cosmography and geography and navigation, as in one of the recent RUTTER Blog posts, we have come across an interesting live example of “saving the phenomena”, straight from the 16th-century Arabian Peninsula.
The context is Ptolemaic through-and-through, with al-Mahrī explaining in Chapter 5 what relates to the “accidents” of the planets in their courses. He takes a while to describe the mechanics of planetary movement, dwelling on the details of retrogradation which were so fundamental to the whole Ptolemaic edifice. So we need to brush up conscientiously on our pre-modern astronomy terms in Arabic, the epicycles, deferents, with their apogees and perigees, to follow carefully the exposition. But then, after a thorough explanation, we come across the following,
Now, it is obvious that the heavenly bodies bring to completion the circular movement inside their orb without experiencing any alteration that touches on the orb. For their movement is neither faster nor slower, nor do they go backwards on their path, or halt their movement in the actual fact itself (nafs al-amr). But all this has to do with the relation between our vision (hasab ru’yatinā) and the composition of the movements (tarkīb al-harakāt).
While it has become commonplace to cite Aristotle on the matter of “saving the phenomena”, it is well known that from the earliest times of Greek philosophy there was a tension between the perfect motion of the spheres—cf. Timaeus, “time is the moving image of eternity”—and the perceived irregularity of the astronomical phenomena. Most notable and seminal are the Platonic passages in Timaeus, Epinomis and the Laws, but for example, and more directly astronomical, here is Geminus of Rhodes (1st century BC),
The Pythagoreans, who were the first to apply themselves to investigations of this kind, assumed the movements of the Sun, the Moon and the five planets to be circular and uniform. They would not admit, with reference to things divine and eternal, any disorder such as would make them move at one time more swiftly, at one time more slowly, and at another time stand still.
Ptolemy (Almagest III, 1 and XIII, 2) is very clear about preserving as much as possible the simplicity of the models (Gr. hypotheseis), and the Middle Ages saw countless back and forth arguments on this matter, which might be said to be a conversation, at times heated!, between cosmology and cosmography, what we know to be de iure, and what we perceive to be de facto. It is all a series of disputationes maybe, lively and truly philosophical. How remarkable, then, that an unassuming Yemeni pilot of the 16th century, man of praxis and adventure, should join the conversation, echoing in his clear, matter-of-fact discourse, the arguments of so many centuries before him—from Pythagoras to al-Mahrī, just a blink of a scientific eye! [JA]
