We enter into the terrestrial region by descending beneath the lunar sphere. This is the region of the four elements, which (in the idealized model) are arranged in concentric spheres, each in its proper place: firs fire, then air, followed by water, and finally earth and the center. Two of the elements - fire and air - are intrinsically light and naturally ascend; the other two -water and earth - are intrinsically light and naturally descend. The elements are continuously transmuted one into another owing to the influence of the sun and other celestial bodies. Thus, for example, water is transformed into air in the process we know as evaporation; conversely, air can be transformed into water to produce rain.
The fiery and aerial spheres were held to be the scene of various other meteorological phenomena such as comets, shooting stars, rainbows, lightning and thunder. Comets were considered to be atmospheric phenomena, the burning of a hot and dry exhalation that has ascended from the earth into the sphere of fire. Rainbows, as it was generally held, are produced when sunlight is reflected from the droplets of water in a cloud; various authors introduced refraction of light into the process; and early in the fourteenth century Theodoric of Freiberg (d. ca. 1310) offered an explanation very close to the modern one, employing the combined reflection and refraction of light to the modern one, employing the combined reflection and refraction of light in individual droplets.
At the center of everything is the sphere of the earth. Every medieval scholar agreed on its sphericity, and ancient estimates of its circumference (about 252,000 stades) were widely known and accepted. The Terrestrial land mass was typically divided into three continents - Europe, Asia and Africa - surrounded by sea. Sometimes a fourth continent was added. Beyond such basics, knowledge of the surface features of the earth and their spatial relationships varied radically with time, place and individual circumstances. Berengar has given a good outline of medieval geographical knowledge, I would just like to go over a few pertinent points here.
Geographical knowledge existed in many forms during the Middle Ages, and we must be careful not to indulge the modern tendency to identify it exclusively with maps or map-like mental images. Of course, medieval people had first-hand, experiential knowledge of their native region. Knowledge of more distant places could come from travelers, of which there were many sorts: merchants, artisans, laborers, pilgrims, missionaries, warriors, troubadours, itinerant scholars, civil and ecclesiastical officials, even fugitives and the homeless. For the few fortunate enough to have access to libraries, books such as Pliny's Natural History or Isidore of Seville's Etymologies offered geographical knowledge of a more exotic sort and on a grander scale in the form of written descriptions. Pliny and Isidore communicated a substantial collection of geographical lore (some of it mythological) through use of the "periplus"- a sequential list of the cities, rivers, mountains and other topographical features encountered as one navigated a coastline. This information was usually accompanied by interesting historical, cultural, and anthropological detail. Drawing on earlier compilations, Pliny and Isidore led their readers on a swift tour of the periphery of the European and African continents. Towards the end of the Middle Ages, new travel literature began to enrich the store of such knowledge.
Traditional literary sources also dealt with climate, dividing the terrestrial globe into climatic zones or "climes." In a typical scheme, there were five of these: two frigid zones (the arctic and antarctic) around the poles, a temperate zone adjacent to each of thee, and a torrid zone straddling the equator and according to some divided into to distinct rings by a great equatorial ocean The torrid zone was considered uninhabitable on account of its heat - though some scholar disputed this claim. Medieval Europeans, of course, found themselves living in the northern temperate zone. On the opposite side of the earth, in the southern temperate zone, are the antipodes. Whether the antipodes are inhabited by antipodeans (people who walk upside down) was a matter of dispute.
There is a natural tendency for those of us familiar with modern maps to organize our geographical knowledge spatially, by the use of map coordinates, thereby reducing geography to geometry. This was not true of medieval people, most of whom had never seen a map of any kind, let alone a map constructed on geometrical principles. Such maps as medieval people produced were not necessarily intended to portray in exact geometrical terms the spatial relationships of the topographical features indicated on them, and the notion of scale was almost nonexistent. Their function may have been symbolic, metaphorical, historical, decorative or didactic. For example, the thirteenth-century Ebstorf map employs the world as a symbol of the body of Christ. To avoid misrepresenting medieval aims and achievements, we must be careful to regard medieval maps as failed attempts at modern mapping.
Among the most numerous, most interesting, and most studied medieval maps are the mappaemundi, or world maps. The most common form of mappaemundi was the T-O map, associated with Isidore of Seville, which gave a schematic representation of the three continents - Europe, Africa and Asia. The "T" inserted with the "O" represents the waterways (the Don and Nile Rivers and the Mediterranean Sea) believed to divide the known land-mass into its major parts: Asia at the top of the map, Europe at the lower left, and Africa at the lower right. Nonschematic versions of the T-O map, which departed from the rigid T-O diagram in order to incorporate a variety of geographical detail, were also produced. Another common type of map was zonal, featuring the climatic zones as its organizing principle.
Medieval mapping took a mathematical turn in the form of the portolan charts, embodying the practical knowledge of sailors and designed to facilitate travel by sea. These maps, invented in the second half of the thirteenth century, offered a "realistic" representation of the coastline and employed a network of "rhumb lines" arranged around a compass rose to convey the distances and directions between any two points. First applied to the Mediterranean sea, portolan charts were later produced for the Black Sea and the Atlantic coastline of Europe. The use of portolan charts made possible more adventurous voyages of exploration, which in turn greatly expanded European geographical knowledge. Cartography was decisively transformed, finally, by the acquisition of Ptolemy's Geographia, translated into Latin early in the fifteenth century, which taught Europeans the mathematical techniques by which to represent a spherical body on a two-dimensional surface.
If map-making seems impressive for its practicality, we may do well to restore balance to this section by concluding with an investigation of a question that will appear (at least on the surface) to have no practical application whatsoever - namely, whether the earth rotates on its axis, and what would happen if it were to do so. Aristotle had convincingly presented the grounds for believing the earth is stationary; and although all medieval scholars agreed with this, several thought the arguments for a rotating earth worth exploring. In looking at this question, they joined good ancient company, for the idea had never entirely disappeared from ancient cosmological and astronomical literature: Aristotle, Ptolemy and Seneca all discussed it. The most searching explorations of the implications of a rotating earth came in the fourteenth century from John Buridan and Nicole Oresme.
Secretum secretorum index - De Mirabilibus Mundi index
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Last modified: Sun Dec 27, 1998 / Jeremiah Genest