Scientists and engineers of the Islamic world

A contribution can be a book, a device, a method or a question. For each person you meet, ask what they added, who says so, and what the record does not claim for them.

One scene from the life of Ibn al-Haytham is a project that failed. The Encyclopaedia of Islam stresses that his biography has numerous gaps ². It says that during the reign of the Fatimid caliph al-Hakim, 386 to 411 AH/996 to 1021, he went to Egypt and tried to regulate the flow of the Nile. He gave up the task when he realised it was impossible, despite his fear of the caliph's anger ². After the caliph's death he returned to Cairo, where he earned his living by copying scientific manuscripts, particularly mathematical ones ². The article counts more than a hundred titles among his writings, most of them on mathematics and physics ².

Neither record preserves a sentence in which the scholar says why he worked. For Ibn al-Haytham, the article sees in his writings a deep knowledge of the Greek authors, notably Ptolemy, whom he edited, studied and criticised ². For al-Jazari, TDV describes an engineer improving earlier work, and records a book commissioned by Nasir al-Din Mahmud ³. In both cases the records show what the man worked on and from whom he started, and they do not say what moved him.

Which way does light travel when we see? According to the Encyclopaedia of Islam article, Ibn al-Haytham, like Ibn Sina and al-Biruni, held that rays of light travel from the object to the eye, and not the reverse as Euclid, Ptolemy and al-Kindi maintained ⁴. The museum's record reports the article's account and gives no verdict. What the earlier authors maintained is likewise the article's report.

The article itself says that his biography has numerous gaps ². Even his death is dated two ways. The Encyclopaedia of Islam gives 430 AH/1039, while TDV discusses differing death reports, including an autograph dated 432 AH/1040, and does not collapse them into one certain date ^2 5. For al-Jazari, the picture of his elephant clock is a later manuscript folio dated 715/1315, not an original working machine ⁶. Ask of each fact whether it comes from the man's own hand or from a later account.

Ibn al-Haytham abandoned the Nile project when he realised it was impossible. Is recognising that a project cannot work a contribution to science, and how would you answer someone who says that only what is built or discovered counts?

• Ibn al-Haytham: his life, his writings and the places where the sources disagree.
• Al-Jazari: his book of machines and the patron who asked for it.
• Optics: the science Ibn al-Haytham studied through light's three conditions: rectilinear radiation, reflection and refraction.
• Al-Farisi's water-sphere rainbow model: the work of the scholar who revised Ibn al-Haytham's Optics.