The first known navigators were the Phoenicians, who 3000 years ago sailed the Mediterranean and beyond from their base near modern Lebanon. Justinian's mission to China in the 6th century A.D., the Viking expeditions of the 9th - 10th centuries, and Marco Polo's trip to China in 1270 opened new horizons. Then Portugal's Prince Henry the Navigator established a school of navigation whose influence touched a young Italian sailor and changed the world. Christopher Columbus sailed west in 1492, a date that began the Age of Exploration. Vasco da Gama in 1497 rounded Africa and sailed to India, opening the route to the east. Expeditions to the Americas by Amerigo Vespucci, Ferdinand Magellan, Cortes, Pizarro, Sir Walter Raleigh, and others soon followed. Over the 16th to 19th centuries came the inland explorations that created the modern world. Expanding settlement and commerce required better maps and navigation methods; a grid system of latitudes and longitudes, originally proposed by the ancient Greeks, was revived. Cartographers struggled with the task of representing a spherical earth on a flat map; dozens of map projections were developed. By the 20th century, new areas of discovery produced better navigational technology, more and more maps, and yet more horizons for future discovery.
Modern chemistry emerged from the historical traditions of metalworking (beginning as early as the Bronze Age in 3500 BC); medicine (especially 'iatrochemistry', which emerged in the Renaissance); and alchemy (the medieval and mystical forerunner of chemistry). Alchemy was based on the Aristotelian concept of elements (earth, air, water, and fire) and Platonic ideas about pure 'essences' (i.e. ideal forms). The modern idea of a chemical element began to emerge in Robert Boyle's The Sceptical Chymist (1661). Boyle established a systematic approach to a vast subject in which detail frequently obscured basic principles. The 18th century theory of 'phlogiston' appeared to explain combustion and respiration as giving off an 'inflammable' substance. In 1774 Joseph Priestly discovered 'dephlogisticated air' (later called oxygen). In Paris, Antoine Lavoisier recognized the real significance of this discovery, and used it to revolutionize chemistry through his 1789 work Traite elementaire de chimie. A chemical theory of atoms emerged in the early 19th century, and 31 new elements were discovered between 1790 and 1830. Dmitry Mendeleyev laid out the periodic table in 1869. Chemistry was ushered into the 20th century by organic chemistry, valence theory, and the electron theory of chemical bonding. Chemistry and physics would now be linked in an alliance that has had dramatic consequences for scientific progress and the modern standard of living.
