Saliba’s wide-ranging book on Islamic astronomy is a fascinating, revisionist account of a science that blossomed in a golden age under the Baghdadi caliphs before fading into obscurity. Saliba persuasively argues that the sciences flourished in the ninth and tenth centuries not so much because of enlightened patronage in a climate of toleration but because of a realignment of the skills and languages required for government positions. In the ensuing translation program, Greek sources replaced Persian and even Syriac writings.
Saliba presents evidence that Islamic astronomy continued to flourish, becoming more sophisticated and paving the way for the European Renaissance in astronomy. His is an argument for continuity, not revolutionary discontinuity. Because the work of Copernicus involved technical details similar to those employed by the Islamic geometricians, Saliba assumes a causal linkage: Islamic astronomy “was in a position to lay the foundation for a revolutionary upset of [the older Greek] tradition (173) and “it seems to have had a seminal impact on Renaissance science” (233). This part of the thesis is, I submit, seriously flawed; in fact Saliba’s account provides the basis for a conclusion diametrically opposed to the one expressed in the title of his book.
In the centuries following the initial burst of translations, geometry and trigonometry developed, leaving behind the clumsy chord function and the solutions afforded by the Menalaus theorem that had powered [End Page 310] Ptolemy’s Almagest (c. 150). The Islamic developments in trigonometry provided a heritage brilliantly employed by Regiomontanus, Copernicus, and other European mathematicians. But the Islamic astronomers busied themselves with the “absurdities” of Ptolemy, that is, his digressions from Aristotelian dogma. Their efforts resulted in ever-more intricate geometrical models composed from combinations of circles with uniform motions. Saliba is so imbued with a medieval Islamic viewpoint that it never occurs to him to notice that these solutions contain their own comparable absurdity—motion around empty points. Those astronomers were chasing a chimera, and ultimately a dead end. The much-criticized Ptolemaic equant is in fact closer to the physical approach of Johannes Kepler’s law of areas than to the thirteenth-and fourteenth-century models of Tusi or Ibn ash-Shatir. Furthermore, there is no convincing argument that their models in any way led to a heliocentric cosmology for Copernicus, and they certainly did not do so for the Islamic astronomers.
Islamic model building was almost entirely divorced from any increase in accuracy of predictions, the one obvious exception being Islamic lunar theory. However, even though this model resulted in an improvement with respect to the moon’s apparent size, no observational input seems to have followed to show that the model was still seriously deficient. Furthermore, a major anomaly in lunar longitude went unnoticed until Tycho Brahe’s measurements. An obvious unification awaited with respect to the unnecessarily complex Ptolemaic Mercury theory, but the Islamic astronomers simply interpreted Ptolemy rather than the sky.
What the Renaissance required was a strategic break with the past. Copernicus was still mired in Islamic-type intricacies (which were greatly admired by the majority of his contemporaries), but his stroke of genius was the heliocentric insight that started the scientific revolution. Islamic trigonometry was a notable factor, but Saliba’s attempt to hitch his star to the Islamic astronomy of uniform circular motion misses the essential transformation of Renaissance science.
At present, there appears only one small avenue where a specific geometrical insight from the Islamic world might have given an indispensable impetus toward the radical heliocentric rearrangement. Around 1430, ‘Ali Qushji, an Islamic astronomer, wrote a small treatise with a parallelogram transformation diagram that reappeared almost identically in Regiomontanus’ Epitome of the Almagest, a volume finally published in 1496. That book, known to have been used by Copernicus, is most likely the source for an essential step toward heliocentrism. Perhaps a connection between Islamic astronomy and the making of the European scientific Renaissance really does exist, but it seems not to be in the place where Saliba has been looking. [End Page 311]