Islamic Science and the Making of the European Renaissance

6. Islamic Science and Renaissance Europe: The Copernican Connection

The new mathematical tools that were developed by the astronomers of the Islamic world did not only prove to be very useful for the emergence of new ways of looking at theoretical astronomy, as we have already seen, but also allowed astronomers to manipulate mathematical models so that they could meet the observational requirements. We have also seen this trend culminate in the works of Khafrī who demonstrated a total mastery of mathematics so much so that he attained complete freedom to use whatever mathematical configuration he wished in order to represent the same physical observational phenomenon. Mathematics became a new language, and became an efficient tool of astronomy, at least as far as the works of Khafrī were concerned.

The works of Ibn al-Shāṭir, on the other hand, with their emphasis on the strict Aristotelian cosmological requirements of abolishing eccentrics, also liberated astronomical models from the often cumbersome multiplicity of shapes and forms and unified all the planetary models with one geocentric format that could be easily applied to one planet at a time by simply changing the parameters of the two epicyclic spheres deployed in each model. In a roundabout way, the unintended consequences of these unified models produced the "strange" development that allowed them to be transferred into heliocentric models, despite the fact that there was no shred of support for such heliocentrism in the then reigning Aristotelian cosmology. All that someone like Copernicus had to do was to take any of Ibn al-Shāṭir's models, hold the sun fixed and then allow the Earth's sphere, together with all the other planetary spheres that were centered on it, to revolve around the sun instead. As we shall soon see that was the very step that was taken by Copernicus when he seemed to have adopted the same geocentric models as those of Ibn al-Shāṭir and then translated them to heliocentric ones whenever the situation called for it.

All those shifts in astronomical thought that took place in Islamic civilization had some very serious consequences. Not only did they expose all the factual and observational errors of Greek astronomy, but also demonstrated, in the most convincing manner, the inconsistencies of that astronomy with its very own cosmological presuppositions. In the later centuries, when Islamic astronomy reached its theoretical maturity, starting with the continuous rise of analytical discussions of planetary theories after the thirteenth century, one could hardly find a serious astronomer who did not make an attempt at reformulating Greek astronomy. At that time, no one could hope to practice astronomy, and be taken seriously, if he did not make an effort to solve the thorny cosmological problems of Greek astronomy. One astronomer after another, tried their hand at devising new mathematical models that represented a much more consistent cosmological picture of the Greek astronomical tradition. At the same time, those models could account perfectly well for the same observations, which were used by Ptolemy, in the first place, to construct his own predictive mathematical models for planetary motions.

This constant search for more consistent representations of planetary motions came to characterize the whole field of Islamic astronomical research, especially in the later centuries following the thirteenth century. The movement of continuously reforming Greek astronomy became so important that it apparently attracted the attention of astronomers from outside the Islamic domain. We know, for example, that Byzantine astronomers, like Gregory Chioniades (fourteenth century) and others, would travel to the Islamic lands in order to learn of the latest developments in Islamic astronomy and to report their findings back to their compatriots in their own Greek language.[305] In fact, one can also document the dependence of the late Byzantine astronomy on Islamic astronomy by simply browsing through the technical terminology that was used by Byzantine astronomers at the time. This terminology demonstrates very clearly that it bore a much closer resemblance to the Arabic sources, from which it was derived, than to the classical Greek texts such as those of Ptolemy.[306]

With the fall of Constantinople in 1453 to the Ottoman Turks, and the ultimate demise of the Byzantine empire, a good number of Byzantine scholars escaped westward, at times together with their books. But by then the Byzantine civilization had been in direct contact with the Islamic civilization for centuries already. And as a result those books inevitably bore the marks of having been influenced by the intellectual production of the Islamic civilization, and thus contained some of the developments that had already taken place in that civilization. In a way, these Byzantine contacts with Europe were much more complex than the contacts that had already taken place during the Middle Ages between the Islamic world and the Latin West. In the first, we saw several Arabic works that were translated into Latin, sometimes undigested, and mostly restricted to the confines of linguistic contours of the texts. With the new Byzantine contacts one can now distinguish a new manner of transfer of texts. Arabic and Persian scientific texts were apparently already digested in the Byzantine Greek sources for a period of about two centuries or so, before those Byzantine texts were brought into Europe. This time, their contents were not apparently translated into Latin. Rather, because of the emphasis of the Renaissance intellectual environment on the Greek language, they were read in the original Greek. The best of their contents, which were originally Arabic and Persian could now be directly assimilated into the Latin texts, without having to translate the whole text into Latin. This method of transfer of knowledge constitutes by itself a new phenomenon that is rarely acknowledged by all those who study the transfer of knowledge across cultures. More importantly, this later transfer of knowledge from the world of Islam to Europe this time spoke directly to the contemporary science of the Renaissance, where its impact can be best detected, as we shall soon see.

About the same period that witnessed the various contacts between Byzantium and the world of Islam there were various other contacts as well. One should pay attention to the several European travelers who performed their pilgrimage to the Islamic world, either to visit the Holy Lands, or to simply seek knowledge from the lands of Islam. This contact too must have brought some of the findings of the Islamic world to the European countries. What did they bring in particular is a matter that is currently under investigation and promises to produce some very interesting results.

Our current state of knowledge, however, can already inform us about some of those contacts and the nature of the information that was exchanged. We already know, for example, that those contacts brought some very advanced theoretical findings from the lands of Islam to Renaissance Europe, findings that were apparently highly appreciated by the

European scientists who consumed this material and ended up incorporating it in their own works.[307] And yet our research in that particular area is still in its infancy and once it is completed, it promises to change much of our world view, about cultural transmissions, cultural contacts, the nature of the European Renaissance, and the earliest roots of modern astronomy.[308]

A sheer accident, in 1957, brought to the attention of Otto Neugebauer, who was then working on the mathematical astronomy of Copernicus, a text that contained the theoretical astronomy of the famous Damascene astronomer Ibn al-Shāṭir (1375). It did not take the genius of Neugebauer much, despite the fact that he did not read Arabic himself, to realize that Ibn al-Shāṭir's lunar model was indeed identical, in every respect, to that of Copernicus (1543) (figure 6.1). The former model, has survived in Ibn al-Shāṭir's text Nihāyat al-sūl fī taṣḥīḥ al-uṣūl (Final Quest Regarding the Corrections of the [Astronomical] Principles), and was brought to Neugebauer's attention by his close associate and friend Edward Kennedy. Kennedy was then a professor of mathematics at the American University of Beirut, and a distinguished historian of Islamic astronomy and mathematics in his own right. His own encounter with Ibn al-Shāṭir's work at the Bodleian Library was in itself a pure accident as well, and now belongs to the world of legends. But that discovery, together with its ensuing discussion with Neugebauer, gave rise to the publication of an article in Isis by Victor Roberts, a student of Kennedy, who called it "The Solar and Lunar Theory of Ibn al-Shāṭir: A pre-Copernican Copernican model."[309]

Naturally, such a finding jolted the scholarly community somewhat, for up till then the prevailing belief was that Renaissance science, unlike its medieval counterpart, was considered to be a European self-contained creation, almost ex nihilo. Or if one were to widen his horizons and look outside the particular confines of the European environment one was supposed to find Renaissance science taking its inspiration from the classical Greek sources, rather than any other source, least of all Islamic sources. Common opinion stipulated a European enmity with things Arabic and Islamic and thus no one would have expected a fruitful contact between the two.[310] For Neugebauer to find that there was a direct connection between the works of Copernicus and the Arabic planetary theories, which were produced in the Islamic world about 200-300 years before, was a discovery that was shocking in its own time and has not been fully digested yet in the secondary sources dealing with the history of science in general. Only a handful of researchers seem to know about it still, and to appreciate its full significance.

Figure 6.1

The lunar model of Ibn al-Shāṭir and Copernicus.

But this finding opened the door to further investigation. It was also Neugebauer who widened the circle of research and began to look for other similarities of ideas between the works of Renaissance scientists and the scientists of the Islamic world. And it was in that context that he revisited a chapter from the Tadhkira fī 'ilm al-hay'a, of Naṣīr al-Dīn al-Ṭūsī (d. 1274), which had already been translated into French by Bernard Carra de Vaux in 1893 and published under the title "Les spheres célestes selon Nasîr-Eddîn Attûsî."[311] In this chapter, which was originally written by Ṭūsī in 1260-61, Ṭūsī formalized as well as generalized and now supplied a rigorous mathematical proof to the famous theorem that has come to be known in the literature as the Ṭūsī Couple, which we have seen before.

We have also seen that the first articulation of this theorem, had already been proposed in 1247, in yet another work by Ṭūsī, the Taḥrīr al-majisṭī (Redaction of the Almagest), which is yet to be edited and published. And, as I have noted, this earlier first articulation was specifically proposed in order to respond to the failings of the Ptolemaic latitude theory of the planets. This background of the theorem was neither mentioned by Ṭūsī nor was it signaled by Carra de Vaux, on his own, nor was it apparently known to Neugebauer who did not work on the Arabic manuscripts directly.

Ṭūsī's Couple, as we have seen, offered a general solution to the problem of generating linear motion from a combination of circular motions. It was expressed in terms of the motion of two spheres, usually called in the Arabic astronomical literature that followed al-kabīra wa-l-ṣaghīra (the large and the small). As has been noted, one of those spheres was taken to be twice the size of the other, and in the initial setting the spheres were taken to be internally tangent at one point. With the motion of the larger sphere at any speed, and the motion of the smaller sphere at twice that speed, in the opposite direction, the point of tangency was then found to oscillate along the diameter of the larger sphere, thus producing the required linear motion. In 1260-61, after supplying the formal mathematical proof to this theorem, Ṭūsī went on to use it in the lunar model and then in the model for the upper planets, as we have already seen.

Carra de Vaux's translation of this chapter gave all the contents of the original Arabic in a rather faithful French, but was then concluded with an assessment by Carra de Vaux himself. In it, and on the basis of his encounter with this particular work of Ṭūsī, de Vaux summed up the general character of Arabic astronomy. In de Vaux's time, and because very little else was known then from the astronomical production of the Islamic civilization from these later periods, de Vaux was emboldened to say, that while Arabic astronomy did not hold Ptolemy's work with much regard [an understatement indeed about a chapter that was devoted specifically to critiquing the problems in Ptolemaic astronomy], it did not, on its own, have enough "génie" to transform astronomy altogether, and instead suffered from a general "faiblesse" and "mesquinerie" that did not allow it to develop further. From such a statement, one has to draw the conclusion that de Vaux could not fully appreciate the importance of the chapter that he was translating at the time. We shall have occasion to return to this issue when we speak about the so-called age of decline of Islamic science.

With a completely different attitude, and being immersed in the mathematical astronomy of Copernicus at the time, Neugebauer could immediately see the essence of Ṭūsī's problem, because he could also see that it was the same problem that was faced by Copernicus later on, in De Revolutionibus III, 4.[312] Both astronomers needed to utilize a mechanism that allowed them to generate linear motion from circular motion or combinations thereof, as I have said several times already. And both used the same Couple, except for one difference: Ṭūsī knew that he was introducing a new theorem in 1247[313] and again in 1260-61, which was nowhere to be found in any earlier Greek source, and said so, while Copernicus silently went ahead and described the same theorem and produced a very similar proof as we shall see, without mentioning that he had invented the theorem or the proof himself, nor that he had seen it in any other source. He only mentions the vague reference to a statement by Proclus,[314] referring to the latter's commentary on Euclid, in which Proclus says that linear motion could be gotten from circular motion. But for those who read Proclus closely will immediately realize that Proclus was talking about curved lines and straight lines being produced from one another and not oscillating motion resulting from complete circular motion as was required by Ṭūsī and Copernicus after him.

By 1973, Willy Hartner discovered a remarkable feature in Copernicus's proof of the same theorem.[315] By comparing Ṭūsī's proof, which was completed in 1260-61, with that of Copernicus, which was published in 1543, Hartner discovered that the two proofs (figure 6.2) carried the same alphabetic designators for the essential geometric points. That is, where Ṭūsī's proof designated a specific point with the Arabic letter "alif", Copernicus's proof signaled that same point with the equivalent phonetic Latin letter "A", where Ṭūsī, had "bā'", Copernicus had "B", etc., except in one case where Ṭūsī had "zain" and Copernicus has "F". On the basis of the letter correspondences, letter to letter, Hartner ventured to say that Copernicus must have known about Ṭūsī's work while in Italy. The implication that was also spelled out by Hartner was that Copernicus must have had access to Ṭūsī's work in some indirect form, since as far as we know neither Copernicus could read Arabic, nor was Ṭūsī's text, in which the theorem appeared, was ever translated into Latin. To Hartner, it meant that Copernicus must have recruited someone who could explain to him the diagram, while he took notes and used those notes later when he came to write the De Revolutionibus.

Figure 6.2

Proofs of the Ṭūsī Couple from the works of Ṭūsī (left) and Copernicus (right), showing the identity of the lettering of the diagrams. Wherever Ṭūsī had alif Copernicus had A, and wherever Ṭūsī had bā' Copernicus had B, and so on, except that where Ṭūsī had zain for the center of the smaller sphere Copernicus had F. See figure 6.3.

In a more recent reassessment of Hartner's results, I added the Arabic manuscripts evidence to account for the variation between the "zain" and the "F" in the two proofs.[316] By comparing Arabic manuscripts from the medieval period, and noting that the two Arabic letters "zain" and "fā"' that were usually used to designate geometric points, the similarities between those two letters were in fact so close that it would be quite easy for someone, who was not experienced enough with Arabic manuscript traditions, to misread the "zain" for a "fā'" (figure 6.3). I ventured to say that either Copernicus himself or someone sitting next to him, looking at an Arabic text of the proof of Ṭūsī, simply misread the "zain" in the original Arabic manuscript for a "fā'", thus leading Copernicus to introduce the sole variation in the lettering of the two proofs.

But misreadings and variations are on their own very useful for detecting textual transmissions. For as a result of these reading "mistakes" I became quite confident about the conclusion just drawn: that Copernicus was either himself working from an Arabic manuscript where he mistook the "zain" for a "fā'" which is unlikely since we do not know that he knew any Arabic at all, or that he was reading, at least the diagram, with someone else's help who made the same mistake. Furthermore, the complete conformity of the other geometric points between the two proofs now makes the issue of coincidence and independent discovery a most unlikely scenario.

Figure 6.3

A medieval Arabic manuscript exhibiting the similarities between the letters zain = Z and fā' = F.

Therefore, not only did Copernicus apparently seek to solve the same problem of the Greek astronomical tradition by adopting the same approach (that is, adding a mathematical theorem that allowed for the generation of linear motion from circular motion); he also used a theorem that had been invented by Ṭūsī about 300 years earlier, and supplied a proof that was very similar to the one supplied by Ṭūsī, with a slight modification in protocol, but still adhered to the same geometric points that were used by Ṭūsī in the original proof. All of this cannot be mere coincidence, as some people still like to think. And future research both in the world and works of Copernicus, as well as the world and works of the Arabic-writing astronomers who preceded him will, I am sure, eventually uncover the exact route by which Copernicus learned of the earlier astronomical findings of the Muslim astronomers.

Mu'ayyad al-Dīn al-'Urḍī (d. 1266) was a colleague of Ṭūsī, and a distinguished astronomer and engineer in his own right. His distinguished fame must have been the deciding factor for Ṭūsī when he hired him to build the observational instruments for the famous Marāgha Observatory.[317] The observatory itself was established in 1259 in the city of Marāgha in northwest modern-day Iran, under the patronage of the Ilkhānid monarchs.[318]Because of the concentration of the astronomers who worked at the observatory, and because of the recently-found connection between their works and the work of Copernicus, this observatory has now become very famous in the secondary literature. 'Urḍī's fame, however, was obviously based on his most important work which was simply called Kitāb al-hay'a (Book on Astronomy).[319] In it he attempted to revamp the whole of Greek astronomy, having been obviously motivated by the same considerations, which had been discussed for generations before him within the intellectual circles of the Islamic Civilization. The most important problem for the time was still encapsulated in the discussion of the inadmissibility of the equant sphere, on account of the well-known absurdity this concept produced.

Trying his own hand at the resolution of this problem, 'Urḍī proposed a new simple theorem which allowed him to reconstruct the Ptolemaic model[320] for the upper planets by adding new spheres and epicycles, but still accounted for the same observations that were reported by Ptolemy, without having any of the absurdities that were adopted by Ptolemy. In 'Urḍī's model, all the spheres moved uniformly in place around axis that passed through their centers. One could therefore say that in this model 'Urḍī managed to avoid the use of the Ptolemaic equant, but did not avoid accounting for its essential observational effects.

The theorem itself (figure 6.4), now known as 'Urḍī's Lemma, is extremely simple. It stipulates that for any two lines (such as AG and BD) that are equal in length and that form equal angles with a base line AB, either internally or externally, the line DG, joining the other extremities of these two lines, is parallel to the base line AB.

Figure 6.4

A general representation of the four cases of 'Urḍī's Lemma as it appeared in the original manuscripts. This illustrates the four cases of possible equations between internal and external angles.

He first used it in his lunar model, and then he incorporated it in the same model for the upper planets that he had borrowed from 'Urḍī, theorem and all. In both of Shīrāzī's works, which were written few years apart in the 1280s, 'Urḍī's model for the upper planets remained to be Shīrāzī's favorite model, despite the fact that both of the said works of Shīrāzī were themselves written as commentaries on the work of Ṭūsī, and not that of 'Urḍī. By preferring "'Urḍī's Lemma over the solutions that were offered by Shīrāzī's very own teacher Ṭūsī, which made use of the Ṭūsī Couple, Shīrāzī's choice can only be taken as a testament to the popularity of 'Urḍī's Lemma.

Ibn al-Shāṭir (d. 1375), who lived a full century later, followed suit. After using the equivalent of the Apollonius theorem to shift the eccentricities to epicyclic attachments, as we have already seen, in order to return to strict geocentric cosmology, he added to what can be called the Apollonius epicycle another 'Urḍī epicycle in order to account for the motion around the equant as was done by 'Urḍī. In essence, Ibn al-Shāṭir's model for the upper planets is the same as that of 'Urḍī, except for the transposition of the eccentricity that was used by 'Urḍī, and which was one and a half times as large as that of Ptolemy, to an epicycle with the same radius. The rest of the model preserved the same properties. That is, it deployed the same dimensions for the 'Urḍī epicycle, and the same motion conditions, exactly as was done by 'Urḍī (figure 6.5).

As a new tool, 'Urḍī's Lemma, was also used by other astronomers and in new areas of application as well, as we have also seen before, most notably by ''Alā al-Dīn al-Qushjī (d. 1474) and by Shams al-Dīn al-Khafrī (d. 1550) in their respective constructions of their models for the motion of the planet Mercury. Both of these astronomers could assume that they had this new tool in their repertoire, to use it whenever they pleased. The fact that it was used by the previous astronomers for some 200 years must have been taken as a proof that first, it withstood the test of time, and second, that it was a more general form of the Apollonius theorem. It clearly allowed for the transposition of eccentricities to deferent circumferences. But most importantly, it also allowed for the transposition of reference points for uniform motions, such as the motion of the equant, or any other center of motion that was required by the observations.

And since Copernicus had used the same model for the upper planets that was used by Ibn al-Shāṭir (figure 6.6), with the additional transposition of the center of the universe to the sun of course, in that sense Copernicus too ended up using 'Urḍī's Lemma, as Ibn al-Shāṭir had done before him.

Figure 6.5

Ibn al-Shāṭir's model for the upper planets, clearly showing the incorporation of 'Urḍī's Lemma.

Copernicus, however, did not apparently realize the full significance of the two components of Ibn al-Shāṭir's model (the Apollonius and the 'Urḍī components), and simply used the model as a whole, by transposing it to heliocentrism as we just said. As a result he did not feel that he had to produce a formal proof for the 'Urḍī component as he had done with the Ṭūsī Couple. It was Kepler (1630) who wrote to his teacher Maestlin (1631) to ask him specifically about this omission on the part of Copernican astronomy, as was already demonstrated by Anthony Grafton.[321] And it was Maestlin who supplied the proof of that specific case of the 'Urḍī Lemma which applied to the model of the upper planets, without supplying the general proof as 'Urḍī had done.

For our purposes, the almost unconscious use of 'Urḍī's Lemma by Copernicus, in a construction that was identical to that of Ibn al-Shāṭir, minus heliocentrism of course, must raise doubts about Copernicus's awareness of the roots of all the mathematical techniques that were put at his disposal. Would he have proposed this very new theorem? And would he have offered a formal proof of it as was done by 'Urḍī, and as he did for the complementary Ṭūsī Couple that he also had to use, had this new theorem not been at his disposal from the Islamic sources? I doubt that very much.

Figure 6.6

A schematic representation of the model for the upper planets as conceived by Ptolemy, 'Urḍī, Ibn al-Shāṭir, Copernicus, and Khafrī. If one thinks of the radii of the spheres as vectors, all the models predict the same position for the planet P.

But this example of the use of Ibn al-Shāṭir's model by Copernicus does not even begin to illustrate the extent of the technical interdependence between the two astronomers. For in addition to the identical construction of the lunar model, which we already discussed before, and now the identity of the model for the upper planets, Ibn al-Shāṭir and Copernicus also used identical techniques for resolving the last model of the classical planetary theory (the Mercury model).

If one were to compare Copernicus's model for the planet Mercury to that of Ibn al-Shāṭir, and if one were to allow for the simple mathematical transposition from geocentrism to heliocentrism and vice versa, one will be struck by the similarities between the works of the two astronomers. In this instance, both Ibn al-Shāṭir and Copernicus used a construction of a mathematical model that deployed in its last connection the use of a Ṭūsī Couple, in order to allow for the planet's epicycle to be brought close to the Earth, at the two perigees which were observed by Ptolemy, and to recede away at the apogee. The complete agreement on the technique of achieving this oscillatory motion, while moving the epicycle nearer and farther, raises the question of the possible influence of one astronomer over the other, especially when we already know of the other similarities that we have already witnessed in the other contexts. But the case of the Mercury model in particular brings some remarkable evidence for the case of the interdependence between the two astronomers; this evidence elevates the discussion of the similarities to a whole new level.

When Swerdlow studied the first version of Mercury's model in Copernicus's Commentariolus, which was itself written before 1514, he immediately realized that Copernicus was not aware of the full significance of the model he was describing. For example, Copernicus thought that the planet would have its largest orbit (i.e. the size of its epicycle would look the largest) at quadrature (i.e. when the center of the epicycle—or the Earth in Copernicus's language — was at 90° away from the apogee) while the model itself would predict two such largest appearances when the center of the epicycle, or the Earth, was at 120° on either side of the apogee, exactly as Ibn al-Shāṭir's and the Ptolemaic models would have predicted, and not at 90° as Copernicus now claimed. Having realized that, Swerdlow said:

While discussing the point, Swerdlow went on to explain why Copernicus did not seem to realize where his model would produce Mercury's closest position to the Earth (figure 6.7):

Figure 6.7

A model depicting the motion of the planet Mercury as described by Ibn al-Shāṭir. Copernicus adopted the same model without fully realizing the manner in which it functioned. Copernicus seems not to have realized that the apparent size of an object depended on the size of the object and on the object's distance from the observer. It seems that Copernicus confused the size of the planet's orbit, as marked by the dashed circles, with its appearance for an observer at point O. Although the planet's orbit indeed reaches its greatest size when the epicyclic center is 90° from the apogee, for an observer at point O the dashed epicycle does not appear the largest at that point, as Copernicus contends. Rather, it appears largest when the epicyclic center reaches ±120° from the apogee, as would be predicted by the observations of Ptolemy which were followed by Ibn al-Shāṭir, and as can be seen from the comparison between the maximum elongation angles at 90° (solid lines) and at 120° (dashed lines).

With all these problems laid bare, Swerdlow concluded:

Later, while assessing Copernican astronomy in the context of Renaissance astronomy, Swerdlow returned to this very point of the connection between Copernicus and his predecessors, and particularly to the problems in the Mercury model:

Taken together, all the previous evidence of the interdependence between the works of Copernicus and those of 'Urḍī, Ṭūsī, and now Ibn al-Shāṭir, must at least strengthen the claim of a westward transmission of astronomical ideas from the world of Islam to Renaissance Europe. The works and newly invented theorems and mathematical techniques of 'Urḍī, Ṭūsī and Ibn al-Shāṭir, were all organically and integrally connected to the preceding results of Islamic astronomy. This evidence clearly demonstrates as well how the totality of those earlier results had by the sixteenth century become the tools of the new astronomy that Copernicus was beginning to construct. When all that evidence is taken together, then it is in that sense that one must understand the statement of Swerdlow and Neugebauer, in their latest book on the mathematical astronomy of Copernicus, when they tried to see Copernicus as the last Marāgha astronomer rather than a completely disconnected figure who was forging a new astronomy completely based on new grounds of his own construction.[326]

All the evidence just cited, and the remarkable similarities between the works of Copernicus and the works of his predecessors from the Islamic world have not gone unnoticed as we have seen. In fact it continues to raise some very fundamental questions about the actual intellectual environment in which Copernicus conceived his path-breaking work. And like all good research results, this connection between Islamic and Copernican astronomies does not only raise new questions for the students of Copernican astronomy, as it must do, but also in turn it raises some very interesting problems for Islamic astronomy as well, as we shall soon see.

Even if one grants the existence of those connections on the intellectual level, still the problem of contacts between Copernicus and his predecessors, in the historical sense, remains further complicated by the fact that we have no evidence whatsoever that Copernicus himself knew any Arabic at all. We also have no evidence that any of the works of 'Urḍī, Ṭūsī or Ibn al-Shāṭir, with which Copernicus seems to be in direct contact, had ever been translated into Latin in the same way that other Arabic sources were translated earlier into Latin. We cannot speak about the works of these astronomers in the same way we speak about the translations of the works of Avicenna or Averroes that went into Latin during the medieval period. We cannot even compare them to the translations that took place during the Renaissance, such as the fresh translations of the Avicennan works that were executed by Andreas Alpagus,[327] for there does not seem to be an equivalent Andreas for the astronomical works. And yet we know that the results that were produced in the Arabic astronomical works mentioned before, seem to have found their way to the technical repertoire of Copernicus so that he could use them so freely in his own construction of his own astronomy, and at times even use them without digesting them fully as we just saw in the case of Mercury.

Furthermore, we know that these same mathematical theorems and techniques, which must have seemed as novelties to Copernicus, were extensively used by Arabic-writing astronomers for centuries, as we just saw, well before Copernicus, as well as contemporaneously with him, and even after his time. They have a continuous tradition in the Islamic domain for which we find no parallel components in the Latin West. There is some mention of the use of the Ṭūsī Couple at the time of Copernicus in the Latin sources,[328] but that is almost the full extent of it. One does not find the multiplicity of similarities that were just discussed.

From a slightly different perspective, and for the purposes of the results that will be drawn later, we should note at this point that those same astronomical results that were established in the Islamic domain were expressly generated in the context of objecting to, reformulating, and casting doubt on the Greek astronomical tradition. In a sense, unlike the works of Avicenna and Averroes that could have been arguably translated into Latin in order to harvest the older Greek Aristotelian thought that they contained, those mathematical and astronomical results represented their own rebellion against those Greek sources. From them one could not recover Greek thought. On the contrary, one rather found the very critique of Greek thought. In themselves, those Arabic astronomical sources were creating alternatives to Greek astronomy instead of "preserving" it as we are often told. And most surprisingly, they all came from the period that has been dubbed, for centuries now, as the period of the deepest decline in Arabic thought.

So why a Renaissance scientist would be interested in recovering information from such sources, when these sources were representatives of a declining culture, if we were to believe the classical narrative of Arabic scientific historiography? Furthermore these sources were written expressly to counter Greek astronomical thought rather than preserve it. So why any Renaissance scientist would be interested in them, if the purpose of the Renaissance intellectual project was the recovery of the sources of classical Greco-Roman antiquity as we are also so often told?

On the other hand, when we remember the iconographic treatment to which Copernicus has been subjected, by those who name revolutions after him, and the portrayal of his revolutionary role as a path breaker, it will become difficult to imagine how and why would the same person seek results from sources that were steeped in saving Aristotelian cosmology, such as the Arabic astronomical sources seem to have been doing. If his purpose was to topple that cosmology altogether, as we are told by the literature about Copernicus, wouldn't he have looked somewhere else? Furthermore, if we are to believe that the works of Copernicus crystallized the spirit of modern Renaissance science, then we would have to contend that the basic technical foundations for this "modern" science were already laid in the Islamic world, centuries before, as we now realize that the only two theorems that were used by Copernicus to construct his own astronomy, that were not already found in Euclid or Ptolemy, were the theorems of 'Urḍī and Ṭūsī. All these questions and reflections force us to review our standard historiography of Renaissance science first, and then, most importantly, the historiography of Islamic science itself.

Among the problems that the project of Islamic historiography must entail is that of explaining which Arabic work may have been available to Copernicus, if we were to continue to think that those astronomical results reached Copernicus directly from Arabic sources. The difficulty becomes critical when we realize that so far we can establish similarities between the works of Copernicus and the works of 'Urḍī, Ṭūsī and Ibn al-Shāṭir, but in such a way that none of those Arabic sources could account for all those similarities. That is, if we were to assume that Copernicus knew of 'Urḍī's work, we cannot explain from that work alone his knowledge of Ṭūsī's Couple. And if we assume he knew of Ṭūsī's work, then we cannot explain his acquaintance with 'Urḍī's work through Ṭūsī's work. And if we assume that he knew of Ibn al-Shāṭir's work, who lived a century after 'Urḍī and Ṭūsī, then we cannot explain Copernicus's insistence on proving the Ṭūsī Couple which is nowhere proved in the work of Ibn al-Shāṭir. And of course it becomes almost impossible to conclude that he knew of all these works individually and that he synthesized them himself when he did not know any Arabic, nor having had any of them available to him in Latin.

The best working hypothesis that can be proposed at this point is to think of Copernicus's acquaintance with some type of an Arabic astronomical work that contained commentaries on earlier works, such as the work of Quṭb al-Dīn al-Shīrāzī (d. 1311) where one could find proofs of Ṭūsī's theorem like the one reproduced by Copernicus, since the works of Shīrāzī were themselves commentaries on Ṭūsī's work. In addition the works of Shīrāzī also contained the adoption of 'Urḍī's model for the upper planets, which was summarily adopted by Copernicus through Ibn al-Shāṭir's work and where he almost unconsciously adopted 'Urḍī's Lemma. We just said that this model was the chosen model for Shīrāzī against the model of his own teacher Ṭūsī. But then Shīrāzī's work does not have the world-view of Ibn al-Shāṭir. And thus it cannot explain the identical lunar model of Ibn al-Shāṭir that was adopted by Copernicus, nor his deployment of the same Ṭūsī Couple technique as was done by Ibn al-Shāṭir while describing the motions of the planet Mercury. If we follow the route of commentaries, then it will be for historians of Arabic astronomy to find a commentator, such as Shīrāzī, who must have lived after Ibn al-Shāṭir, and who must have probably written a lengthy commentary on Ibn al-Shāṭir and tried to place Ibn al-Shāṭir's works in the context of the earlier works of 'Urḍī and Ṭūsī. But no one knows of such a commentary and the problem is yet to be solved.

The historiographic lesson, though, is the following: Had it not been for those similarities that have now surfaced between the works of Copernicus and the earlier astronomers of the Islamic domain, this problem would not have arisen in the first place, and we would not have even suspected that such commentaries may even exist.

There is yet another line of research that has to be pursued as well, this time taking a direction well rooted in the works of Ṭūsī. The later commentators on Ṭūsī's Tadhkira have already started this research but very few people have pursued it in the modern literature.[329] The research in question has to do with implications of the rupture of the Aristotelian universe by the Ṭūsī Couple. The rupture is in the following sense. As we have already said before, Aristotle had already divided he universe, on the basis of the natural motion of its elements, into two basic divisions: the celestial region (which moved by the natural circular motion of the element ether of which the celestial world is made) and the sublunar region (where linear motion predominated). With Ṭūsī's Couple, one can now demonstrate that circular motion could produce linear motion, and vice versa. Does that mean that the Aristotelian division has to collapse as a result, to what extent, and what can be saved of it if any? Only future research will uncover such repercussions.

Returning to the problem of contacts with Europe, the fundamental question for the intercultural science still remains: How could Copernicus know about those Arabic results, at such a late date, with all the known conditions of the Renaissance? The answer to this question has to presuppose other questions about Copernicus himself. Did he know Arabic at all? Was he in contact with Arabists? How well did the Arabists that he knew know about technical Arabic science? All these questions go to the very core of the intellectual environment during the Renaissance, and will have to be tackled from both sides of the Mediterranean.

So far the assumption had been that Copernicus did not know any Arabic, and since the Arabic sources were not translated into Latin, he must have known about them through some other language to which they were "translated" and that Copernicus could read. Again it was Neugebauer who assumed correctly that Copernicus, like all other well educated Renaissance men, could read both Greek and Latin. Since Latin could not be considered as the language of translation for there was no evidence that the Arabic texts were translated into it, that left Greek as the only possibility, according to Neugebauer's implied reasoning. This train of thought led Neugebauer to examine the Byzantine Greek sources for clues to the solution of the problem of transmission. At the time when Neugebauer first came in contact with the Arabic material that signaled possible contacts with Copernicus, he had already been working on the Byzantine astronomical texts for his own Studies in Byzantine Astronomical Terminology. So at first glance, Byzantine Greek looked like a plausible route for such a transmission. Within few years Neugebauer's diligent search quickly yielded a very interesting fruit in the form of a Byzantine Greek manuscript now kept at the Vatican library as Gr. 211. The manuscript in question contained a Greek version of Ṭūsī's couple, and thus seemed like a good lead to pursue. But now that the same manuscript has been published,[330] we can clearly see that although it seems to have a qualitative description of the Ṭūsī Couple, it does not seem to have the proof of that Couple. And as we have seen before, there were remarkable similarities between the proofs of the Ṭūsī Couple in the Arabic work of Ṭūsī and the Latin work of Copernicus. And we have seen that both proofs depended greatly on the identical usage of the same letters of the alphabet to designate the same geometrical points. So the proofs are essential to explain this phenomenon and to clench the argument of the possible connections between the two. Nor does the Vatican Greek manuscript contain any of the material of 'Urḍī or Ibn al-Shāṭir, which we have seen were very relevant to Copernicus and somehow made available to him.

All those issues and questions go beyond the accepted historiography of science, as it is now generally understood. Copernicus's connection to earlier Islamic material is such a new field of research that it has not yet had the chance to have an impact on the general history of science. But whatever information we now possess, inevitably leads us to the conclusion that there must have been an intimate connection, at least on the theoretical mathematical level, between the works of Copernicus and the works of his predecessors in the Islamic world.

A word of caution is in order so that these issues of contacts between Copernicus and his predecessors in the Islamic world will not be confused with Copernicus's genius idea of heliocentrism. None of the astronomers who worked in the Islamic world, and who have been mentioned so far, had any interest in such concepts as heliocentrism. In my estimate, they were so closely wed to the stubborn, but all comprehensive, Aristotelian cosmology, which dictated a geocentric universe, and which continued to reign supreme in the world of astronomy all the way till the time of Newton. This despite the hints and disparaging remarks one would hear about it from time to time by astronomers working on both sides of the Mediterranean.

In this context too, one is also forced to raise the question of the scientific legitimacy of heliocentrism itself in a pre-Newtonian universe, where no alternative cosmology was yet available. Copernican scholars, who have been busy trying to explain the origins of Copernican heliocentrism, have yet to explain how could Copernicus convince himself that he could shift the center of motion to the sun without having to propose some non- Aristotelian cosmological theory that could hold the world together in the same way the Aristotelian cosmology did.[331] That is, without the benefit of the Newtonian law of universal gravitation, how could he have hoped to maintain the system together?

What Copernicus's predecessors were doing was well within the limits of Aristotelian cosmology. And in that sense they were perfectly consistent in their attempt to replace the Ptolemaic models with alternative models that behaved much more consistently by avoiding the absurdities of the Ptolemaic models. But for Copernicus to complain, in the introduction of his Commentariolus about the equants, a complaint that made sense only in an Aristotelian universe, and then go ahead and abandon all that system, and retain the modified models that avoided the absurdity of the Ptolemaic equant, is very puzzling indeed. The models that were developed in the Islamic world to solve the problem of the Ptolemaic equant, were developed specifically so that the models would be consistent with Aristotelian cosmological considerations. So if one was willing to abandon the Aristotelian universe, then why retain those models? Such problems will have to be left for the Copernican scholars to handle.

All the attempts that were developed in the Islamic world to revamp Ptolemaic astronomy were, in essence, motivated by the simple and straightforward requirement of keeping astronomical theory consistent with its premises. That is, all those astronomers took Ptolemy at his word that he wished to develop astronomical models all based on a universe made of Aristotelian spheres, and all spheres moved around their own centers, in place, at uniform speed. When they found the Ptolemaic models wanting, they developed their own alternative models, for which, at times, they had to develop the right mathematical theorems in order to maintain the correspondence between those models and the observations upon which the models were based in the first place.

With that attitude, they managed to introduce the feature of consistency into astronomical theory, and to subsume mathematics as a tool of that theory. These astronomers who did not tolerate the Ptolemaic transgression into elegant mathematics at the expense of the physical nature of the presupposed spheres, would not in all likelihood have tolerated a whole new heliocentric system where the very foundations of the spheres, that were still retained by Copernicus, no longer made sense in the heliocentric world. Consistency between the presuppositions, the physical nature of the spheres, and the mathematics that represented the motions of those spheres, on the one hand, and models that served as predictive models for the behavior of the planets at any time and place, on the other, became the guiding principle of Islamic astronomy at this stage. Only at a later stage, i.e. toward the middle of the sixteenth century, would mathematics take its proper role as a tool of astronomical theory.

The fact that Copernicus too launched his own research, in the Commentariolus, with the same attitude of wishing to solve the problem of the equants, simply means that at the early date of the sixteenth century, if not well before, the flow of ideas across the Mediterranean was already in full gear. And now that we can document the similarities between the works of Copernicus and those of his predecessors in the Islamic world, they only confirm the fluidity of this traffic. Once that becomes clear, one can then readdress the question of "locality" versus "essence" of Islamic science by basing the discussion on concrete examples such as the ones that are being raised here.[332] If the solution of a problem that was developed in Damascus in the middle of the thirteenth century, and still made perfect sense to someone like Copernicus who was writing within the context of the Latin world of the Renaissance, then it becomes obvious that neither the passage of time nor the cultural borders could inhibit this motion of perfectly valid solutions. So what is "local" and what is "essence" about the solutions of such problems?

These findings do not only explain the background and motivation of the Copernican works; they also explain the continuity of thought from the Middle Ages into the Renaissance time, without having to make wild assumptions about ideas being born in abstract contexts. Their sheer number and complexity, as well as their technical nature also remove the possibility of coincidental discovery, and force us to agree with Swerdlow and Neugebauer that it is no longer the problem of "if" but "when, where and in what form" did Copernicus learn of those earlier works.[333] The answer to this question promises to change our common understanding of the history of science itself, as well as change our understanding of the nature of the relationship between Europe and the Islamic world at this crucial time in history.

So far I have limited the discussion of the possible routes of contacts between Copernicus and the Islamic world to the language that Copernicus could read and into which the Arabic sources could have been translated: Byzantine Greek. But since the discovery of the Byzantine manuscript, Gr 211, of the Vatican, by Neugebauer, other hints of possible routes have come to light, mainly from the Arabic manuscripts themselves. One such manuscript, also kept at Vatican, Arabo 319, is another copy of the Tadhkira of Naṣīr al-Dīn al-Ṭūsī, in which, of course, there is a chapter that included the proof of the Ṭūsī Couple. The manuscript itself was passed on to the Vatican Library as part of the legacy of a Frenchman by the name of Guillaume Postel (1510-1581) who was a younger contemporary of Copernicus.[334]

What makes this Vatican manuscript quite unusual is the fact that it is titled "Epitome Almagesti". With Della Vida's help it was then determined that the identification was done by Postel himself. But more importantly, the manuscript also contains marginal annotations in Latin, also by Postel, that indicate his ability to read this highly technical astronomical text of Ṭūsī. He could clearly comment on it, although very briefly, which means that he understood what he was reading. The text is reasonably well preserved, especially around the chapter that included the statement and proof of the Ṭūsī Couple, and thus could have presented no material difficulty to someone who was capable of understanding its contents.

The existence of such a manuscript also indicates that there were Renaissance men who knew Arabic, and definitely knew of the contents of technical scientific texts.[335] The problem is to determine whether Copernicus himself ever came to know such men. For if he did, then it would be quite possible to assume with Willy Hartner that someone could have briefed him about the contents of such manuscripts, that is, bring him up to date on the latest in Arabic astronomy.

Such a scenario may inadvertently help solve the problem of Copernicus's indebtedness to more than one Arabic text and for which I had to speculate about the existence of a text that was written after the time of Ibn al-Shāṭir in the form of a commentary that included elements from the works of Ṭūsī, 'Urḍī, and Ibn al-Shāṭir; texts that we know have come to the attention of Copernicus. Assuming the existence of such a colleague, to whom Copernicus could go for consultation, may solve that problem: it would make the colleague the gatherer of such information from various texts, and it could make him responsible for passing it on to Copernicus.

But once it was known that Postel owned at least one technical Arabic astronomical manuscript, it was reasonable to investigate other collections and see if they also included such manuscripts that were owned by him, in order to determine the extent of Postel's own commentaries. The hope was that this kind of research would shed light on the kinds of texts such contemporaries of Copernicus were reading. We would also know if the Vatican manuscript was an exception or a unique occurrence.

The search was then enlarged to include the astronomical texts that are still preserved in other European libraries. Luckily the first step in that research was immediately rewarded by the collection of the Bibliothèque Nationale of Paris. Among the Arabic manuscripts still kept in that collection there appeared another technical text, called Muntahā al-idrāk fī taqāsīm al-aflāk (The Ultimate Grasp of the Divisions of Spheres), this time written by Abū Muḥammad 'Abd al-Jabbār al-Kharaqī (1138/9). The manuscript is definitely devoted to mathematical astronomy as is clearly indicated in the title. Furthermore, it is explicitly marked as having been owned by the same Guillaume Postel with the phrase "ex libris guilielmi postelli" clearly marked on the title page.[336] On the first flyleaf, the manuscript also states that it was bought in Constantinople in 1536, as it is clearly marked: "G. postellus Contantinopoli 1536". The year 1536 also happens to be the year that culminated the mission of the delegation that had been sent to Constantinople by the French King François I (1515-47) to negotiate a treaty with the Ottoman Sultan, Suleiman the Magnificent (1520-66). The treaty was in fact signed in that year.[337] This Postel was apparently a member of the delegation. And we know that he was charged to buy Greek books by Budé, the Librarian of François I. But apparently Postel opted to buy Arabic scientific texts instead.

The earlier background of Postel, his childhood, education, and his acquisition of Hebrew and Arabic, as well as the other languages that he apparently knew, remain obscure. But the fact that he was selected to join the French delegation to Constantinople must mean that he had already acquired some fame as someone who knew what was then known as oriental languages, so that he could possibly act as an interpreter to the French delegation. It would be most interesting to find out the name of the Person who could have taught him Arabic in Paris in the early part of the sixteenth century. And was the Paris environment, in terms of exposure to such oriental languages as Arabic, much different from other cities in Eastern Europe and northern Italy where Copernicus spent his professional career, or was it the norm? Such a question bears directly on Copernicus's access to Arabic scientific material, which did not have to be translated into Latin.

Postel's trip to Constantinople was apparently quite successful, for in addition to the two Arabic manuscripts that he owned there were others that were signaled by Della Vida, which may have ended up in other European libraries.[338] And because of the signature of the treaty, which must have pleased the French king,[339] Postel was apparently rewarded with an appointment as professor of mathematics and oriental languages at the Collège Royal which later became the Collège de France. The philosophical Arabic manuscript, of the Leiden Library, clearly attests to this appointment since it is signed "Royal Professor of mathematics",[340] which must refer to his official appointment to the College.

But Postel did not last long at the Collège, and for reasons that remain partially obscure he was dismissed of this post by 1543, the year when Copernicus died. From then on, his life took a dramatic turn as he began to pursue cultural and religious topics, but continued to make further trips to the Islamic world and to acquire other Arabic scientific texts, most notably between the years 1548 and 1551. Several of his trips took him through northern Italy, where he was finally involved in a spiritual conversion that may have cost him his demise and his eventual imprisonment by the Pope and his retreat to a convent near Paris where he finally passed away in 1581.

Other manuscripts at other libraries such as the Bodleian (Oxford) and the Laurentiana (Florence), some from Copernicus's lifetime while others from after his death, also contain similar marginal annotations, and sometimes even interlinear translations.[341] Such evidence attests to a widespread interest in most European cities in the Islamic sciences contained in those manuscripts.

The causes of this European interest in Islamic science at these latter ages remain very poorly studied. One can understand the reasons for it from the period of Copernicus's own lifetime, since the status of science in the European cities at that time was almost on equal footing with that which had been known in the Islamic lands. But the interest seems to continue well into the seventeenth and eighteenth centuries. And that becomes much more puzzling.[342]

Other questions remain of interest in this respect, and relate to the image of Arabic/Islamic science in those European cities in contrast to the image of the more ancient sciences. From the evidence that has survived so far, and this widespread interest in almost all fields of science, one may safely speculate that to a Renaissance person of the sixteenth and early seventeenth centuries Arabic science must have seemed quite advanced over and above the more classical Greek science, especially in the field of Astronomy. Such a person would have known from several sources, and particularly from the often quoted disparaging remarks that were made by Averroes himself in his own commentaries on the Aristotelian works, that Ptolemaic astronomy had been under attack in the Islamic world. Someone like Andreas Alpagus (d. 1522), who lived and studied in Damascus for about 15 years and who returned to Padua, probably near the turn of the sixteenth century, to assume the chair of medicine at Padua in 1505, thus possibly overlapping with Copernicus's sojourn in that general area where he acquired his last degree in canon law from nearby Ferrara, may have known of the attacks against Ptolemaic astronomy, or may even have heard about the remarkable reform of that astronomy that had been accomplished by Ibn al-Shāṭir (1375) of the same city of Damascus nearly 100 years earlier.

All these contacts with the Islamic world, of which we gave here the bare minimum by way of examples,[343] would have easily brought the news that the old Greek astronomy was already in great dispute in the Islamic lands, and that its results as well as its basic foundations were severely questioned and at times even overturned. A Renaissance person would then have every reason to seek information about these latest reforms that took place already in the Islamic world, and would in all likelihood only keep an antiquarian interest in the details of Greek astronomy. In such a setting, the image of Islamic science in Renaissance Europe would have attained a status similar to the one it attained in Byzantium in the early part of the fourteenth century, where astronomers would travel from Constantinople to Trebizond, in order to acquire the latest of Islamic astronomy, as was done by the author of the Byzantine Greek manuscript who brought the Ṭūsī Couple into Greek.

There is no doubt, then, that there were enough Arabists in various European cities who were not only writing Arabic grammars, as Postel did, but who were like Postel equally competent enough to read the technical contents of scientific manuscripts and to understand their import and thus pass them on either orally or even by request in a tutorial fashion. With Poland, where Copernicus was born, being so close to the borders of the Ottoman empire at the time, and with the free flow of books, trade, and scholars across the Mediterranean through the northern Italian cities, where Copernicus received his education, we must suspect that there were many people like Postel who could have advised or even tutored Copernicus on the contents of Arabic astronomical texts. Now that we have established the likelihood of another route, one hopes that future research will continue to explore it in order to explain the likelihood of such a scenario.

Lest we think that planetary theories were a special case of their own, and that contacts between the world of Islam and Renaissance Europe were restricted to connections with Copernican astronomy only, it is important to note that similar exchanges were taking place in a variety of other disciplines.[344] At this point, a few examples from cognate fields like the field of scientific instruments should be enough to make the point. Such supplementary evidence points to two curious instances that demonstrate a close connection between the instruments that were being produced in Renaissance Europe and those that were already produced in the Islamic world. Those instruments were produced centuries apart and their existence simply signals the range of contacts between the Islamic world and Renaissance Europe.

The first instance of contacts between the Islamic world and Renaissance Europe in the field of scientific instruments concerns Antonio de Sangallo the Younger (1484-1546), one of the most famous architects of Renaissance Italy. Among his papers, now still kept at the Uffizi in Florence,[345] there is one sheet that contains, on one face of it, a detailed drawing of an astrolabe that was made in Baghdad around the year 850, and on the back a drawing of the rete of the same astrolabe.[346] The reason we know such details about the drawing of this astrolabe is due to the meticulousness of de Sangallo, who not only copied the astrolabe on paper, face and back and rete, but, with great care, he also copied the name of the original maker of the astrolabe that was etched along the edge of the upper right hand quadrant on the back of the astrolabe. Unlike most other art objects that were produced in the Islamic domain, and did not usually carry the name of the artist, astrolabes were usually inscribed on the back with the name of the maker. So this astrolabe was not an exception.

The name of the original Baghdad maker was Khafīf. He apparently apprenticed with a more famous astrolabist who lived in Baghdad around the year 850, by the name of 'Alī b. 'Īsā.[347] Because of that relationship, Khafīf signed his name on the back of the astrolabe as "ṣana'ahu Khafīf ghulām 'Alī b. 'Īsā", which means: "It was made by Khafīf the apprentice of 'Alī b. 'Īsā." De Sangallo dutifully copied this signature, which has no astronomical significance whatsoever. The question that this sole paper of the Uffizi poses is: Why was someone like de Sangallo interested, in the first place, in an astrolabe that was made some 800 years earlier? This, when we know that de Sangallo was in his own right a famous architect who was entrusted with the building of St. Peter's cathedral in Rome, a monument that continues to stand witness to his skill and mastery. My suspicion is that the scientifically oriented men of the Renaissance, especially during the sixteenth century, must have thought very highly of all scientific things coming to them from the Islamic world, even instruments that were made centuries earlier.

To complicate the puzzle somehow, and to point to directions already signaled in the case of the contacts with Copernicus, in astronomy, and with Michael Servetus and Realdo Colombo in medicine, here too, there is no evidence that de Sangallo knew any Arabic. My suspicion is that the drawing, which duplicates all the Arabic inscriptions from that astrolabe, down to the signature of the maker, only attests to his ability as a draftsman. And that in itself does not constitute enough evidence to conclude that he knew any Arabic, unless someone can demonstrate that de Sangallo ever learned Arabic, which would be very curious indeed.

The second instance concerns the Renaissance reception of this particular area of scientific instrument, and the extent to which this field was particularly interesting to Renaissance men.[348] The interest itself can be easily demonstrated by other contacts between the world of Islam and such famous astrolabe makers like the Arsenius family of astrolabists, who worked in northern Europe, mainly in the Flemish area, sometime toward the end of the sixteenth century. To illustrate the contact between this family of astrolabists and the Islamic world, consider the extant astrolabe (figure 6.8) that was originally made in Muslim Spain, and whose mater, back and plates were inscribed in Arabic by Muḥammad Ibn Fattūḥ al-Khamā'irī in 619 A.H. = 1222 A.D. As is obvious from the picture, a member of the Arsenius family fitted the rete of this astrolabe with Latin inscriptions, and produced a plate that would work for the northern European clime.[349] The existence of this astrolabe, in this form, could only mean that some member of that family was in fact working with Arabic astrolabes, and must have been somehow competent in Arabic. Or say that at least he must have been bilingual enough in order to use the new rete properly with the mater that was made by Khamā'irī. The reason is that the rete was inscribed with the Latin names of the star, while the rim, against which the altitudes of those stars had to be read, still carried the Arabic alphabetical numerals that were originally inscribed by Khamā'irī. Therefore, we can only conclude that either Arsenius himself, the maker of the new rete and plate, or the user of the resulting hybrid astrolabe must have been able to read some Arabic at least, and that must illustrate some interest in the Islamic scientific instruments toward the end of the sixteenth century at such northern climes as the Netherlands.

Other such hybrid astrolabes are probably still waiting in private collections to be discovered. King's study of Instruments of Mass Calculations[350] has many examples of such influences and thus it is highly likely that such hybrids exist.

Figure 6.8

A hybrid astrolabe that was once kept at the Time Museum. The mater was made by al-Khamā'irī in 1222, as clearly signed in the picture on the right. The rete, which carries the standard design of the Arsenius family, was made by one of the members of that family toward the end of the sixteenth century.

The same design of the retes that were commonly produced by the members of the Arsenius family (figure 6.9, right) may also demonstrate another connection between astrolabes that were made in the Islamic world and those that were made in Renaissance Europe and thereafter. In his most recent publication, just cited, David King of Frankfurt raised the possibility that those designs may not at all represent tulips, as they are usually taken to do, but should rather be seen as skeletal representations of the Arabic calligraphic phrase bism'Allāh al-Raḥmān al-Raḥīm (In the name of Allāh, the Compassionate and the Merciful), which is the opening phrase of most chapters of the Qur'an.[351] As is obvious from figure 6.9 (left), the inscription of the phrase is beautifully interwoven among the leafy star pointers of the rete. The Arabic calligraphic design of this particular rete, on the left, comes from a slightly later astrolabe, which was made in Persia by Muḥammad Zamān in 1651-52. And the astrolabe itself is still preserved at the Metropolitan Museum of Art, in New York City. But despite the later date of the astrolabe, the rete design may have descended from an earlier astrolabe rete that utilized the same mirror image calligraphy of the phrase, or from a similar design on other art objects that were produced in the Islamic world. The existence of calligraphic designs drawn in the shapes of animals or other objects are ubiquitously found among the artistic treasures of the Islamic world and may have influenced the production of such retes.[352]

Figure 6.9

Right: A standard rete produced by a member of the Arsenius family. This rete is thought to represent the form of a tulip. Left: A rete produced by Muḥammad Zamān of Persia in 1651-52, which has the same design but for the Qur'anic verse bism'Allāh al-Raḥmān al-Raḥīm.

The claim that I wish to make here is that the very similarity between the calligraphic design of the Arabic phrase and the shape of the tulip may have motivated the Arsenius astrolabists to produce such similar retes, thus at once paying a very clever homage to the Islamic tradition, which they knew rather well when they fitted retes for Arabic astrolabes, and to the tulip craze that hit the Netherlands during their time. The craze itself appears to have been occasioned by the importation of tulips from the sixteenth-century Ottoman domain.[353] The solution of this very intriguing problem has to wait for further work on Islamic metal works, astrolabes, and calligraphic designs in general, and on the routes that those works followed as they came into Europe. For now, the striking similarities between the two retes remain interesting as they demonstrate a certain relationship between the astrolabists of the Islamic domain and their European counterparts, even if that relationship may not be as well confirmed as the relationship of fitting a Latin rete on an Arabic astrolabe mater, as was done by one Arsenius astrolabist.

For those who work in the field of Instruments, very many other such instances will readily come to mind. And I am almost certain that they will agree with me that these examples can be multiplied manifold. But the two examples we have supplied so far should give us enough indication that the cognate field of instruments should also be investigated in the same context of contacts between the world of Islam and Renaissance Europe.

Up to this point in the discussion, I have given few examples of the activities of European Arabists and orientalists in their pursuit of science from Islamic land, and tried to assess the reasons for such interests. I had not intended an exhaustive treatment of the subject, which is worthy of a whole monograph by itself.[354] I only needed to hint to the possible sites of interaction between Renaissance Europe and the world of Islam. But I have neglected to mention that we do have some evidence of men of science who crossed over from the Islamic lands into various European cities, and of course brought with them the sciences that they knew from their old countries.

The case of al-Ḥasan b. Muḥammad Ibn al-Wazzān, better known as Leo Africanus (d. ca. 1550), immediately comes to mind.[355] Although Leo came from the western part of the Islamic world, he nevertheless had traveled extensively over all of North Africa and parts of the east. What concerns us here is that he was a man of great intellect, and was apparently very well acquainted with the Islamic intellectual scene of his day. More importantly, Leo was a contemporary of Copernicus, and a man of great scientific knowledge, who also taught Arabic at Bologna.[356] He may have come across people, or even taught some, who knew Copernicus themselves. His teaching Arabic at Bologna is significant in itself as well. For Bologna fell along the famous corridor from Venice to Florence, along which many Renaissance intellectual activities took place. Leo's personal output is slightly better known than others on account of his geographical writings that included tidbits of his personal accounts. But his intellectual life and his impact on Renaissance scientists, as well as his role in introducing scientific ideas from Arabic into Latin, is still not fully investigated from the perspective of the Renaissance knowledge of Arabic Islamic science. A scientific biography of this distinguished pioneer scientist and belletrist is long overdue.

There were others too. For example, one could easily name members of the circle of the distinguished orientalist, Jean-Albert Widmanstadt (1506-c.1559), who was also a contemporary of Copernicus, and who may have also played a very important role in the transmission of Islamic scientific ideas to Europe; a role at least just as important as that of Guillaume Postel, whose input was already noted before.[357] A quick search for Widmenstadt's role revealed, to my pleasant surprise, that this Widmanstadt was himself a student of Leo Africanus,[358] and also knew much Arabic material as well as the scientific contents of Arabic astronomical texts. In our context his role should be seen as part of the influence of Leo Africanus on Renaissance thought, but should also be considered as part of the network of orientalists who were contemporaries of Copernicus and who may have known about the achievements of Islamic astronomy and were competent enough to bring it to the attention of Copernicus.

One can be certain that there were many more people who came in contact with Leo Africanus, and who may have either received information about scientific ideas directly from him or were guided by him to others who could supply the same. But until the field is fully explored with those questions in mind, we cannot be certain about the kind of information that was transmitted, nor about the people who played as conduits for this transmission. One thing we can be sure of is that there are much too many coincidences of ideas appearing first in Arabic texts, usually written between the twelfth and the fifteenth century, which reappear, without much explanation, in Latin sources of the sixteenth and seventeenth centuries. In most cases the original Arabic texts containing these ideas had never been "translated" into Latin in the strict sense of the word.

Others who followed similar routes as that of Leo Africanus, but at least under slightly different circumstances—if not of their own volition as far as we can tell—included people such as the Syriac Jacobite patriarch Ni'matallāh, better known by his Latin name Nehemias (d. 1590).[359] This patriarch was involved in a series of conflicts in his native town, Diyār Bakr, of southeast modern Turkey, and in his own patriarchate of Antioch and All the East. At one point, his life became so endangered that he felt he had to flee to the Papal see via Venice. And in order to secure a generous Papal reception he used the excuse that he would help bring his followers back to the fold of the Roman church, and under the Papal flag. A note left at the margin of an elementary mathematical manuscript, still kept at the Laurentiana Library in Florence, describes in some personal nostalgic terms the difficulties of his trip, saying that he was being tossed by the waves of the Adriatic Sea, during the year 1888 of the Greeks (1577 A.D.), on his way to Venice.[360]

Once in Venice, apparently without knowing a word of Latin or Italian, he was attached to an eastern "traveler" by the name of Paolo Orsini. Orsini, who then acted as Ni'matallāh's interpreter, was originally a captured Turkish soldier, who, like Leo Africanus before him, accepted to convert to Christianity. The two went to Rome, of course via Florence, as most people were prone to do in those days. Along the way, or maybe more likely in Rome itself, he made the acquaintance of the Cardinal Ferdinand de Medici who later became the Duke of Tuscany. Like all the Medici's, Ferdinand could quickly recognize a commercial enterprise when he saw one. With the invention of printing nearly 100 years old, and with Arabic not yet being exploited for that purpose, the Arabic books that the Patriarch was trucking along, which were all in manuscript form were too tempting to Ferdinand. He saw in them the possibility of starting an Arabic press and using those books, as the bases for the printed versions.[361]

Of course, the excuse Ferdinand used, at least openly, was that he would use the press to produce reading material for the missionaries who could go out and convert the Muslims to Christianity. But the actual record of what was printed and sold at the Medici Oriental Press tells a different story.[362] While it may be quite understandable to produce 1,500 copies of the Arabic Bible for missionary activities, it would be much harder to justify the production of 3,000 copies of Euclid's Elements for the same purpose. And if one were to think that the publication of the Elements served a wider Renaissance purpose of recovering the scientific works of classical antiquity, one will be disappointed to learn that the Elements that were published by the Medici Oriental Press were not of the original Arabic translations of the Greek Elements (and two good translations are still extant), but rather a slightly modified version of the Elements. And what the Medici press published as Euclid's Elements was in turn a re-working of yet another re-working that was already produced toward the middle of the thirteenth century by the very same astronomer/mathematician Naṣīr al-Dīn al-Ṭūsī who was mentioned several times already.

Still, the disproportionate number of copies that were produced in the first place calls for a comment. Did the Medici Oriental Press prospector expect the missionaries to use more of the Elements than they would use the Bible for the conversion activity? And if that was the purpose, the actual sales seem to support such a contention. The records show that the Arabic Bible sold 934 copies, while the re-worked Elements outdid that and sold 1,033 copies. Based on sheer numbers alone, could one draw the ironic conclusion that a re-working of Euclid's Elements served a better purpose in converting people to Christianity than the Bible itself?

Similarly, one has to wonder also as to why the first six Arabic books that were published by this press would include four that had something to do with linguistic or demonstrative sciences and not that much relevance to religious material. Such linguistic and scientific texts were abundantly available in manuscript form all over the lands of Islam, as any survey of extant library holdings can demonstrate. So what kind of profit a good Medici businessman could have expected to make by shipping those books to the lands of Islam?

When we consider the Renaissance environment, which apparently witnessed a great interest in Arabic scientific texts, one has to conclude that the real market for the Medici Oriental Press was in fact the European centers of learning who were calling for a return to the original Arabic rather than depending on translations. Didn't Andreas Alpagus (d. 1522) use the excuse of the unreliable medieval translations from Arabic in order to go to Damascus and learn Arabic so that he can produce new translations of Avicenna's works, a feat that he actually accomplished? And didn't Zacharias Rosenbach (c. 1614), when the press was still functioning, propose that the learning of Arabic be introduced in the Herborn Academy for the medical students so that they could read Avicenna's Canon in the original?[363] All these calls for Arabic texts must have sounded enticing for a good businessman seeking an investment, and Patriarch Ni'matallāh's library came in handy as it supplied the raw material for such an enterprising publishing endeavor.

That most of Ni'matallāh's books are still held in the Laurentiana Library speaks directly to this engagement between the Medicis and the Patriarch. But this was not the only contribution the Patriarch was to make to the intellectual life of the Renaissance. Sixteenth-century Europe had been obsessed with the problem of reforming the calendar as the celebration of Easter was continuing to slip backwards. And earlier councils, to which even Copernicus made a proposal for reforming the calendar, could not agree on the reform.[364] The job was finally left to the committee that was appointed by Pope Gregory XIII in order that it would specifically accomplish this task.

One of the distinguished members of that committee was the same Patriarch Ni'matallāh. His role on that committee should be quite understandable as he was the one who had brought along with him astronomical books that contained values for the lunar month and the solar year that were much more refined than the values that were found in the old Greek sources, or the prevailing medieval European sources.[365] With his services on that committee, Ni'matallāh became an actual participant in the making of the European Renaissance, just as much as his two predecessors Leo Africanus and Paolo Orsini did before.

What bearing does all this have on the works of Copernicus, and the problem of the transmission of Islamic scientific ideas to him, as most of these names and activities mentioned here date either to the late or to the post Copernican period? In fact, the more we can document the reliance on Arabic scientific sources from the period following Copernicus, when the whole world view was supposed to have been changed by him, and by others like him who created what is now called the Copernican Revolution, the more one is forced to ask why was there such a need for Arabic texts in the latter part of the sixteenth century and early seventeenth? And if one can document that interest, as the few examples we have given here seem to do together with many more that were left unmentioned, then shouldn't one expect even a greater eagerness on the part of Renaissance scientists to learn from those Arabic sources in the earlier period when the revolution had not yet taken place?

With all this evidence that was admittedly gathered here solely for the purpose of explaining the specific connections that seem to exist between the Copernican astronomical texts and the Arabic antecedents from the world of Islam, things begin to look like we unintentionally stumbled on a Pandora's box. And with very little effort in documenting the connections whole areas of research have come to life as a result. Churchmen like Postel and Widmanstadt, who seemed like they were involved in strict church activities, turn out to have been knowledgeable Arabists and men of science in their own right. We can even tell that they were following in the footsteps of other Arabists like Ambroseo Taseo (d. 1539), Andrea Alpagus (d. 1522), and before them Hieronimo Ramnusio (d. 1486 in Beirut) who were even much more glorious than them, and who may have laid the foundation for this intercultural exchange whose import we are now just beginning to appreciate.

But by looking at the works of these men, whether in the form of the fresh translations of Arabic scientific and philosophical texts by Andreas, or the still extant commentaries of Postel on more sophisticated astronomical texts, we cannot avoid but reach the conclusion that the Renaissance engagement with the Islamic world was of a completely different order than the engagement that took place during the Middle Ages. In the Middle Ages people relied more on the translations, and waited for them to be produced before they could use them. That was how the Latin translations of Averroes made their impact on Latin thinkers. But by the Renaissance time, men of science themselves apparently became Arabists and no longer needed the translations. They could go directly to the Arabic texts and exploit the ideas contained therein. Otherwise, how else can we explain the several occurrences we noted so far in astronomy and medicine as well as in the other sciences where we have original ideas that were developed in the Islamic world, expressly to object and reformulate the Greek classical scientific tradition, only to reappear a couple of centuries later in the works of Renaissance scientists without ever having those Arabic texts translated into Latin? Copernicus or his collaborator or instructors, Michael Servetus and Realdo Colombo in medicine, all seem to have followed that route.

This evidence can only lead us to look further into the works of these Renaissance men of science, not only to document those ideas, but in order to understand the nature of Renaissance science itself, and to understand the methods and techniques that were integral to the formation of that science. Most strikingly though, it looks like the Renaissance men of science were apparently looking to the world of Islam for the latest in scientific activities rather than looking to the Greek classical sources, especially for those sciences that were more of the empirical type like astronomy and medicine which needed to be constantly updated. In fact, one can hardly see an astronomical value adopted by a Renaissance scientist that was derived directly from the ancient Greek sources. For example, one no longer found a precession value that was as badly off as that of Ptolemy, or the inclination of the ecliptic as reported by Ptolemy, or the fixed solar apogee that was already proved wrong in ninth-century Baghdad. Even the kind of reasoning that was followed by Ptolemy, while constructing his mathematical predictive models, also became obsolete. Rather one found the latest results that were developed in the Arabic sources that could answer much better the same problems the Greek classical tradition had to answer.

In the final analysis, I do not think that we can understand the building blocks of Copernican astronomy, without paying close attention to the results that were already achieved in the Islamic world. Not only because those results preceded the works of Copernicus and hence it is legitimate to ask if there has been any transmission of ideas from east to west, but because in the Arabic tradition we understand better the accumulative process of scientific production, and can witness the slow growth of those ideas over the centuries, a feat that we cannot follow in the works of Copernicus, with the same rigor, if we assume that all those similarities were just coincidences. And when people think of the spirit of the Renaissance as characterized by that change in the scientific thought that shunned the ancient authority, now one can find the roots of that thought already documented in the works of generations of astronomers and scientists working in the Islamic world and writing their objections to Greek thought. And they did not only object, we now know that they were developing real alternatives to that thought. One can even go as far as to say that by the time Renaissance Europe came to know of Islamic science, especially as documented in the astronomical discipline, that science was by then a mature science on its own, confident of its ability to invest in the creation of new mathematical theorems to solve new astronomical problems, or even to deploy mathematics in more abstract ways in order to divest it of the physical truth it once laid claim to and return it to the realm of the descriptive language that could be applied to the physical phenomena.

By the time of the Renaissance, and if the words of Vesalius are any guide when he says "those Arabs who are now rightly as familiar to us as are the Greeks",[366] we can conclude that Arabic science was by then a competitive science that stood at least on equal footing as the science of the Greeks, as far as Vesalius could see. But in matters of observational science, it looks like Arabic science was by then thought of as being definitely far superior to Greek science once all the mistakes of the latter had been laid bare.