THE FOLLOWING IS ADOPTED FROM THE TEXT: IBN AL HAYTHAM OPTICS VOL. I (Original in Arabic) TRANSLATOR A. I. SABRA

Chapter 1

Ibn al Haytham while writing about the Nature of Vision in his Book I writes, "...... perplexity prevails, certainty is hard to come by, and there is no assurance of attaining the object of inquiry. How strong, in addition to all this, is the excuse for the truth to be confused, and how manifest is the proof that certainty is difficult to achieve! For the truths are obscure, the ends hidden, the doubts manifold, the minds turbid, the reasonings various; the premisses are gleaned from the senses, and the senses (which are our tools) are not immune from error. The path of investigation is therefore is obliterated and the inquirer, however diligent, is not infallible. Consequently, inquiry concerns subtle matters, perplexity grows, views diverge, opinions vary, conclusions differ and certainty becomes difficult to obtain."

In order to examine the perception of visible objects by sight, one should aim at one of these objects, put one end of this ruler close to the lower eyelid of one eye and the other end close to the surface of the object, cover the other eye, and while in this condition, look through the opening in the tube: he will see that part of the object which is opposite the opening of the tube at the end of the ruler. If he covers the opening of the tube with an opaque body; that part of the object will be screened off which he has seen through the opening.

CHAPTER 3: PROPERTIES OF LIGHT AND MANNER OF ITS RADIATION

[2] We also find that radiation of all lights takes place only in straight lines and that no light radiates from a luminous object except in straight lines- provided the air or transparent body between the luminous object and the body on which the light appears is continuous and of similar transparency.

[14] "....... the light of the sun radiates from every part of the body of the sun to every side directly opposite that part.

[19] It is therefore evident from all that we said that from every part of every self luminous body, light radiates in every straight line extending from that part.

[21] Alhazen named those lights which start out from self luminous bodies to be Primary lights.

[23] Before sunrise and just after sunset, the atmosphere is still very well illuminated, the ground is less illuminated by a light called manifest light.

[34] ......Some light proceeds from the atmosphere illuminated by the morning light to opposite places; that it so proceeds in straight lines; and that the daylight radiating upon the earth before sunrise and after sunset is but a light radiating upon it from the atmosphere illuminated by sun light opposite the earth's surface. If the experimenter also examines in the same manner the luminous atmosphere during the rest of the day, hev will find that the light radiates from it in straight lines.

[35] But, if some light emanates from the illuminated air to the opposite places, then from every part of the air that is illuminated by any light whatever, some light emanates in all directions; and that light emanationg from the air will be weaker than that existing in the air

[40] "........the whole atmosphere is illuminated by sunlight at all times; no part of it is dark or concealed from the sun except the conic umbra which is the earth's shadow. However, the light emanating from the illuminated atmosphere is weak, and the further it extends the weaker it becomes, this being the characreristic property of light. Thus some light always radiates in all directions from the sunlit atmosphere and penetrates into the atmosphere that is shaded by the earth's shadow. But this light weakens as it recedes from the sunlit atmosphere from which it proceeds." Note thoery of scattering of light by atmospheric air.

[44] "..........air is a very transparent body. It is not only extremely

transparent but has a little density.

INSTRUMENTS

Chapter 1: rulers and tubes,

(page 7) Take a very sound and straight ruler and draw along the middle of its surface a straight line parallel to its sides. Take a hollow cylindrical tube, very straight in length, perfectly round and ending in parallel circles; let its thickness be the same throughout and let it be fairly wide but not wider than the eye socket (note his example!); draw on its outer surface a straight line extending from a point on the circumference of one base to the opposite point on the other side; and let this tube be a little shorter in length than the ruler. Divide the line along the middle of the ruler into three parts, and let the intermediate part be of the same length as the line on the surface of the tube; the remaining parts on either side may be of any length. Attach the tube to the surface of the ruler, placing the line on its exterior upon the intermediate segment of the line in the middle of the ruler's surface; and make sure that the end of the tube coincide with the points marking off the middle segment. The tube should be so closely and firmly fastened that it cannot be loosened or displaced.

Chapter 2: Sun, moon, solar and lunar eclipses, sun rise, sun set, expanding and shrinking moon from crescent to full moon and from full moon to darkness,

Ordinary fire, lamp with a broad, bright wick (page 18), narrow slits, apertures, circular holes, cylindrical tube,

........fairly wide copper sheet with fairly large cicular hole, slide through this hole a well straightened cylindrical tube of regular circularity and convenient length; let the width of the hole and that of the tube be of the same magnitude and let the tube's aperture not exceed the thickness of a needle; insert the tube into the hole so that its end may be level with the sheet's surface; attach this sheet to some object at a point above the ground, and let it stand vertically on its edge.

Chapter 3:

[25] ... a dark chamber with a door facing an adjacent wall on which sunlight may shine. The chamber hould not be exposed to the sky. Thus the light should reach the facing wall through an opening or door at the top of the wall of the dark chamber, assuming this wall to be higher than the chamber's roof. The space between the two walls, namely the wall with the chamber door and the wall facing it should be roofed above the opening or shaded by an opaque body. And let the back of the chamber face east. The experimenter should observe the place when morning light shines on that wall through the opening opposite, which should be fairly wide. He will find the chamber illuminated by that light, and the light in the chamber weaker than the light on that wall. .........

[26] Suppose now that inside the chamber there is another dark chamber whose door is exposed to the wall facing the first door. .......

[29] .......radiation of lights from accidental lights in straight lines (at dawn and dusk)

[48] "............ employ a pure white wall which can be exposed to daylight and to sunlight and moonlight; and opposite, near and parallel to this wall let another wall stand. Behind each of the walls let there be a chamber into which light may enter only through a door. Let the experimenter then take a block of wood not less than one cubit in length, breadth and depth. Let him smooth its surfaces, making them as plane and parallel as possible, and let its edges be straight and parallel. He should then draw, in the middle of two facing surfaces, two straight and parallel lines, each parallel to two edges of the surface in which it is drawn. Then, from the ends of each of these lines,, let him cut off two equal segments, neither of them more than breadth of two digits. Two points are thus marked on each of the two lines.

[52] "............... turn it in a lathe....."

Measurement:

One cubit = 15.3 inches = 39 cm

IBN AL HAYTHAM OPTICS VOL. II

TRANSLATOR A. I. SABRA

INTRODUCTION: ..........

Ibn al-Haytham (IH) Book III 18 (On spherical Burning Mirrors), III 19 (On parabolic Burning Mirrors) and III 77 (On the burning spheres) proves correctly the following five propositions concerning mirrors that form part of a sphere on whose concave surface the rays from the sunfall along lines parallel to the mirror axis:

1. All such incident rays will be reflected to points on the axis.

2. If P is a point to which rays are reflected from the circumference of a circle on the mirror surface, then no other reflected rays will pass through P.

3. The distance of P from the mirror's center is greater than a quarter of the mirror's diameter.

.............

The above mentioned propositions. whatever may be their sources, Sabra writes, make up the most complete and most coherent account of burning mirrors that we have from any writer in antiquityor in the middle ages up to IH time. Sabra continues that IH has claimed to his credit the first satisfactory proof of the focal property of the parabola. Sabra says IH claim is supported by historical evidence. In III 18 and 19, IH goes beyond exposition of the theories of spherical and parabolic mirrors to explain in detail how to costruct mirrors of these types from steel. These two treatises thus belong to the history of technological ideas as well as to the history of optics.

In III 77, IH shows that a sphere of glass, crystal or the like, will refract parallel rays from the sun at the circumference of a circle on the sphere to a single point outside the sphere on the line that joins the centers of the sun and the sphere. In showing this, and in his remarkable investigation of the phenomenon now called "Spherical Aberration", he relies on the rules of refraction set forth in Book VII of his Optics, to which he refers. He further investigates the behavior of rays refracted into the glass sphere as the points of incidence gradually recede from the pole of the sphere facing the sun. Assuming the values for the angles of incidence and refraction which he obtains from the refraction tables in Book V of Ptolemy's Optics, IH shows that the points of second refraction (where the rays emerge from the sphere) will similarly recede from the opposite pole of the sphere, reaching a maximum distance from it when the angles of the first incidence reach 50 degrees, and begin to move in the opposite direction.

IH's own treatise " On the rainbow and the halo" (no. III 8) which exists, explanation of rainbow is significantly different from Aristotle explanation. For example IH places the position of the sun much further from the eye than the cloud, a fact known to Aristotle but ignored in his representation. Also, IH places the observer at the center of the spherical cloud and he strictly adheres to the equality of angles in reflection. IH seems to consider the rainbow problem to be a special case of reflection from concave spherical mirrors.

In his introduction on Alhazen, Omar says

, "An autobiography cited by Ibn Abi Usaybi'a says he was frustrated intensely with the conflicts he found in the then religious sciences. This frustration created in him a state of doubt which forced him to seek the truth. I saw, he wrote, that I can reach the truth only through concepts whose matters are sensible things, whose form is rational."

[Did Alhazen leave Baghdad for a better patronage or did sufism (conceptual religious intuition as opposed to scientific practice/tradition) drove him out of Baghdad?]

Lovell writes in the preface,

........What is light? ........Light is that which permits vision,..........such an answer provides ....no understanding of the nature of light. It says no more than "light is light."

Light emits from hot bodies, lightning discharges, some insects and the stars.

...... The poet William Wordsworth, wrote, My heart leaps up when i behold / A rainbow in the sky.

...deeper appreciation of rainbows, ......fascinating phenomena as halos, mirages, and phantasmagoria. ......Blue of the sky, the red of the setting sun, the whiteness of the clouds, blue shadows on the snow covered fields, and the colors of flowers and birds, the colorful scenes and species under the sea.

Technology......telescope, microscope, photography, lasers, optical fibers and light emitting diodes.

History of man's investigations of the nature of light encompasses a large cast of characters who interact with all facets of the history of mankind and whose searches included drama, adventure, humor, political and religious entanglements, pestilence and the beauty. Some of these men displayed enormous conceit, others were humble. Some were born to wealth and others had to overcome poverty.

Optics in antiquity: page 1

....stick mounted vertically on the ground to find the time of the day, the season, all from the movement of the sun and the shadow cast by sunlight.

........pyramids of Egypt and massive sarsen stone circle at Stonehenge (4000 B.C.) in Wiltshire, England; once thought of religious edifices or tombs of vainglorious pharohs, now seen to reflect early man's awareness of terrestrial motion in the solar system.

425 B.C. recorded account of the use of lenses by Aristophanes in his "The Clouds".

Egyptians and the Mesopotamians achieved sporadic gains fro 3500 to 500 B.C. The Greeks learnt from them in about 600 B.C., "...but within a millenneum their remarkable advances were silenced. However impact they made influences much of science today." [ This is where my criticism comes. The fact the knowledge was cultivated by human civilizations all over the world, from the plains of Central America to the plains of the ancient China. Yes, at anyone time, it was either domintaed by the Arabs or the Chinese or the American Indians in their endeavour to seek knowledge. To say that only the ancient Greeks influenced much of science today does not hold ground. They are getting credit which is more than their share of knowledge. It is the tendency of western scholars starting from the period of renaissance in Europe to undermine the contribution of the scholars of the Islamic civilization just before them and to blow up the contributions made by the Greeks. By the same arguments, to me the splendor of Olympic games just did not start at Greece. I think it must have been at least as much spectacular in the earlier civilizations at Mesopotamia or in the Indus Valley civilization in India.]

Plato 427 to 347 B.C.

Aristotle 384 to 322 B.C.

Alexander the great 356 to 323 B.C.

Euclid 300B.C. "Elements of Geometry", OPTICS andd CATOPTRICS

Seneca 4 B.C. to 65 A.D. observed white light dispersed by a prism.

Ptolemy 150 A.D. Almagest and Geography, OPTICS

Attila the king of the Huns took power in 433 A.D., responsible for destruction of 70 prospering cities. Rome ......... suffered from internal cancer that rotted its economic, social, and moral structure. European scientific pursuits stagnated into dark age. Fortunately, knowledge amassed was preserved for the renaissance.

page 5

The greatest authority on Optics in the middle ages -----

Ibn al-Haytham

Patriotic chauvinism and religious prejudice often attributed the scientific achievements to one's own country or their own allies. The impression one gets while opening a text in science (whether in physics, biology or chemistry or math), that knowledge started with ancient Greek and passed onto the west and USA by way of renaissance movement in Europe. [I must admit that such a notion is false and to preserve such a notion is to live in fool's paradise. Why is not there a mention of Mhammad (pbuh) and his epoch making history?]

About 540 A.D., in the city of Mecca in Modern Saudi Arabia, a humble boy was born, who came to be known as Muhammad (meaning praise worthy or highly praised). He was well known in his city for truthfulness and honesty (the qualities which utterly lacks in among US politics and the politicians). He revived and restated the Abrahamic faith of one God and everything else to be God's creation. His followers revitalized the pursuit of knowledge in the Islamic civilization and became heir to the hellenistic knowledge in all fields. When the Muslim scholars dominated knowledge in the middle ages, much of today's Europe lived in dark ages.

The difficulty of depicting the advances made by the Muslim scholars is not only attributable to the prejudices of the Chistian Europe, but also due to loss of original manuscripts which are lost due to bloody wars and poverty which followed. [I must say that while the Arabs did an excellent job of translating Greek knowledge, the Europeans never showed any enthusiasm to give credit to the scholars of Islamic world.]

There is sufficient evidence exists to ascertain the considerable progress and development which took place during Islamic civilization.

Abu Yusuf Yaqub Ibn Ishaq (813 to 873 A.D.) known as Al Kindi was born in Kufa. Lived in Basra and Baghdad where his efforts were directed towards learning broad aspects of physics. He wrote De Aspectibus in which he dealt explicitly with optical problems. He asserted that the vision had to take place by means of visual rays which promote a physical reaction upon the eye. ................

Abu Ali Muhammad Ibn al-Hasan Ibn al-Haitham was born in 965 A.D. in Basra, generally known in the west as Alhazen. He belonged to a middle class family who provided him with education. But his parents were not rich enough to provide with the leisure to seek higher learning. He secured a job in the government office, suggesting he must have done well in his studies and his family exerted some local influence. The government job provided him with a means of living but no intellectual stimulation. That was acquired in spare time by studying astronomy, mathematics, physics, and medicine. His confidence in learning natural philosophy grew and he desired a position in the court of Fatimid ruler Al-Hakim, who was a patron of learning and gathered many scholars in his court. He suggested building a dam to control the water of the Nile. This attracted the king's notice and he was invited to Cairo for the project when he was about 40. He soon realized the difficulty of constructing the dam over the river Nile. This was beyond the engineering capabilities of the time. The king grew impatient with him and he feigned madness to avoid harsh punishment. The Caliph Al Hakim threw him into the prison and confiscated all his books and instruments. Al Hakim died in 1021 A.D. and Ibn al-Haytham was released. He returned to his scholarly works, living near al-Azhar university. He earned his living by copying Euclid's Elements of Geometry and Ptolemy's Almagest. At this time, he plunged into the passion of his life - the scietific pursuit. When he was in his mid fifties, he began to make valuable contributions to geometrical and physiological optics which continued for over two decades. The results of his optical works are recorded in "Kitab ul Manazir" (Treatise on Optics). Aristotle's ideas were firmly rooted at the time and he called him "the master". But, he was not afraid of criticizing the blind belief in Aristotle. He insisted on experimentation to study and analyze a physical phenomenon and then to settle on the final judgement. This was his methods and scientific traditions. He was the first to establish in clear terms that the rays of light moves in straight lines from the object, and reaches the eye for perception. He divided the transparent objects into two classes, celestial and subcelestial. The celestial body is absolutely transparent and became the forerunner of the concept of the ether. The subcelestial bodies were divided into three sub-categories consisting of gas, liquid and solid. He showed the propagation of light through a transparent body to be a physical characteristic of all kinds of light, rather than a characteristic of the body.

Ibn al-Haytham studied reflection and refraction phenomena, showing experimentally that the incident ray, the reflected (or refracted) ray and the surface normal all lie in a plane. His method is often used today to illustrate this. He showed the ratio of the angle of incidence to the angle of refraction in an interface of air and water is 1.3 for incident angles less that 20 degrees. Muslim mathematicians did workout the relation of sine of the angles at the time, but it took 600 years to produce the correct sine law of refraction, now attributed to Snell. Alhazen studied the formation of images by spherical and parabolic mirrors. His pioneering works in this field were accepted as the standard for several centuries. He also made a pinhole camera and described how an inverted image of a candle is formed thereby. His contribution is greatest in the field of physiological optics. He described the various parts of the eye and their function. The opaque coating which is the white of the eye called sclera, the horny transparent element in front of the eye called cornea, the membrane behind the cornea (the choroid), the iris, the aquous humor, and the retina. His description of the eye has been termed masterly and remains the basis for description down to modern age. Several of his terms were literally translated to Latin and are used today. For instance, the lens of the eye suggested to al-Haytham a certain grain, so he used the word ADASA which is the Arabic word for this grain. This particular grain, lentil, is known as lens in Latin. Thus, adasa was translated as lens.

Ibn Haytham also described the formation of Halo, the scattering of light that produces day light, and the partial light of the sun before sunrise and after sunset. He described scattering of light by dust particles in a darkened room, cause and duration of twilight. He died at the age of 74. Although today's Wsterners may be unaware of life, he has been called the greatest authority on optics in the middle ages. His works had a profound influence on Roger Bacon, Wittelo, Leonardo da Vinci, Kepler and Newton. And this was accomplished by a Muslim scholar of the Islamic civilization after he was released from prison at the age of about 50 years.

WEBSITES ON ALHAZEN: DR. A. ZAHUR

COMMENTS: M. Azad Islam