Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham (
Arabic:
أبو علي، الحسن بن الحسن بن الهيثم), frequently referred to as
Ibn al-Haytham (Arabic:
ابن الهيثم,
Latinized as
Alhazen[Notes 1] or
Alhacen;
c. 965 –
c. 1040), was an
Arab,
[8] Muslim,
scientist,
polymath,
mathematician,
astronomer and
philosopher who made significant contributions to the principles of
optics,
astronomy,
mathematics,
meteorology,
[9] visual perception and the
scientific method.
According to one version of his biography,
[18] al-Haytham, confident about the practical application of his mathematical knowledge, assumed he could regulate the floods of the
Nile. Having been ordered to do so by
Al-Hakim bi-Amr Allah, the sixth ruler of the
Fatimid caliphate, he quickly realised its impossibility. Fearing for his life, he
feigned madness[1][19] and was placed under
house arrest. Once Al-Hakim had died, he was able to prove that he was not mad and for the rest of his life made money copying texts while writing mathematical works and teaching.
[20]Overview
Biography
One account of his career has him called to Egypt by
Al-Hakim bi-Amr Allah, ruler of the
Fatimid Caliphate, to regulate the
flooding of the Nile, a task requiring an early attempt at building a
dam at the present site of the
Aswan Dam.
[24] After deciding the scheme was impractical and fearing the
caliph's anger, he
feigned madness. He was kept under
house arrest from 1011 until al-Hakim's death in 1021.
[25] During this time, he wrote his influential
Book of Optics. After his house arrest ended, he wrote scores of other treatises on
physics,
astronomy and
mathematics. He later traveled to
Islamic Spain. During this period, he had ample time for his scientific pursuits, which included optics, mathematics, physics,
medicine, and practical experiments.
Some biographers have claimed that Alhazen fled to Syria, ventured into Baghdad later in his life, or was in Basra when he pretended to be insane. In any case, he was in Egypt by 1038.
[17] Accounts state that during his time in Cairo he lived near and studied at the
Al-Azhar Mosque.
[26]Among his students were
Sorkhab (
Sohrab), a
Persian from
Iran's
Semnan who was his student for over 3 years, and
Abu al-Wafa Mubashir ibn Fatek, an
Egyptian scientist who learned mathematics from Alhazan.
[27]Legacy
Front page of a Latin edition of Alhazen's
Thesaurus opticus, showing how
Archimedes set on fire the Roman ships before
Syracuse with the help of parabolic mirrors.
Alhazen made significant improvements in optics, physical science, and the scientific method. Alhazen's work on optics is credited with contributing a new emphasis on experiment. Alhazen is considered by British-Iraqi physicist,
Jim Al-Khalili, to be the "first true scientist" based on Alhazen's pioneering work on the
scientific method.
[14]His main work,
Kitab al-Manazir (
Book of Optics) had little direct influence in the
Islamic Middle East, being known mainly through a thirteenth-century commentary by
Kamāl al-Dīn al-Fārisī, the
Tanqīḥ al-Manāẓir
li-dhawī l-abṣār wa l-baṣā'ir.
[28] In
Islamic Spain, it was used by the eleventh-century mathematician,
al-Mu'taman ibn Hūd, and a
Latin translation was produced in the thirteenth century.
[29][30] This translation was read by and greatly influenced a number of Western scientists including:
Roger Bacon,
[31] Robert Grosseteste,
[32] Witelo,
Giambattista della Porta,
[33] Leonardo Da Vinci,
[34] Galileo Galilei,
[35] Christian Huygens,
[36] René Descartes,
[35] and
Johannes Kepler.
[37] His research in
catoptrics (the study of optical systems using mirrors) centred on spherical and
parabolic mirrors and
spherical aberration. He made the observation that the ratio between the
angle of incidence and
refraction does not remain constant, and investigated the
magnifying power of a
lens. His work on catoptrics also contains the problem known as "
Alhazen's problem".
[38] Meanwhile in the Islamic world, Alhazen's work influenced
Averroes' writings on optics,
[39] and his legacy was further advanced through the 'reforming' of his
Optics by Persian scientist
Kamal al-Din al-Farisi (died ca. 1320) in the latter's
Kitab Tanqih al-Manazir (
The Revision of [Ibn al-Haytham's]
Optics).
[40] Alhazen wrote as many as 200 books, although only 55 have survived, and many of those have not yet been translated from Arabic.
[citation needed] Some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on
cosmology were translated into Latin,
Hebrew and other languages. The crater
Alhazen on the Moon is named in his honour,
[41] as was the
asteroid 59239 Alhazen.
[42] 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".
[43] Alhazen, by the name Ibn al-Haytham, is featured on the obverse of the Iraqi 10,000-dinar banknote issued in 2003,
[44] and on 10-dinar notes from 1982. A research facility that
UN weapons inspectors suspected of conducting chemical and biological weapons research in
Saddam Hussein's Iraq was also named after him.
[44][45]Book of Optics
Main article:
Book of OpticsAlhazen's most famous work is his seven-volume treatise on
optics Kitab al-Manazir (
Book of Optics), written from 1011 to 1021.
Optics was
translated into Latin by an unknown scholar at the end of the 12th century or the beginning of the 13th century.
[46] 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 : Optics treasure: Arab Alhazeni seven books, published for the first time: The book of the Twilight of the clouds and ascensions).
[47] Risner is also the author of the name variant "Alhazen"; before Risner he was known in the west as Alhacen, which is the correct transcription of the Arabic name.
[48] This work enjoyed a great reputation during the
Middle Ages. Works by Alhazen on geometric subjects were discovered in the
Bibliothèque nationale in
Paris in 1834 by E. A. Sedillot. Other manuscripts are preserved in the
Bodleian Library at
Oxford and in the library of
Leiden.
Theory of vision
Alhazen on Iraqi 10 Dinars
Two major theories on vision prevailed in
classical antiquity. The first theory, the
emission theory, was supported by such thinkers as
Euclid and
Ptolemy, who believed that sight worked by the eye emitting
rays of
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; Alhazen's achievement was to come up with a theory which 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".
[49] This however 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.
[49] He attempted to resolve this by asserting that only perpendicular rays from the object would be perceived by the eye; for any one point on the eye, only the ray which 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.
[50] He later asserted (in book seven of the
Optics) that other rays would be refracted through the eye and perceived
as if perpendicular.
[51]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?
[52] His later argument that refracted rays would be perceived as if perpendicular does not seem persuasive.
[53] 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 inspired much of the activity in optics which occurred between the 13th and 17th centuries."
[54] 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.
[54]Alhazen showed through experiment that light travels in straight lines, and carried out various experiments with
lenses,
mirrors,
refraction, and
reflection.
[38] He was the first to consider separately the vertical and horizontal components of reflected and refracted light rays, which was an important step in understanding optics geometrically.
[55]The
camera obscura was known to the Chinese, and Aristotle had discussed the principle behind it in his
Problems, however it is Alhazen's work which contains the first clear description
[56] and early analysis
[57] of the device.
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 which were 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 had a description of vertical
horopters which predates
Aguilonius by 600 years and is actually closer to the modern definition than Aguilonius's; and his work on
binocular disparity was repeated by Panum in 1858.
[58] 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, who Alhazen was extremely familiar with. 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.
[59] In general, Alhazen built on and expanded the optics of Ptolemy.
[60][61] In a more detailed account of Ibn al-Haytham's contribution to the study of binocular vision based on Lejeune
[62] and Sabra,
[18] Raynaud
[63] 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.
[64] His understanding of pinhole projection from his experiments appears to have influenced his consideration of image inversion in the eye,
[65] which he sought to avoid.
[66] 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.
[67] 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.
[68]Scientific method
“ | 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: إعتبار) 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 refraction of light).
[40] Bradley Steffens in his book
Ibn Al-Haytham: First Scientist has argued that Alhazen's approach to testing and experimentation made an important contribution to the scientific method. 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.
[69]
G. J. Toomer expressed some skepticism regarding Schramm's view, arguing that caution is needed to avoid reading anachronistically particular passages in Alhazen's very large body of work, and while acknowledging Alhazen's importance in developing experimental techniques, argued that he should not be considered in isolation from other Islamic and ancient thinkers.
[70]Alhazen's problem
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 cue ball at a given point must be aimed in order to carom off the edge of the table 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.
[17][71] 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.
[72] 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,
[73] with a new solution being found in 1997 by the Oxford mathematician
Peter M. Neumann.
[74] Recently,
Mitsubishi Electric Research Laboratories(MERL) researchers Amit Agrawal, Yuichi Taguchi and Srikumar Ramalingam solved the extension of Alhazen's problem to general rotationally symmetric quadric mirrors including hyperbolic, parabolic and elliptical mirrors.
[75] They showed that the mirror reflection point can be computed by solving an eighth degree equation in the most general case. If the camera (eye) is placed on the axis of the mirror, the degree of the equation reduces to six.
[76] Alhazen's problem can also be extended to multiple refractions from a spherical ball. Given a light source and a spherical ball of certain refractive index, the closest point on the spherical ball where the light is refracted to the eye of the observer can be obtained by solving a tenth degree equation.
[76]Other contributions
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 a description of his conclusions is: "it was only the impact of
perpendicular projectiles on surfaces which was forceful enough to enable them to penetrate whereas the
oblique ones were deflected. 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 would break the slate and pass through, whereas an oblique one with equal force and from an equal distance would not."
[77] 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 there could only be one such ray from each point on the surface of the object which could penetrate the eye."
[77]Sudanese psychologist Omar Khaleefa has argued that Alhazen should be considered be the "founder of
experimental psychology", for his pioneering work on the psychology of visual perception and
optical illusions.
[78] Khaleefa has also argued that Alhazen should also be considered the "founder of
psychophysics", a sub-discipline and precursor to modern psychology.
[78] Although Alhazen made many subjective reports regarding vision, there is no evidence that he used quantitative psychophysical techniques and the claim has been rebuffed.
[59]Alhazen offered an explanation of the
Moon illusion, an illusion that played an important role in the scientific tradition of medieval Europe.
[79] 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, a debate that is still unresolved. 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
Roger Bacon,
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.
[80] Although Alhazen is often credited with the perceived distance explanation, he was not the first author to offer it.
Cleomedes (
c. 2nd century) gave this account (in addition to refraction), and he credited it to
Posidonius (
c. 135-50 BC).
[81] Ptolemy may also have offered this explanation in his
Optics, but the text is obscure.
[82] 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.
Other works on physics
Optical treatises
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
luminance, the
rainbow,
eclipses, twilight, and
moonlight. Experiments with mirrors and
magnifying lenses provided the foundation for his theories on
catoptrics.
[83]Celestial physics
Alhazen discussed the
physics of the celestial region in his
Epitome of Astronomy, arguing that Ptolemaic models needed to 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.
[84]In
Mizan al-Hikmah (
Balance of Wisdom), Alhazen discussed the theories of
attraction between
masses.
[38] He also wrote
Maqala fi daw al-qamar (
On the Light of the Moon).
Mechanics
In his work, Alhazen discussed theories on the
motion of a body.
[83] 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.
[85]
Astronomical works
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.
[86]
Doubts Concerning Ptolemy
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.
[89] 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:
[90]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.
[91][92]
Having pointed out the problems, Alhazen appears to have intended to resolve the contradictions he pointed out in Ptolemy in a later work. Alhazen's belief was that there was a "true configuration" of the planets which Ptolemy had failed to grasp; his intention was to complete and repair Ptolemy's system, not to replace it completely.
[89]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...
[18]
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 made no attempt to provide a causal explanation of the motions, but concentrated on providing a complete, geometric description which could be used to explain observed motions, without the contradictions inherent in Ptolemy's model.
[93]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 argued for a distant location, based on the fact that it does not move in relation to the fixed stars.
[94] The fourth group consists of ten works on astronomical theory, including the
Doubts and
Model of the Motions discussed above.
[95]Mathematical works
Geometry
The lunes of Alhazen. The two blue lunes together have the same area as the green right triangle.
In
geometry, Alhazen developed
analytical geometry and the link between
algebra and geometry.
[96] He developed a formula for adding the first 100 natural numbers, using a geometric proof to prove the formula.
[97]Alhazen explored what is now known as the
Euclidean parallel postulate, the fifth
postulate in
Euclid's Elements, using a
proof by contradiction,
[98] and in effect introducing the concept of motion into geometry.
[99] He formulated the
Lambert quadrilateral, which Boris Abramovich Rozenfeld names the "Ibn al-Haytham–Lambert quadrilateral".
[100] His theorems on
quadrilaterals, including the Lambert quadrilateral, were the first theorems on
elliptical geometry and
hyperbolic geometry. These theorems, along with his alternative postulates, such as Playfair's axiom, can be seen as marking the beginning of
non-Euclidean geometry. His work had a considerable influence on its development among the later Persian geometers
Omar Khayyám and
Nasīr al-Dīn al-Tūsī, and the European geometers
Witelo,
Gersonides, and
Alfonso.
[101]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.
[17] 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.
[102]Number theory
His contributions to
number theory include his work on
perfect numbers. In his
Analysis and Synthesis, Alhazen may have been the first to state that every even perfect number is of the form 2
n−1(2
n − 1) where 2
n − 1 is
prime, but he was not able to prove this result successfully (
Euler later proved it in the 18th century).
[17]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.
[17]Other works
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.
Engineering
Philosophy
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.
[85] 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.
[85]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, Alhacen 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."
[104]Theology
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.
[109] He also wrote a treatise entitled
Finding the Direction of Qibla by Calculation in which he discussed finding the
Qibla, where
Salat prayers are directed towards, mathematically.
[110]He wrote in his 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...
[111]
In The Winding Motion, Alhazen further wrote:
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.
[112]
Alhazen described his theology:
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.
[113]
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.
[114] Not all his surviving works have yet been studied, but some of the ones that have are given below.
[95][110]- Book of Optics
- Analysis and Synthesis
- Balance of Wisdom
- Corrections to the Almagest
- Discourse on Place
- Exact Determination of the Pole
- Exact Determination of the Meridian
- Finding the Direction of Qibla by Calculation
- Horizontal Sundials
- Hour Lines
- Doubts Concerning Ptolemy
- Maqala fi'l-Qarastun
- On Completion of the Conics
- On Seeing the Stars
- On Squaring the Circle
- On the Burning Sphere
- On the Configuration of the World
- On the Form of Eclipse
- On the Light of Stars
- On the Light of the Moon
- On the Milky Way
- On the Nature of Shadows
- On the Rainbow and Halo
- Opuscula
- Resolution of Doubts Concerning the Almagest
- Resolution of Doubts Concerning the Winding Motion
- The Correction of the Operations in Astronomy
- The Different Heights of the Planets
- The Direction of Mecca
- The Model of the Motions of Each of the Seven Planets
- The Model of the Universe
- The Motion of the Moon
- The Ratios of Hourly Arcs to their Heights
- The Winding Motion
- Treatise on Light
- Treatise on Place
- Treatise on the Influence of Melodies on the Souls of Animals[115]
Commemorations
Ibn Al-Haytham's work has been commemorated by the naming of the
Alhazen crater on the
moon after him. The asteroid
59239 Alhazen was also named in his honour.
UNESCO has declared 2015 the
International Year of Light and will be celebrating Ibn Al-Haytham's achievements in optics, mathematics and astronomy, and his importance in laying the foundations of the present day
scientific experimental method, through an international campaign titled
1001 Inventions and the World of Ibn Al-Haytham featuring a series of interactive exhibits, workshops and live shows about his work. The campaign will be produced by the
1001 Inventions organisation.
[116] See also