Kepler, Johannes

4to (192 x 138mm.), 4 leaves (of 8), title within typographic border, woodcut tailpiece, later vellum, contemporary manuscript note in gutter of A2v with mention of Clavius's edition of De Sphaera, lacking final four leaves, each leaf remounted, small tear in title-page

Christopher Clavius (1538-1612), presentation inscription at foot of title-page; Alessandro de Mihalik (Sándor Mihalik, 1900-1969, art historian and museum director in Hungary), Rome, 1928, inscription at end

Caspar 25; Zinner 4047; Kepler, Gesammelte Werke IV (Munich, 1941), pp.424-425

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ONE OF FOUR RECORDED COPIES OF KEPLER'S LETTER ABOUT A SOLAR ECLIPSE, PRESENTATION COPY TO CHRISTOPHER CLAVIUS. The other known copies are in Munich, Vienna, Zurich and Harvard University (which acquired its copy in 2013). The pamphlet was in two parts: the actual letter to fellow astronomers, and the brief tract with Kepler's own observations of the eclipse, which he felt were less than satisfactory. The Kepler manuscripts at the Pulkovo Observatory in St Petersburg contain a list of intended recipients of the letter, including Clavius; other notable scientists included Maestlin and Magini.

The eclipse was due to take place on 12 October 1605, and Kepler had alerted the scientific community in advance. He watched it from the balcony in the Emperor's gardens in Prague but was unable to take sufficient observations. His letter, dated St Martin's day (11 November), particularly addressed to those in northern Spain, southern France and the islands of Corsica and Sicily (where the eclipse was total), requested help with details of observations from other astronomers in different geographical locations in order to record the eclipse accurately. The letter was distributed from early December onwards, particularly by envoys to the court of Rudolph II and by the Jesuits, and Kepler began receiving replies a few weeks later, beginning with Aegidius Martin in Antwerp, the Jesuits Nicolaus Serarius and Johann Reinhard Ziegler in Mainz, Stanislaus Crzistanowic in Louvain and Eberhard Schele in Osteel, the latter of which mentions that Kepler had sent him seven copies of De solis deliquio for distribution. Peter Casal, secretary to Archduke Ferdinand in Graz, sent out three copies of the letter to Italian correspondents and sent replies back to Kepler in July 1606, though few of the observations Kepler received were of much assistance. Clavius did not send a reply, though Kepler had hoped for one.

Clavius (1537-1612) was based in Rome and contributed to the Gregorian calendar reform; he was probably the most prominent mathematician of his day. As a Jesuit he was firmly opposed to the Copernican system but he did confirm Galileo's sighting of the satellites of Jupiter and the phases of Venus, published in 1610, both of which rendered the Ptolemaic system invalid.