6.1 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Al-Kindi | 3/6 | https://en.wikipedia.org/wiki/Al-Kindi | reference | science, encyclopedia | 2026-05-05T16:26:16.851905+00:00 | kb-cron |
=== Medicine === There are more than thirty treatises attributed to al-Kindi in the field of medicine, in which he was chiefly influenced by the ideas of Galen. His most important work in this field is probably De Gradibus, in which he demonstrates the application of mathematics to medicine, particularly in the field of pharmacology. For example, he developed a mathematical scale to quantify the strength of a drug, and a system (based on the phases of the moon) that would allow a doctor to determine in advance the most critical days of a patient's illness. According to Plinio Prioreschi, this was the first attempt at serious quantification in medicine.
=== Chemistry === Al-Kindi denied the possibility of transmuting base metals into precious metals such as gold and silver, a position that was later attacked by the Persian alchemist and physician Abu Bakr al-Razi (c. 865 – c. 925). One work attributed to al-Kindi, variously known as the Kitāb al-Taraffuq fī l-ʿiṭr ("The Book of Gentleness on Perfume") or the Kitāb Kīmiyāʾ al-ʿiṭr wa-l-taṣʿīdāt ("The Book of the Chemistry of Perfume and Distillations"), contains one of the earliest known references to the distillation of wine. The work also describes the distillation process for extracting rose oils, and provides recipes for 107 different kinds of perfumes.
=== Mathematics ===
Al-Kindi authored works on a number of important mathematical subjects, including arithmetic, geometry, the Hindu numbers, the harmony of numbers, lines and multiplication with numbers, relative quantities, measuring proportion and time, and numerical procedures and cancellation. He also wrote four volumes, On the Use of the Hindu Numerals (Arabic: كتاب في استعمال الأعداد الهندية Kitāb fī Istimāl al-'Adād al-Hindīyyah) which contributed greatly to diffusion of the Hindu system of numeration in the Middle-East and the West. In geometry, among other works, he wrote on the theory of parallels. Also related to geometry were two works on optics. One of the ways in which he made use of mathematics as a philosopher was to attempt to disprove the eternity of the world by demonstrating that actual infinity is a mathematical and logical absurdity.
=== Cryptography ===
Al-Kindi is credited with developing a method whereby variations in the frequency of the occurrence of letters could be analyzed and exploited to break ciphers (i.e. cryptanalysis by frequency analysis). His book on this topic is Risāla fī Istikhrāj al-Kutub al-Mu'ammāh (رسالة في استخراج الكتب المعماة; literally: On Extracting Obscured Correspondence, more contemporarily: On Decrypting Encrypted Correspondence). In his treatise on cryptanalysis, he wrote:One way to solve an encrypted message, if we know its language, is to find a different plaintext of the same language long enough to fill one sheet or so, and then we count the occurrences of each letter. We call the most frequently occurring letter the "first", the next most occurring letter the "second", the following most occurring letter the "third", and so on, until we account for all the different letters in the plaintext sample. Then we look at the cipher text we want to solve and we also classify its symbols. We find the most occurring symbol and change it to the form of the "first" letter of the plaintext sample, the next most common symbol is changed to the form of the "second" letter, and the following most common symbol is changed to the form of the "third" letter, and so on, until we account for all symbols of the cryptogram we want to solve. Al-Kindi was influenced by the work of al-Khalil (717–786), who wrote the Book of Cryptographic Messages, which contains the first use of permutations and combinations to list all possible Arabic words with and without vowels.
=== Meteorology === In a treatise entitled as Risala fi l-Illa al-Failali l-Madd wa l-Fazr (Treatise on the Efficient Cause of the Flow and Ebb), al-Kindi presents a theory on tides which "depends on the changes which take place in bodies owing to the rise and fall of temperature." In order to support his argument, he gave a description of a scientific experiment as follows:
One can also observe by the senses... how in consequence of extreme cold air changes into water. To do this, one takes a glass bottle, fills it completely with snow, and closes its end carefully. Then one determines its weight by weighing. One places it in a container... which has previously been weighed. On the surface of the bottle the air changes into water, and appears upon it like the drops on large porous pitchers, so that a considerable amount of water gradually collects inside the container. One then weighs the bottle, the water and the container, and finds their weight greater than previously, which proves the change. [...] Some foolish persons are of opinion that the snow exudes through the glass. This is impossible. There is no process by which water or snow can be made to pass through glass. In explaining the natural cause of the wind, and the difference for its directions based on time and location, he wrote:
When the sun is in its northern declination northerly places will heat up and it will be cold towards the south. Then the northern air will expand in a southerly direction because of the heat due to the contraction of the southern air. Therefore most of the summer winds are merits and most of the winter winds are not.
=== Music theory === Al-Kindi was the first theoretician of music in the Arab-Islamic world whose works have come down to us. He transferred the Greek tonal system to the Arabic lute. Although he used tone letters (i.e. the Arabic alphabet), he also transferred the Greek tonal names to Arabic. He added a fifth string to the 'ud. He is known to have written treatises on music theory. The known indexes list a varying number of writings attributed to him, but only four have survived and can be attributed to him with certainty: