Although highly anticipated the expectation placed upon De revolutionibus and the reactions to it were highly diverse and covered a very wide spectrum from complete acceptance to total rejection with many variation in between. It would be impossible in a blog post series such as this one to deal with the multitude of single reactions that would require a fairly substantial book; in fact I have two such books sitting next to my computer at the moment–Pietro Daniel Omodeo, Copernicus in the Cultural Debates of the Renaissance: Reception, Legacy, Transformation (Brill, 2014) & Jerzy Dobrzycki ed., The Reception of Copernicus’ Heliocentric Theory (D Reidel, 1972)–which I recommend to anybody who wants an in depth, blow by blow account. What I intend to do here is sketch the basic trends of that reception.
Famously Robert Westman once claimed that only ten people in the whole world accepted Copernicus’ heliocentric hypothesis, including his cosmology, completely between its publication in 1553 and the year 1600. His list actually misses a couple of total accepters such as Gemma Frisius, who acknowledged his acceptance in his foreword to Johannes Stadius’ ephemerides, and the Englishman John Feild who made the same acknowledgement in his ephemerides. However, it does include three others who either dropped or appeared to drop their acceptance. Christoph Rothmann (born between 1550 & 1560 died probably after 1600) one of Wilhelm IV’s astronomers (of which more later), who had an extensive dispute with Tycho Brahe, who of course didn’t accept Copernicus’ cosmology, on the subject and in the end, and according to Tycho was converted to his point of view. Diego de Zúñiga (1536–1597), a Spanish Augustinian hermit and academic, who wrote a defence of the heliocentric hypothesis in his In Job commentaria (1584) but later in life rejected Copernicus’ hypothesis as incompatible with Aristotelian philosophy, probably under religious pressure from his superiors. The most peculiar renegade was Copernicus’ first and initially strongest supporter, Rheticus. Having gone quiet on Copernicus and his hypothesis for some time after he moved to Kraków, in a correspondence with Pierre de la Ramée (1515-1572) he announced that he had erected a large gnomon in Kraków and was now practicing the true astronomy of the Egyptians, whatever that might be. Summa summarum, one can say without much contradiction that there were never more than about fifteen, and probably less, true Copernican in the world before 1600 or even before 1609/10 when the publications of Kepler and the invention of the telescope became game changers.
There were a few astronomers, who simply rejected Copernicus’ hypothesis without comment and some, who simply ignored it but they won’t interest us here because the evidence shows that the vast majority did react to it in some way or another. As already mentioned earlier Owen Gingerich carried out a survey of all known surviving copies of the 1st(Nürnberg 1543) and 2nd(Basel 1566) editions of De revolutionibusand his analysis of the annotation and marginalia of the readers clearly shows that the majority took very little notice of the first cosmological part of the book but concentrated their reading instead on the technical parts of the book, the mathematical models and the data.
This rejection of the heliocentric aspect of Copernicus’ work was a simple and direct consequence of the fact that he could not provide any empirical evidence to support his claims that the Earth revolved on its own axis and that it orbited a stationary Sun. Both claims very clearly contradicted the evidence of one’s own senses, we still say the Sun rises and sets, and suggested consequences that Copernicus was unable to answer. If the Earth is rotating at approximately 1600 kilometres an hour at the equator, why doesn’t everything on the surface get blown off by the headwind? And if the Earth is orbiting the Sun, why can’t we detect stellar parallax? These are just two of the possible objections to which Copernicus could not provide scientific answers.
The answers, based on assumptions, which he did propose would prove with time and new developments in science to be fundamentally correct but at the time there were merely unsubstantiated assumptions. In answer to the first he suggested that everything on the Earth’s surface would be carried along with it in some sort of envelope. This turned out to be correct but Copernicus lacked the physics necessary to explain how this would function. In fact the history of physics of the seventeenth century, as we shall see, consisted to a large extent of developing the knowledge to provide this explanation. As far as stellar parallax was concerned, or rather the lack of it, Copernicus simply and correctly assumed that the stars were simply too far away for the parallax to be detected with the naked-eye. However, Copernicus and almost all of his contemporaries still believed in the sphere of the fixed stars and if this sphere was so far away that stellar parallax was undetectable then the distance between the orbit of Saturn and the sphere of the fixed stars would have to be inconceivably vast and thus not very acceptable. Simply put, why all of that empty space out there?
The ambivalence towards Copernicus magnum opus is nicely illustrated by the Welsh mathematicus Robert Recorde (c. 1512–1558) in his The Castle of Knowledge (1556) the first English text to refer to the Copernican hypothesis. On the subject of the possible motion of the Earth he wrote:
But as for the quietness of the earth, I need not to spend any time in proving of it, since that opinion is so firmly fixed in most men’s heads, that they accompt it mere madness to bring the question in doubt. And therefore it is as much folly to travail to prove that which no man denieth, as it were with great study to dissuade that thing which no man doth covet, neither any man allow: or to blame that which no man praiseth, neither any man liketh.
Scholar: Yet sometimes it chanceth, that the opinion most generally received, is not most true
Master: And so do some man judge of this matter, for not only Eraclides [Heraclides] Ponticus, a great Philosopher, and two great clerks of Pythagoas school, Philolaus and Ecphantus, were of the contrary opinion, but also Nicias [Hicetas] Syracusius, and Aristarchus Samius, seem with strong arguments to approve it: but the reasons are too difficult for this first Introduction, and therefore I will omit them till another time. And so I will do the reasons that Ptolemy, Theon and others do allege, to prove the earth to be without motion: and the rather, because those reasons do not proceed so demonstrably, but they may be answered fully, of him that holds the contrary. I mean, concerning circular motion: marry, direct motion out of the centre of the world seemeth more easy to be confuted, and that by the same reasons, which were before alleged for proving the earth to be in the middle and centre of the world.
Scholar: I perceive it well: for as if the earth were always out of the centre of the world, those former absurdities would at all times appear: so if at any time the earth should move out of his place, those inconveniences would then appear.
Master: That is truly to be gathered: how be it, Copernicus, a man of great learning, of much experience, and of wonderful diligence in observation, hath renewed the opinion of Aristarchus Samius, and affirmeth that the earth not only moveth circularly about its centre, but also may be, yea and is, continually out of the precise centre of the world 38 hundred thousand miles: but because the understanding of that controversy dependeth of profounder knowledge than in this Introduction may be uttered conveniently, I will let it pass till some other time.
Scholar: Nay sir in good faith, I desire not to hear such vain fantasies, so far against common reason, and repugnant to the consent of all the multitude of Writers, and therefore let it pass for ever, and a day longer.
Master: You are too young to be a good judge in so great a matter: it passeth for your learning, and theirs also that are much better learned than you to improve [i.e. disprove] his supposition by good arguments, and therefore you were best to condemn nothing that you do not well understand but another time, as I said, I will so declare his supposition, that you shall not only wonder to hear it, but also peradventure be as earnest then to credit it, as you are now to condemn it.
In this exchange Recorde appears to both reject and praise Copernicus’ hypothesis. Unfortunately we will never know his true opinion as he died before he could write the advanced text that he promises his readers here. What, however, is very clear is that Recorde is very well informed about the history of both diurnal rotation and the heliocentric hypothesis.
Some of the readers, who only considered the mathematical parts of the book, simply took Copernicus’ models for the various planets and applied them to a geocentric system, hoping thereby to produce a better predictive model for the position of the planets. Other took this remodelling a step further and using Copernicus’ mathematical models revived the Capellan model, well-known and much loved in the Middle Ages; a geocentric system in which Mercury and Venus orbit the Sun, which in turn orbits the Earth.
Others took this thought one step further and developed, what is now known the Tychonic system, named after Tycho Brahe (1546–1601), although he was by no means the first or the only astronomer to publish this system in the second half of the sixteenth century, all claiming to have developed it independently. In this helio-geocentric system all of the planets except the Moon, orbit the Sun, which together with the Moon orbits the stationary Earth. Heliocentric, geocentric and helio-centric model based on Copernicus’ parameters and mathematical model can and have been shown to be mathematically equivalent with nothing to recommend one over the other, without further information.
One interesting but slightly confusing development was that some geocentric and helio-geocentric astronomers accepted the arguments for the Earth spinning on its own axis, diurnal rotation, whilst still rejecting the Earth orbiting the Sun. As I wrote here in an earlier blog post, this idea goes back at least to Heraclides Ponticus (c.390 BCE–c.310 BCE) and was adopted or discussed and rejected many times over the centuries down to Copernicus’ times. The argument in its favour is a purely physical one. It is much simpler for the comparatively small Earth to rotate than for the vastly larger and heavier sphere of the fixed stars. This acceptance of diurnal rotation would prove to be an important steeping stone to the complete acceptance of the heliocentric model in the seventeenth century.
On major group, who showed great interest in Copernicus’ mathematics and above all in the planetary tables and ephemerides that they delivered were the astrologers. This basically means all professional and half professional astronomers, as they were almost all practicing astrologers. As stated above Robert Westman once claimed that there were only ten Copernicans in the whole world between 1543 and 1600, a historian of astrology correctly pointed out that all ten were practicing astrologers. Like Regiomontanus in the previous century (see Part II of this series) they all thought that more accurate astronomical data would improve the quality of their astronomical prognoses. Not only did they avidly consult the ephemerides of Stadius and Feild but several of them such as the Italian mathematicus Giovanni Antonio Magini (1555–1617) unsatisfied with Stadius’ and Feild’s accuracy also calculated their own new ephemerides. In the end, however, the astrologers recognised that although the errors in Copernican tables were different to those in Ptolemaic ones they were not much more accurate as we will see in the next instalment.