[Perpetual calendar for 1801-1950]

[France? 1800 or 1801?]

2, 105, 3, 3 leaves | leaves 110 x 288 mm in case 126 x 301 mm

A complete perpetual calendar for the years 1801-1950, neatly handwritten on 105 oblong leaves, preceded by a 2-leaf tableau indicateur (more or less a traditional computus for calculating Easter), then followed by a 3-leaf calendrier lunaire (mapped to the former and allowing one to find the moon phase for any given day) and a 3-leaf tableau chronologique des eclipses (a table of upcoming solar and lunar eclipses through 1857). ¶  The perpetual calendar provides daily data for each of the 35 possible Easter-based calendar configurations: each day's date, day of the week (for both standard and leap years), fixed feasts, and movable feasts. The preceding tableau indicateur indicates which of the 35 daily calendars to use in a given year, 1801-1950, and additionally provides the day on which Easter falls, the year's dominical letter (linking dates to their days of the week), and the lunar epact (mapped to the calendrier lunaire and here allowing one to identify the moon phase for any given day). The calendrier lunaire also includes each year's dominical letter and its golden number (marking its place in the 19-year Metonic lunar cycle). The table of eclipses provides both solar and lunar eclipses, providing both the date and time of occurrence. All calculations appear to be quite accurate. We spot checked the lunar eclipses against NASA's chart, for example, and the moon phase calculations largely fall within 3% of those reported by moonpage.com (what we'd consider a daily margin of error for a table that doesn't provide the exact time of a particular phase). ¶ In some ways, this kind of perpetual calendar is itself an anachronism. The genre dates to the middle ages, and we can find printed ancestors in the calendars and almanacs commonly appended to books of hours and early liturgical texts. These typically omitted movable feasts and used dominical letters instead of the days' names, rendering them useful for many years—especially if one had separate tables to calculate the missing information. "As the rise of the printing press and the decreasing cost of printed books in the sixteenth century made textual calendars more disposable, time itself came to seem more temporary. Calendars, and especially the calendars proliferating in almanacs, were more likely to be accurate only for a certain year" (Chapman). Annual almanacs were in, perpetual calendars were out. Perhaps this calendar's saving grace is that it COMBINES THE BEST OF BOTH: it offers the multi-year utility of those medieval calendars, but deploys additional cross-referenced tables to provide the astronomical details and modern names of the days that came to characterize the annual disposable almanac. In any case, this manuscript's epact-based approach would soon be superseded by more modern mathematical approaches. Karl Friedrich Gauss is often credited with introducing the first algorithm in 1800. ¶ If this manuscript was indeed produced in France in 1800 or 1801, which seems most likely, then it coincided with the end of an unlikely crackdown on both Christianity and its traditional Gregorian calendar. In the early 1790s, both were abolished in France, casualties of the revolution's inexorable march toward wholesale secularization. It wasn't until July 1801 that the French state, under Napoleon's control, reconciled its relationship with the Catholic Church. While this Concordat of 1801 did not return the church's seized property, it did restore Catholicism as the country's primary religion. It's easy to imagine this manuscript serving a renewed, fundamental need that had essentially been outlawed in France for the better part of a decade. During those years, obtaining this information in published form must have become relatively difficult. While Catholicism may have been welcomed back, the traditional church calendar, at least officially, had not. The French Republican Calendar remained in effect through 1805. Given this history of suppression, there's something QUIETLY AND ODDLY SUBVERSIVE about this literally quotidian data. ¶  We can only speculate as to the manuscript's end use. Perhaps the calculations were made with a plan to publish. Or perhaps these represent the invisible calculations behind the great variety of perpetual calendars—metal pocket dials, portable paper instruments, etc. Or maybe the manuscript is its own end product, a series of comprehensive tables that could be put to a variety of uses both ecclesiastical and astronomical. Whatever the case, with a projection of 150 years, it's a stunning collection of practical calculations.

CONDITION: Handwritten in brown and red ink on the rectos only of printed forms, and of course we love anything that blends these two different methods of bookmaking. The forms have so many columns—more than we suspect any standard accounting practice would demand—that we wonder if they were printed specifically for this manuscript. The 105 calendar leaves are loose, as they always have been, but each of the three smaller components is tied with a pair of green ribbons at the inner margin. All housed in a later marbled chemise and slipcase. ¶ Folios 63 and 87 each with a small patch, presumably to correct errors; scattered mild foxing; first leaf of the tableau indicateur a little soiled, this essentially the title leaf; some corners and edges just gently bumped and creased. Chemise with several creases and its spine darkened; slipcase rubbed and darkened. Really in excellent condition.

REFERENCES: Alison A. Chapman, "Marking Time: Astrology, Almanacs, and English Protestantism," Renaissance Quarterly 60.4 (Winter 2007), p. 1270 (cited above); Reinhold Bien, "Gauß and Beyond: The Making of Easter Algorithms," Archive for History of Exact Sciences 58.5 (July 2004), p. 440 ("In August 1800 C.F. Gauß published an algorithm for determining the date of Easter day for any given year...It is often said that Gauß was the first scholar who worked out such a rule. This is not quite true. In 1776 J.H. Lambert published some lengthy and clumsy remarks...where he demonstrated a rule for finding the Eastern Easter only."); A. Cappelli, Cronologia, cronografia et calendario perpetuo (Hoepli, 1969), p. 35-105 (perpetual calendar for the 35 Paschal configurations); Faith Wallis, "What a Medieval Diagram Shows: A Case Study of 'Computus,'" Studies in Iconography 36 (2015), p. 8 (on a manuscript computus of ca. 1110, but her commentary still relevant here: "As tables, both the calendar and the paschal table visually store, distinguish, and arrange information that is inherently nonsyntactic. The units of information need to be kept discrete but also inflexibly correlated...The paschal table simply retains information for reference, but other kinds of tables permit information to be combined to generate the desired results. The calendar aligns the dates of the month with the various types of key letters that can be used with other tables to generate data about the weekday, or the age of the moon, or the position of the moon within the zodiac. Unlike the paschal table, these tables not only store information but permit the combination of data.")

Item #657