Parallel (geometry) as a pair of straight lines in a plane which do not meet appears as Definition 23 in Book I of Euclid's Elements. Alternative definitions were discussed by other Greeks, often as part of an attempt to prove the parallel postulate. Proclus attributes a definition of parallel lines as equidistant lines to Posidonius and quotes Geminus in a similar vein. Simplicius also mentions Posidonius' definition as well as its modification by the philosopher Aganis. At the end of the nineteenth century, in England, Euclid's Elements was still the standard textbook in secondary schools. The traditional treatment of geometry was being
Ptolemy II Philadelphus in the Library of Alexandria Ptolemy II Philadelphus in the Library of Alexandria Ptolemy Philadelphus in the Library of Alexandria is an 1813 oil on canvas painting by Vincenzo Camuccini. It is now in the National Museum of Capodimonte in Naples. The work was commissioned by Napoleon I along with "Charlemagne Ordering Italian Scholars to Found the University of Paris", both for the central hall of Rome's Palazzo del Quirinale. It shows Ptolemy II Philadelphus in red robes among several philosophers in the Library of Alexandria. The artist had recently returned to Italy from Paris and decided to accept the commission. "Ptolemy" was then moved