Placidus’s decade of the sky—the first-edition ephemeris that powered Placidian practice. THE BOOK Placido Titi (Placidus de Titis). Continuatio Ephemeridum Caelestium Motuum ab initio anni 1666 usque ad finem 1675. Pavia (Ticinum Regium): Apud Ioannem Ghidinum, [1666]. First edition. 4to. Full contemporary parchment. Very rare, only three copies in institutions. MOUSEION CURATOR NOTE “This is the ephemeris as instrument. Where Placidus’s Primum Mobile expounds doctrine, this Pavia printing supplies the numbers, times, and canonical figures by which a seventeenth-century reader actually judged nativities, revolutions, and public auguries. Its dual reckoning of event times—in civil P.M. hours and Italian hours from sunset—reveals an Italian readership attentive to local practice; the quarterly ingress charts and eclipse dossiers confirm a book at the hinge of astronomy and astrology.” BOOK DESCRIPTION First edition of the decade tables (1666–1675), a Pavia imprint adjusted to Italian longitudes and timekeeping. Placidus (Placido Titi) is a 17th-century mathematician/astronomer-astrologer who popularized the Placidus house system, today the most commonly used quadrant house method in Western astrology. Foundation for Placidian work: the numeric architecture from which charts are raised. This volume provides year-by-year positions and phenomena for 1666–1675. Its computational basis, explicitly stated on the title, follows the hypotheses of Philippe van Lansberge. Month by month the volume lays out daily planetary longitudes and motions, then braids them to practice with facing registers of “Aspectus Lunae cum Planetis”—subdivided by Vesperi and Matutin. for timed elections—and a running column of “Aspectus Planetarum mutui” (☌ ☍ △ □ ✶ at a glance). It goes further than ordinary almanac fare: quarterly Ingressus Solis supply the cardinal-sign ingresses for mundane judgment, while eclipse dossiers deliver a complete working kit—diagram and horoscope headed Caelestis Figura, parameters including anomaly and semidiameter, and the triad Initium / Medium / Finis given twice, in civil P.M. hours and in Italian hours counted from sunset. The result is a book that sits exactly where astronomy meets astrology: observatory arithmetic tuned to the needs of the astrologer’s desk. Crucially, the volume presupposes rather than teaches the Placidian house system. Here we have the numerical armature by which that doctrine is made to work, the “daily bread” without which no figure could be raised. As John Cooper would later praise Primum Mobile, “both the Physical and Mathematical parts of Astrology are most clearly explained”; this ephemeris supplies the timed data that make such clarity actionable. And in the long view—“Placidus is the most popular house system”—these decade tables are the engine that kept the method in motion. PROVENANCE Ex libris Owen Gingerich — bookplate on pastedown Harvard astronomer and historian of science, renowned for his census and marginalia study of De revolutionibus. With interesting early marginalia—apparently a late seventeenth-century Italian hand—extending the Aspectus tables. CONDITION REPORT Complete, and preserved in its original contemporary limp vellum binding, the volume’s leaves are clean and sound with only light, even toning—a well-kept working copy. Quarto; half-title present; Binding: full contemporary parchment, worn; collation A⁴, [–]⁴, A–Z⁴, Aa–Nn⁴; size 8¼ × 6¼ in (21.0 × 15.9 cm). Early marginalia. ADDITIONAL INFORMATION Placidus’s standing in both astronomy and astrology is unusual: professor at Pavia, yet remembered in technical literature for the “natural” division of houses still current in modern practice—context that helps explain the dual audience for his ephemerides. As Terentianus Maurus’s old maxim has it, Pro captu lectoris habent sua fata libelli—“according to the reader’s capacity, books have their destinies.” It fits both the working life of ephemerides and the scholarly afterlife of this ex-Gingerich copy.