KEPLER, Johannes (1571-1630). Narratio de observatis a se quatuor Iouis satellitibus erronibus, quos Galilaeus Galilaeus … iure inventiones Medicaea sidera nuncupavit. Florence: Cosmo Giunta, 1611.

The third of Kepler’s three works written in response to Galileo’s Starry Messenger: this one, on Jupiter’s moons, records the first observations which Kepler made with a telescope. Second edition. “Not until August 1610 was Kepler’s great desire to use a telescope satisfied, when Elector Ernest of Cologne lent him one. From 30 August to 9 September, Kepler observed Jupiter; he published the results in Narratio de Jovis satellitibus [in Frankfurt], a booklet that was quickly reprinted in Florence. It provided a strong witness to the authenticity of [Galileo’s] new discoveries” (DNB). It further includes information on the mountains of the Earth’s moon. The Dissertatio was pirated by a different Florentine publisher in 1610—much to Kepler’s chagrin, 2as it harmed the sales of his self-financed Prague edition—but Caspar does not mention if the same was true for the Narratio. Caspar 38.

Quarto (205 x 150mm). Complete in 8 pages. (Light spotting to title-page.) Modern quarter morocco.