Differential (mechanical device)A differential is a gear train with three drive shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others. A common use of differentials is in motor vehicles, to allow the wheels at each end of a drive axle to rotate at different speeds while cornering. Other uses include clocks and analog computers. Differentials can also provide a gear ratio between the input and output shafts (called the "axle ratio" or "diff ratio").
EpigraphyEpigraphy () is the study of inscriptions, or epigraphs, as writing; it is the science of identifying graphemes, clarifying their meanings, classifying their uses according to dates and cultural contexts, and drawing conclusions about the writing and the writers. Specifically excluded from epigraphy are the historical significance of an epigraph as a document and the artistic value of a literary composition. A person using the methods of epigraphy is called an epigrapher or epigraphist.
Islamic Golden AgeThe Islamic Golden Age was a period of scientific, economic and cultural flourishing in the history of Islam, traditionally dated from the 8th century to the 13th century. This period is traditionally understood to have begun during the reign of the Abbasid caliph Harun al-Rashid (786 to 809) with the inauguration of the House of Wisdom, which saw scholars from all over the Muslim world flock to Baghdad, the world's largest city by then, to translate the known world's classical knowledge into Arabic and Persian.
Lunar monthIn lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. In Shona, Middle Eastern, and European traditions, the month starts when the young crescent moon first becomes visible, at evening, after conjunction with the Sun one or two days before that evening (e.g., in the Islamic calendar). In ancient Egypt, the lunar month began on the day when the waning moon could no longer be seen just before sunrise.
AlmagestThe Almagest ˈælmədʒɛst is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy ( AD 100 – 170) in Koine Greek. One of the most influential scientific texts in history, it canonized a geocentric model of the Universe that was accepted for more than 1,200 years from its origin in Hellenistic Alexandria, in the medieval Byzantine and Islamic worlds, and in Western Europe through the Middle Ages and early Renaissance until Copernicus.
National Archaeological Museum, AthensThe National Archaeological Museum (Εθνικό Αρχαιολογικό Μουσείο) in Athens houses some of the most important artifacts from a variety of archaeological locations around Greece from prehistory to late antiquity. It is considered one of the greatest museums in the world and contains the richest collection of Greek Antiquity artifacts worldwide. It is situated in the Exarcheia area in central Athens between Epirus Street, Bouboulinas Street and Tositsas Street while its entrance is on the Patission Street adjacent to the historical building of the Athens Polytechnic university.
Prague astronomical clockThe Prague astronomical clock or Prague Orloj (Pražský orloj praʃskiː orloj) is a medieval astronomical clock attached to the Old Town Hall in Prague, the capital of the Czech Republic. The clock was first installed in 1410, making it the third-oldest astronomical clock in the world and the oldest clock still in operation. The Orloj is mounted on the southern wall of Old Town Hall in the Old Town Square.
Richard of WallingfordRichard of Wallingford (1292–1336) was an English mathematician, astronomer, horologist, and cleric who made major contributions to astronomy and horology while serving as abbot of St Albans Abbey in Hertfordshire. Richard was born, the son of a blacksmith, at Wallingford in Berkshire (now Oxfordshire) in England in 1292. When he was orphaned he was taken to William de Kirkeby the Prior of Wallingford Priory and dedicated to the Holy Trinity.
EquatoriumAn equatorium (plural, equatoria) is an astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to represent the position of a given celestial body. In his comment on Ptolemy's Handy Tables, 4th century mathematician Theon of Alexandria introduced some diagrams to geometrically compute the position of the planets based on Ptolemy's epicyclical theory.
Ancient Greek technologyAncient Greek technology developed during the 5th century BC, continuing up to and including the Roman period, and beyond. Inventions that are credited to the ancient Greeks include the gear, screw, rotary mills, bronze casting techniques, water clock, water organ, the torsion catapult, the use of steam to operate some experimental machines and toys, and a chart to find prime numbers. Many of these inventions occurred late in the Greek period, often inspired by the need to improve weapons and tactics in war.
