Abu Yusuf Ya Qub Ibn Ishaq Al-Sabbah Al-Kindi (Alkindus)
c. 801-c. 866
Arab Philosopher, Astronomer, Mathematician, Physician, and Geographer
Al-Kindi, known in the West as Alkindus, was one of the Islamic world's most important and prolific scholars. The scope of his work was encyclopedic, encompassing alchemy, astronomy, philosophy, mathematics, medicine, geography, music, pharmacology, and more. Al-Kindi's ideaswere highly influential in the Latin West during the Middle Ages due to a number of translations by Gerard of Cremona (1114?-1187).
Al-Kindi was born around 801 to a noble family of the Kinda tribe of Yemen. He was the first important Islamic philosopher of Arabic (Bedouin) origin and is commonly referred to as the first Arab philosopher. He was educated at the important intellectual center of Kufa (in modern Iraq) and later at Baghdad, where he attracted the attention of Caliph al-Ma'mun (786-833). Al-Ma'mun made him a member of his scientific academy, called the House of Wisdom (Bayt al-Hilkmah). After the Caliph's death, his successor, al-Mu'tasim, selected al-Kindi to tutor his son. Al-Kindi fell out of favor with al-Mu'tasim's successors and spent the last years of his life in relative isolation. He died sometime during the reign of al-M'utamid.
As a member of the House of Wisdom, al-Kindi played an important role in the preservation of Hellenistic science. He redacted many translations of Greek treatises, and his summaries and commentaries established the Neoplatonic interpretation of Aristotle (384-322 B.C.) that dominated Arabic Aristotelianism until the time of Ibn Rushd, or Averroës (1126-1198). Much of al-Kindi's effort was devoted to restoring incomplete works and gaps in the body of inherited scientific literature. Additionally, he sought to augment, extend, and correct this knowledge when necessary.
De aspectibus was al-Kindi's primary optical treatise. Working within the Greek optical tradition, he leveled a devastating critique against the intromission theory (of forms), which asserted that vision is the result of objects emitting thin films or images of themselves through the intervening space to the eye. (The rival position was the extromission theory, which argued that the eye emits an invisible fire that "touches" objects of vision to reveal their colors and shape.) He demonstrated that the intromission theory was incompatible with the laws of perspective. If the theory were true, then a circle viewed on edge would be perceived in all its circularity; but experience shows that it is perceived as a line. Al-Kindi also argued that objects do not emit radiation from their surfaces as a whole. Rather, each point on a surface radiates light in all directions. Though implicit in early theories, al-Kindi was the first to state this principle explicitly.
Al-Kindi wrote two treatises on mineralogy, Risala fi anwa al-jawahir al-thaminah wa ghayriha (Treatise on various types of precious stones and other kinds of stones) and Risalah fi anwa al-hijarah wa'l-jawahir (Treatise on various types of stones and jewels). These works were the first of their kind in Arabic. He also produced the first Arabic book on metallurgy, Risalah fi anwa alsuyuf al-hadid (Treatise on various kinds of steel swords). In the study of acoustics, he developed a means for determining pitch and showed that the different notes combining to produce harmony have a specific pitch. Furthermore, he argued that sound is caused by air waves striking the eardrum. His musical treatises were among the best such works in Arabic.
An accomplished physician, al-Kindi naturally delved into pharmacology. According to Galen (130-c. 200), each of the four qualities of medicine (heat, cold, dryness, and humidity) could assume, at different times, one of four degrees of intensity. Al-Kindi attempted to quantify these intensities. His research on the links between dosage variations and their qualitative effects led him to create a systematic quantitative system for determining the composition of medical preparations.
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