Telesio’s writing On The Comets and the Milky Way, composed around 1580, was first published in Venice in 1590, two years after Telesio’s death, by his pupil Antonio Persio. The new Latin version by Miguel Á. Granada is based on the first modern critical edition (edited by De Franco, 1981), which he improved by taking into account the two major manuscripts left (Biblioteca Nazionale of Naples, ms. VIII. C. 29 and Vind. Lat. 69). With rare and praiseworthy attention to Telesio’s lexical and rhetorical choices, Granada offers the modern reader the first translation of a Telesian work into Spanish. The text is introduced by an extensive study of Telesio’s life and work, presenting some of the turning points of Telesio’s physics and cosmology in the context of the sixteenth-century debate about the nature of the heavens. A large section is devoted to the major Telesian work, De rerum natura, analyzed in the three different editions of 1565, 1570, and 1589. In 1572 and 1577 Europe was impressed by two extraordinary phenomena: the nova, that is the supernova that was visible in Cassiopea, and the appearance of a comet. Telesio’s De cometis was directly influenced by these events and by the discussions they raised. Granada emphasizes the fact that Telesio still conceived the universe in terms of an internal modification of the geocentric, finite model of the world offered by the Aristotelian tradition. Until the second edition of the De rerum natura (1570), Telesio would maintain that comets were sublunar phenomena. In the booklet he does not mention any of his modern or ancient sources. It is clear though that his position has changed: comets are not, as Aristotle supposed, burning exhalations situated in the sublunar regions, nor are they brightening portions of condensed celestial matter, as Cardano, for example, supposed. Comets are not miracles, but natural phenomena, that can be explained as exhalations produced in the sublunar regions, which sometimes rise up to the celestial one. The light they emit is not their own, but reflected solar light, according to the “optical theory” maintained by Tycho Brahe and others. For Telesio the existence of exhalations above the moon does not imply the denial of the existence of the spheres. On the contrary: the last edition of the treatise (1586) confirms that stars are fixed on solid spheres. “Solid,” though, does not mean “hard” to Telesio, as Granada points out. If the existence of celestial comets had brought astronomers like Brahe, Johannes Praetorius, or Christoph Rothmann to reject the existence of the spheres, Telesio would preserve the traditional structure of the cosmos, conceiving them, however, as porous and penetrable. The same point had been maintained by some astronomers (like Caspar Peucer and Johann Hardeg) during the public debate — finely reconstructed by Granada — at the University of Wittemberg in 1573.

The nature of the Milky Way had been discussed by Telesio in the first edition of his treatise (1565). It was situated in the supralunar heavens and had been explained as existing on an intermediate level between the celestial fire, fine and invisible, and the stars, dense and brightening. The reference had disappeared in the edition of 1570, but Telesio came back to the problem in the second of the manuscripts containing his writing on the comets (ms. Vindob. Lat. 69), and introduced the passages on the galaxy in the final edition of his booklet. He maintained the same conception of the galaxy through the years. Opposing Aristotle, he considered the galaxy a genuine celestial phenomenon. The galaxy is in fact described as immutable: its movements are the same movements of the fixed stars. Its brilliance is due to the condensation of the matter it is made of. The same positions are maintained and discussed in the last edition of the treatise, referring in particular — as Granada argues — to Francesco Vimercati.

Granada’s introduction, edition, and translation are a solid contribution to a detailed theoretical and historical reconstruction of Telesio’s cosmology and, moreover, a remarkable step toward the interpretation of his thought in general. This makes the work a particularly worthwhile read for both students and scholars interested in the man whom Francis Bacon considered the first of the moderns.