**IBN-AL-HAYTHAM**

**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] polymath and philosopher who is widely considered as one of the most influential scientists of all time. Referred to as the father of experimental physics and modern optics and scientific methodology, he made significant contributions to the principles of optics, astronomy, mathematics, meteorology, visual perception and the scientific method.**

INTRODUCTION

Alhazen is regarded
to be the first theoretical physicist and he has been the earliest to discover
that a hypothesis has the necessity to be experimented through confirmable
procedures or mathematical evidence, hence developing the scientific method 200
years before it was approved by Renaissance scientists.In medieval Europe, he
was honored as Ptolemaeus Secundus ("Ptolemy the Second") or simply
called "The Physicist". He is also sometimes called al-Basri (Arabic:
البصري)
after Basra, his birthplace. He spent most of his life close to the court of
the Fatimid Caliphate in Cairo and earned his living authoring various
treatises and tutoring members of the nobilities.

Biography

Ibn al-Haytham
(Alhazen) was born c. 965 in Basra, which was then part of the Buyid emirate, to
an Arab family.

Alhazen arrived in
Cairo under the reign of Fatimid Caliph al-Hakim, a patron of the sciences who
was particularly interested in astronomy. He proposed to the Caliph a hydraulic
project to improve regulation of the flooding of the Nile, a task requiring an
early attempt at building a dam at the present site of the Aswan Dam, but later
his field work convinced him of the technical impracticality of this scheme.
Alhazen continued to live in Cairo, in the neighborhood of the famous University
of al-Azhar, until his death in 1040. Legend has it that after deciding the
scheme was impractical and fearing the caliph's anger, Alhazen feigned madness
and was kept under house arrest from 1011 until al-Hakim's death in 1021.
During this time, he wrote his influential Book of Optics and continued to
write further treatises on
astronomy, geometry, number theory, optics and natural philosophy.

Among his students
were Sorkhab (Sohrab), a Persian from Semnan who was his student for over 3
years, and Abu al-Wafa Mubashir ibn Fatek, an Egyptian prince who learned
mathematics from Alhazen.

Alhazen's most
famous work is his seven-volume treatise on optics Kitab al-Manazir (Book of
Optics), written from 1011 to 1021.

Theory of Ibn Haytham |

Optics was
translated into Latin by an unknown scholar at the end of the 12th century or
the beginning of the 13th century. It was printed by Friedrich Risner in 1572,
with the title Optics treasure: Arab Alhazeni seven books, published for the
first time: The book of the Twilight of the clouds and ascensions). 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. 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. 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 B.ruges

THEORY OF VISION

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. 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". 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.

Refraction

Smith 2010 has noted
that Alhazen's treatment of refraction describes an experimental setup without
publication of data. Ptolemy published his experimental results for refraction,
in contrast. One generation before Alhazen, Ibn Sahl discovered his statement
of the lengths of the hypotenuse for each incident and refracted right
triangle, respectively. This is equivalent to Descartes' formulation for
refraction. Alhazen's convention for describing the incident and refracted
angles is still in use. His failure to publish his data is an open question.

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, andmoonlight. Experiments with mirrors and magnifying lenses
provided the foundation for his theories on catoptrics.

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.

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. 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.

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.

**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.

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.

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...[58]

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.

**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. The fourth group consists of ten works on astronomical theory,
including the Doubts and Model of the Motions discussed above.

Mathematical works

In mathematics,
Alhazen built on the mathematical works of Euclid and Thabit ibn Qurra and
worked on "the beginnings of the link between algebra and geometry.”

He developed a
formula for adding the first 100 natural numbers, using a geometric proof to
prove the formula.

__Geometry__
The two blue lunes
together have the same area as the green right triangle.

Alhazen explored
what is now known as the Euclidean parallel postulate, the fifth postulate in
Euclid's Elements, using a proof by contradiction, and in effect introducing
the concept of motion into geometry. He formulated the Lambert quadrilateral,
which Boris Abramovich Rozenfeld names the "Ibn al-Haytham–Lambert
quadrilateral". 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.

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.

**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 2n−1(2n − 1) where 2n − 1 is prime, but he was not able
to prove this result successfully (Euler later proved it in the 18th century).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.

LIST OF WORK

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.

1. Book of Optics (كتاب المناظر )

2. Analysis and Synthesis (مقالة في التحليل
والتركيب)

3. Balance of Wisdom (ميزان الحكمة. )

4. Corrections to the Almagest (تصويبات على المجسطي. )

5. Discourse on Place (مقالة في المكان. )

6. Exact Determination of the Pole (التحديد الدقيق
للقطب)

7. Exact Determination of the Meridian (رسالة في الشفق)

8. Finding the Direction of Qibla by
Calculation (كيفية حساب اتجاه القبلة)

9. Horizontal Sundials (المزولة الأفقية)

10. Hour Lines

11. Doubts Concerning Ptolemy (شكوك على بطليموس.)

12. Maqala fi'l-Qarastun (مقالة في قرسطون)

13. On Completion of the Conics (إكمال المخاريط )

14. On Seeing the Stars (رؤية الكواكب )

15. On Squaring the Circle (مقالة فی تربیع
الدائرة )

16. On the Burning Sphere ( المرايا المحرقة
بالدوائر)

17. On the Configuration of the World (تكوين العالم.-)

18. On the Form of Eclipse (مقالة فی صورة الکسوف-)

19. On the Light of Stars (مقالة في ضوء النجوم - )

20. On the Light of the Moon (مقالة في ضوء القمر)

21. On the Milky Way (مقالة في درب التبانة.)

22. On the Nature of Shadows (كيفيات الإظلال)

23. On the Rainbow and Halo (مقالة في قوس قزح)

24. Opuscula

25. Resolution of Doubts Concerning the Almagest

26. Resolution of Doubts Concerning the Winding
Motion

27. The Correction of the Operations in Astronomy

28. The Different Heights of the Planets

29. The Direction of Mecca (اتجاه القبلة)

30. The Model of the Motions of Each of the Seven
Planets (نماذج حركات الكواكب السبعة)

31. The Model of the Universe (نموذج الكون)

32. The Motion of the Moon (حركة القمر)

33. The Ratios of Hourly Arcs to their Heights

34. The Winding Motion (الحركة المتعرجة)

35. Treatise on Light (رسالة في الضوء)

36. Treatise on Place (رسالة في المكان)

37. Treatise on the Influence of Melodies on the
Souls of Animals (تأثير اللحون الموسيقية في النفوس الحيوانية )

38. (كتاب في تحليل المسائل
الهندسية
)

39. (الجامع في أصول
الحساب)

40. قول فی مساحة الکرة.

41. القول المعروف بالغریب
فی حساب المعاملات)

42. خواص المثلث من
جهة العمود.)

43. رسالة فی مساحة
المسجم المکافی

44. شرح أصول إقليدس

45. المرايا المحرقة
بالقطوع

**Lost works**

1. A Book in which I have Summarized the
Science of Optics from the Two Books of Euclid and Ptolemy, to which I have
added the Notions of the First Discourse which is Missing from Ptolemy's Book.

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.

In 2014, the
"Hiding in the Light" episode of Cosmos: A Spacetime Odyssey,
presented by Neil deGrasse Tyson, focused on the accomplishments of Ibn
al-Haytham. He was voiced by Alfred Molina in the episode.

UNESCO has declared
2015 the International Year of Light. Amongst others, this will be celebrating
Ibn Al-Haytham's achievements in optics, mathematics and astronomy. An
international campaign, created by the1001 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 will partner 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, which
is notable for being the final movie role for actor Omar Sharif before his
death in July 2015. 1001 Inventions is a founding partner of the International
Year of Light.

UNESCO's website on
Ibn al-Haytham copies a part from Jim Al-Khalili's popular history Pathfinders:
The Golden Age of Arabic Science.

**Hameem Arif**

**XII-A**