KEPLER, Johannes (1571-1630). Dissertatio com nuncio sidereo nuper ad mortales misso Galilaeo Galilaeo. Frankfurt: Zacharias Palthenius, 1611.

Kepler’s endorsement of Galileo’s observations with the telescope. Third, pirated edition. Galileo published his "Starry Messenger" in early March 1610, and Kepler received a personal copy from the author on April 8 in his capacity as Imperial Mathematician to Rudolph II, via the Tuscan ambassador at Prague. Gone were the days when Galileo did not deign to reply to Kepler's request to review his own book!

Kepler's reply to Galileo's letter was dated April 19. Kepler left the letter unsealed so that the ambassador could read it if he wished. In the event, so many people were interested in what the great Kepler had to say about Galileo's extraordinary discoveries, that Kepler decided to print this letter at his own expense. The present pamphlet is the text of the 19 April letter, with a dedication to the ambassador, an address to the reader, and a postscript. It was first printed in May 1610 in Prague and was the first of three treatises in reply to Galileo. Kepler's work helped Galileo to persuade some of his critics in Italy. Galileo wrote to Kepler: "I thank you because you were the first one, and practically the only one, to have complete faith in my assertions" (DSB). Casper 37.

Octavo (149 x 85mm). Woodcut initials and ornaments (title-page browned and rehinged, other leaves toned). 19th-century marbled boards (backstrip lacking, tender). Provenance: Christian Frisch, 1802-1882, historian of Kepler (note by:) – V. Šafařík, probably Vojtěch Šafařík, 1829-1902, Czech chemist and amateur astronomer for whom a crater on the Moon is named (ownership inscription dated 1882) – Owen Gingerich (bookplate).