[Map of the Moon]

Engraved map, 557 x 567mm. First state of the reprint by Cassini IV, of the rare and beautiful map of the moon established by his great-grandfather Jean-Dominique, called Cassini I.

Jean-Dominique Cassini, known as Cassini IV, (1748-1845) was born at the Paris observatory to which his great-grandfather, also called Jean-Dominique Cassini, (1625-1712) collaborated. The latter was born in Liguria and studied at the observatory of Panzano under Giovanni Battista Riccioli and Francesco Maria Grimaldi. In 1669, he moved to France at the invitation of Colbert to help in the creation of the new Observatory of Paris before becoming its first director. Cassini ordered a 34-foot telescope from the great instrument maker Giuseppe Campani, which would prove crucial in the creation of his lunar map. With the help of artists Sebastien Leclerc and Jean Patigny. Cassini made about sixty drawings of the Moon between 1671 and 1679 from observations made during lunar eclipses (when possible), thus obtaining a clearer view of the surface and unusual light patterns. Fifty-seven of these drawings are preserved in the library of the Paris Observatory.

The map engraved on copper by Claude Mellan, was realized from these drawings. The technology and the observations made were so fascinating that a handwritten map showing the aspects of the Moon is reproduced in a 1680 painting in Versailles by Henri Testelin, showing Colbert presenting the members of the Academy of Sciences to Louis XIV. The quality of the three-dimensional rendering of the lunar features by Patigny and Mellan remained unmatched until the advent of photography.

It is the first faithful map of the Moon; it totally supplants the little detailed realizations of Cassini's predecessors whose simplicity was underlined by the observers of the time: thus, Robert Hooke compared the representation of the lunar formation of Hipparchus by Johannes Hevelius and by Riccioli, Cassini's teacher, to show the relative scarcity of the information they provided. Cassini's map shows a level of detail that can only be seen through a telescope twenty feet long or more. The dimensions and positions of the major features are relatively accurate, but the real strength of the map lies in the wealth of reliable information that is given about the lunar limb. The moon is oriented to the south, but with the lunar axis rotated 30 to 45 degrees clockwise. In addition to representing a scientific breakthrough, Cassini's map also played a role in a religious controversy; the moon has long been associated with the Virgin Mary by an analogy established between the supposed purity of its surface and the chastity of the Virgin, although from Galileo onwards, observations of the moon showed that its surface was far from perfect. It was indeed made of craters and mountain ranges. Cassini's map was therefore another refutation of the immaculate moon theory: despite this, Catholic astronomers did not abandon the concept until the end of the 17th century.

The map has two charming features that presumably refer to the wives of the men involved. In the lower half, on the Promontorium Heraclides mountain range along the Gulf of Rainbows, is a woman's head in profile, with long flowing hair. It is based on a real lunar structure, but is supposed to have been modeled after Cassini's wife, Geneviève de Laistre. Cassini had indeed had a pen-and-ink portrait of his wife done the year before the map was published by Patigny's son, so the identification could be correct. The other is the marking in the shape of the Greek letter phi (?) that appears in the Serenity Sea. In addition to having the approximate shape of a heart, it also begins with the Greek word philos, which means love or affection.

Also an astronomer, Cassini IV succeeded his father in 1784 as director of the Paris Observatory. In 1787, he found in the archives of the Observatory the original copperplate engraving of his great-grandfather's map of the moon and republished it. This second edition is identical to the first one, except for the addition of "Carte de la Lune... de Jean Dominique Cassini" on the lower edge. Cassini IV also published his own reduced version the following year. After the French Revolution of 1789, friction between Cassini IV and the National Assembly led him to resign as director. Briefly imprisoned the following year, he retired to Thury where he lived and worked until the end of his life.

The map includes an interesting handwritten addition: a small cross in one of the craters in the upper half of the moon corresponding to an inscription stating "Ville natale de l'abbe Vurtz". This may be a reference to Abbé Jean Mendel Wurtz (1760-1826), a relatively unknown clergyman who came to public attention in France after publishing several mystical texts, one of which condemned the French church and another identifying Napoleon as the Antichrist. Contemporary history describes his ideas as "productions of a sick imagination"; he was considered an ultimately harmless eccentric. Locating his birthplace on the moon could refer to one of his books, or could play on the cultural link between the moon and madness to suggest that he was mentally ill.

Albert van Helden,'The Telescope in the Seventeenth Century', ISIS 65 (1974); Helge Kragh, The Moon that Wasn't (New York:Springer, 2008); Françoise Launay, 'The moon maiden of Cassini's map', Astronomy and Geophysics 44 (2003); Launay, 'The woman's head on Cassini's moon map. A Declaration of Love', Astronomy 117 (2003); Scott L. Montgomery, The Moon and the Western Imagination (Tucson: University of Arizona Press, 1999); Ewen A. Whitaker, Mapping and Naming the Moon (Cambridge, 2003); Whitaker, 'Selenography in the Seventeenth Century' in R. Taton and C. Wilson (eds.), Planetary Astronomy from the Renaissance to the Rise of Astrophysics (Cambridge: Cambridge University Press, 2003).