Pathfinders

by Jim Al-Khalili

  In another case study, we get a glimpse of the sort of natural remedies that were around during the time of al-Rāzi. In his treatise on smallpox and measles he is particularly concerned with protecting the eye, for corneal damage from smallpox was a major cause of blindness in the Middle East up until relatively modern times:

  As soon as the symptoms of smallpox appear, drop rose water into the eyes from time to time, and wash the face with cold water. For if the disease be favourable and the pustules few in number, you find that this mode of treatment prevents their breaking out in the eyes. But when you see the ebullition is vehement and the pustules numerous in the beginning of the eruption, with itching of the eyelids and redness of the whites of the eyes, in this case pustules will certainly break out there unless very strong measures are adopted; and therefore you should immediately drop into the eyes several times in the day rose water in which sumach [a red lemony spice] has been macerated … Drop into the eyes some of the juice of the pulp of the acid pomegranate, first chewed, or squeezed in a cloth. Then cleanse the eyelids with the collyrium [eye wash] composed of the red horn poppy, the juice of unripe grapes, rusot, aloa and acacia, of each one part, and a tenth part of saffron; and if you also drop some of this collyrium into the eyes, it will be useful at this time.10

  Returning briefly to his book on alchemy, The Book of Secrets (Kitab al-Asrār), we see little trace of alchemical mysticism and symbolism, despite the evocative title.11 For al-Rāzi, despite living during the times he did, was not impressed by anything that could not be proven experimentally and have its validity tested. Like the two other great Muslim scientists to follow him in the next century, Ibn al-Haytham and al-Bīrūni, he was meticulous about recording details of his apparatus, methods, experimental conditions and the results of his careful measurements. This was not a text on alchemical magic but rather a real chemical laboratory manual.

  On philosophy, al-Rāzi was probably the most free-thinking scholar in the whole of Islam. He believed – as did the Greeks – that a competent physician should also be a philosopher, well versed in the fundamental questions regarding existence. He disagreed with al-Kindi, for example, on the issue of infinity. For him, God did not create the universe from nothing but arranged it out of existing principles. He argued that time exists as absolute and infinite. It does not need motion (and thus matter in space) in order to exist. This is very close to the view of the nature of time reached by Newton (itself overthrown by Einstein).

  Finally, what many find most surprising about al-Rāzi is his attitude towards religion. Here is a famous quotation from him:

  If the people of religion are asked about proof for the soundness of their religion, they flare up, get angry and spill the blood of whoever confronts them with this question. They forbid rational speculation, and strive to kill their adversaries. This is why truth became thoroughly silenced and concealed.12

  He was particularly harsh in his criticism of all prophetically revealed religions. He says: ‘How can anyone think philosophically while committed to those old wives’ tales, founded on contradictions, obdurate ignorance, and dogmatism?’13 This was clearly a dangerous and radical view for someone to adopt at that time and al-Rāzi was branded as a heretic. And yet he was such an important figure in science that any anti-religious views he held are to some extent forgiven. Today, Iran still celebrates ‘Rāzi Day’ (or ‘Pharmacy Day’) every year on 27 August.

  Before we leave al-Rāzi, here is one final quotation from the man himself that appears in Ibn al-Nadīm’s Fihrist:

  A man from China came to seek me and dwelt with me for about a year. In five months of this time he learned Arabic, both spoken and written, becoming proficient in style, as well as expert and rapid in reading. When he desired to return to his country, he said to me a month in advance, ‘I am about to set forth and wish that you would dictate to me the sixteen books of Galen, so that I can write them down.’ I said, ‘Your time is short and the length of your stay is sufficient for you to copy only a small part of it.’ Then the young man said, ‘I ask you to devote yourself to me for the length of my stay and to dictate to me as fast as you can. I will keep up with you in writing.’14

  Ibn al-Nadīm does not record whether al-Rāzi agreed to this.

  So far, I may have given the impression that the seat of power of the caliphate in Baghdad is where all the action took place and I have said little about what was going on in other parts of the Islamic world. By the time of al-Rāzi, the Abbāsid dynasty was already weakened and beginning to fragment – partly, one should say, owing to the practical difficulties of governing such a vast empire.

  As early as the reign of al-Ma’mūn, various Persian factions had begun to flex their military muscle and to exercise independent authority in the East. A number of autonomous dynasties, such as the Samanids and Saffarids, soon gained power over much of Persia. These dynasties took on the characteristics of de facto states, with hereditary sultans and princes, armies and revenues. All nominally recognized the sovereignty of the caliphate in Baghdad but knew that it no longer held real power within their borders. By the mid-tenth century, even the pretence of Baghdad’s autonomy had disappeared with the rise of the Buyid and Ghaznavid empires. These were then followed by the Turkish Seljuks, marking the end of Abbāsid political dominion over the region.

  Al-Rāzi’s Baghdad was a vast city and the centre of the civilized world. But by the tenth century, and as a hub of scientific scholarship, it already had rivals elsewhere within the empire. Three cities in particular, separated by thousands of miles, had grown to be centres of scientific activity and flourishing scholarship, with vast libraries, generous patronage and famous sons. They were Bukhara, capital of the Samanid dynasty in Central Asia, the new city of Cairo, where a second House of Wisdom would be established, and, to the far west of the empire in Muslim Spain, Córdoba, for a while the most glorious city in Europe.

  So it is now that we leave Baghdad to explore the riches and scientific legacy elsewhere. At the end of the tenth and the beginning of the eleventh centuries we see the zenith (another Arabic word by the way15) of scientific achievement. For this is the age of three of the greatest minds in history, probably the only three men portrayed here worthy of the greatness reserved for such as Aristotle, Leonardo da Vinci, Newton and Einstein.

  11

  The Physicist

  The seeker after truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and demonstration and not the sayings of human beings whose nature is fraught with all kinds of imperfection and deficiency. Thus the duty of the man who investigates the writings of scientists, if learning the truth is 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. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency.

  Ibn al-Haytham

  By the end of the tenth century the translation movement was coming to an end, the Abbāsid Empire was crumbling, less-enlightened caliphs were cracking down on freedom of speech and rationalist enquiry, and the great names associated with the House of Wisdom were already a distant memory. But to infer from this that the golden age of Arabic science was on the wane would be utterly wrong, for the best was yet to come. Despite appearances, this was a period of competitive patronage of the sciences among dynastic rulers across the Islamic world, with enticements offered from many of the courts around the Middle East and Central Asia to attract the very best scholars.

  It was during the second half of the tenth century that we see the three most outstanding thinkers in the history of Islam arriving on the scene. The first of these was a man after my own heart: a physicist; in fact, the greatest physicist since Archimedes and the like of whom would not be se
en until Isaac Newton seven hundred years later. And acknowledging someone as being the greatest physicist in a span of nearly two thousand years is not done lightly.1

  The Arab polymath Abū Ali al-Hassan ibn al-Haytham was born in Basra in southern Iraq in c. 965. He is often said to be Egyptian, because he spent his later, most productive years there. In fact, I would no more think of him as Egyptian than I would think of Einstein as an American rather than a German. Even more tenuously, it has been argued that he was a Persian rather than an Arab, on the basis that his city of birth, Basra, was under the rule of the Persian Buyid dynasty at the time. Al-Haytham was his grandfather’s name, so he is fact ibn ibn al-Haytham. His Latinized name, Alhazen (or Alhacen) comes from his first name, al-Hassan, but he is known nowadays simply as Ibn al-Haytham.2

  What I find disappointing – as is often the case with this subject – is the inaccuracies and errors one reads about Ibn al-Haytham’s life and achievements. For instance, it is widely stated that he invented the pinhole camera to explain the workings of the eye, and that he beat the Europeans to the law of refraction by six hundred years. Both of these claims are wrong, and my desire to correct these mistakes is not an issue of pedantry but because such trivialities detract from his real legacy, as we shall see.

  Ibn al-Haytham was a wonderful experimental scientist and a very colourful character about whom we have a considerable amount of evidence, not all of it reliable, however. Many details about his life have been lost over the years, but thanks to his fame and status there is no shortage of commentaries on his life, some in direct contradiction with each other.

  As a young man, he received an excellent education, which suggests that his family were financially secure and moved in the right political and social circles. He showed early promise as a mathematical and scientific prodigy and built up a scientific reputation that quickly spread far and wide. He was given a government post in Basra but, according to an account by a thirteenth-century scholar in Cairo by the name of Qaysar al-Hanafi, he became quickly bored and frustrated by his administrative duties, which took him away from his intellectual pursuits and research. It is unclear what happened at this point but it is said that he was dismissed from his post because of mental illness. What cannot be verified is whether this illness was genuine or whether Ibn al-Haytham deliberately feigned madness to get himself out of an awkward situation – an extreme measure to take for someone dissatisfied with his job.

  Around the beginning of the new millennium he wrote an interesting treatise on an enormously ambitious potential civil engineering project. Ibn al-Haytham knew of the importance of the Nile for the prosperity of the people of Egypt and claimed that he could build a dam across the great river that would control its flow and alleviate the twin problems of droughts and floods. He wrote that the Nile’s autumn floodwaters could be held by a system of dikes and canals, preserving its waters in reservoirs until the summer drought, when they were needed. News of this work soon reached the ambitious young ruler of Egypt, the Fātimid Caliph al-Hākim.

  The Fātimids were a Shi’a dynasty who claimed to be directly descended from the Prophet Muhammad through his daughter Fātima and her husband, Imam Ali. The Fātimids came to power in 909 and ruled over an expanding empire stretching across North Africa. They built their new capital, Cairo, in 969, which, like Baghdad two centuries earlier, rapidly grew in size and importance and would eventually rival Baghdad as a centre of scholarship. The Fātimids regarded themselves as being in direct opposition to the Abbāsids to the east and referred to their own rulers as imams or caliphs. Al-Hākim bi’amr Illāh (985–1021) was the most famous of these. He was known as the Mad Caliph – an unfair title for someone who was really no madder than many other rulers in the medieval world.

  While it is true that al-Hākim was regarded as eccentric and somewhat whimsical in his policies – he once famously ordered the killing of all the dogs in Cairo because their barking annoyed him – he also showed his compassionate side when, during a famine, he made a number of sensible laws to ensure the distribution of food to his people.

  He had become caliph in 996 at the tender age of 11 and assumed full power at 14. In his early years of rule, there are accounts of his religious persecution of Sunni Muslims, Christians and Jews. But these were not the wilful and randomly violent actions of a mad tyrant but the actions of a ruler desperately trying to hold his struggling empire together. And certainly by the middle of the first decade of the eleventh century he had stabilized his borders and we see in his actions a more tolerant approach. He was most famously a great patron of science and built a library to rival that of Baghdad. It became known as Dar al-Hikma, which also translates as the House of Wisdom, but the word dar here refers to a larger, grander residence than a mere bayt, implying that he was aiming at something not only to rival the Baghdad Bayt al-Hikma, but to exceed it in glory.3 Like al-Ma’mūn in Baghdad, he was keen to attract the big names from around the empire to his new House of Wisdom, the most famous of whom was the great astronomer Ibn Yūnus.

  It is not clear whether al-Hākim, impressed with Ibn al-Haytham’s reputation as a mathematician, headhunted him, or whether Ibn al-Haytham himself, seeing a chance to move to a prosperous and exciting city, with a brand-new library and generous patron, wrote to the caliph with his idea for the dam. In any case, the Fātimid caliph came to be aware of Ibn al-Haytham’s proposal and invited him to Cairo around 1010. Eager to begin, Ibn al-Haytham travelled south to near the location of the modern-day Aswan dam. But he quickly realized that the sheer size of the engineering undertaking was beyond him. While this story, and what happened next, is by no means established, it has become part of Arab folklore. According to the most widely accepted account, as soon as Ibn al-Haytham realized he had bitten off more than he could chew he again feigned madness. For this was the only way he knew to escape the wrath of the caliph. Instead, the caliph consigned him to a mental asylum and there he remained until 1021 when the caliph died. Or, more correctly, when he mysteriously vanished one night while taking a walk. In any case, Ibn al-Haytham was released and he took up lodging in a small apartment near the al-Azhar Mosque in the centre of Cairo.

  In common with all scholars throughout history, Ibn al-Haytham badly needed the time and isolation to focus on writing his treatises. His many years in the asylum certainly granted him the seclusion to think and to write. But after his release he began to produce work at a prolific rate. He earned his living through tuition and as a scribe but at the same time worked feverishly on his experiments in optics. It is not clear how much of his greatest work, the Book of Optics (Kitab al-Manāthir), he had already written by then but the complete text comes to us in seven volumes and has been hugely influential in the history of the field. It would be no exaggeration to say that it ranks alongside Newton’s Principia Mathematica as one of the most important books in the history of physics.

  To most people in the West, and indeed in the Muslim world, Isaac Newton is the undisputed father of modern optics; at least, that is what we are told at school, where our textbooks abound with his famous experiments with lenses and prisms, his study of the nature of light and its reflection, refraction and decomposition into the colours of the rainbow. Even historians of science who acknowledge that work on optics predates Newton often do not go back any earlier than other notables from the European scientific revolution of the seventeenth century such as René Descartes, Willebrord Snell and Johannes Kepler. But studies of the properties of light, particularly catoptrics (reflection of light by mirrors) and dioptrics (refraction of light through lenses) go back all the way to the Greeks.

  An interest in optics began in antiquity, with the Babylonians, Egyptians and Assyrians all making use of polished quartz to make rudimentary lenses. The basic principles of geometric optics were laid down by Plato and Euclid and included ideas such as the propagation of light in straight lines and the simple laws of reflection from plane mirrors, while the earliest serious contribution to t
he field in the Islamic world came from al-Kindi.

  Ibn Sahl’s diagram showing the law of refraction of light (through a plano-convex lens) for the very first time. Of interest are the two embedded right-angled triangles in the top left of the diagram. He writes his law in terms of ratios of sides of the two triangles made up from the original path of a light beam and its refracted path as it passes through the lens.

  Far less well known than these men was a scholar who flourished in Baghdad in the late tenth century, a few years before Ibn al-Haytham, who would advance the subject of optics in a way that has until recently been almost completely ignored. His name was Ibn Sahl and he wrote a treatise around 984 called On the Burning Instruments (by which is meant lenses and mirrors that can be used to focus sunlight to create a hot spot). Although such burning methods had been known in antiquity – there is a story that Archimedes used concave bronze mirrors to focus sunlight on Roman warships and set them on fire – the work of Ibn Sahl is regarded as the first serious mathematical study of lenses for focusing light.4 The manuscript’s pages were recently discovered in two different locations, one part in Damascus and the other in Tehran. The historian Roshdi Rashed was able to fit the two pieces together and reconstruct the full original text, earning himself worldwide acclaim in the early 1990s. The most incredible insight in this work is something that everyone learns about at school: what we call Snell’s law of refraction.