מסעות גילוי, והמהפיכה הקוסמוגרפית

1. שקיעת העולם האריסטוטלי מסעות גילוי, והמהפיכה הקוסמוגרפית

2. oikouménē - οἰκουμένη Phoenician and Carthaginian voyages around Africa, according to Herodotus As for Libya [Africa], we know it to be washed on all sides by the sea, except where it is attached to Asia. This discovery was first made by Necos, the Egyptian king, who on desisting from the canal which he had begun between the Nile and the Arabian Gulf, sent to sea a number of ships manned by Phoenicians, with orders to make for the Pillars of Hercules, and return to Egypt through them, and by the Mediterranean. 

3. oikouménē - οἰκουμένη Phoenician and Carthaginian voyages around Africa, according to Herodotus The Phoenicians took their departure from Egypt by way of the Erythraean Sea, and so sailed into the southern ocean. When autumn came, they went ashore, wherever they might happen to be, and having sown a tract of land with corn, waited until the grain was fit to cut. Having reaped it, they again set sail; and thus it came to pass that two whole years went by, and it was not till the third year that they doubled the Pillars of Hercules, and made good their voyage home. On their return, they declared - I for my part do not believe them, but perhaps others may - that in sailing round Libya they had the sun upon their right hand. In this way was the extent of Libya first discovered.

4. oikouménē - οἰκουμένη Phoenician and Carthaginian voyages around Africa, according to Herodotus I for my part do not believe them, but perhaps others may, that in sailing round Libya they had the sun upon their right hand. [i.e., after turning West (Cape of Good Hope?) Sun was at noon to the North ] Impossible for believers in a flat world (Herodotos?), or in a geocentric system (Aristotle – Ptolemy). Possible in the Copernican world!

5. Ptolemy’s Geographia Translated into Latin around 1406 (Jacopo d’Angelo); First printed edition with maps, in 1477 (Rome) – perhaps the first printed book with engraved illustrations. Italian cosmography – dominated by scholars and merchants.

6. Fra Mauro (1450) • Under a commission by king Alfonso V of Portugal. • Orientation with the South at the top, one of the usual conventions of Muslim maps.

7. Fra Mauro (1450) • "I do not think it derogatory to Ptolemy if I do not follow his Cosmografia, because, to have observed his meridians or parallels or degrees, it would be necessary in respect to the setting out of the known parts of this circumference, to leave out many provinces not mentioned by Ptolemy.”

8. Fra Mauro (1450) • “Jerusalem is indeed the center of the inhabited world latitudinally, though longitudinally it is somewhat to the west, but since the western portion is more thickly populated by reason of Europe, therefore Jerusalem is also the center longitudinally if we regard not empty space but the density of population.”

9. Fra Mauro (1450) • “Jerusalem is indeed the center of the inhabited world latitudinally, though longitudinally it is somewhat to the west, but since the western portion is more thickly populated by reason of Europe, therefore Jerusalem is also the center longitudinally if we regard not empty space but the density of population.”

10. Fra Mauro (1450) • Basic conventions: • The world as a sphere • The continents surrounded by water within the shape of a disc • The approximate size of the world ???

11. Fra Mauro (1450) • “Likewise I have found various opinions regarding this circumference, but it is not possible to verify them. It is said to be 22,500 or 24,000 miglia or more, or less according to various considerations and opinions, but they are not of much authenticity, since they have not been tested.”

12. Johannes de Sacrobosco(c. 1195 – c. 1256) ‘Tractatus de Sphaera’ (c. 1230) Ptolemy’s cosmology and cosmography

13. The accepted Islamic and Latin medieval view: A smaller sphere of earth rested lightly and eccentrically inside the sphere of water, surfacing above it only in the oikumene

14. Consequence: No antipodes opposite to the known world

15. Explanation (Aristotelian): • Jean Burdian (1300-ca. 1358)Quaestio on De caelo et mundo (“On the Heaven and the Earth”) • Center of gravity vs. Center of volume, in the spherical Earth, because water is of uniform density. • Sphere of earth emerged from the sphere of water, and the earth's center of gravity is displaced downwards. • The visible surface of the earth is kept dry because of the heat of the sun and other influences.

16. Explanation (Aristotelian): • Jean Burdian (1300-ca. 1358)Quaestio on De caelo et mundo (“On the Heaven and the Earth”) • Due to the continual dryness of the upper hemisphere that showed above the surface of the water, this condition remained stable. • Rivers eroded solid pieces of the upper hemisphere, taking the earth's center of gravity further down. • In this way, the sphere of earth would be continually rising out of the sphere of water.

17. Explanation (theological): • Bishop Paul of Burgos, (1351-1435) Based on Genesis, 3d day of creation • In Day 3, God had displaced the sphere of water in perpetuity away from the center of the cosmos. This was countered only once, during the Flood.

18. Fra Mauro (1450) • “God distributed weight unevenly within the spheres of earth and water. The resulting emergence of the inhabited hemisphere of earth from the sphere of water made it providentially possible for living beings to inhabit the land.” • [The confinement of the oikumene to one hemi-sphere resulted simultaneously from God's will and the laws of celestial physics.]

19. Portuguese Voyages of Discovery (1415-1486) 1440: Cape Verde 1474: the equator 1486: Cape of Good Hope Basic conceptions about the oikoumene start to be doubted. The idea of a single habited hemisphereremained!

20. Crossing the Ocean? • Cristoforo Colombo - Cristóbal Colón (1451-1506) • Contemporaries’ Main Objections: • A Western trip to Asia would take three years, • The Western ocean was boundless and impossible to sail, • The antipodes do not exist (most of the earth is submerged in water).

21. Crossing the Ocean? • Cristoforo Colombo - Cristóbal Colón (1451-1506) • Colón’s (wrong) idea: a low estimate of the westward distance from Europe to Asia. • A low estimate of the size of the Earth, • A high estimate of the size of the Eurasian landmass, • A wrong belief that Japan and other inhabited islands lay far to the east of the coast of China.

22. Crossing the Ocean? • Cristoforo Colombo - Cristóbal Colón (1451-1506) • Colón’s relevant knowledge (know-how): • Navigation techniques • The trade winds which would prove to be the key to his successful navigation of the Atlantic Ocean

23. Crossing the Ocean? • Cristoforo Colombo - Cristóbal Colón (1451-1506) • Colón’s right idea (based on wrong considerations): • “Earth and water together form one round body .”

24. Crossing the Ocean? • The antipodes do not exist (most of the earth is submerged in water). • vs. • “Earth and water together form one round body .” • How to decide? • Colón’s trip as the first big experiment of modern science!!

25. Crossing the Ocean? • Colón’s trip as the first big experiment of modern science?? • The first unexpected result of modern science!!!!!

26. Crossing the Ocean? • Colón’s trip as the first big experiment of modern science • The first unexpected result of modern science. • Initially: no clear account of the situation, no changes in cosmographical conceptions • Main consequence: many new exploration trips.

27. Amerigo Vespucci (1451-1512) • Cosmographer and seafarer: • Mundus Novus (1505) • “Classical authors claim that there is no continent beyond and south of the equator, but merely sea which they called the Atlantic; furthermore, if any of them did affirm that a continent was there, they gave many arguments to deny that it was a habitable land. But this last voyage of mine has demonstrated that this opinion of theirs is false and contradicts all truth.”

28. Amerigo Vespucci (1451-1512) • Cosmographer and seafarer: • Mundus Novus (1505) • There are Southern antipodes • There is no inhabited “upper hemisphere” (Europa, Mediterranean Africa, Asia), not covered by water and “lower hemisphere” (submerged) • Colón was right: “Earth and water together form one round body .” • The Cosmographic Revolution!

29. There are Southern antipodes • There is no inhabited “upper hemisphere” (Europa, Mediterranean Africa, Asia), not covered by water and “lower hemisphere” (submerged) • Colón was right: “Earth and water together form one round body .” • The Cosmographic Revolution? • No change in the Aristotelian universe • A problem with Aristotelian gravity as a comprehensive principle

30. שקיעת העולם האריסטוטלי מסעות גילוי, והמהפיכה הקוסמוגרפית