ISLAM’S CONTRIBUTION TO MODERN SCIENCE

of the eye, as the vitreous humor, the cornea, and the retina, are still retained by anatomists. Al-Haytham carried forward these studies, and made the first recorded scientific estimate of the phenomena of twilight and of the height of the atmosphere. The persistence of a glow in the atmosphere after the sun has disappeared beneath the horizon is so familiar a phenomenon that the ancient philosophers seem not to have thought of it as requiring an explanation. Yet a moment’s consideration makes it clear that, if light travels in straight lines and the rays of the sun were not deflected, the complete darkness of night should instantly succeed to day when the sun passes below the horizon. That this sudden change does not occur, al-Haytham explained as due to the reflection of light by the Earth’s atmosphere. Chemistry In Chemistry, we find the greatest Arabian name that of Jabir ibn Hayyan (d. AD 815), who taught in the College of Seville in the first half of the eighth century. The most important researches of this remarkable experimenter had to do with the acids. The ancient world had no knowledge of any acid more powerful than acetic acid. Jabir vastly increased the possibilities of chemical experiment by the discovery of sulphuric, nitric, and nitromuriatic acids. He made use also of the processes of sublimation and filtration, and his works describe the water bath and the chemical oven. Among the important chemicals which he first differentiated is oxide of mercury, and his studies of sulphur in its various compounds have peculiar interest. In particular is this true of his observation that, under certain conditions of oxidation, the weight of a metal was lessened. Medicine Among Arabian physicians, there were always some investigators who turned constantly to nature for hidden truths, and were ready to uphold the superiority of actual observation to mere reading. Thus, the physician Abd al-Latif al-Baghdadi (d. AD 1231), while in Egypt, made careful studies of a mound of bones containing more than twenty It is certain that in the time when Western Europe was paying little attention to science or education, the Caliphs and viziers were encouraging physicians and philosophers, building schools, and erecting libraries and hospitals.