Abu Ali Hasan Ibn
alHaitham. Also known as ‘Alhazen’
Said to have been
born in Basra, Persia in 965, and to have died in Cairo in 1040
A THOUSAND YEARS
AGO THIS OUTSTANDING SCIENTIST:
 Discovered the principle of inertia
 600 years before Galileo
 Developed analytical geometry  600
years before Descartes
 Discovered the laws of the refraction
of light – centuries before Snell and Descartes
 Found that white light is a mix of
different colours  anticipating Newton and others
 Was the first to describe accurately
the various parts of the eye, and thereby:
 Became known as the father of modern optics
 Gave a scientific explanation of
the process of vision
 Studied magnifying lenses, parabolic
and spherical mirrors.
 Made the earliest use of the Camera
Obscura
 Studied atmospheric refraction,
whereby he:
 Gave the correct explanation for
variations of apparent sizes of the Sun and the Moon as they
approach the horizon.
 Discovered that twilight only
ceases or begins when the sun is 19° below the horizon.
 Deduced the height of the atmosphere:
55 miles, which is basically correct
 Discussed theories of attraction between
masses
 Apparently became aware of the magnitude
of acceleration due to gravity
 Wrote a book about evolution – eight
centuries before Darwin
After his birth in or near Basrah (presentday
Iraq), he was educated in Baah and Baghdad. As a youth, he thought about
the conflicting religious views of the various faiths and came to the
conclusion that none of them represented the truth. He decided to devote
himself entirely to a study of science which he found most clearly described
in the writings of Aristotle. He spent his life in Spain – where there
were many Arabic people at the time – and in Egypt, researching and writing.
Some say Alhazen wrote 92 books, others put the number as high as 200.
Some 55 have survived.
The main topics on which he wrote were optics
including a theory of light and a theory of vision – as well as astronomy
and mathematics, including geometry and number theory. He conducted research
in optics, mathematics, physics, medicine as well as the development of
scientific understanding.
In AlHaitham's writings, one finds
a clear explanation of the scientific methods as worked out and applied
by the Muslims. He made a major contribution to scientific methodology,
as distinct from guesswork. His was a crucial influence in the force placing
of scientific study on a solid foundation comprising a systematic relationship
between observation, hypothesis and verification.
He wrote an autobiography in 1027, but it
concentrates on his intellectual development. There are varying accounts
of his biographical details.
According to one story, he pretended
to be mad for several years. It is said
that he had proposed a plan to control the flooding of the Nile.
He was summoned to Egypt by a Caliph – alHakim
 and appointed head engineer. But he had not anticipated the might of
the Nile. He gave up his plans to regulate the flow of water with massive
constructions. Now, he had also not anticipated the might of the Caliph,
a man who was keen on astronomy and other science, but was also rather
fond of slaughter. To avoid the Caliph’s wrath, Alhazen pretended to be
mad – for years remaining confined to his house until the Caliph died
in 1021.
It is told that one advantage of this was
that throughout that time he was able to continue with his important scientific
work, undisturbed. After alHakim's death, so the story goes, he was able
to show that he had only pretended to be mad.
Apparently he lived out the next 20 years
near the Azhar Mosque in Cairo writing mathematics texts, and teaching,
on occasion even working as a scribe for extra money.
A seven volume work on optics, Kitab alManazir,
is considered by many to be ibn alHaitham's most important work contribution.
It was translated into Latin as Opticae Thesaurus Alhazeni in 1270.
His aim was "criticising premises and exercising caution in drawing conclusions"
while he wished aimed "to employ justice, not follow prejudice, and to
take care in all that we judge and criticise that we seek the truth and
not be swayed by opinions". He makes it clear that his investigations
will be based on experimental evidence rather than on abstract theory.
In his time he had conducted experiments
on the propagation of light and colours, optical illusions and reflections,
detailing many experiments with spherical segments (glass vessels filled
with water). He came very close to discovering the theory of magnifying
lenses which was developed in Italy three centuries later. He dealt at
length with the theory of various physical phenomena such as sunsets,
rainbows, shadows, and eclipses. Roger Bacon (thirteenth century), Pole
Witelo (Vitellio) and all Medieval Western writers on Optics base their
optical work primarily on AlHaitham's 'Opticae Thesaurus.'
His work also influenced Leonardo da Vinci
and Johann Kepler. In Physics, he studied the mechanics of motion
of a body and was the first to propose that a body moves perpetually at
constant velocity and in a straight line unless an external force stops
it or changes its direction of motion. This is strikingly similar to the
first law of motion. It is also a startlingly counterintuitive insight:
we never see this happen on earth.
The ideas contained in his book on evolution
are worth reading and useful even today. He wrote commentaries on Aristotle,
Galen, Euclid and Ptolemy. Indeed, he contradicted Ptolemy's and Euclid's
theory of vision that objects are seen by rays of light emanating from
the eyes; according to him the rays originate in the object
of vision and not in the eye.
ALHAZEN’S BILLIARD PROBLEM
In 1997, Alhazen’s name was briefly
in the news. He had worked extensively on a problem formulated by Ptolemy
in A.D. 150. Alhazen wrestled so hard with it that it became known as
‘Alhazen’s Problem’, or even ‘Alhazen’s billiard problem, because the
questions it deals with can apply to billiard balls as well as spherical
mirrors. It was not solved until more than a thousand years after Alhazen’s
death, by an Oxford don in 1997.
It was known as ‘the last great problem
of classical geometry’, and for Alhazen it could be posed in this way.
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.
Adapted to become "Alhazen's Billiards Problem",
it may also be formulated in this way: How does one find the point on
the boundary of a circular billiards table at which the
cue ball must be aimed, if it is to hit the cushion and then the black
ball? Dr. Peter Neumann, a fellow of Queen’s College, Oxford cracked this
riddle, which had baffled mathematicians for a millennium. The great difficulty
in the problem lay in the fact that mathematicians envisage spherical
mirrors or billiard balls as infinitely small points. Classical rulerandcompass
methods developed by Euclid, the Greek mathematician, were not helpful
in this case. They did not provide the means to derive a cube root. Neumann
translated the billiards table geometry into coordinates on two axes.
These may be called X and Y. It was an insight Neumann took from the work
of Descartes in the 17th Century.
Then the problem could be tackled using
a theory formulated in 1830 by an 18yearold called Evariste Galois (Incidentally,
he died in a duel two years later). Galois's theory in its modern version
is the theory of equations as studied by thirdyear mathematics students.
So, once he had arrived at that stage, Dr. Neumann’s work was swiftly
done. At the time, Dr. Neumann explained that his proof would have no
practical use at all – neither in optics, no billiards, nor – as he put
it – " for designing light bulbs, let alone finding the number of
people to change them."
Beer and Medler in their famous
work Der Mond (1837) mention one of the surface features of the moon named
after Alhazen. It is the name of a ringshaped plain to the west of the
hypothetical Mare Crisium in Section No.12.
