By JOSÉ RICARDO FIGUEIREDO*
Common sense and the most widespread prejudices can be powerful political weapons
The reaction to heliocentrism in the forms of religious condemnation of Copernicus' book and Galileo's trial is well known. Another scientific revolution had occurred two millennia earlier, with the discovery of the Earth's sphericity, but little is known about a flat-Earth reaction; a brief paragraph by Francis Bacon will give a clue to this.
The sphericity of the Earth was already admitted by the Pythagoreans and by Plato (427-347 BC) and his Academy, therefore since the 384th century BC, or before. The topic is treated by Aristotle (322-XNUMX BC) with arguments a posteriori e beforehand. Arguments a posteriori These would be, for example, the shape of the Earth's shadow during lunar eclipses, as well as the appearance and disappearance of constellations for a traveler in the North-South direction. A classic argument, also based on the experience of sea travel, would be added by Adrastus: “Often, during a voyage, one cannot see land or an approaching ship from the deck, while sailors who climb to the top of the mast can see these things because they are much higher and thus overcome the convexity of the sea, which is the obstacle” [1].
The argument beforehand of Aristotle relates to his view of dynamic phenomena. He conceived of two types of movements: natural and forced. The forced movement would be due to external causes, while the natural movement would correspond to the tendency of bodies to go to the center of the Earth, which would also be the center of the Universe. Although this tendency towards the center of the Universe acted on all bodies, “the more powerful weights are able to displace the smaller ones”, so that the natural place of heavier bodies would be low heights, and the natural place of light bodies would be the greater heights. The weight would not rigorously prove that the Earth would be spherical, it would only introduce a tendency in this direction; however, in the case of water surfaces, the fluidity of the liquid to minimally lower positions would lead to sphericity [1].
Aristotle reports a measurement carried out by mathematicians linked to him, calculating the circumference of the Earth in 400.000 stadia. Archimedes (287-212 BC) estimated it at 300.000 stadia. As is known, Eratosthenes (276-194 BC) found a method that allowed him to reach the figure of 250.000 stadia. This unit of measurement was not standardized; the Greek stadium was equivalent to around 185 meters, but the stadium used by Eratosthenes would be 157,5 meters according to Porto da Silveira [2], or 158,76 meters according to Rey [3], so that the 250.000 stadiums would be equivalent to 39.375 kilometers or 39.690 kilometers respectively. In both cases, the measurement is surprisingly close to the 40.009 kilometers currently recognized for the Earth's polar circumference.
This feat of Eratosthenes cannot be explained without reference to the historical and personal context. Eratosthenes worked at the Alexandria Museum, an institution created after the dismemberment of Alexander's empire (356-323 BC) by Ptolemy I (367-283 BC) or Ptolemy II (309-246 BC), and which was controlled successively by the Ptolemaic Kingdom, by the Roman Republic and the Roman Empire.
Bernal [4] notes that the Museum was the first research institute subsidized by a State, in a conscious and deliberate attempt to develop science, and observes that in the Alexandria Museum “Greek science grew in direct contact with the problems of both technical as well as the science of ancient Asian cultures, and not only of Egypt and Mesopotamia but also, to a certain extent, of India”. Among those who studied or worked in Alexandria are the mathematicians and astronomers Archimedes, Aristarchus of Samos (310-230 BC), Euclid (300 BC-?), Hipparchus (190-129 BC), Heron (5?-70 AD ), Claudio Ptolemy (90-168 AD), Papus (?-350 AD) and others, as well as literati and doctors.
Eratosthenes was a mathematician and geographer, author of a treatise called Geography. He was the first to give this science a mathematical basis, referring to the Earth as a globe and recording distances measured along what are now called parallels of latitude and meridians of longitude. As a baseline for his mapping, he employed a parallel that stretched from Gibraltar, across the mid-Mediterranean, to the Himalayas. [5]
The known description of the measurement of the Earth's circumference follows a report by the astronomer Cleomedes, who lived 200 years later. Eratosthenes started from the information that in Siena, today Aswan (located on the Tropic of Cancer), the Sun was absolutely overhead at noon on the summer solstice, and it was possible to see it reflected at the bottom of a well. He measured the tilt of the Sun on the same solar date and time in Alexandria, obtaining 7o12', equivalent to 1/50 of the 360o of the circumference. The relevant distance between both locations was determined at 5.000 stadia, which multiplied by 50 leads to 250.000 stadia for the circumference of the Earth. The method of measuring long distances was based on bimetatistes, surveyors trained to walk with regular steps [5], a method instituted by Alexander and Ptolemy I, imitating the Babylonians [3].
Rey [3] considers that Cleomedes' report would be simplistic because it does not make reference to the difference in longitude of 3o between Aswan and Alexandria. However, using Eratosthenes' geometric method, the problem does not exactly depend on the distance between the cities, but on the distance, measured along a meridian, between the parallels that pass through Aswan and Alexandria, which would be 5.000 stadia. The 3o difference in longitude do not interfere: they correspond to a difference of around 12 minutes between the solar noon of those cities, so that the experiment in Alexandria repeated what had happened, around 12 minutes earlier, at the intersection of the Alexandria parallel with the Aswan meridian.
Later, Hipparchus would correct the value of the Earth's circumference to 252.000 stadia, which is rather a confirmation than a correction.
In the face of such a scientific achievement, it is difficult to conceive of a setback. But a brief mention of a flat-earth reaction appears in Francis Bacon [6], for whom Natural Philosophy faced at all times, as tough adversaries, “superstition and the blind and immoderate zeal of religion”. He recalls the accusation of impiety against the first Greek thinkers who proposed natural causes for thunder and storms, and then comments: “some of the ancient priests (or fathers, parents in the original) of the Christian Church did not show greater tolerance towards those who, on the most convincing grounds (such that no one in their senses would think to contradict) maintained that the Earth was round, and consequently affirmed the existence of antipodes.”
The expression “ancient fathers of the Christian church” refers to the beginning of the affirmation of the Catholic Church, after being legalized and institutionalized in the empire of Constantine (306-337 AD). Two episodes are known from this period, relating to the Alexandria museum and the Platonic Academy.
Although it lost dynamism with the purge of intellectuals by Ptolemy VIII in 145 BC, as well as during Roman domination, the Alexandria Museum and its Library survived for a few centuries. One of the last directors was Theon (335-405 AD), whose daughter Hypatia (355?-415 AD) followed in his academic footsteps. Neoplatonic philosopher, mathematician and astronomer, Hypatia was also a respected public voice. She had the support of Orestes, Roman Prefect of Alexandria, who was facing a power struggle with Cyril, Bishop of Alexandria, who saw the Museum and the Library as pagan institutions to be defeated. At a time of worsening political tension, Hypatia was kidnapped and murdered after horrible tortures by a mob of Cyril's followers. Orestes would abandon his position after that. Cyril would later be canonized as Saint Cyril of Alexandria.
In the same vein, in 529 AD, the Byzantine emperor Justinian closed Plato's almost millennia-old Academy as a policy of abolishing pagan Hellenistic culture.
Would there be a fundamental incompatibility between Christianity and Greek philosophy? This is denied by history. Aurelius Augustine of Hippo (354-430 AD), after converting to Christianity in 386, introduced Plato's philosophy into Christian circles, and was canonized as Saint Augustine. Aristotle would become a fundamental reference for the Catholic Church after Thomas Aquinas (1225-1275).
As we see today, common sense and the most widespread prejudices can be powerful political weapons. In the murder of Hypatia, misogyny stands out. The intolerant flat-earthism cited by Bacon must have been very functional in the fight of “some of the ancient priests (or fathers) of the Christian Church” against the intellectuals of the Alexandria Museum and Plato's Academy.
*Jose Ricardo Figueiredo He is a retired professor at the Faculty of Mechanical Engineering at Unicamp. Author of Ways of seeing production in Brazil (Associated Authors\EDUC). [https://amzn.to/40FsVgH]
Notes
[1] Dugas, R., A History of Mechanics, Dover Publications, New York, 1988.
[2] Porto da Silveira, JA, Erathostenes and the measurement of the Earth, UFRGS.
[3] Rey, A., El Apogeo de la Ciencia Tecnica Griega, Union Tipographica Editorial Hispano Americana, Mexico, 1962.
[4] Bernal, J.D., Social History of Science, v.1, Science in history, Ediciones Península, Barcelona, 1967.
[5] Ronan, CA, Illustrated History of Science, viI, From origins to Greece, Zahar, Rio de Janeiro, 1983.
[6] Bacon, F., The New Organonin Selected Philosophical Works, Hackett Publishing Company, Indianapolis, 1999.
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