Columbus and the shape of the Earth, a “Holywood” story

It is said that Washington Irving’s biography of Christopher Columbus, published in 1828, was the work that started the legend that the discoverer of America was the person that convinced the ‘nearly medieval’ Europeans of his time of the sphericity of the earth, a legend that has captured the popular imagination since then. Nothing could be, however, farther from the truth, for all educated people during the Middle Ages knew perfectly that the earth was round, especially after the cosmological works of Plato (Timaeus), Aristotle (De Caelo, Physics) and Ptolemy (Almagest) were translated into Latin and commented by scholastic philosophers after the 11^th and 12^th centuries. Actually, the roundness of the earth was such a trivial fact that Thomas Aquinas, in is Summa Theologica (13^th century) put it as an example of a fact that is beyond any reasonable doubt, for there are many ways of proving it, the most important ones being that mountains are seen before the cost from ships approaching land from the see, that the shadow of the earth during moon eclipses is always round, and that, since the earth is the most heavy element, tending naturally towards the centre of the universe, it would tend to accumulate there from all directions with the same intensity. The two former arguments are ‘empirical’, and equally valid in Aquinas time than now, whereas the third one is ‘theoretical’, grounded in a theory (ancient Greek cosmology) in which we don’t already believe, but that is closely reminiscent of our own explanation of why planets are round due to the influence of gravitation.

But, if the roundness of the earth was common knowledge within cultivated Europeans of the time of Columbus, what was all the fuss about? It is well known that the great discoverer grossly underestimated the size of the earth: whereas most of the astronomers of his time accepted a figure very close to the real one, and based on Eratostenes measures in the 3^rd century BC, Columbus thought it was much smaller, so that the distance from Spain to Japan crossing the Atlantic should be of around 3000 miles, instead of the approximately 12000 miles really separating them. Of course, had no big mass of land existed in between, the travel would have taken too much time for a ship to transport enough provisions. It is reasonable, hence, that most of the governments of the time refused to finance such a crazy and suicidal expedition… But what made the project really suicidal for Renaissance intellectuals was not their (mostly right) assumption about the real distance between Europe and Asia through open see, for after all, there could be some intermediate land between both continents, like the Canary Islands of the Azores Archipelago, colonised by Spain and Portugal less than a century before. Or couldn’t they?

Well, the fact is that the learned people of the time had an argument, or believed in a theory, according to which it was actually impossible that something like America, nor even a set of small islands, could exist in the mid of the ocean, that is, in the mid of the ocean assumed to extend from Western Europe to Easter Asia. The responsible of this theory was a man of probably English ascent called John of Holywood (not to confuse with Hollywood), better known by his Latinized name Johannes de Sacrobosco, the author of the most influential treatise of astronomy during the late Middle Ages, and well into the 17^th century, De Sphera (written approx. 1230 AD), and also one of the introducers of Arabic numerals in Europe.

Though the title of his book refers not to the sphere of the earth, but to the shape of the whole universe, whose most external limit would be the sphere of the fixed stars, it also clearly demonstrated the sphericity of the earth itself, by basically the same arguments we have mentioned regarding Aquinas, and that date back at least to Aristotle in the 4^th century BC. Actually, Sacrobosco’s schema of the world is basically that of Aristotle’s cosmos, implemented with the planetary theory of Ptolomy (i.e., the theory of epycicles), of which De Sphera is a short popularisation, and the first systematic introduction in Western Europe to the Almagest after its translation from Arabic to Latin in Toledo a few decades before.

As in the case of Aquinas, Sacrobosco, also a monk, attempted to combine in a systematic exposition the known empirical facts (observations of the skies and of the earth’s surface) and the theoretical understanding of the world, that came basically from Aristotle’s Physics. It is known that, according to that cosmology, the universe is made out of five different ‘elements’: ether, of which the celestial spheres are made, and the ‘sub-lunar’ four classical elements. These four elements are ordered in the world according to their density, the denser ones occupying the closest positions to the centre of the cosmos, and hence earth is in the most ‘inferior’ position, then it is placed water, on top of which is air, and finally fire, that rises till touching the orbit of the moon. Ether would be still ‘lighter’ than fire, and this is the reason why it occupies the most privileged, celestial position.

This vision of the cosmos also implied that (for what we would now call ‘reasons of symmetry’) of every element there would be an equivalent amount (i.e, ‘mass’, or simply ‘weight’): this is why the size of the celestial orbits is so incredibly bigger than the ‘sub-lunar’ world (i.e., the space comprised between the moon and the earth): because ether weights very, very little. Analogously, fire weights much less than air, and air much less than water, and this is why the moon is relatively so far from the surface of the earth (‘far’ in a human scale, but, as we have just seen, very close as compared to the total size of the universe, or as compared to the distance from the moon’s orbit to the fixed stars), for the space between the surface of the earth and the orbit of the moon has to contain a incredibly large volume of air and fire.

And, what happens with the two remaining elements, water and earth. The same reasons of symmetry still rule here, and hence, since water is less dense than ‘earth’ (by between one fifth or one tenth, more or less, depending on what kind of nature we assumed ‘pure’ earth has, i.e., more ‘earthy’, more ‘rocky’, or more ‘metallic’), there should exist a much bigger volume of water than of earth in the world, so that the total ‘weight’ of both elements remain the same. Hence, the complete picture of the Aristotle-Holywood cosmos would be roughly the following: a tiny sphere of ‘earth’ in the middle, surrounded by a sphere of water of about ten times the size of the former, this surrounded by a sphere of air still much bigger, this one surrounded by a sphere of fire much, much, much bigger, and this one surrounded by an astonishingly (‘astronomically’) big system of spheres made of ether (those of the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and the fixed stars, in order of distance from the centre of the world). This is a nice picture, but one that has a major problem of empirical adequacy: if it were true, we would be drowned by a few thousands of kilometres of water, which obviously is not the case. The question is, hence: if earth weights more than water, why it is that there is some earth over the surface of water? Why is not all earth just sunk?

The monkish mind of Sacrobosco had an expedient answer: when creating the world, God displaced a little bit the sphere of earth from the centre of the universe, so that a tiny fraction of earth emerged out of the surface of the sphere of water, a part big enough to contain the continents known by the time (Europe, Asia and Africa, i.e., the ‘old world’), a portion of dry land of which it could be easily assumed it had an approximately circular shape. A clear and obvious consequence of this image of the world is that no other masses of dry land can exist, apart of the ‘old world’, for, as we started to navigate on a ship from, say, Lisbon towards the west, the surface of the earth sphere is progressively more and more deeply submerged under the surface of the sea (the water sphere), exactly till the middle of the trip, when we the distance between the surfaces of both spheres starts to decrease again.

Since this idea of the cosmological distribution of the four elements was the prevailing one in Columbus times, it was clear for the minds of most intellectuals that nothing like America could exist. And this was why its discovery started not only to change the societies of both sides of the Atlantic ocean (especially those of the west side), but also to break into pieces the idea that Aristotle and Ptolemy were people in which could trust enough when trying to understand the structure of the cosmos. By the way, this also would lead to the modern idea of the ‘earth globe’, i.e., a planet basically made out of solid rock, with just a tiny amount of water scattered on its surface, and also a tiny layer of air surrounding it, something that, in its turn, started to discredit the theory of the ‘four elements’.

References

Sacrobosco, J., De Sphera, translation of L. Thorndyke, online

Wootton, D., 2015, The invention of science, London, Harper Collins.