But those same nineteenth-century orientalists summarily dismissed the scientific texts that were written after the Ghazālī period. And until very recently no one had ever bothered to investigate the kind of science they contained. In this sense those texts too were very poorly read if they were read at all. As an example of this misreading of texts, we have already seen the efforts of the two famous nineteenth-century orientalists who looked at two works from the post-Ghazālī period, and who read them very carefully, and still could not see the originality that was embedded in them, simply because those orientalists were not looking for any originality during this period.[369] And their self-fulfilling prophecies indeed materialized.[370]
The second group which saw Islamic history more in political terms, and thus portrayed it as a succession of dynasties and battles, with little attention paid to intellectual history, the bête noire that was made responsible for the decline of science in the Islamic civilization was after all Hulagu Khan.[371] Hulagu's devastating blow came at a time when he actually managed to destroy the city of Baghdad, in 1258, in his westward bid from Central Asia to conquer the rest of the world. Those who blamed Hulagu for the death of Islamic science took literally the anecdotes preserved in the historical sources, which were incidentally mainly written further west, in Mamluk areas that were not conquered by the invading Mongols. Those historical sources spoke of the water of the Tigris turning black from the dissolving ink of the manuscripts that were tossed into the river by that barbarian invader. They presented a scene of destruction that continues to stand in the collective memory of most Arabs, and Muslims in general, as the ultimate of disaster and the epitome of barbarity.[372]
In a sense, the dates of the death of Ghazālī (1111) and the devastation of Baghdad (1258) seem to allow for the conversion of the two historiographic traditions just mentioned, one of which saw Islamic intellectual history as an unfolding of religious thought and one of which saw it simply as a sequence of political events. No wonder then that most people could easily conclude that those two fateful centuries, the eleventh and the thirteenth, indeed ushered in the decline of Islamic civilization and with it the decline of science in general. This conclusion was especially true for people who also remarked that they no longer saw during those later centuries the emergence of religious legal schools that were anywhere similar to the four schools that had already emerged during the eighth and the ninth centuries, and was also true for people who no longer saw a continuity of the Islamic caliphate after the fall of Baghdad.
In that sense, the thirteenth century was in fact a fateful century, as it witnessed the final disappearance of a system of caliphate that had up till then functioned tolerably well. But as far as intellectual history is concerned, the extant scientific sources do suggest a different scenario. They suggest that the thirteenth century was an age where new creative scientific thought continued to prosper, and more importantly, they even support the claim that the disappearance of the caliphal system of government was almost a blessing in disguise. For the loss of that system did not seem to have brought the end of the scientific activity. On the contrary it seems to have opened up other centers of production in the lesser capitals, such as Diyār Bakr, Iṣfahān, Damascus, and Cairo, to name only a few, that continued to produce excellent scientific works.
In summary, and as has already been stated, none of those narratives of the age of decline can really explain the greater number of sources that seem to signal a real upsurge of scientific production both well after the death of Ghazālī and well after the Mongol devastation of Baghdad. And if one focuses on the discipline of astronomy in particular, as we have been doing up till now, the problem of pinning down the cause of the decline according to one of those two narratives becomes even much harder to solve.
In a separate book devoted to the study of one aspect of Arabic astronomy: the aspect of planetary theories, I went so far as to call that same age of decline the golden age of Islamic astronomy. In that book I traced the developments in Arabic planetary theories between the eleventh and the fifteenth centuries and demonstrated the fecundity of that discipline. That book, and the various articles that have appeared since then, dealing mainly with the work of the sixteenth-century astronomer Shams al-Dīn al-Khafrī, described an unparalleled originality during that period that would be difficult if not impossible to dismiss.
If one takes either explanation of the age of decline, as offered by either group of the proponents of the classical narrative, one is then faced with problems that will not easily disappear. In the first case, and for those who hold Ghazālī responsible for the age of decline, they will have to explain the production of tens of scientists, almost in every discipline, who continued to produce scientific texts that were in many ways superior to the texts that were produced before the time of Ghazālī. In the case of astronomy, one cannot even compare the sophistication of the post- Ghazālī texts with the pre-Ghazālī ones, for the former were in fact far superior both in theoretical mathematical sophistication, as was demonstrated by Khafrī, as well as in blending observational astronomy with theoretical astronomy, as was exhibited by Ibn al-Shāṭir. Similar original production can be easily documented as well in mechanical engineering, in medicine, and in optics, to say nothing of the whole class of astronomers who were all working after the thirteenth century, and whose purpose was to push the frontiers of planetary theories into the realm of alternative astronomy or "New Astronomy" as was proposed by Ibn al-Shāṭir.
To take only few examples, compare the works of 'Izz al-Dīn al-Jazarī (c. 1206),[373] who worked nearly 100 years after the death of Ghazālī, with those of Banū Mūsā in the ninth century.[374] Earlier in the ninth century period, Banū Mūsā focused on developing new devices and new techniques that were not known from the Greek tradition. For instance, we note the development of the conic valve in the works of Banū Mūsā, which is nowhere documented in the earlier Greek sources. We also note a shift from the Greek tradition that relied mainly on nature's abhorrence of void to animate the machines that they designed, to a more instrumental approach by Banū Mūsā where they used concepts of sources of power as running water, or flowing sand, to achieve similar animations. For Philo of Byzantium[375] or Hero of Alexandria,[376] for example, the siphon worked by water replacing the void, while for Banū Mūsā water flew and was interrupted by turning a conic valve on and off, by means of floats and other mechanisms that did not depend on the concept of void. It was in these later developments that they had to invent such tools as the conic valve and the like. This does not mean that Banū Mūsā did not understand the way void worked in nature and in the design of machines, but that they used it together with other techniques that they themselves developed.
370
From the modern period we see people like Huff, and even Sabra and King, almost always referring to the works of Ibn al-Shāṭir as the climax of astronomical thought, implying of course that they were the last flicker in a dying civilization, and that post Ibn al-Shāṭir period may not be worth the attention. See Toby Huff,
371
A recent and well balanced assessment of this factor in the decline of Islamic science, discussed with other factors as well, has been elegantly summarized by Aḥmad Yūsuf al-Ḥassan, "Factors behind the Decline of Islamic Science after the Sixteenth Century", in
372
As a result the names of Hulagu and his grandfather Gengis Khan are usually followed by the expression "May God curse him", as in Abū al-Fidā's,
374
For the works of Banū Mūsā, see the English translation by Donald Hill,
375
See Carra de Vaux, "Le Livre des appareils pneumatiques et des machines hydroliques par Philon de Byzance",