The (fact that the) motion is uniform around the center of the world, rather than around its own center [meaning the center of the deferent], that is one of the problems (ishkālāt) in this discipline... I have various other methods (for solving it), which I have explained in (the book) al-Hay'a al-manṣūrīya, and have also referred to (still) other marvelous methods in (the book) al-Lawāmi' wa-l-ma'ārij.[220]
And while explaining the prosneusis problem in the safīr, he went on to say: "This prosneusis is also among the problems (ishkālāt)... The truth (concerning) it is what I have established in al-Hay'a al-manṣūrīya, which shines with the sparkles (Lawāmi') of light."[221]
And in the course of discussing the equant problem in the configuration for the upper planets, he went on to say: "This too is among the problems (ishkālāt), which al-Hay'a al-manṣūrīya is capable of solving."[222]
With such explicit references, there is no doubt that this sixteenth- century astronomer was interested in pursuing the critical tradition that had already grown around the problems of Ptolemaic astronomy. But here too, unless his other two works are identified and studied in some depth, their actual contents and their real import still remain enigmatic and only speculative at this point.
Similarly, the Syrian astronomer Ghars al-Dīn Aḥmad b. Khalīl al-Ḥalabī (d. 1563) voiced similar concerns in his telling treatise that he called Tanbīh al-nuqqād 'alā mā fī al-hay'a al-mashhūra min al-fasād (Warning the Critics About the Faults of the Generally Accepted Astronomy). In it he even raised an issue that has not been raised so far in this discussion, but which will be taken up in the section dealing with the relationship between astronomy and philosophy. For our current purposes, it is enough to signal that the issue itself expressed doubts regarding the permissibility of the eccentrics that were used in the Ptolemaic configurations. In that context, Ghars al-Dīn proclaimed:
Since the generally accepted astronomy is not free from doubts (shukūk), especially those regarding the eccentrics, I have confronted them in this treatise, not in order to belittle the principles of this craft (i.e. astronomy), but (to point to) slips where the intention did not match (the results), and to have that as a proof of what we have written (elsewhere)...[223]
The fourth chapter of that treatise was devoted to the problems of the lunar configuration, and the treatise itself was dated to 1551 A.D.
The same century also witnessed the most extensive, ingenious and unparalleled works of Shams al-Dīn al-Khafrī (d. 1550), which combined both the critical tradition as well as the tradition of alternative constructions to Ptolemaic astronomy. Some of those works have already been subjected to some analysis by the present author, and we shall have occasion to return to them in the section dealing with alternatives to Ptolemaic astronomy.[224]
The next century witnessed the production of the prolific scientist Bahā' al-Dīn al-'Āmilī (d. 1622), who did not seem to have confronted the Ptolemaic problems directly, as they do not seem to be especially mentioned in his treatise Tashrīḥ al-aflāk. But his commentators did not observe such reserve. Instead they composed full texts of their own, or added marginalia to 'Āmilī's text which was by then heavily read and widely distributed in schools, and thus continued to expose and indirectly popularize the faults of Ptolemaic astronomy. One of those commentators on al-'Āmilī's text added a marginal note in which he gave a quasi history of those faults and the people who had addressed them before. In one manuscript, the note reads:
The first among the moderns who spoke about the solution of the insoluble (problems) was al-Waḥīd al-Jurjānī, the student of al-Ra'īs Abū 'Alī Ibn Sīnā [sic., meaning 'Abd al-Waḥīd al-Jūzjānī], He wrote a treatise, which he called Tarkīb al-aflāk (The Structure of the [Celestial] Spheres], and mentioned in it the models with which these problems (ishkālāt) could be solved. After him came Abū 'Alī b. Al-Haitham, then the inquirer Ṭūsī, and then the learned Shīrāzī, who collected from his contemporaries such as Muḥyī al-Dīn al-Maghribī—because the Principle of the inclined (al-mumayyila/al-mumīla) is copied from him —, and then the excellent master Shams al-Dīn Muḥammad b. 'Alī b. Muḥammad al-Ḥammādī (?). You should note that the statements of Abū 'Ubayd were very weak, and nothing could be solved with Ibn al-Haitham's words, as it was already stated in the Tadhkira by the inquirer Ṭūsī. With the words of the inquirer (Ṭūsī) himself, as we have copied their gist, the problems of the porsneusis, Mercury's equant, and the latitudes of the cinctures (manāṭiq) of the epicycles and the deferents could not be solved. As for the author of the Tuḥfa [i.e. Quṭb al-Dīn al-Shīrāzī], he had elaborated too much. The master Muḥammad al-Munajjim al-Ḥammādī composed a treatise, in which he claimed that these problems (ishkālāt) could all be solved with one hundred and forty spheres. He indeed established three principles, which were, in reality, erroneous. Anyone requiring (more information about) them he should seek them in al-Ma'ārij [part] of the Lawāmi ' of al-Manṣūrīya.[225]
This quasi-historical synopsis, despite its historical shortcomings, at least reveals two important trends: First, it signaled that there were people who were themselves interested in the history of astronomy, and second that the problems of Ptolemaic astronomy continued to be discussed after the middle of the seventeenth century when this note was probably written. In addition, it also reveals that the works of Dashtaghī had by then become the standard references, at least as far as the author of this marginal note was concerned.
Historians of Arabic astronomy have not yet made any forays in the centuries that followed in order to determine the extent of criticism, if there was any, or to find out if the later astronomers continued to construct alternatives to Ptolemaic astronomy. This particular research would be of the utmost importance, especially in light of the fact that in these later centuries one would want to know how those astronomers dealt with the reception of modern post-Copernican astronomy in Islamic countries. Or whether the old Ptolemaic astronomy could still survive the onslaught of post Copernican astronomy. What little research has been done in this domain, i.e. in the domain of criticism of the natural philosophical underpinnings, reveals that during the latter part of the nineteenth century there were still those who defended Ptolemaic astronomy against its detractors, when the detractors had by then adopted the alternative Copernican and more modern astronomy.[226]
Finally, there were objections of another kind: more theoretical in nature, in the sense that they addressed such theoretical issues that touched upon the very foundations of all scientific activities and were not only restricted to astronomy. And there were those who proposed new mathematical models to account for the same observations of Ptolemy, without explaining their motivations. But their alternative works can only mean that they were dissatisfied with the existing Ptolemaic models, and thus their activity must be perceived as an objection in itself. So when we come to survey the various alternative models that were proposed to replace the Ptolemaic ones, one could read that survey as an elaborate statement of theoretical objections to Ptolemaic astronomy as well.
224
See Saliba, "A Sixteenth-Century Arabic Critique"; Saliba, "A Redeployment"; Saliba, "The Ultimate Challenge."
226
G. Saliba, "Copernican Astronomy in the Arab East: Theories of the Earth's Motion in the Nineteenth Century", in