Sami Hamarneh writes in "Medicine and Pharmacy under the Fatimids" (cf. "Ismaili Contribution to Islamic Culture" ed. by Seyyed Hossein Nasr, Tehran, 1977, p. 163) that, "It seems plausible to speculate that the generosity of al-Hakim towards scholars and scientists had attracted the migration to Fatimid Egypt of eminent figure, Abu Ali Muhammad bin al-Hasan bin al-Haytham (Latin Alhazen) of Basra in southern Iraq."
Ibn al-Haytham (354-429/965-1039), the greatest physicist was born in Basra, and was originally appointed to a civil post at Basra. He was avidly consumed by the desire to learn mathematics and philosophy, for which he could not get spare time in his post, therefore, he feigned madness and was dismissed as a result from the post. Our informations about his pre-Egyptian days are deficient, but according to a few accounts of his life, it is known that he managed to leave Basra in order to proceed to Egypt, where he had been invited by the Fatimid Imam al-Hakim.
It must be known on this juncture that in the summer following the rainy reason, the Nile river and the canals overflew with water, causing millions of tons of fertile silt, containing phosphoric acid, potash and nitrogen. But in the winter, the level of water fell down, making the cultivation of the crops impossible, and in annual inundation it used to cause devastation of life and property. With his brilliant mind, the famous physicist and the founder of the science of optics, Abu Ali Muhammad bin al-Hasan bin al-Haytham came to the conclusion in Iraq that if some of the surplus water available immediately after the rains, could be stored, not only could it be used in the dry season for more cultivation of land, but it would also help to prevent the periodic flood inflicting heavy damage. According to Ibn Abi Usaibia (d. 668/1270) in his "Uyn al-Anba fi tabakat al-Attiba" (2nd vol., p. 91), Ibn al-Haytham had also claimed that, "Had I been in Egypt I could have done something to regulate the Nile, so that the people could derive benefit at its ebb and flow." Thus, he prepared a plan to build a three-way embankment dam near Aswan for harnessing the Nile waters, and sent his report to al-Hakim. He even suggested for a site near Aswan where the river emerged from a gorge into the flat country. Haidar Bammate writes in "Muslim Contribution to Civilization" (Lahore, 1981, p. 21) that, "Al-Haytham was the first to advocate the construction of a dam at Aswan to raise the level of the Nile."
Al-Hakim was deeply impressed when he received the outline of the project and sent one of his emissaries with adequate funds to Ibn al- Haytham in Basra and invited him to Cairo. He readily accepted the royal invitation and after a short stay in Cairo, he was sent up the river with a large sum of money and retinue of workers. He undertook the journey to Aswan, which is situated at a distance of over 400 miles to the south of Cairo as the crow flies. He inspected the site at Aswan and came to the conclusion that such a colossal scheme of works was not feasible under the working conditions. According to Ibn Abi Usaibia, "He saw the pyramids at first glance and became awed by the engineering and geometrical skills of the ancients. Had it been possible he thought, the ancient Egyptians must have done it before." (op. cit., 2nd vol., p. 91). Having realized the enormous magnitude of the project, he failed to execute it with the technical means he had at his disposal. Instead therefore of undertaking the start-up of the projected dam, he returned to Cairo and confessed to al-Hakim his sheer unability to go ahead with the proposed plan.
Al-Hakim assigned him some office pertaining to revenue, but he is said to have feigned madness, and retired to a place near al-Azhar university. Different stories have been advanced to discredit the personality of al-Hakim in this context. Prof. Abdul Ghafur writes in "Ibn al-Haitham" (cf. "Ibn al-Haitham", Karachi, 1970, pp. 111-2) that, "From this, it should be obvious that, even after Ibn al- Haitham's inability to go ahead with the plan for construction of the dam at Aswan, al-Hakim had considerable respect for Ibn al- Haitham. It might be that there were monetary difficulties involved in the implementation of the scheme or some other snag. However, the reputation of Ibn al-Haitham remain unscathed in this affair. The plea of insanity was not new to Ibn al-Haitham. He had used this subterfuge once before at Basra. It is therefore plausible to assume that he adopted this ruse in order to devote himself to studies. Qifti, Baihiqi and Ibn Abi Usaibia unanimously held that Ibn al-Haitham was a self-contented person and devoid of avarice or worldly self-aggrandizment."
Baihiqi however wrongly narrates in his "Timat al-Sawan al-Hikmat" that Ibn al-Haytham steathily left Cairo at the dead night and lived in Syria. This narration contradicts the established fact that he lived in Cairo till his death. The story of the flight of Ibn al- Haytham from Cairo for fear of execution by al-Hakim is the fabrication of the historians. Had he known of his murder, he would have fled from Aswan and never came to Cairo. He however spent the last 19 years of his life in scientific pursuits and experimental research under the shadow of the domes and arches of al-Azhar university, and composed almost 209 books on mathematics, astronomy, physics, philosophy and medicine of which the most celebrated is his "Kitab al-Manazir" (treatise on optics), which was translated into Latin by Witelo in 1270 and published by Frederick Risner in 1572 at Basel. This was the first comprehensive treatise on optics in the world and immensely influenced the writings of Witelo, Peckham, Roger Bacon, Leonardo de Vinici and John Kepler. He is the first to have discussed the anatomy of the eye. He also discussed the propagation of light and colours, optic illusions and reflection, with experiments for testing the angles of incidence and reflection. Theorically he had almost discovered magnifying lenses through his experiments, which came into existence in Italy three centuries later. For the first time Ibn al-Haytham offered a correct explanation for the apparent increase in the size of the sun and the moon when near the horizon. His another remarkable achievement is his employment of the camera obscura.
Another notable figure was Ali bin Yunus, the great mathematician and astronomer, who invented pendulum and the sun-dial, for whom al- Hakim had the observatory built on Jabal al-Muqattam.
Hence Dar al-Hikmah became a leading academy of Islamic learning for the intellectualists. Dr. Amir Hasan Siddiqui writes in "Cultural Centres of Islam" (Karachi, 1970, p. 62) that, "Al-Hakim was personally interested in astrological calculations; he built on al-Muqattam an observatory to which he often rode before dawn on his grey ass. An informant of the contemporary historian Ibn Hammad (d. 628/1230) saw the astrolabe-like copper instrument erected by al-Hakim on two towers and measured one of its signs of the Zodiac, which was three spans in length."
It is also learnt that al-Hakim had stroke his interest in collecting the old relics. Zakir Hussain writes in "Tarikh-i Salatin Fatimiyya" (Jabalpur, 1938, p. 87) that, "In 400/1010, al-Hakim sent Hamiduddin Kirmani to Medina with instructions that he should there find a house, which had belonged to his ancestor, Jafar Sadik, and to dig up in it some arms and books dealing with Shiite doctrines, and to bring them to him. This he did, and found a Holy Koran, a bed and some household goods."
According to "Encyclopaedia of World Art" (Rome, 1958, 5th vol., p. 367) that, "Rice correctly read the Arabic text carved on it, which does not simply banal good wishes to the owner of the ewer as was previously thought, but says that the ewer was made for the personal use of al-Hakim's commander."
It will be further interesting to note that Abul Kassim Ammar bin Ali al-Mausili was the most important eye-surgeon in Cairo, and acquired great prestige under the patronage of al-Hakim. He compiled "al-Muntakhab fi ilm al-Ayn wa Mudawatiha bi'l Adwiya wal Hadid" in 400/1010. It deals the anatomy and physiology of the eye, its diseases and treatment by drugs and surgery. To avoid the dangers of using a breakable glass tube referred to in Greek writings, Ammar invented a hollowed metallic needle used successfully in cataract operations.