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Ptolemy

Ptolemy
Ptolemy after an engraving of the sixteenth century German
Ptolemy after an engraving of the sixteenth century German
Birth About 90
Upper Egypt
Roman province of Egypt
Deaths 168
Canopus
Roman province of Egypt
Field (s) Astronomy , mathematics , geography , astrology
Famous for Almagest
48 constellations ( Andromeda , Cygnus , Lyra ) Orion , Sagittarius ) ...

Claudius Ptolemy (in Greek in Latin commonly known as Ptolemy (Ptolemais in Thebaid ( Upper Egypt ) to 90 - Canopus to 168) was an astronomer and astrologer who lived in Greek Alexandria ( Egypt ). It is also one of the pioneers of geography. His life is uncertain. His cognomen Ptolemaeus suggests Greco-Egyptian origins, and his nomen Claudius Roman citizenship. His praenomen is unknown.

Ptolemy was the author of several scientific treatises, two of which were subsequently exercised a great influence on Western science and Eastern. One is the astronomical treatise that is now known by the name of Almagest (Arabization , Great Composition then, the vast al-Mijisti, but the original title in Greek was , Composition mathematical). The other is the Geography , which is a thorough discussion of the geographical knowledge of the world Greco-Roman.

The work of Ptolemy is a peak and the culmination of his time in a long evolution of ancient science based on observation of the stars, numbers, calculation and measurement. With Aristotle's work is mainly through it, passed by both the Arabs and the Byzantines, the West rediscovers Greek science in medieval , leaving their predecessors in the dark . Yet Ptolemy does not fail to make ample reference to them in his writings.

Summary

/ / Astronomy
Main article: Almagest.
Ptolemaic system

The Almagest is the only comprehensive book on astronomy from antiquity that has survived. Babylonian astronomers had developed computational methods for predicting astronomical phenomena. Above all, they were carefully recorded for centuries, valuable observations (positions of stars, eclipses ...) The Greek astronomers such that Eudoxus of Cnidus and especially Hipparchus , had incorporated these observations and models in their geometry (theory of epicycles ) to calculate the movement of certain celestial bodies. In his treatise, Ptolemy takes these astronomical models and improves , including adding the notion of equant . His comments, combined with previous data that were available to offer back a very precise measurement of astronomical movements, since the set covers a period of almost nine centuries. His "tables" of data needed to determine the position of the stars have in fact as a starting point on the first day of the Egyptian calendar the first year of the reign of Nabonassar , that is to say 26 February 747 BC. AD . Ptolemy devotes so the model -centric Hipparchus, who was often attributed and was accepted for over 1300 years, albeit intermittently. In Western Europe, in fact, he sank into oblivion in the early Middle Ages, before being rediscovered at the end of this period. This legacy, however, was preserved in the Arab world and, with ups and downs in the Eastern Roman Empire to Byzantium, and more specifically . His method and calculation model have also been adopted with some amendments in the Arabic speaking world and in India as they were of sufficient accuracy to meet the needs of astronomers, astrologers, holders of calendars and browsers.

Ptolemy realized as a kind of very practical manual, called "The tables are easy" or sometimes "The tables manually ( ) derived from the Almagest and perform calculations for the position of the stars and eclipses.

Contrary to popular belief, Ptolemy did not resume his own the idea of Aristotle that the stars were placed on crystal spheres . He even says explicitly that "the stars are swimming in a perfect fluid which opposes no resistance to their movements . Whether this vision, close to the notion of emptiness, was already present in Hipparchus or whether it should be put to the credit of Ptolemy. For the latter, deferent and epicycles are immaterial. Nicolas Halma further believes that its choice of system of epicycles rather than that of eccentric resulted more from a desire to make the calculations more convenient, as a faith in the material reality of the system .

During the next thirteen centuries, astronomy is hardly progressed. The Almagest tables and easily received only minor corrections, although they have undergone, at the end of antiquity, many publications from the "commentators" , the best known is Theon of Alexandria. It was so tables and texts of Ptolemy, which were used directly or indirectly as reference until the development of the means of observation and theory developed by Nicolas Copernicus and perfected by Johannes Kepler do its abandonment. But it was with great difficulty: the system heliocentric Copernican (1543), supported by Galileo (1630) was rejected by the Catholic Church and Galileo was forced to recant his theories in 1633 officially. The Ptolemy's model was not finally abandoned by the Church under Pope Benedict XIV in 1750 .

The Almagest also contains a catalog of 1022 stars and a list of forty-eight constellations. Although not covering the entire celestial sphere , this system was the model for many centuries. Ptolemy also described the astrolabe , invented probably by Hipparchus.

Geography

Main article: Geography (Ptolemy).
The world map of Ptolemy, reconstructed in the fifteenth century from his Geography , says the country Serica, Sina ( China ) to the extreme right, beyond the island of Taprobane ( Sri Lanka , too large) and Aurea Chersonesus ( Southeast Asia )

Its geography is another masterpiece. This is a compilation of knowledge of world geography at the time of the Roman Empire during the reign of Hadrian (125). Ptolemy relied heavily on the work of another geographer Marinus of Tyre , and on gazetteers of the Roman and Persian , but most of his sources beyond the perimeter of the empire were of dubious origins.

The first part of the Geography is a discussion on data and methods he used. As for the model of the solar system in the Almagest, Ptolemy united in a large ensemble all the information he had. He attributed the coordinates to all locations and geographic features he knew, in a grid covering the globe. The latitude was measured from the equator , like today, but Ptolemy preferred to express it according to the length of the longest day rather than degrees (the term of Solstice summer from 12 am to 24 pm gradually with distance from the equator to the polar circle ). He stared at the meridian of longitude 0 at the point further west he knew, the islands 'Fortunata' (or islands Bl ), which presumably correspond to the islands of Cape Verde, and not to the Canaries , as has often said. .

Astrology

Main article: Tetrabiblos.

The Treaty of Ptolemy on astrology, Tetrabiblos (Greek tetra means "four" and biblos "book") was the most popular astrological work of antiquity, but did not attain the status of the Almagest. He exercised great influence in the study of celestial bodies in the sphere sublunary. Thus, it provided an explanation of how the astrological planets , depending on their impact heating, cooling, wetting and drying. It deals in particular horoscopic astrology in four books which consists of a thematic interpretation using the erection of a map based on a table identifying the location of the seven planets (including Sun) known to the time at a given time.

Ptolemy believed that astrology was like medicine that is hypothetical because many variable factors to consider. These factors were mainly for him, race, country and education that would affect a person as well as the position of planets in the sky at the time of birth.

Unlike Vettius Valens , it seems that Ptolemy, best known for his treatise on astronomy, was a compiler (a theorist) in astrology .

It should be noted that there is, in Ptolemy, no confusion between astronomy and astrology: everything about this last subject is contained in Tetrabiblos, not a line about it in the Almagest.

Detail of The School of Athens by Raphael , showing Zoroaster and Ptolemy.

Music

Ptolemy also wrote the harmonics, a treaty of musicology reference on theory and mathematical principles of music . After a critique of his predecessors, Ptolemy argued for basing it on musical intervals on mathematical ratios (in contrast to the supporters of Aristoxenus) supported by empirical observation (in contrast to the purely theoretical approach to the Pythagorean School ). He presented his own divisions of the tetrachord and the octave , which he derived with the aid of a monotone. The interest in astronomy of Ptolemy also appears in a discussion on the music of the spheres.

Harmonics contributed greatly to the development of music theory in the sixteenth century.

Mathematics

Main article: Ptolemy's theorem.

Ptolemy discovered a theorem that bears his name in a convex quadrilateral inscribed in a circle, the product of the diagonals equals the sum of products of opposite sides .

In its mathematical Composition (Almagest), Ptolemy wants to follow the rigorous method of geometry and proceed with the demonstration made by the mathematicians of ancient Greece , whose representative is essential Euclid. Its trigonometry is based on that of Hipparchus, but he is also aware of the work of Menelaus , who developed spherical trigonometry and he cites in the Almagest .

Optics

In the Optics, Ptolemy deals with the properties of light, including the reflection , the refraction and color , and a theory of vision, based on a combination of the properties of observed objects, light and a "visual flow (visual acuity in the Latin text) from the eyes. This work is an important part of the history of optics , but it came in through a Latin translation made by the Emir Eugene of Sicily in 1150, itself the result of an Arabic translation rather imperfect and incomplete .

In this matter as in others, Ptolemy has previous contributions. Some optical elements are present in Euclidean , Archimedes and Heron of Alexandria , but the specific sources of Ptolemy are discussed . The wording of Optics is after the Almagest, as evidenced in particular some progress made by Ptolemy in the meantime. Thus, the exposed optical phenomenon of atmospheric refraction that occurs when observing the sun or moon, a phenomenon totally ignored in the Almagest .

References

Notes

  1. Essentially the twelfth century, Gerard of Cremona to Arab sources.
  2. In particular Hipparchus. See for example Almagest IV, 2, in which he emphasized the quality of his observations of the lunar anomaly. But Gerard of Cremona in his translation of the Almagest Hipparchus does not recognize its name in Arabic Abrash.
  3. Many cuneiform tablets with this type of content we have received. The oldest we have are from the seventh century BC. AD
  4. We often speak of "the system of Ptolemy." This is not false, if by that we mean "the system used by Ptolemy, but the term suggests it is the initiator, which is incorrect. Ptolemy himself, in the Almagest, discusses the epicycles of Hipparchus in several passages noted in the preface of N. Halma (N. Halma, The Almagest of Ptolemy, editing and translation, Paris, 2 vols., 1813-1817, reprinted by Hermann, Paris - 1927)).
  5. Some tables are however more accurate than in the Almagest, sometimes until the sixth angle (the third is 1 / 60 of a second, the fourth 1 / 60 for third etc.).. This shows that Ptolemy, even after publication of the Almagest, has continued to refine his work. The "Tables Easy" is also included in the edition Halma, where they are considered a kind of appendix to the Almagest. But they are clearly later.
  6. On this point see the analysis of very sharp Halma, preface: "(Ptolemy) is not looked upon himself, his (its assumptions), as real, but only as means to explain the celestial order that it had seemed impossible to Hipparchus to explain other than by this complication of circles. We think, "he said in his lib. III, which should demonstrate the phenomena by the simplest assumptions, provided that that they assume no parish contradicts anything important by the observations (...) It is confirmed by the way Ptolemy sets out these assumptions and the inferences he draws from. It is almost always future will be, or conditional instead of the present tense, as in ch. 4 of pounds. IV, where he says that the similarities not only reports but also times of one and the other movement seroient and saved ( ). The arbitrary choice suggested in his lib. III, the eccentric or epicycle to explain the movement of the sun, although it shows no one looked more real as the other. He selected means that the geometry fournissoit him, those he judged most likely to represent the effects of which he wished to report, "The geometry is only an instrument in the hands of the astronomer," said Bailly, This instrument creates nothing but lend themselves to the use made of good observations, it gives accurate results. "
  7. This de facto abandonment took place in several stages. See heliocentrism.
  8. Marinus integrates itself flows Eratosthenes and Hipparchus. See History of geography.
  9. Specifically, these are Catoptrica (Theory of mirrors) attributed to Euclid. But its authorship, this piece is not certain. Cf A. Mark Smith, Ptolemy's theory of visual perception: an Franais Translation of the Optics With Introduction and Commentary, The American Philosophical Society, Philadelphia, 1996 4 and 14-17.

References

  1. See Medieval Renaissance.
  2. Greek Science - Middle Age - Figure of the Earth in ancient times - L. Gnicot, ridge lines of the Middle Ages, Casterman, 1961
  3. These facts are indicated by small strokes in the Almagest itself and highlighted in the preface of the edition Halma (See bibliography).
  4. See geocentrism.
  5. Babylonian Astronomy - J. Mogenet, A. Tihon, R. Royez, A. Berg, Nicephorus Gregori: Calculation of the solar eclipse of July 16, 1330, Corpus of Byzantine astronomers, I Gleben, 1983, page 96. ( ISBN 9789070265342 ) - Ptolemy, Almagest III, 6.
  6. See Science and technology in the Byzantine Empire
  7. P. Couderc, History of Astronomy, Que sais-je n 165, pp.56 ff.
  8. Almagest, XIII, 12. - Halma, Op cit., preface, pp. 15-16.
  9. A. Tihon, Theon of Alexandria and "Easy Tables" of Ptolemy, International Archives of the History of Science, 1985 (35), No. 1124-115, p. 106-123. ISSN 0003-9810.
  10. As an example of employment late texts of Ptolemy, one can find the details of a calculation of eclipse by the Almagest and in the table easily in J. Mogenet, A. Tihon, R. Royez, A. Berg Op cit.
  11. New general biography since the earliest times until today. From Hoefer (Jean Chrtien Ferdinand), Volume 41, page 161 (Firmin Didot, Paris - 1866)
  12. Source: (en) A history of astrology horoscopic by James Herschel Holden American Federation of Astrologers, 2nd edition, 1996)
  13. Studies on Plato's Timaeus. Thomas Henry Martin, Plato. Volume I, page 412 (Ladrange, Paris - 1841)
  14. Almagest, I, 9 - (en) Ptolemy the personal website of Serge Mehl
  15. Almagest VII, 3.
  16. Or Eugene of Palermo. Albert Lejeune, L'Optique of Claudius Ptolemy, in the Latin version from the Arab Emir Eugene of Sicily., Critical and exegetical edition plus a French translation and additions, Louvain, Bibl. University, 1956, 2nd ed. : Brill (Leiden, New York), 1989. See p. 9-20 and 132-135. Book I, which contains the theory of vision is lost. Its content is known only by a brief summary at the beginning of Book II. The outline of the theory of Ptolemy's vision can also be deduced from information scattered throughout the text, eg II, 12.
  17. A. Mark Smith, Ptolemy's theory of visual perception: an Franais Translation of the Optics With Introduction and Commentary, The American Philosophical Society, Philadelphia, 1996 4 and 14-17. Available online Bibliography

    Works by Claudius Ptolemy


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