ABU ALI HASAN IBN AL-HAITHAM

(965-1040 C.E.)

Abu Ali Hasan Ibn al-Haitham was one of the most eminent physicists, whose contributions to optics and the scientific methods are outstanding. Known in the West as Alhazen, Ibn al-Haitham was born in 965 C.E. in Basrah, and was educated in Basrah and Baghdad. Thereafter, he went to Egypt, where he was asked to find ways of controlling the flood of the Nile. Being unsuccessful in this, he feigned madness until the death of Caliph al-Hakim. He also travelled to Spain and, during this period, he had ample time for his scientific pursuits, which included optics, mathematics, physics, medicine and development of scientific methods on each of which he has left several outstanding books.

He made a thorough examination of the passage of light through various media and discovered the laws of refraction. He also carried out the first experiments on the dispersion of light into its constituent colours. His book Kitab-al-Manadhir was translated into Latin in the Middle Ages, as also his book dealing with the colours of sunset. He dealt at length with the theory of various physical phenomena like shadows, eclipses, the rainbow, and speculated on the physical nature of light.

Eye Diagram Ibn al-Haytham (11th Century)

He is the first to describe accurately the various parts of the eye and give a scientific explanation of the process of vision. He also attempted to explain binocular vision, and gave a correct explanation of the apparent increase in size of the sun and the moon when near the horizon. He is known for the earliest use of the camera obscura. He contradicted Ptolemy's and Euclid's theory of vision that objects are seen by rays of light emanating from the eyes; according to him the rays originate in the object of vision and not in the eye. Through these extensive researches on optics, he has been considered as the father of modern Optics.

Optics (dated 1083):  Ibn al-Haytham's Optics, written in Eqypt in the first half of the 11th Century, represented a theory of vision that went beyond Galen, Euclid and Ptolemy. This diagram of the two eyes seen from above, shows the principal tunics and humours and the optic nerves connecting the eyeballs to the brain

The Latin translation of his main work, Kitab-al-Manadhir, exerted a great influence upon Western science e.g. on the work of Roger Bacon and Kepler. It brought about a great progress in experimental methods. His research in catoptrics centred on spherical and parabolic mirrors and spherical aberration. He made the important observation that the ratio between the angle of incidence and refraction does not remain constant and investigated the magnifying power of a lens. His catoptrics contain the important problem known as Alhazen's problem. It comprises drawing lines from two points in the plane of a circle meeting at a point on the circumference and making equal angles with the norrnal at that point. This leads to an equation of the fourth degree.

In his book Mizan al-Hikmah Ibn al-Haitham has discussed the density of the atmosphere and developed a relation between it and the height. He also studied atmospheric refraction. He discovered that the twilight only ceases or begins when the sun is 19° below the horizon and attempted to measure the height of the atmosphere on that basis. He has also discussed the theories of attraction between masses, and it seems that he was aware of the magnitude of acceleration due to gravity.

His contribution to mathematics and physics was extensive. In mathematics, he developed analytical geometry by establishing linkage between algebra and geometry. He studied the mechanics of motion of a body and was the first to maintain that a body moves perpetually unless an external force stops it or changes its direction of motion. This would seem equivalent to the first law of motion.

The list of his books runs to 200 or so, very few of which have survived. Even his monumental treatise on optics survived through its Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew and other languages. He has also written on the subject of evolution a book that deserves serious attention even today.

In his writing, one can see a clear development of the scientific methods as developed and applied by the Muslims and comprising the systematic observation of physical phenomena and their linking together into a scientific theory. This was a major breakthrough in scientific methodology, as distinct from guess and gesture, and placed scientific pursuits on a sound foundation comprising systematic relationship between observation, hypothesis and verification.

Ibn al-Haitham's influence on physical sciences in general, and optics in particular, has been held in high esteem and, in fact, it ushered in a new era in optical research, both in theory and practice.

Ibn Al-Haytham's anatomy of the eye

One of the most distinguished and prolific mathematicians in the medieval tradition of Arabic Islamic science, al-Hasan ibn al-Haytham (Latinized as Alhacen or Alhazen) became known in Europe in the thirteenth century as the author of a monumental book on optics—the mathematical theory of vision. In his Kitâb al-Manâdhir (De aspectibus), the eleventh-century scholar offered a new solution to the problem of vision, combining experimental investigations of the behavior of light with inventive geometrical proofs and constant forays into the psychology of visual perception—all systematically tied together to form a coherent alternative to the Euclidean and Ptolemaic theories of "visual rays" issuing from the eye.

Like his contemporaries Ibn Sînâ (Avicenna), the most influential Islamic philosopher, and al-Bîrûnî, one of the great scientific minds in all history, Ibn al-Haytham lived in a period of competitive patronage of the sciences, especially mathematics and astronomy, in the Middle East and Central Asia. He is said to have been a high administrative official in a small principality made up of Basra, in what is now Iraq, and the adjacent region of Ahwâz—but when the job encroached on his scientific interests, he moved to Egypt. He ended up living in what is described as a domed structure, probably a modest mausoleum, outside the Azhar Mosque and its famous school in Cairo. There he supported himself by teaching and by copying Arabic translations of Greek mathematical classics such as Euclid's Elements and Ptolemy's Almagest.

A story from the thirteenth century, which may well be true, says Ibn al-Haytham went to Egypt hoping to persuade its ruler to undertake an engineering project to regulate the flow of the Nile. But the prospective site, just south of Aswân, did not match the scholar's expectations, and he admitted failure. To escape almost certain punishment at the hands of the notoriously unbalanced ruler, he had to feign madness until his patron died, in 1021.

In a short autobiography, Ibn al-Haytham tells us that in his youth he scrutinized the claims of the many religious sects teeming around him. In the end it was the empirical strain and rational thinking he recognized in Aristotelian natural philosophy, and the rigor of mathematics, that finally won his heart. An early essay of his, now lost, was entitled "All matters secular and religious are the fruits of the philosophical sciences." In his time "philosophy" comprised all of mathematics, the natural sciences, and theology or metaphysics. He wrote on arithmetic, astronomy, music, ethics, politics, and poetry; defended astrology as a science based on mathematical proof; and criticized contemporary Muslim theological theses as well as positions taken by followers of the Christian philosopher-theologian Philoponus who were active in Baghdad.

Geometry was Ibn al-Haytham's forte: the subject in which most of his writings have survived and for which he was most appreciated. In these writings he was drawn to tackle problems in Greek mathematics, both elementary (Euclidean) and advanced (Apollonian and Archimedean), some of which he was the first to solve. The word "doubt" (aporia in Greek), indicating the critical bent of his mind, occurs in the titles of several of his geometrical essays, even when presented as commentaries. Other works concern the philosophy and methodology of mathematics.

Above: Proofs and diagrams from the Arabic translation of the Conics of Apollonius, transcribed and drawn by Ibn al-Haytham himself (MS Aya Sofya, no. 2762, Istanbul). Ibn al-Haytham (at left) and Galileo appear on the frontispiece of Selenographia, a 1647 description of the moon by Johannes Hevelius. The frontispiece presents the two scientists as explorers of nature by means of rational thought (ratione—note the geometrical diagram in Ibn al-Haytham's hand) and by observation (sensu—illustrated prominently by the long telescope in Galileo's hand). The two approaches were probably conceived here as complementary, a view both scientists would have shared.

But it was Ibn al-Haytham's early embrace of empiricism and trust in mathematical proof that underlay the revolutionary project of his mature magnum opus, the Optics, the book that pointed the science of vision in the direction later pursued in seventeenth-century Europe. It was wholly composed of systematically arranged experiments and geometrical proofs, all expressed in clear, consistent vocabulary and orderly exposition. The Latin translation influenced medieval European scientists and philosophers such as Roger Bacon and Witelo. But the book came into its own later, when it attracted the attention of mathematicians like Kepler, Descartes, and Huygens, thanks in part to Friedrich Risner's edition published in Basel in 1572.

Relatively late in his life, apparently stimulated by controversies with contemporaries about truth and authority and the role of criticism in scientific research, Ibn al-Haytham articulated some remarkably sophisticated statements on the practice of science and the growth of scientific knowledge. In a critical treatise, Aporias against Ptolemy, he asserts that "Truth is sought for itself"—but "the truths," he warns, "are immersed in uncertainties" and the scientific authorities (such as Ptolemy, whom he greatly respected) are "not immune from error...." Nor, he said, is human nature itself: "Therefore, the seeker after the 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 to the sayings of a human being 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."

The Influence of the Kitab al-Manadhir
From a scientific point of view, the Kitab al-Manadhir presents a radically new approach to the studies of optics in the Middle Ages, starting from the basic physiological principle according to which, “Sight (al-basar) is composed of various layers, coats and bodies, its principle and origin lying in the frontal part of the brain.”  Thus, Ibn al-Haytham provided an important analysis on the physical process of sight, based on his observation of the functioning of light and colour:

Sight perceives (yuhiss) the light and the colour existing on the surface of the contemplated object (mubsar), thanks to the shape that expands from the light and the colour existing on the surface of this object through an intermediary diaphanous body (al-jism al-mushiff al-mutawassit) between vision and its object. Vision perceives necessarily all the objects through supposed straight lines [i.e. lines of perspective] that spread themselves between the object and the central point of the sight (markaz al-basar).
Significantly, this theory explains, for the first time in the Middle Ages, the two principles of light and perspective that will have such a profound impact upon European culture of the medieval and modern eras. In fact, Ibn al-Haytham’s treatise belongs to a wider Muslim scientific trend of works on optics (especially after Euclid) that was to exert a profound influence upon the whole of medieval civilisation, both Muslim and Christian. From the end of the 12th century and throughout the 13th century, Christian scholars confirmed the importance of physics, mathematics and geometry to explain the structure of the universe, deriving their theories from the threefold influence of the Arabic sciences, Saint Augustine and Neo-Platonism. Robert Grosseteste (1168-1253), Abbot of Lincoln (1175-1253), who was particularly aware of these Arabic sciences, claimed:

It is impossible to know nature without geometry: its principles hold true within the entire universe and within every part of it: it is through its lines, angles and figures that we have to represent all the causes of natural phenomena: it is impossible without this means to reach the ‘proper quid’ in nature.

Around 1200, translations of the De Perspectiva or De Aspectibus by Alhacen are copied: he affirms the spherical diffusion of light, he develops as a mathematician the theory of reflection and the refraction of luminous rays, and as a positivist the psycho-physiological doctrine of visual sensation. Alhacen exerts a big influence on Grosseteste and Bacon and the perspectivists, for example, Witelo and Jean Peckham. The De Perspectiva treatise of Witelo, dedicated to Guillaume de Moerbeke (around 1270), will be commented on by Kepler, the second one by Peckham inspires deeply the Trattato della pittura (The Treatise of Painting) by Leonardo da Vinci, from whom aesthetic-scientific trends are well known.

Observable Beauty

During the early Renaissance in the 15th century, philosophical theories were developed concerning the aesthetics of human proportion. These were based on symmetry as a fundamental concept of perfection, and were first notably employed in the work of the famous Italian artist Ghiberti (1378-1455). One of the main sources for these theories, if not the main one, is Ibn al-Haytham’s concept of observable beauty that he defined originally in terms of objective visual concepts (al-ma’ani al-mubsara). Among these concepts, the Muslim thinker revived the central notions of order (tartib) and symmetry in Aristotle and Plato’s aesthetics, and dealt with derived notions such as regularity (muntazim) and proportional correspondence (mutanasib) as factors producing beauty; notions that became so important for the definition of the arts in particular and knowledge in general, during this important period of European civilisation. Ibn al-Haytham analyzes the character of a beautiful face in the following terms:

The proportion (tanasub) only produces beauty if each one of the members taken separately is not ugly even though they do not reach a high degree of beauty. If we join in the same form the beauty of the figure of each part of it and the beauty of its measures, like the beauty of its composition and the proportion of the members as well as their respective shapes, sizes and dispositions as all what must be proportioned, and moreover, the members are proportioned according to the figure and the measure of the face as a whole, this will raise the top of beauty.

Then, dealing with the principle of proportion in objects in general, Ibn al-Haytham continues:

If the beautiful forms of all kinds of visible objects are investigated, one will verify that proportion produces in them a beauty that none of the other visual concepts taken separately produces ... If the beautiful concepts produced by the conjunction of particular concepts are observed, one will see the beauty that manifests itself, starting from the so called conjunction, is due to the proportion existing between these concepts and its harmonisation (i’tilaf).