The Muslim legacy included advances in technology too. Ibn al-Haytham, for example, wrote The Book of Optics, in which he gives a detailed treatment of the anatomy of the eye, correctly deducing that the eye receives light from the object perceived and laying the foundation for modern photography. In the tenth century he proposed a plan to dam the Nile. Muslim engineers also perfected the waterwheel and constructed elaborate underground water channels called qanats. Requiring a high degree of engineering skill, qanats were built some fifty feet underground with a very slight inclination over long distances to tap underground water and were provided with manholes so that they could be cleaned and repaired.
Agricultural advances are also part of the Muslim legacy.
Important books were written on soil analysis, water, and what kinds of crops were suited to what soil. The introduction of numerous varieties of fruits and vegetables and other plants to the West via the Islamic empire was, however, largely the result of the vast expansion of trade during the Golden Age. The 'Abbasids, therefore, were forced to develop extensive and complicated patterns of trade. To obtain food, for example, Baghdad had to import wheat from Syria and Egypt, rice from the Fayyum in Egypt, southern Morocco, and Spain, and olive oil from Tunisia. To obtain scarce metals the 'Abbasids had to turn elsewhere.