78

Pierre Gassendi (1592-1655)

Mercurius in Sole Visus et Venus Invisa Parisiis, Anno 1631. The First Observation of the Transit of Mercury.

Paris: Sumptibus Sebastiani Cramoisy, 1632.
Quarto, first edition; rare at auction this copy was sold in the Macclesfield sale in 2004, tucked into a group lot; full modern calf with gilt tooling; 6 3/4 x 4 3/4 in.

[Together with] Wilhelm Schickard's (1592-1635) Pars Responsi ad Epistolas P. Gassendi de Mercurio sub Sole Viso, Tubingen: Typis Theodorici Werlini; impensis Philiberti Brunni, 1632, first edition, quarto, written in response to Gassendi's pamphlet; bound in full 19th century red morocco tooled in gilt, marbled paper pastedowns; 7 x 5 in.

Gassendi's very rare first edition account gives the first published description of the Transit of Mercury. As predicted, Mercury passed before the sun on 7 November 1631, and Gassendi was there to watch and take notes.

"When the historian of astronomy writes about the historical importance of transits of Venus and Mercury across the Sun, it is usually with reference to the internationally coordinated observations of the 18th century, designed to produce an accurate measure of solar parallax. The first transit ever observed, however, that of Mercury of 1631, was important for an entirely different reason: it supplied for the first time an indisputable quantitative measure of the apparent magnitude of a planetary disc."

"It appears that most serious astronomers who had an opportunity made preparations to observe these predicted transits. Kepler had advised them to project the image of the Sun on paper by means of a telescope, or by means of a simple camera obscura if they did not have a proper telescopic setup. For a number of reasons only a few men in Europe succeeded in observing the transit of Mercury. Most were foiled by the weather, which is usually less than cooperative in November and December in most parts of Europe. Moreover, the transit of Venus was, in fact, not visible in Europe, and there is no record of anyone attempting the observation in the New World. Out of all this effort came only one published and usable observations of the transit of Mercury of 1631, that made by Pierre Gassendi. Gassendi was in Paris at the time, and when he read Kepler's admonition he began making preparations for the observations. The apparatus he used for observing sunspots from time to time would obviously suit his purpose best. Gassendi used a darkened room in which the image of the Sun was admitted through a simple Galilean telescope and projected onto a piece of paper. [...] An assistant was stationed in the room immediately below, where he was to measure the Sun's altitude with a two-foot quadrant each time Gassendi stamped his foot." (Quoted from Albert van Helden's "The Importance of the Transit of Mercury of 1631," as published in the Journal for the History of Astronomy, Vol.7, 1976).

From the same article: "[...] Schickhard himself could not believe that Mercury could be as small as Gassendi had seen it, and tried to explain how the planet could be as large as everyone had thought it to be and could yet appear so small. He tried by various optical arguments to preserve for Mercury a diameter of at least one minute of arc."

See also lot 101 for Hortensius's work on the Transit of Mercury.

  • Notes: Ex libris Professor, Astronomer, Historian & Bibliophile Owen Gingerich.
  • Condition: Gasssendi: A-F4. Strickland: A-E4.

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