HUYGENS, Christiaan (1629-1695). Systema Saturnium. The Hague: Adriaan Vlacq, 1659.

First edition, first state, of the first full announcement of the ring and satellite of Saturn. The mystery of Saturn's "arms" had puzzled astronomers in the decades following Galileo's observation in 1610 of the planet's oval shape. Starting in the 1650s, Huygens and his brother Constantijn acquired great skill in the grinding and polishing of spherical lenses, and the telescopes that they built were the best of their time. In 1655, using their first greatly improved telescope, Huygens spotted a satellite of Saturn, later named Titan. Although still unable to physically make out the cause of Saturn's odd and variable shape, Huygens theorized that it was due to a single flat ring, whose inclination to the line of sight varies. "He arrived at this solution partly through the use of better observational equipment, but also by an acute argument based on the use of the Cartesian vortex (the whirl of 'celestial matter' around a heavenly body supporting its satellites)" (DSB). In 1656 Huygens presented his theory in a one-sentence anagram included in Pierre Borel's De vero telescopii inventore, thus securing priority of the discovery. Systema Saturnium contains as well "many other observations on the planets and their satellites, all contributing to an emphatic defense of the Copernican system" (Norman), and an observation and illustration of the Orion nebula. This is the first state of the text, with the correct orientation of the plate on page 18 mounted directly over the incorrectly printed one (see Raymond Giordano, The Antiquarian Scientist, No. 33 (2002)). Norman 1136.

Quarto (181 x 135mm). With errata. Folding engraved plate, 11 engraved illustrations, 8 woodcut diagrams and initials (title-page stained with repairs to gutter and outer margin, leaves trimmed just grazing running title in a couple places, 4 engravings trimmed beyond platemark). Modern calf, gilt ornaments on spine, red spine label. Provenance: Harvard College (release stamp on verso of title-page).