Ibn al-Haytham was the first to correctly explain the theory of vision, and to argue that vision occurs in the brain, pointing to observations that it is subjective and affected by personal experience. He also stated the principle of least time for refraction which would later become the
Fermat's principle. He made major contributions to catoptrics and dioptrics by studying reflection, refraction and nature of images formed by light rays. Ibn al-Haytham was an early proponent of the concept that a hypothesis must be supported by experiments based on confirmable procedures or mathematical reasoning—an early pioneer in the
scientific method five centuries before
Renaissance scientists. On account of this, he is sometimes described as the world's "first true scientist". He was also a
polymath, writing on
Basra, he spent most of his productive period in the
Fatimid capital of
Cairo and earned his living authoring various treatises and tutoring members of the nobilities. Ibn al-Haytham is sometimes given the
bynameal-Baṣrī after his birthplace, or al-Miṣrī ("the Egyptian"). Al-Haytham was dubbed the "Second
Abu'l-Hasan Bayhaqi and "The Physicist" by
John Peckham. Ibn al-Haytham paved the way for the modern science of physical optics.
Ibn al-Haytham (Alhazen) was born c. 965 to a family of Arab or Persian origin in
Iraq, which was at the time part of the
Buyid emirate. His initial influences were in the study of religion and service to the community. At the time, society had a number of conflicting views of religion that he ultimately sought to step aside from religion. This led to him delving into the study of mathematics and science. He held a position with the title
vizier in his native Basra, and made a name for himself on his knowledge of applied mathematics. As he claimed to be able to regulate the
flooding of the Nile, he was invited to meet the
al-Hakim in order to realise a
hydraulic project at
Aswan. However, Ibn al-Haytham was forced to concede the impracticability of his project.
Upon his return to Cairo, he was given an administrative post. After he proved unable to fulfill this task as well, he contracted the ire of the caliph al-Hakim, and is said to have been forced into hiding until the caliph's death in 1021, after which his confiscated possessions were returned to him.
Legend has it that Alhazen
feigned madness and was kept under house arrest during this period. During this time, he wrote his influential Book of Optics. Alhazen continued to live in Cairo, in the neighborhood of the famous
University of al-Azhar, and lived from the proceeds of his literary production until his death in c. 1040. (A copy of
Apollonius' Conics, written in Ibn al-Haytham's own handwriting exists in
Aya Sofya: (MS Aya Sofya 2762, 307 fob., dated Safar 415 A.H. ).): Note 2
Alhazen's most famous work is his seven-volume treatise on
opticsKitab al-Manazir (Book of Optics), written from 1011 to 1021. In it, Ibn al-Haytham was the first to explain that vision occurs when light reflects from an object and then passes to one's eyes, and to argue that vision occurs in the brain, pointing to observations that it is subjective and affected by personal experience.
This work enjoyed a great reputation during the
Middle Ages. The Latin version of De aspectibus was translated at the end of the 14th century into Italian vernacular, under the title De li aspecti.
It was printed by
Friedrich Risner in 1572, with the title Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus (English: Treasury of Optics: seven books by the Arab Alhazen, first edition; by the same, on twilight and the height of clouds).
Risner is also the author of the name variant "Alhazen"; before Risner he was known in the west as Alhacen.
Works by Alhazen on geometric subjects were discovered in the
Bibliothèque nationale in
Paris in 1834 by E. A. Sedillot. In all, A. Mark Smith has accounted for 18 full or near-complete manuscripts, and five fragments, which are preserved in 14 locations, including one in the
Bodleian Library at
Oxford, and one in the library of
Two major theories on vision prevailed in
classical antiquity. The first theory, the
emission theory, was supported by such thinkers as
Ptolemy, who believed that sight worked by the
light. The second theory, the
intromission theory supported by
Aristotle and his followers, had physical forms entering the eye from an object. Previous Islamic writers (such as
al-Kindi) had argued essentially on Euclidean, Galenist, or Aristotelian lines. The strongest influence on the Book of Optics was from Ptolemy's
Optics, while the description of the anatomy and physiology of the eye was based on Galen's account. Alhazen's achievement was to come up with a theory that successfully combined parts of the mathematical ray arguments of Euclid, the medical tradition of
Galen, and the intromission theories of Aristotle. Alhazen's intromission theory followed al-Kindi (and broke with Aristotle) in asserting that "from each point of every colored body, illuminated by any light, issue light and color along every straight line that can be drawn from that point". This left him with the problem of explaining how a coherent image was formed from many independent sources of radiation; in particular, every point of an object would send rays to every point on the eye.
What Alhazen needed was for each point on an object to correspond to one point only on the eye. He attempted to resolve this by asserting that the eye would only perceive perpendicular rays from the object—for any one point on the eye, only the ray that reached it directly, without being refracted by any other part of the eye, would be perceived. He argued, using a physical analogy, that perpendicular rays were stronger than oblique rays: in the same way that a ball thrown directly at a board might break the board, whereas a ball thrown obliquely at the board would glance off, perpendicular rays were stronger than refracted rays, and it was only perpendicular rays which were perceived by the eye. As there was only one perpendicular ray that would enter the eye at any one point, and all these rays would converge on the centre of the eye in a cone, this allowed him to resolve the problem of each point on an object sending many rays to the eye; if only the perpendicular ray mattered, then he had a one-to-one correspondence and the confusion could be resolved. He later asserted (in book seven of the Optics) that other rays would be refracted through the eye and perceived as if perpendicular. His arguments regarding perpendicular rays do not clearly explain why only perpendicular rays were perceived; why would the weaker oblique rays not be perceived more weakly? His later argument that refracted rays would be perceived as if perpendicular does not seem persuasive. However, despite its weaknesses, no other theory of the time was so comprehensive, and it was enormously influential, particularly in Western Europe. Directly or indirectly, his De Aspectibus (
Book of Optics) inspired much activity in optics between the 13th and 17th centuries.
Kepler's later theory of the
retinal image (which resolved the problem of the correspondence of points on an object and points in the eye) built directly on the conceptual framework of Alhazen.
Alhazen showed through experiment that light travels in straight lines, and carried out various experiments with
reflection. His analyses of reflection and refraction considered the vertical and horizontal components of light rays separately.
Alhazen studied the process of sight, the structure of the eye, image formation in the eye, and the
visual system. Ian P. Howard argued in a 1996 Perception article that Alhazen should be credited with many discoveries and theories previously attributed to Western Europeans writing centuries later. For example, he described what became in the 19th century
Hering's law of equal innervation. He wrote a description of vertical
horopters 600 years before
Aguilonius that is actually closer to the modern definition than Aguilonius's—and his work on
binocular disparity was repeated by Panum in 1858. Craig Aaen-Stockdale, while agreeing that Alhazen should be credited with many advances, has expressed some caution, especially when considering Alhazen in isolation from
Ptolemy, with whom Alhazen was extremely familiar. Alhazen corrected a significant error of Ptolemy regarding binocular vision, but otherwise his account is very similar; Ptolemy also attempted to explain what is now called Hering's law. In general, Alhazen built on and expanded the optics of Ptolemy.
In a more detailed account of Ibn al-Haytham's contribution to the study of binocular vision based on Lejeune and Sabra, Raynaud showed that the concepts of correspondence, homonymous and crossed diplopia were in place in Ibn al-Haytham's optics. But contrary to Howard, he explained why Ibn al-Haytham did not give the circular figure of the horopter and why, by reasoning experimentally, he was in fact closer to the discovery of Panum's fusional area than that of the Vieth-Müller circle. In this regard, Ibn al-Haytham's theory of binocular vision faced two main limits: the lack of recognition of the role of the retina, and obviously the lack of an experimental investigation of ocular tracts.
Alhazen's most original contribution was that, after describing how he thought the eye was anatomically constructed, he went on to consider how this anatomy would behave functionally as an optical system. His understanding of
pinhole projection from his experiments appears to have influenced his consideration of image inversion in the eye, which he sought to avoid. He maintained that the rays that fell perpendicularly on the lens (or glacial humor as he called it) were further refracted outward as they left the glacial humor and the resulting image thus passed upright into the optic nerve at the back of the eye. He followed
Galen in believing that the
lens was the receptive organ of sight, although some of his work hints that he thought the
retina was also involved.
Alhazen's synthesis of light and vision adhered to the Aristotelian scheme, exhaustively describing the process of vision in a logical, complete fashion.
Alhazen was the first physicist to give complete statement of the law of reflection. He was first to state that the incident ray, the reflected ray, and the normal to the surface all lie in a same plane perpendicular to reflecting plane.
His work on
catoptrics in Book V of the Book of Optics contains a discussion of what is now known as Alhazen's problem, first formulated by
Ptolemy in 150 AD. 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
normal at that point. This is equivalent to finding the point on the edge of a circular
billiard table at which a player must aim a cue ball at a given point to make it bounce off the table edge and hit another ball at a second given point. Thus, its main application in optics is to solve the problem, "Given a light source and a spherical mirror, find the point on the mirror where the light will be reflected to the eye of an observer." This leads to an
equation of the fourth degree. This eventually led Alhazen to derive a formula for the sum of
fourth powers, where previously only the formulas for the sums of squares and cubes had been stated. His method can be readily generalized to find the formula for the sum of any integral powers, although he did not himself do this (perhaps because he only needed the fourth power to calculate the volume of the paraboloid he was interested in). He used his result on sums of integral powers to perform what would now be called an
integration, where the formulas for the sums of integral squares and fourth powers allowed him to calculate the volume of a
paraboloid. Alhazen eventually solved the problem using
conic sections and a geometric proof. His solution was extremely long and complicated and may not have been understood by mathematicians reading him in Latin translation.
Later mathematicians used
Descartes' analytical methods to analyse the problem. An algebraic solution to the problem was finally found in 1965 by Jack M. Elkin, an actuarian. Other solutions were discovered in 1989, by Harald Riede and in 1997 by the
Peter M. Neumann.
Mitsubishi Electric Research Laboratories (MERL) researchers solved the extension of Alhazen's problem to general rotationally symmetric quadric mirrors including hyperbolic, parabolic and elliptical mirrors.
Ibn al-Haytham used a
camera obscura mainly to observe a partial solar eclipse.
In his essay, Ibn al-Haytham writes that he observed the sickle-like shape of the sun at the time of an eclipse. The introduction reads as follows: "The image of the sun at the time of the eclipse, unless it is total, demonstrates that when its light passes through a narrow, round hole and is cast on a plane opposite to the hole it takes on the form of a moonsickle."
It is admitted that his findings solidified the importance in the history of the
camera obscura but this treatise is important in many other respects.
Ancient optics and medieval optics were divided into optics and burning mirrors. Optics proper mainly focused on the study of vision, while burning mirrors focused on the properties of light and luminous rays. On the shape of the eclipse is probably one of the first attempts made by Ibn al-Haytham to articulate these two sciences.
Very often Ibn al-Haytham's discoveries benefited from the intersection of mathematical and experimental contributions. This is the case with On the shape of the eclipse. Besides the fact that this treatise allowed more people to study partial eclipses of the sun, it especially allowed to better understand how the camera obscura works. This treatise is a physico-mathematical study of image formation inside the camera obscura. Ibn al-Haytham takes an experimental approach, and determines the result by varying the size and the shape of the aperture, the focal length of the camera, the shape and intensity of the light source.
In his work he explains the inversion of the image in the camera obscura, the fact that the image is similar to the source when the hole is small, but also the fact that the image can differ from the source when the hole is large. All these results are produced by using a point analysis of the image.
In the seventh tract of his book of optics, Alhazen described an apparatus for experimenting with various cases of refraction, in order to investigate the relations between the angle of incidence, the angle of refraction and the angle of deflection. This apparatus was a modified version of an apparatus used by Ptolemy for similar purpose.
Alhazen basically states the concept of unconscious inference in his discussion of colour before adding that the inferential step between sensing colour and differentiating it is shorter than the time taken between sensing and any other visible characteristic (aside from light), and that "time is so short as not to be clearly apparent to the beholder." Naturally, this suggests that the colour and form are perceived elsewhere. Alhazen goes on to say that information must travel to the central nerve cavity for processing and:
the sentient organ does not sense the forms that reach it from the visible objects until
after it has been affected by these forms; thus it does not sense color as color or light as light until after it has been affected by the form of color or light. Now the affectation received by the sentient organ from the form of color or of light is a certain change; and change must take place in time; …..and it is in the time during which the form extends from the sentient organ's surface to the cavity of the common nerve, and in (the time) following that, that the sensitive faculty, which exists in the whole of the sentient body will perceive color as color…Thus the last sentient's perception of color as such and of light as such takes place at a time following that in which the form arrives from the surface of the sentient organ to the cavity of the common nerve.
color constancy by observing that the light reflected from an object is modified by the object's color. He explained that the quality of the light and the color of the object are mixed, and the visual system separates light and color. In Book II, Chapter 3 he writes:
Again the light does not travel from the colored object to the eye unaccompanied by the color, nor does the form of the color pass from the colored object to the eye unaccompanied by the light. Neither the form of the light nor that of the color existing in the colored object can pass except as mingled together and the last sentient can only
perceive them as mingled together. Nevertheless, the sentient perceives that the visible object is luminous and that the light seen in the object is other than the color and that these are two properties.
The Kitab al-Manazir (Book of Optics) describes several experimental observations that Alhazen made and how he used his results to explain certain optical phenomena using mechanical analogies. He conducted experiments with
projectiles and concluded that only the impact of
perpendicular projectiles on surfaces was forceful enough to make them penetrate, whereas surfaces tended to deflect
oblique projectile strikes. For example, to explain refraction from a rare to a dense medium, he used the mechanical analogy of an iron ball thrown at a thin slate covering a wide hole in a metal sheet. A perpendicular throw breaks the slate and passes through, whereas an oblique one with equal force and from an equal distance does not. He also used this result to explain how intense, direct light hurts the eye, using a mechanical analogy: Alhazen associated 'strong' lights with perpendicular rays and 'weak' lights with oblique ones. The obvious answer to the problem of multiple rays and the eye was in the choice of the perpendicular ray, since only one such ray from each point on the surface of the object could penetrate the eye.
Sudanese psychologist Omar Khaleefa has argued that Alhazen should be considered the founder of
experimental psychology, for his pioneering work on the psychology of visual perception and
optical illusions. Khaleefa has also argued that Alhazen should also be considered the "founder of
psychophysics", a sub-discipline and precursor to modern psychology. Although Alhazen made many subjective reports regarding vision, there is no evidence that he used quantitative psychophysical techniques and the claim has been rebuffed.
Alhazen offered an explanation of the
Moon illusion, an illusion that played an important role in the scientific tradition of medieval Europe. Many authors repeated explanations that attempted to solve the problem of the Moon appearing larger near the horizon than it does when higher up in the sky. Alhazen argued against Ptolemy's refraction theory, and defined the problem in terms of perceived, rather than real, enlargement. He said that judging the distance of an object depends on there being an uninterrupted sequence of intervening bodies between the object and the observer. When the Moon is high in the sky there are no intervening objects, so the Moon appears close. The perceived size of an object of constant angular size varies with its perceived distance. Therefore, the Moon appears closer and smaller high in the sky, and further and larger on the horizon. Through works by
John Pecham and Witelo based on Alhazen's explanation, the Moon illusion gradually came to be accepted as a psychological phenomenon, with the refraction theory being rejected in the 17th century. Although Alhazen is often credited with the perceived distance explanation, he was not the first author to offer it.
c. 2nd century) gave this account (in addition to refraction), and he credited it to
c. 135–50 BCE). Ptolemy may also have offered this explanation in his Optics, but the text is obscure. Alhazen's writings were more widely available in the Middle Ages than those of these earlier authors, and that probably explains why Alhazen received the credit.
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. 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 ... 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.
An aspect associated with Alhazen's optical research is related to systemic and methodological reliance on experimentation (i'tibar)(Arabic: اختبار) and
controlled testing in his scientific inquiries. Moreover, his experimental directives rested on combining classical physics (ilm tabi'i) with mathematics (ta'alim; geometry in particular). This mathematical-physical approach to experimental science supported most of his propositions in Kitab al-Manazir (The Optics; De aspectibus or Perspectivae) and grounded his theories of vision, light and colour, as well as his research in catoptrics and
dioptrics (the study of the reflection and refraction of light, respectively).
According to Matthias Schramm, Alhazen "was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the
moonlight through two small
apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up." G. J. Toomer expressed some skepticism regarding Schramm's view, partly because at the time (1964) the Book of Optics had not yet been fully translated from Arabic, and Toomer was concerned that without context, specific passages might be read anachronistically. While acknowledging Alhazen's importance in developing experimental techniques, Toomer argued that Alhazen should not be considered in isolation from other Islamic and ancient thinkers. Toomer concluded his review by saying that it would not be possible to assess Schramm's claim that Ibn al-Haytham was the true founder of modern physics without translating more of Alhazen's work and fully investigating his influence on later medieval writers.
Other works on physics
Besides the Book of Optics, Alhazen wrote several other treatises on the same subject, including his Risala fi l-Daw' (Treatise on Light). He investigated the properties of
moonlight. Experiments with mirrors and the refractive interfaces between air, water, and glass cubes, hemispheres, and quarter-spheres provided the foundation for his theories on
Alhazen discussed the
physics of the celestial region in his Epitome of Astronomy, arguing that Ptolemaic models must be understood in terms of physical objects rather than abstract hypotheses—in other words that it should be possible to create physical models where (for example) none of the celestial bodies would collide with each other. The suggestion of mechanical models for the Earth centred
Ptolemaic model "greatly contributed to the eventual triumph of the Ptolemaic system among the Christians of the West". Alhazen's determination to root astronomy in the realm of physical objects was important, however, because it meant astronomical hypotheses "were accountable to the
laws of physics", and could be criticised and improved upon in those terms.
He also wrote Maqala fi daw al-qamar (On the Light of the Moon).
In his work, Alhazen discussed theories on the
motion of a body. In his Treatise on Place, Alhazen disagreed with
Aristotle's view that nature abhors a void, and he used
geometry in an attempt to demonstrate that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body.
On the Configuration of the World
In his On the Configuration of the World Alhazen presented a detailed description of the physical structure of the earth:
The earth as a whole is a round sphere whose center is the center of the world. It is stationary in its [the world's] middle, fixed in it and not moving in any direction nor moving with any of the varieties of motion, but always at rest.
In his Al-Shukūk ‛alā Batlamyūs, variously translated as Doubts Concerning Ptolemy or Aporias against Ptolemy, published at some time between 1025 and 1028, Alhazen criticized
Ptolemy's Almagest, Planetary Hypotheses, and Optics, pointing out various contradictions he found in these works, particularly in astronomy. Ptolemy's Almagest concerned mathematical theories regarding the motion of the planets, whereas the Hypotheses concerned what Ptolemy thought was the actual configuration of the planets. Ptolemy himself acknowledged that his theories and configurations did not always agree with each other, arguing that this was not a problem provided it did not result in noticeable error, but Alhazen was particularly scathing in his criticism of the inherent contradictions in Ptolemy's works. He considered that some of the mathematical devices Ptolemy introduced into astronomy, especially the
equant, failed to satisfy the physical requirement of uniform circular motion, and noted the absurdity of relating actual physical motions to imaginary mathematical points, lines and circles:
Ptolemy assumed an arrangement (hay'a) that cannot exist, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist... [F]or a man to imagine a circle in the heavens, and to imagine the planet moving in it does not bring about the planet's motion.
Having pointed out the problems, Alhazen appears to have intended to resolve the contradictions he pointed out in Ptolemy in a later work. Alhazen believed there was a "true configuration" of the planets that Ptolemy had failed to grasp. He intended to complete and repair Ptolemy's system, not to replace it completely. In the Doubts Concerning Ptolemy Alhazen set out his views on the difficulty of attaining scientific knowledge and the need to question existing authorities and theories:
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...
He held that the criticism of existing theories—which dominated this book—holds a special place in the growth of scientific knowledge.
Model of the Motions of Each of the Seven Planets
Alhazen's The Model of the Motions of Each of the Seven Planets was written
c. 1038. Only one damaged manuscript has been found, with only the introduction and the first section, on the theory of planetary motion, surviving. (There was also a second section on astronomical calculation, and a third section, on astronomical instruments.) Following on from his Doubts on Ptolemy, Alhazen described a new, geometry-based planetary model, describing the motions of the planets in terms of spherical geometry, infinitesimal geometry and trigonometry. He kept a geocentric universe and assumed that celestial motions are uniformly circular, which required the inclusion of
epicycles to explain observed motion, but he managed to eliminate Ptolemy's
equant. In general, his model didn't try to provide a causal explanation of the motions, but concentrated on providing a complete, geometric description that could explain observed motions without the contradictions inherent in Ptolemy's model.
Other astronomical works
Alhazen wrote a total of twenty-five astronomical works, some concerning technical issues such as Exact Determination of the Meridian, a second group concerning accurate astronomical observation, a third group concerning various astronomical problems and questions such as the location of the
Milky Way; Alhazen made the first systematic effort of evaluating the Milky Way's parallax, combining Ptolemy's data and his own. He concluded that the parallax is (probably very much) smaller than Lunar parallax, and the Milky way should be a celestial object. Though he was not the first who argued that the Milky Way does not belong to the atmosphere, he is the first who did quantitative analysis for the claim.
The fourth group consists of ten works on astronomical theory, including the Doubts and Model of the Motions discussed above.
In elementary geometry, Alhazen attempted to solve the problem of
squaring the circle using the area of
lunes (crescent shapes), but later gave up on the impossible task. The two lunes formed from a
right triangle by erecting a semicircle on each of the triangle's sides, inward for the hypotenuse and outward for the other two sides, are known as the
lunes of Alhazen; they have the same total area as the triangle itself.
Alhazen's contributions to
number theory include his work on
perfect numbers. In his Analysis and Synthesis, he may have been the first to state that every even perfect number is of the form 2n−1(2n − 1) where 2n − 1 is
prime, but he was not able to prove this result;
Euler later proved it in the 18th century, and it is now called the
Alhazen solved problems involving
congruences using what is now called
Wilson's theorem. In his Opuscula, Alhazen considers the solution of a system of congruences, and gives two general methods of solution. His first method, the canonical method, involved Wilson's theorem, while his second method involved a version of the
Chinese remainder theorem.
Alhazen discovered the sum formula for the fourth power, using a method that could be generally used to determine the sum for any integral power. He used this to find the volume of a
paraboloid. He could find the integral formula for any polynomial without having developed a general formula.
Influence of Melodies on the Souls of Animals
Alhazen also wrote a Treatise on the Influence of Melodies on the Souls of Animals, although no copies have survived. It appears to have been concerned with the question of whether animals could react to music, for example whether a camel would increase or decrease its pace.
In his Treatise on Place, Alhazen disagreed with
Aristotle's view that nature abhors a
void, and he used
geometry in an attempt to demonstrate that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body.Abd-el-latif, a supporter of Aristotle's philosophical view of place, later criticized the work in Fi al-Radd 'ala Ibn al-Haytham fi al-makan (A refutation of Ibn al-Haytham's place) for its geometrization of place.
Alhazen also discussed
space perception and its
epistemological implications in his Book of Optics. In "tying the visual perception of space to prior bodily experience, Alhazen unequivocally rejected the intuitiveness of spatial perception and, therefore, the autonomy of vision. Without tangible notions of distance and size for
correlation, sight can tell us next to nothing about such things." Alhazen came up with many theories that shattered what was known of reality at the time. These ideas of optics and perspective did not just tie into physical science, rather existential philosophy. This led to religious viewpoints being upheld to the point that there is an observer and their perspective, which in this case is reality.
Alhazen wrote a work on Islamic theology in which he discussed prophethood and developed a system of philosophical criteria to discern its false claimants in his time.
He also wrote a treatise entitled Finding the Direction of Qibla by Calculation in which he discussed finding the
Qibla, where prayers (
salat) are directed towards, mathematically.
There are occasional references to theology or religious sentiment in his technical works, e.g.
in Doubts Concerning Ptolemy:
Truth is sought for its own sake ... Finding the truth is difficult, and the road to it is rough. For the truths are plunged in obscurity. ... God, however, has not preserved the scientist from error and has not safeguarded science from shortcomings and faults. If this had been the case, scientists would not have disagreed upon any point of science...
In The Winding Motion:
From the statements made by the noble Shaykh, it is clear that he believes in Ptolemy's words in everything he says, without relying on a demonstration or calling on a proof, but by pure imitation (taqlid); that is how experts in the prophetic tradition have faith in Prophets, may the blessing of God be upon them. But it is not the way that mathematicians have faith in specialists in the demonstrative sciences.
Regarding the relation of objective truth and God:
I constantly sought knowledge and truth, and it became my belief that for gaining access to the effulgence and closeness to God, there is no better way than that of searching for truth and knowledge.
Alhazen made significant contributions to optics, number theory, geometry, astronomy and natural philosophy. Alhazen's work on optics is credited with contributing a new emphasis on experiment.
"They spoke of Alhazen and Vitello,
And Aristotle, who wrote, in their lives,
On strange mirrors and optical instruments."
impact craterAlhazen on the Moon is named in his honour, as was the
asteroid59239 Alhazen. In honour of Alhazen, the
Aga Khan University (Pakistan) named its Ophthalmology endowed chair as "The Ibn-e-Haitham Associate Professor and Chief of Ophthalmology". Alhazen, by the name Ibn al-Haytham, is featured on the obverse of the Iraqi 10,000-
dinar banknote issued in 2003, and on 10-dinar notes from 1982.
Over forty years previously,
Jacob Bronowski presented Alhazen's work in a similar television documentary (and the corresponding book), The Ascent of Man. In episode 5 (The Music of the Spheres), Bronowski remarked that in his view, Alhazen was "the one really original scientific mind that Arab culture produced", whose theory of optics was not improved on till the time of Newton and Leibniz.
H. J. J. Winter, a British historian of science, summing up the importance of Ibn al-Haytham in the history of
After the death of Archimedes no really great physicist appeared until Ibn al-Haytham. If, therefore, we confine our interest only to the history of physics, there is a long period of over twelve hundred years during which the Golden Age of Greece gave way to the era of Muslim Scholasticism, and the experimental spirit of the noblest physicist of Antiquity lived again in the Arab Scholar from Basra.
UNESCO declared 2015 the
International Year of Light and its Director-General Irina Bokova dubbed Ibn al-Haytham 'the father of optics'. Amongst others, this was to celebrate Ibn Al-Haytham's achievements in optics, mathematics and astronomy. An international campaign, created by the
1001 Inventions organisation, titled 1001 Inventions and the World of Ibn Al-Haytham featuring a series of interactive exhibits, workshops and live shows about his work, partnering with science centers, science festivals, museums, and educational institutions, as well as digital and social media platforms. The campaign also produced and released the short educational film
1001 Inventions and the World of Ibn Al-Haytham.
List of works
According to medieval biographers, Alhazen wrote more than 200 works on a wide range of subjects, of which at least 96 of his scientific works are known. Most of his works are now lost, but more than 50 of them have survived to some extent. Nearly half of his surviving works are on mathematics, 23 of them are on astronomy, and 14 of them are on optics, with a few on other subjects. Not all his surviving works have yet been studied, but some of the ones that have are given below.
^ A. Mark Smith has determined that there were at least two translators, based on their facility with Arabic; the first, more experienced scholar began the translation at the beginning of Book One, and handed it off in the middle of Chapter Three of Book Three.
Smith 200191 Volume 1: Commentary and Latin text pp.xx-xxi. See also his 2006, 2008, 2010 translations.
^El-Bizri 2010, p. 11: "Ibn al-Haytham's groundbreaking studies in optics, including his research in catoptrics and dioptrics (respectively the sciences investigating the principles and instruments pertaining to the reflection and refraction of light), were principally gathered in his monumental opus: Kitåb al-manåóir (The Optics; De Aspectibus or Perspectivae; composed between 1028 CE and 1038 CE)."
^Rooney 2012, p. 39: "As a rigorous experimental physicist, he is sometimes credited with inventing the scientific method."
^Baker 2012, p. 449: "As shown earlier, Ibn al-Haytham was among the first scholars to experiment with animal psychology.
^Also Alhacen, Avennathan, Avenetan, etc.; the identity of "Alhazen" with Ibn al-Haytham al-Basri "was identified towards the end of the 19th century". (
Vernet 1996, p. 788)
^Esposito, John L. (2000). The Oxford History of Islam. Oxford University Press. p. 192.: "Ibn al-Haytham (d. 1039), known in the West as Alhazan, was a leading Arab mathematician, astronomer, and physicist. His optical compendium, Kitab al-Manazir, is the greatest medieval work on optics."
abFor the description of his main fields, see e.g.
Vernet 1996, p. 788 ("He is one of the principal Arab mathematicians and, without any doubt, the best physicist.")
Kalin, Ayduz & Dagli 2009 ("Ibn al-Ḥaytam was an eminent eleventh-century Arab optician, geometer, arithmetician, algebraist, astronomer, and engineer."),
Dallal 1999 ("Ibn al-Haytham (d. 1039), known in the West as Alhazan, was a leading Arab mathematician, astronomer, and physicist. His optical compendium, Kitab al-Manazir, is the greatest medieval work on optics.")
“Alhazen Arab mathematician and physicist who was born around 965 in what is now Iraq.” Critical Companion to Chaucer: A Literary Reference to His Life and Work
^Esposito (2000)، The Oxford History of Islam، Oxford University Press، P. 192. : “Ibn al-Haytham (d. 1039), known in the West as Alhazan, was a leading Arab mathematician, astronomer, and physicist. His optical compendium, Kitab al-Manazir, is the greatest medieval work on optics”
Child, Shuter & Taylor 1992, p. 70), (
Dessel, Nehrich & Voran 1973, p. 164), Understanding History by John Child, Paul Shuter, David Taylor - Page 70. "Alhazen, a Persian scientist, showed that the eye saw light from other objects. This started optics, the science of light. The Arabs also studied astronomy, the study of the stars. "
^Enrico Narducci (1871). "Nota intorno ad una traduzione italiana fatta nel secolo decimoquarto del trattato d'ottica d'Alhazen". Bollettino di Bibliografia e di Storia delle Scienze Matematiche e Fisiche. 4: 1–40.. On this version, see
Raynaud 2020, pp. 139–153.
^Wade & Finger 2001: "The principles of the camera obscura first began to be correctly analysed in the eleventh century, when they were outlined by Ibn al-Haytham."
^German physicist Eilhard Wiedemann first provided an abridged German translation of On the shape of the eclipse: Eilhard Wiedemann (1914). "Über der Camera obscura bei Ibn al Haiṭam". Sitzungsberichte phys.-med. Sozietät in Erlangen. 46: 155–169. The work is now available in full:
^Eder, Josef (1945). History of Photography. New York: Columbia University Press. p. 37.
^G. J. Toomer.
Review on JSTOR, Toomer's 1964 review of Matthias Schramm (1963) Ibn Al-Haythams Weg Zur Physik Toomer p. 464: "Schramm sums up [Ibn Al-Haytham's] achievement in the development of scientific method.", p. 465: "Schramm has demonstrated .. beyond any dispute that Ibn al-Haytham is a major figure in the Islamic scientific tradition, particularly in the creation of experimental techniques." p. 465: "Only when the influence of ibn al-Haytam and others on the mainstream of later medieval physical writings has been seriously investigated can Schramm's claim that ibn al-Haytam was the true founder of modern physics be evaluated."
^Faruqi 2006, pp. 395–96:
In seventeenth century Europe the problems formulated by Ibn al-Haytham (965–1041) became known as 'Alhazen's problem'. ... Al-Haytham's contributions to geometry and number theory went well beyond the Archimedean tradition. Al-Haytham also worked on analytical geometry and the beginnings of the link between algebra and geometry. Subsequently, this work led in pure mathematics to the harmonious fusion of algebra and geometry that was epitomised by Descartes in geometric analysis and by Newton in the calculus. Al-Haytham was a scientist who made major contributions to the fields of mathematics, physics and astronomy during the latter half of the tenth century.
^Ishaq, Usep Mohamad, and Wan Mohd Nor Wan Daud. "Tinjauan biografi-bibliografi Ibn al-haytham." HISTORIA: Jurnal Program Studi Pendidikan Sejarah 5.2 (2017): 107–24.
^Kaminski, Joseph J. "The Trajectory of the Development of Islamic Thought – A Comparison Between Two Earlier and Two Later Scholars." The Contemporary Islamic Governed State. Palgrave Macmillan, Cham, 2017. 31–70. "For example, Ibn al-Haytham and Abū Rayhān al-Bīrūnī were among the most important medieval scholars who used the scientific method in their approach to natural science, and they were both Ash'arites"
^Authier 2013, p. 23: "Alhazen's works in turn inspired many scientists of the Middle Ages, such as the English bishop, Robert Grosseteste (c. 1175–1253), and the English Franciscan, Roger Bacon (c. 1214–1294), Erazmus Ciolek Witelo, or Witelon (ca 1230* 1280), a Silesian-born Polish friar, philosopher and scholar, published in ca 1270 a treatise on optics, Perspectiva, largely based on Alhazen's works."
^Magill & Aves 1998, p. 66: "Roger Bacon, John Peckham, and Giambattista della Porta are only some of the many thinkers who were influenced by Alhazen's work."
^Zewail & Thomas 2010, p. 5: "The Latin translation of Alhazen's work influenced scientists and philosophers such as (Roger) Bacon and da Vinci, and formed the foundation for the work by mathematicians like Kepler, Descartes and Huygens..."
^El-Bizri 2010, p. 12: "This [Latin] version of Ibn al-Haytham's Optics, which became available in print, was read and consulted by scientists and philosophers of the caliber of Kepler, Galileo, Descartes, and Huygens as discussed by
^Magill & Aves 1998, p. 66: "Sabra discusses in detail the impact of Alhazen's ideas on the optical discoveries of such men as Descartes and Christiaan Huygens; see also
^Magill & Aves 1998, p. 66: "Even Kepler, however, used some of Alhazen's ideas, for example, the one-to-one correspondence between points on the object and points in the eye. It would not be going too far to say that Alhazen's optical theories defined the scope and goals of the field from his day to ours."
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Buchhandlung Walther-König - KWB 45: Variantology 4