SNEL, Willebrord (1580-1626) and Christoph ROTHMANN (1560-1600). Descriptio cometae, qui anno 1618 mense Novembri primum effulsit. Leiden: Elzevir, 1619.

First edition of Snel’s account of the 1618 comets, accompanied by the first publication of Christoph Rothmann’s account of the 1585 comet. Snel and Rothmann, who was also the constructor of the first modern star catalogue, both knew Tycho Brahe. "After observing the comet of 1585, Rothmann was one of the first astronomers to conclude that comets are cosmic objects. Rothmann had observed the comet from 8 October to 8 November, did not find a parallax, and determined the distance between the comet and the Earth to be 500,000 German miles; therefore it must have been far beyond the sphere of the Moon" (Hamel and Rothenberg, in Biographical Encyclopedia of Astronomers I, p 987). This observation was contra the wisdom of Aristotle; Rothman was also a dedicated Copernican. Although Snel, an accomplished mathematician, also observed that comets existed beyond the moon, he remained an adherent of the old Ptolemaic system. Bierens de Haan 4393; Willems 165W.

Quarto (201 x 157mm). Greek and Latin types. Woodcut device on title, diagrams in text (very faint dampstain to corner of last few gatherings, some sheets gently toned). Contemporary Dutch limp vellum, title in ink on spine (remains of green silk ties).