- BuyFlorence and Baghdad: Renaissance Art and Arab Science by Hans Belting, translated by Deborah Lucas Schneider
Harvard, 303 pp, £25.00, September 2011, ISBN 978 0 674 05004 4
‘A daring undertaking’, the German art historian Hans Belting calls his book. Florence and Baghdad is his attempt to get two civilisations to define each other in terms of their attitudes to eyesight and, more specifically, in terms of what Ernst Cassirer, writing in the 1920s, called ‘symbolic form’. A symbolic form is a cohesive set of symbols within which you might give shape to the world. In classical Islam – Islam, that is, between the tenth and 13th centuries – a set emerged that centred on abstract geometry; in 15th-century Italy a related but different symbolic form came together in pictorial perspective, a principle later mechanised by photography. The hinge to Belting’s argument is that the perspective familiar to Western modernity is an application of a visual geometry devised within classical Islam.
People sometimes suppose, when they look for instance at Pompeian architectural frescoes, that the ancient Greeks and Romans must have had some geometrical system of perspective, but they are reading the clues wrong. Artists in antiquity were adept at making use of observed effects such as the diagonals at which rooflines recede from view, but they had no conceptual back-up from theorists. Plato, Euclid and Ptolemy were fixated on the active, probing aspects of vision: the way we peer out and construe the world before us. Their formulation, which now seems at once kooky and clunky, described eyesight as ‘extramission’ – a kind of radar. The eyes send out rays of light, rather as the sun does. These rays reach out to objects through the supporting medium of sunlight and bring back to the brain little copies of themselves that the objects have generated – copies termed ‘images’ or ‘simulacra’.
Aristotle saw there were problems with this hypothesis, but for a long time it remained the default account of vision – probably because it answers to the intuition that if I see you, I have some sort of hold on you. It was only under the Fatimid caliphs of Cairo, around the year 1000, that investigations of vision moved significantly forward. The scientist who is central to Belting’s story, Ibn al-Haytham, Europeanised as ‘Alhazen’, was born in Iraq, but the book’s title misleads: he left Baghdad, then under a dry and doctrinaire Abbasid caliphate, to spend most of his working life in a relatively open-minded Egypt.
Alhazen was a proto-Popperian. ‘The duty of the man who investigates the writings of scientists,’ he wrote, ‘if learning the truth be his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side.’ Suspect your faith in the writings of the ancients, he counselled, and submit it to experiment. So doing, Alhazen elegantly reduced visual theory. There was no need for little object copies and there was no need for visual rays zapping out to obtain them. All you needed was the single physical phenomenon of light, the light-receiving mechanism of the eyes, and then the brain, which interprets incoming information and translates it into images. Alhazen described the geometry by which light runs from objects to eyes, and, extending his research into light’s workings, devised the first known camera obscura.
Alhazen’s Kitab al-Manazir (‘book of optics’) was translated into Latin in Spain around 1200, under the title Perspectiva. The text, though opposed by some philosophers, soon became a standby of European academic life. It wasn’t until around 1420 in Florence, however, that Filippo Brunelleschi thought of applying Alhazen’s geometry to painting, designing images of objects by means of ‘artificial perspective’ – a truly momentous innovation. Much of Belting’s task is to account for the contrast between the two men’s achievements by setting them in their respective cultural contexts. But he also has historical complications to consider. Though Alhazen invented the camera obscura, with its aperture projecting light onto a back wall, he didn’t relate that wall to the eye’s retina, an anatomical feature of which he was unaware. This connection was made by Johannes Kepler around 1600, with the result that images inside the head returned as the dominant issue, sidelining the 2D analogues to a 3D world generated by Florentine perspective. For theorists from Descartes onwards (and indeed arguably for painters), the way the brain apprehends the world via the lens and retina settled in as an increasingly complex, if not inscrutable conundrum. Meanwhile the physical mechanism of the camera, conjoined with 19th-century chemistry, has helped to persuade us that a certain type of one-point perspectival picture constitutes a ‘normal’ representation of the world.