There is a mention of Pliny in the dedicatory letter to Emperor Rudolph II that precedes the New astronomy: “It is he [Mars] who is the most potent conqueror of human inventions, who, ridiculing all the sallies of the Astronomers, escaping their devices, and striking down the hostile throngs, kept safe the secret of his empire, well guarded through all ages past, and performed his rounds in perfect freedom with no restraints: Hence, the chief complaint registered by that Priest of Nature's Mysteries and most distinguished of the Latins, C. Pliny, that ‘Mars is the untrackable star’”, KeplerJ., New astronomy, transl. by DonahueWilliam H. (Cambridge, 1992; all references to New astronomy are to this translation), 32; KGW (Johannes Kepler Gesammelte Werke, ed. by CasparM. (Munich, 1937–)), iii, 8. Cf. Pliny, Natural history, Books 1–2, transl. by RackhamH. (Cambridge, MA, 2004), 221: “… Martis sidere (cuius maxime inobservabilis cursus est)”.
2.
Kepler's notebooks on Mars survive. They belong to the Russian Academy of Science, and are kept in St Petersburg.
3.
StephensonB., Kepler's physical astronomy (New York, 1987), KoyréA., La révolution astronomique: Copernic, Kepler, Borelli (Paris, 1961), and WilsonC. A., “Kepler's derivation of the elliptical path”, Isis, lix (1958), 1958–25, are among those who have contributed to the elucidation of the argument of the New astronomy.
4.
GingerichOwen, “The computer versus Kepler revisited”, The eye of heaven (New York, 1993), 367–75, p. 371. The article was originally published in 1973.
5.
Stephenson, op. cit. (ref. 3), 3. A fuller account is provided by VoelkelJ. R., The composition of Kepler's Astronomia nova (Princeton, 2001), pp. xiii–xvii.
6.
DonahueW. H., “Kepler's fabricated figures: Covering up the mess in the New astronomy”, Journal for the history of astronomy, xix (1988), 217–37.
7.
See Voelkel, op. cit. (ref. 5).
8.
Kepler indeed writes in chap. 6 of the New astronomy: “I, in the demonstrations that follow, shall link together all three author's forms. For Tycho, too, whenever I suggested this, answered that he was about to do this on his own initiative even if I had kept silent (and he would have done it had he survived), and on his death bed asked me, whom he knew to be of the Copernican persuasion, that I demonstrate everything in his hypothesis.” New astronomy, 157; KGW, iii, 89. This passage, often adduced as the sole explanation for the content of the first two parts of the New astronomy, conceals the role of the observational equivalence of geometrical hypotheses in the argument of the New astronomy.
9.
Cf. Donahue, op. cit. (ref. 6), 234.
10.
Cf. Stephenson, op. cit. (ref. 3).
11.
While composing the New astronomy, Kepler published his Optics (1604). There the author displays a deep influence stemming from the Oxford School, evident from the very title of the book: Ad Vitellionem paralipomena, quibus astronomiae pars optica traditur. Witelo's optics seems to have been strongly influenced by the works of Robert Grosseteste and Roger Bacon, cf. LindbergD. C., Theories of vision from Al-Kindi to Kepler (Chicago, 1976), 119. Methodological questions were dealt with by both Grosseteste and Bacon in opuscula dedicated to the solution of specific scientific questions. Cf. CrombieA. C., Robert Grosseteste and the origins of experimental science (Oxford, 1971), 87, 140, and 213–14. The motion of Mars, cuius est maxime inobservabilis cursus, may well be regarded as a problem particularly fit for the exposition of the adequate method for the study of planetary motions. See ItokazuA. G., “Astronomia nova: A história da guerra contra Marte como exposição do método astronômico de Kepler”, PhD thesis, University of Campinas, IFCH, 2006.
12.
The Latin text of the Defence is provided by JardineNicholas, The birth of history and philosophy of science: Kepler's A defence of Tycho against Ursus (Cambridge, 1988), along with an excellent English translation and several essays on its origin and significance. All references to Kepler's Defence of Tycho are to Jardine's edition. Since this article was prepared, an edition with French translation has appeared: Nicholas Jardine and Alain-Philippe Segonds, La guerre des astronomes (2 vols, Paris, 2008).
13.
Ursus's views on the nature of hypotheses may be appreciated in the extract from his “Tractatus” translated by Jardine, op. cit. (ref. 12), 41–57.
14.
The term ‘realism’ was well-expressed by Karl Popper in the twentieth century: “For the scientific tradition in its turn is, or was until recently, characterized by what may be called scientific realism. That is to say, it was inspired by the idea of finding true solutions to its problems: Solutions which corresponded to the facts.” PopperKarl, “A realist view of logic, physics and history”, Objective knowledge: An evolutionary approach (Oxford, 1972), 285–318, p. 290.
15.
Kepler, Defence of Tycho, 148; KGW, xx/1, 25.
16.
Ibid., 153–4; KGW, xx/1, 28.
17.
Cf. RussellJ. L., “Kepler and scientific method”, in BeerA.BeerP. (eds), Kepler: Four hundred years. Conference held in honour of Johannes Kepler, Philadelphia, 1971 (Oxford, 1975), 733–45, p. 734.
18.
Kepler, Defence of Tycho, 148; KGW, xx/1, 25.
19.
Kepler, Defence of Tycho, 138; KGW, xx/1, 20.
20.
Kepler, Defence of Tycho, 143; KGW, xx/1, 22.
21.
Kepler, Defence of Tycho, 143; KGW, xx/1, 22.
22.
Kepler, Defence of Tycho, 136; KGW, xx/1, 18–19.
23.
Kepler, Defence of Tycho, 139; KGW, xx/1, 20.
24.
On the introduction of the concept of ‘world system’, see LernerMichel, “The origin and meaning of ‘world system’”, Journal for the history of astronomy, xxxvi (2005), 407–41.
25.
Kepler, Defence of Tycho, 141; KGW, xx/1, 21.
26.
Kepler, Defence of Tycho, 141; KGW, xx/1, 21.
27.
Kepler, Defence of Tycho, 142; KGW, xx/1, 22.
28.
SzczeciniarzJ.-J., Copernic et la révolution copernicienne (Paris, 1998), 345.
29.
Kepler, Defence of Tycho, 140; KGW, xx/1, 21.
30.
Kepler, Defence of Tycho, 146; KGW, xx/1, 24.
31.
WestmanR. S., “Kepler's theory of hypothesis and the ‘realist dilemma’”, in BeerBeer (eds), op. cit. (ref. 17), 721–4, p. 721.
32.
WestmanR. S., “Kepler's theory of hypothesis”, Ibid., 713–20, p. 715.
33.
Kepler, Defence of Tycho, 141–2; KGW, xx/1, 22. It should be noted that these two tests lead to the establishment of Keplerian heliocentrism. The applicability to other correlate phenomena is typical of heliocentric planetary models, while Keplerian celestial physics is essentially heliocentric.
34.
“There were three things in particular about which I persistently sought the reasons why they were such and not otherwise: The number, the size and the motion of the circles”, KeplerJ., Mysterium cosmographicum — The secret of the universe, transl. by DuncanA. M. (New York, 1981; all references to this work are to the Duncan translation), 63; KGW, i, 9.
35.
Kepler, The secret of the universe, 75; KGW, i, 15.
36.
Kepler, The secret of the universe, 77; KGW, i, 15–16.
37.
Kepler, Defence of Tycho, 155; KGW, xx/1, 29.
38.
Kepler, New astronomy, 78; KGW, iii, 36.
39.
Cf. KeplerJ., Les fondements de l'optique moderne — Paralipomènes à Vitellion, transl. by ChevalleyCatherine (Paris, 1980), 99–101; Optics, transl. by DonahueWilliam H. (Santa Fe, NM, 2000), 13–15; KGW, ii, 14–15.
40.
Kepler, Defence of Tycho, 144; KGW, xx/1, 23.
41.
Kepler, New astronomy, 117; KGW, iii, 62.
42.
Kepler, Defence of Tycho, 154–5; KGW, xx/1, 29.
43.
Kepler attributes Thales's knowledge of eclipses to his contact with either the Babylonians or the Egyptians, for “he cannot have obtained a method for predicting eclipses on his own, since it is not the work of one lifetime to trace enough anomalies of the Moon for prediction of an eclipse of the Sun”, Defence of Tycho, 158; KGW, xx/1, 31.
44.
Kepler, New astronomy, 117; KGW, iii, 62.
45.
Kepler, New astronomy, 117; KGW, iii, 62–63.
46.
Kepler, New astronomy, 120; KGW, iii, 65.
47.
Kepler, New astronomy, 126; KGW, iii, 69. As we have emphasized throughout this article, Kepler ascribes the cause of planetary motions to the solar motive force. In this passage, all he means is that, since there are no solid orbs, any geometrical model that is to be physically acceptable must reckon the planetary body as the relevant point.
48.
In the New astronomy, as Rhonda Martens has noticed, even planetary minds and souls, if they exist, must operate naturally, that is, with reference to some body; otherwise they could not be efficient causes. Cf. MartensR., Kepler's philosophy and the New astronomy (Princeton, 2000), 82.
49.
Kepler, New astronomy, 127; KGW, iii, 69–70.
50.
“In adopting this account, we would indeed approach more closely the geometrical suppositions of the ancients, but we would stray very far from physical theory, as is shown in ch. 2”, Kepler, New astronomy, 410; KGW, iii, 258.
51.
Cf. Kepler, New astronomy, 137–8; KGW, iii, 75–76.
52.
It should be noted that in this chapter Kepler introduces a problem that later on would lead him to the adoption of the elliptic orbit: “But if, in addition, the planet's path is a perfect circle, as Ptolemy certainly thought, the planet also has to have some perception of the swiftness and slowness by which it is carried along by the other external power, in order to adjust its own approach and recession in such accord with the power's prescriptions that the path DE itself is made to be a circle.” Kepler, New astronomy, 135; KGW, iii, 74. The issue is dealt with in detail in chaps. 45 and 46 of the New astronomy.
53.
Kepler, New astronomy, 323–4; KGW, iii, 203.
54.
Cf. Stephenson, op. cit. (ref. 3), 53.
55.
Kepler, New astronomy, 152; KGW, iii. 85.
56.
Kepler, New astronomy, 152; KGW, iii, 85.
57.
The second inequality is that explained by Copernicus as the reflection of the motion of the Earth around the Sun on the other planets' motions.
