Paris: L'Imprimerie de P. Fr. Gueffier, Libraire-Imprimeur, rue de la Harpe, 1774. 12mo (13.6 × 7.8 cm). Later green marbled boards with gilt-tooled leather spine; 110,  pp., illustrated with 6 folding tables of calendrical data (hors-texte) and three volvelles, affixed to leaf of card stock following p. 92. Followed by 12 perpetual monthly calendars, along with a "Table des fêtes mobiles." The adjoining pages 93- are pasted in pairs, with movable letterpress leaves inserted within cut-out windows. Contemporary signature to author's printed initials on title page. All tables and volvelles in proper working order, save for snapped-string to one volvelle. With errata slip pasted to verso of title. Very good.
The author prefaces this work with a critique of other "so-called" perpetual calendars, which he claims to be either too difficult to use or not truly "perpetual," as they lack the complexity to carry out the full range of possible computations. Instead, the author has created a remarkable instance of "proto-computer" engineering, a small volume which uses moveable paper to achieve the necessary calculations from the first day of the Christian calendar and until the End of Days; "on peut le regarder comme le Manuel le plus précieux, le plus intéressant, & le plus nécessaire pour tous ceux qui s'appliquent, ou par goût, ou par état, à l'étude de l'Histoire, de la Chronologie, & comme pouvant suppléer en beaucoup d'occasions le grand Ouvrage de l'Art de vérifier les Dates." Each of the three volvelles comprises two rotating circular parts with calendrical data used for calculations: one is a concordance of the solar cycle with the dominical (Sunday) letters; a second juxtaposes the Golden numbers (nombres d'or) and the epact numbers, typically used to calculate the date of Easter; the third allows matching days of the week with dominical letters and their corresponding months. The folding tables contains such information as a perpetual chart of dominical letters and information on calculating lunar cycles. The twelve perpetual monthly calendar leaves list each of the saints, the time of sunrise and sunset, and the dominical letters; a moveable strip of paper allows for assigning different weekdays for each calendar day. The work also mentions perpetual calendars engraved on glass, available from same bookseller. The book features several irregularities in pagination (as recorded by the Iowa State catalog entry): “five of the six folded leaves of tables bear page numbers, which duplicate numbers already in used in the main sequence (46, 57, 68, 72, 107). The loose table, i.e. the fifth one, is unnumbered.; Includes six double leaves. These twelve pages are tables, one for each month. To account for the days of the week, each table has a narrow vertical window with a strip of printed paper inserted behind it.; Irregularities in pagination: the doubled leaves are part of the main sequence, but their numbering is as follows: 97, 98; 100, 99; 101, 102; 103, 104; 105, 105; and 107, 107. In spite of this, the order of the months is correct... Finally, the pages following the double leaves should be numbered 109-112; instead, they are 108-110, .” As of August 2019, KVK, OCLC show five copies in North America: at Yale, Princeton (imperfect copy), Cincinatti, Iowa State, and Texas Austin.
Book ID: 50085