Copernican Ephemerists on Hypotheses, Astrology and Natural Philosophy

chapter 3 Beyond Computation: Copernican Ephemerists on Hypotheses, Astrology and Natural Philosophy

It has long been almost a commonplace that sixteenth-century Copernican compilers of tables and ephemerides focused on computation and astronomical prediction and had no marked interest in cosmological and natural issues, that is, in questions related to planetary hypotheses and physics.1 In the preceding chapter, I already pointed out the weakness of this opinion due to the realist commitment of several German mathematicians. The concern for the “real” planetary order also emerges from the publications on ephemerides by several followers of Reinhold in different countries: Johannes Stadius in Flanders, Francesco Giuntini in France, Giovanni Antonio Magini in Italy and David Origanus in Germany. Besides these schools, I shall consider Reiner Gemma Frisius and Giovanni Battista Benedetti, Renaissance mathematicians who concentrated, among many other things, on computation along with (Copernican) cosmology. All of these scholars accompanied their work on tables and ephemerides with speculations on planetary hypotheses, although they did not necessarily share the same views, especially on terrestrial motion and heliocentrism. The variety of their opinions bears witness to the dimen- sions of the theoretical and philosophical debate involving scholars who have often been considered to be concerned exclusively with “saving the phenom- ena.” As I will show in the following, in many cases the circulation of tables and ephemerides was intended as a contribution to the debate on hypotheses as well as a means to stress the cultural value of astronomy, both theoretical and practical. As Renaissance ephemerists’ work was closely connected with astrological practice, I shall consider this aspect as well.

1 A Premise: Gemma Frisius as a Reader of Copernicus

Valuable evidence of an early reception of the heliocentric system as a physical reality is a letter by Gemma Frisius to his pupil Johannes Stadius. It was printed posthumously as a preface to the latter’s Ephemerides novae et exactae for the years 1554–1570 (New and Exact Ephemerides, 1556). Before I consider this

1 Duhem, To Save, chap. 6.

witness, it would be expedient to introduce Frisius and recount his acquain- tance with Copernicus. Frisius was a Flemish pupil of Peter Apian and a skillful inventor of globes and mathematical instruments. His correspondence shows intense contacts with Varmia, in particular with bishop Dantyszek.2 As a professor of medicine and mathematics at Leuven (beginning in 1541), he taught outstanding stu- dents like Mercator, Stadius and Dee. One of his major scientific contributions was a complete treatment of the principles of triangulation in a Libellus de locorum describendorum ratione (Booklet on How to Describe Places), which first appeared as an appendix to the Antwerp edition of Apian’s Cosmographicus liber in 1533, which was to influence famous scholars like Brahe and Snellius.3 Thanks to Frisius, Copernicus’s work and views spread throughout Flanders and beyond. Notably, references to Copernicus’s astronomy can be found in writings on mathematical instruments that are apparently far removed from the theoretical concerns of De revolutionibus, as for instance in the treatise De radio astronomico et geometrico (On the Astronomical and Geometrical Staff, 1545). The radius was “an astronomical and geometrical” instrument which served to “measure all the heavens and the Earth,” as its inventor claimed. Its purpose was to measure longitudes and latitudes, distances and heights in topography as well as in astronomy. Frisius celebrated the renewal of sciences in his time, especially that of medicine, which he regarded as an essential part of natural philosophy, and of mathematics (mathematicae artes). These disciplines, according to Platonizing neo-Pythagoreanism, should raise man to the cognition of the highest truths (maximae res). In De radio, Frisius was cautious about the astronomical novel- ties of those who, in his words, “aimed at, I do not dare say accomplished,” the emendation of astronomy. This seems to be a reference to Copernicus. In the same context, Frisius praised the recent advancements of astronomy and did not spare Ptolemy’s parameters, whose shortcomings had long since become evident through astronomical observation.4 He read and painstakingly annotated the chapters of De revolutionibus dealing with trigonometry5 and referred to Copernicus, together with Euclid and Regiomontanus, for the explanation of the geometrical and trigonometri- cal properties of his radius.6 In chapter 16, “On the Distances of Stars in the

2 See GA VI/1, passim. 3 Cf. Haasbroek, Frisius. For an introduction to Gemma Frisius, see: Hallyn, Gemma Frisius. 4 Frisius, De radio, f. 4r. 5 Gingerich, Annotated Census, 146–50. 6 For a eulogy on Copernicus’s trigonometry, see Gemma Frisius, De radio, ff. 35v–36r.