Ptolemy’s Legacy


The most influential of all ancient Roman scientists proved to be the most durable authority on astrology. Ptolemy (Claudius Ptolemaeus of Alex- andria) provided the solid treatise which would give substance and respecta- bility tothis science for the next thousand years. But his reputation has suffered from the overadvertised fate of two of his crucially erroneous theories. Both were current in his time, both were developed and per- petuated in his writings. The geocentric, or Ptolemaic, theory of the uni- verse would become a modern byword for astronomical error. Similarly, the land-dominant view, the view that dry land comprised most of the earth’s surface, became a byword for geographic error. These two popular miscon- ceptions were destined to obscure Ptolemy’s colossal achievements. But never since Ptolemy has anyone provided so comprehensive a survey of the whole scientific knowledge of an age…

…Ptolemy dominated the popular and literary view of the universe throughout the Middle Ages. The world as depicted in Dante’s Divine Comedy came right out of Ptolemy’s Almagest. In many ways Ptolemy spoke as a prophet. For he enlarged the uses of mathematics in the service of science. While he drew on the best observations made before him, he emphasized the need for repeated, increasingly precise observation. In fact,Ptolemy was a harbinger of the scientific spirit, an unsung pioneer of the experimental method. In trigonometry, for example, his table of chords has been found accurate tofivedecimal places. In spherical geometry he offered an elegant solution to the problems of sundials, which had special signifi- cance in that age before mechanical clocks. There was no branch of physical science that he did not survey and organize into newly usable forms. Geog- raphy, astronomy, optics, harmonics—each he expounded in a system. The best known of these was his treatise on astronomy, the Almagest. His Geography, which aimed to map the whole known world, pioneered in listing places systematically by latitude and longitude. There, too, he offered his own improved method for projecting spherical surfaces on flat maps. In view of the scanty factual reports available to him, Ptolemy’s maps of his “known world,” the Roman Empire, were a remarkable accomplishment. He showed the crucial scientific talents—shaping theories to fit available facts and testing old theories by new facts.


Boorstin, Daniel J., and Clare Boothe Luce. The Discoverers. New York: Random House, 1983. Print. 20-21. 


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