The 6th August was the 456th anniversary of the death of the Renaissance medicus Girolamo Fracastoro. He is most famous for having given the disease syphilis its name in his poem Syphilis, sive morbi gallici i.e. Syphilis or the French disease. This tells the story of the shepherd Syphilis, who is struck down by the new disease because he has blasphemed. The name if the Latinised version of the Greek name Syphilos which can be translated as ‘lover of swine’, maybe Fracastoro is trying to say that syphilis is the result of bestiality.
His other well known achievement as a doctor was his book from 1546 De contagionibus et contagiis morbis et eorum curatione, (Three Books on Contagions, the Contagious Diseases and their Treatment) which contains scientific descriptions of the plague, typhoid and foot and mouth disease. The book is also notable for Fracastoro’s contention that diseases are caused by seed-like entities a premise that foreshadows the germ theory of disease; although it should be pointed out that there are no links between Fracastoro and Koch.
Now some of you might wonder why I as a historian of mathematics should be interested in a mere medic? The answer is quite simple Fracastoro was, like many Renaissance medics, also an astronomer; the link being astrology, the main form of medicine in the Renaissance being astro-medicine or iatromathematics.*
In his capacity as astronomer/astrologer Fracastoro made two major contributions to the astronomical debate in the 16th century, firstly, he was one of several Paduan scholars who advocated a rejection of the Ptolemaic epicycle-deferent astronomy and a return to the Aristotelian homocentric astronomy. This was not new, the Islamic Aristotelian Averroes had suggested the same step in the 12th century criticising the Ptolemaic astronomy as infringing on the Aristotelian cosmological principle of homo-centricity i.e. that all heavenly bodies have a common centre of rotation, the earth. In the Ptolemaic system individual planets rotate around the centres of their epicycles that in turn rotate around the centres of their deferents, the earth. Averroes only criticised the Ptolemaic model as non-Aristotelian but al-Bitruji (fl. 1190) actually produced an improved mathematical homocentric model. Similarly in the early 16th century in Padua both Giovanni Battista Amico (1511? – 1536) and Fracastoro produced new homocentric models, Fracastoro publishing his Homocentricorum sive de stellis (Homocentric [Spheres] or Concerning the Stars) in 1538.
Now you may well ask what possible interest the publication of such a retrograde system, and the homocentric model is very inferior to the Ptolemaic system in explanatory power, could have for the evolution of astronomy? The answer is that it is part of the evidence that exposes a wide spread myth in the history of astronomy and cosmology. It is generally claimed in the popular presentations of the history of astronomy that Ptolemaeus’ geocentric view of the world reigned supreme, went unchallenged or was not questioned for 1400 years until Copernicus published his De revolutionibus. A different version of the same myth is that the scholastic synthesis of Aristotelian cosmology and Ptolemaic astronomy dominated the academic discourse without challenge until Copernicus etc. This is simply not true, both the Ptolemaic astronomy and the scholastic synthesis were criticised and questioned on many occasions and in the 16th century there were very lively debates amongst the astronomers and cosmologists of Europe on a large number of topics. The homocentricity of Fracastoro is just one example of these debates and Christoph Clavius the most influential arbitrator of all things astronomical and cosmological at the end of the 16th and beginning of the 17th centuries regarded the system of Fracastoro as at least as great a treat to his own preferred Ptolemaic system as the heliocentrism of Copernicus.
Another of the 16th century astronomical debates to which Fracastoro made a significant contribution concerned the nature of comets. In the 1530s Europe was visited by a series of spectacular comets and this produced several reactions under the leading astronomers. In Nürnberg, Johannes Schöner edited and published Regiomontanus’ book on comets and the measurement of cometary parallax that had been written in the 60s of the previous century but had remained unpublished due to his untimely death. In Ingolstadt Peter Apian published a series of pamphlets on his observations of these comets that included his observation, now know as Apian’s law, that the tails of comets always point away from the sun. This had already been known for a long time by the Chinese but was unknown in Europe. A lively debate developed between Gemma Frisius in Leuven, Jean Pena in Paris and Copernicus in Frauenburg concerning the nature of comets with Frisius concluding that comets were supra-lunar objects that focused the rays of the sun. This was of course in direct contradiction to the Aristotelian cosmology that stated that comets were sub-lunar. It was this debate that led the astronomers of Europe to try and measure the parallax of the 1577 comet with Tycho and Mästlin concluding that comets were supra-lunar and Tycho deducing from this that the crystalline spheres of Greek cosmology couldn’t exist. In Italy Fracastoro also observed the comets and independently arrived at Apian’s law, he also arrived at a very similar theory of comets to Frisius but reversing Tycho’s logic argued that comets must be sub-lunar because otherwise they would disturb the crystalline spheres; Fracastoro’s theories on the comets were taken up by Cardano.
There is a certain irony to the fact that Fracastoro published important texts on both syphilis and comets, as one of the prevailing medical theories of the period was that syphilis was a curse caused by comets. Fracastoro is a typical example of a relatively minor scholar who is today virtually unknown but in his own times made important contributions to the debate that propels the development of science.
*I shall post a detailed explanation of the connections between medicine and mathematics sometime in the future.