# Mr. Elhajj's Blog

### Geometry worksheet a

Before you can add or subtract fractions, the fractions need ...

### Tips for working wit

There are 4 combination methods (SSS-SAS-ASA-AAS) that allow us to ...

### Grade 9 - final exam

Lesson 5-2: Zero and negative exponents (updated) Lesson 5-3: Scientific notation and ...

### How old?

Bilal, Ahmad, Salem and Ali are friends. They are all different ages 5, ...

Years ago, a man named Pythagoras found an amazing fact ...

## Ibn al-Haytham الحسن بن الحسن بن الهيثم

Abu Ali al-Hasan ibn al-Hasan ibn al-Haytham (965 in Basra – c. 1040 in Cairo) was a prominent scientist and polymath from the ‘Golden Age’ of Muslim civilization. He is commonly referred to as Ibn al-Haytham, and sometimes as al-Basri, after his birthplace in the city of Basra. He is also known by his Latinized name of Alhzen or Alhacen.

Ibn al-Haytham made significant contributions to the principles of optics, as well as to physics, astronomy, mathematics, ophthalmology, philosophy, visual perception, and to the scientific method. He was also nicknamed Ptolemaeus Secundus (“Ptolemy the Second”) or simply “The Physicist” in medieval Europe. Ibn al-Haytham wrote insightful commentaries on works by Aristotle, Ptolemy, and the Greek mathematician Euclid.

Born circa 965, in Basra, Iraq, he lived mainly in Cairo, Egypt, dying there at age 76. Over-confident about practical application of his mathematical knowledge, he assumed that he could regulate the floods of the Nile.

After being ordered by al-Hakim bi-Amr Allah, the sixth ruler of the Fatimid caliphate, to carry out this operation, he quickly perceived the difficulty of what he was attempting to do, and retired from engineering. Fearing for his life, he feigned madness and was placed under house arrest, during and after which he devoted himself to his scientific work until his death.

A crater on the moon is named in his honor, as is the asteroid 59239 Alhazen.

Experimental Scientific Method

Ibn al-Haytham used experimental evidence to check his theories, which was unusual for his time because physics before him was more like philosophy, without experiment. He was the first to introduce experimental evidence as a requirement for accepting a theory, and his Book of Optics was actually a critique of Ptolemy’s book Almagest. A thousand years on, this optics book is still quoted by professors training research students to be factual and not be swayed by opinions or prejudice. Some science historians believe that Snell’s Law, in optics, actually resides in the work of Ibn Sahl and Ibn al-Haytham.

Neuroscientist Rosanna Gorini notes that “according to the majority of the historians al-Haytham was the pioneer of the modern scientific method.” From this point of view, Ibn Al-Haytham developed rigorous experimental methods of controlled scientific testing to verify theoretical hypotheses and substantiate inductive conjectures. Other historians of science place his experiments in the tradition of Ptolemy and see in such interpretations a “tendency to ‘modernize’ Alhazen … [which] serves to wrench him slightly out of proper historical focus.”

An aspect associated with Alhazen’s optical research is related to systemic and methodological reliance on experimentation (i’tibar) 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) in terms of devising the rudiments of what may be designated as a hypothetico-deductive procedure in scientific research. 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). His legacy was further advanced through the ‘reforming’ of his Optics by Kamal al-Din al-Farisi (d. ca. 1320) in the latter’s Kitab Tanqih al-Manazir (The Revision of [Ibn al-Haytham's] Optics).

The concept of Occam’s razor is also present in the Book of Optics. For example, after demonstrating that light is generated by luminous objects and emitted or reflected into the eyes, he states that therefore “the extramission of [visual] rays is superfluous and useless.”

The Camera Obscura

Like many eminent philosophers and mathematicians, Ibn Al-Haytham was a keen observer. While in a room one day he noticed light coming through a small hole made in the window shutters. It fell onto the wall opposite and it was the half-moon shape of the sun’s image during eclipses. He said: ‘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 place opposite to the hole it takes on the form of a moon-sickle.’

From his experiments, he explained that light travelled in a straight line and when the rays were reflected off a bright subject they passed through the small hole and did not scatter but crossed and reformed as an upside-down image on a flat white surface parallel to the hole. He then established that the smaller the hole, the clearer the picture.

His experimental conclusions were that when the sunlight reached and penetrated the hole, it made a conic shape at the meeting point with the pinhole, and later formed another conic shape in reverse to the first one on the opposite wall in the dark room.

‘Light issues in all directions opposite any body that is illuminated with any light [and of course, also opposite any self-luminous body]. Therefore when the eye is opposite a visible object and the object is illuminated with light of any sort, light comes to the surface of the eye from the light of the visible object.’ (10th-century Ibn al-Haytham from his ‘Book of Optics)

In later stages, these discoveries led to the invention of the camera obscura, and Ibn Al-Haytham built the first camera, a camera obscura or pinhole camera, in history. He went on to explain that we see objects upright and not upside-down, as the camera does, because of the connection of he optic nerve with the brain, which analyses and defines the image.

During his practical experiments, Ibn Al-Haytham often used the term al-Bayt al-Muthim, which was translated into Latin as camera obscura, or dark, private or closed room or enclosed space. Camera is still used today, as is qamara in Arabic which still means a private or dark room.

Many of Ibn Al-Haytham’s works, especially his huge Book of Optics, were translated into Latin by the medieval scholar Gerard of Cremona. This has a profound impact on the 13th-century big thinkers like Roger Bacon and Witelo, and even on the 15th-century works of Leonardo da Vinci.

Today, the camera has gone from the humble beginnings of Ibn-Al-Haytham’s dark front room, the qamara, to become a sophisticated digital process, while the study of optics has blossomed into a whole science covering lasers, optical sectioning of the human retina and researching red bioluminescence in jelly fish.

References

• Ibn al-Haitham and vision
• Omar, S.B.(1977), ‘Ibn al-Haytham’s Optics’: Bibliotheca Islamica; Chicago.
• Lindberg, D.C.(1983), ‘Studies in the History of medieval optics’, Varorium, London.
• Lindberg, D.C. (1972), ‘Introduction: Optica Thesaurus: Alhazen and Witelo;
• editor: H. Woolf. Johnson Reprint Corporation, New York, London, p.15.
• Ibn al-Haitham camera obscura Using holes in Window shutters
• Durant, W.(1950), ‘The Age of Faith’, Simon and Shuster, New York; p. 288.
• Baron Carra de Vaux (1921), ‘Les Penseurs de l’Islam’, vol 2, Librairie Paul Geuthner, p.249.