The Iranian Muslim mathematician and physicist, Kamal od-Din Hassan ibn Ali al-Farisi

Compiled by: Syed Ali Shahbaz
On 19th of the Islamic month of Zil-Qa'dah in 718 AH, the Iranian Muslim mathematician and physicist, Kamal od-Din Hassan ibn Ali al-Farisi, passed away. He was born in Tabriz and made two major contributions to science, one on optics, the other on number theory. He was a student of the great astronomer and mathematician Qutb od-Din al-Shirazi, who in turn was a student of the celebrated theologian and polymath Khwaja Naseer od-Din Tusi.
His work on optics was prompted by a question put to him concerning the refraction of light. Shirazi advised him to consult the Book of Optics (Kitab al-Manazer) of Ibn al-Haytham (Alhacen), and Farisi made such a deep study of this treatise that Shirazi suggested that he write what is essentially a revision of that major work, which came to be called the "Tanqih al-Manazer".
Farisi is known for giving the first mathematically satisfactory explanation of the rainbow, and an explication of the nature of colours. He also made a number of important contributions to the number theory. His most impressive work in this regard is on amicable numbers. In his work "Tadhkirat al-Ahbaab fi Bayan at-Tahabb" (Memorandum for Friends on the proof of Amicability) he introduced a major new approach to the whole area of number theory, introducing ideas concerning factorization and combinatorial methods. In fact Farisi's approach is based on the unique factorization of an integer into powers of prime numbers.