SOURCE: “The Problem of the Calendar,” in Time's Alteration: Calendar Reform in Early Modern England, UCL Press, 1998, pp. 31-44.

Easter is a feast, not a planet. You do not determine it to hours, minutes and seconds.

Kepler

Since the start of the Christian era, the calendar has been one of the most fertile of all sources of theological controversy.¹ The calendar was never merely a system of calibrating the year, capable of being perfected, for there was no single agreed natural standard against which it could be measured out. Rather, there were several reference standards: solar (the year), lunar (the month), and terrestrial (the day). Onto the framework created from these incommensurable natural quantities was laid a cycle of feasts and festivals which were human in origin, part civil and part religious. In the end, the choice of a calendar—and even the question of who had the authority to alter it—was a religious and cultural matter. In the Europe of the reformation and counter-reformation, calendar reform was bound to be controversial, and there was no purely scientific solution.

The calendar was complicated: but why had it become such a problem? Why, indeed, had the need to reform it arisen at all? To understand this one must take a long view. A clock takes days to gain or lose time; a calendar takes centuries. In setting a clock, one has only to check it against a better clock. In setting a calendar, it is necessary to look back to its inception to find an appropriate reference point, and to locate rules, principles and authority for the exercise. The extent to which the calendar is a cultural rather than a natural construct then becomes apparent. Until the late seventeenth century, most writers on the calendar in England worked from religious assumptions, using religious arguments, and with reference to religious issues: the papal origins of the Gregorian calendar made this inevitable. The historical legitimacy of the Church of England was a significant issue at the time of the English rejection of the Gregorian calendar in 1583, and was also prominent around the time of the second English rejection of calendar reform in 1699–1700. It was, in the end, not possible for a country which had rejected the pope, without achieving security for its own church, to embrace his calendar. It would be easy to dismiss this as an example of English insularity and prejudice, but the Gregorian reform itself was born of religious concerns. To appreciate this, we must adopt the perspective of the calendar reformers themselves and look not to sixteenth-century Europe but first to ancient Rome.

THE WESTERN CALENDAR AND THE PROBLEM OF EASTER

The Julian calendar, which still forms the framework of the western calendar, was instituted in imperious style by Julius Caesar in 45 bc. The solar calendar, inherited from Egypt, had fallen far out of line with the movements of the solar system upon which it was supposed to be based, apparently owing to manipulation of the erratic system of intercalary months (that is, “leap months”) for political and religious reasons by the priests responsible for its regulation. The calendar eventually drifted nearly three months out of true. The vernal (spring) equinox, which should have marked the boundary between winter and spring (with day and night roughly equal), now fell in mid-winter, the winter solstice in early autumn, and so on. Julius Caesar, advised by the Greek astronomer Sosigenes, ordered that the year 46 bc should have 445 days to return the equinoxes back to their intended stations; this was dubbed the “year of confusion”. Taking the length of the year as 365[frac14] days, he introduced the current system of twelve months of roughly similar length and the practice of keeping the calendar closely in line with the seasons by adding a leap day every fourth February.

Caesar's calendar obtains today, modified slightly by Caesar's successor Augustus, in order to perpetuate his own name in a full-length month, and by the Gregorian adjustment of 1582. The vision of Caesar and his immediate successors can be seen as a project to institute a universal, solar time, centred historically and physically upon Rome. In 10 bc an obelisk was erected in the Campus Martius, set in a vast plaza inscribed in a grid pattern marked with the hours, days and signs of the zodiac. As Borst explains, “No-one entering the Campus Martius could fail to see that the Caesars united heaven and earth, the Orient and the Western world, and the origin and evolution of time and history, or that they marked the beginning of a universal time”.²

The Julian calendar became the official calendar of the whole Christian church at the first council of Nicaea in ad 325. As the first general council of the Christian church, summoned by the first Christian emperor, Constantine, the council of Nicaea predated the split between the eastern and western churches, and its decisions continued to command the assent of virtually all Christians even after the protestant reformation. During the middle ages, however, it became increasingly obvious that the Julian calendar did not measure the year accurately; its figure of 365[frac14] days was too long by some eleven minutes, the error amounting to around one day every 114 years. The vernal equinox, which had in ad 325 fallen around 21 March, fell in the sixteenth century around 11 March. An exact solution to this problem was hampered by a medieval cosmology based on the beliefs that the earth was at the centre of the universe, and that all heavenly motions were perfect and therefore circular. Such a cosmology was incapable of explaining inconsistencies caused by imperfections such as the elliptical orbits of the moon and planets, the difference between the tropical and sidereal years, and the slow wobble of the earth's axis which caused the mysterious precession of the equinoxes. Nonetheless, medieval measurements of these motions were accurate enough for calendrical purposes. The calculation that the solar calendar had drifted by ten days since the time of Nicaea was not seriously contested. If this had been the only consideration, the reform of the calendar would not have been controversial.

The unique complication in the Christian calendar was Easter. The crucifixion and resurrection of Christ had, in the biblical account, taken place around the time of the Jewish festival of the Passover, which in turn was determined by the time of the first full moon of the month Nisan. This lunar event was complicated to track in the solar calendar of Rome, but need not have been a problem had the Christian church been willing to fix Easter either to the full moon or to the Passover. The church, however, wanted to observe Easter on a Sunday. This served the wider aim of distancing Christian festivals from Jewish ones, and thus Christianity from Judaism. Easter therefore became a moveable feast, determined by an artifical lunisolar formula whose nature and purpose were never quite agreed even by those who understood it. In time, an understanding of the problem of Easter became an almost indispensable part of the mental equipment of any clergyman. It was also until recently an indispensable part of the undergraduate modern history curriculum at Oxford, even though—or perhaps because—as J. D. North sighs, “It is hard to look into the history of Easter celebration without growing despondent at the excesses of misplaced scientific zeal to which it testifies”.³

Easter was simply very difficult to calculate. It was governed by three variables (the equinox, the full moon, and the Sunday) whose relationship was so complex that it was 1876 before a mathematical formula subtle enough to describe it could be discovered.⁴ Easter is the theological equivalent of the Schleswig-Holstein question, that Gordian knot of nineteenth-century diplomacy of which it was said that all who had ever understood it had either died, gone mad or forgotten all about it. It has that defining characteristic of all great insoluble controversies: the more one tries to simplify it, the more complicated it becomes. Yet understand it we must, in order to see why it was important to contemporaries and why the reform of the calendar was controversial in its day.

In the early Christian church, Easter was celebrated on various dates: by some on the Jewish Passover, by others on the nearest Sunday (which might coincide with the Passover), and by the church of Rome on a Sunday which was always after the Passover. Both Jewish and Greek methods of calculating the lunar cycle were in use, but the date of Easter itself was determined annually, and by local observation of the moon, which in turn could yield a different date in different longitudes. The whole point of the pronouncements of the council of Nicaea on the calendar was to ensure that all Christians should celebrate Easter at the same time, part of a project to secure general Christian uniformity. The adoption of the Julian calendar was the first step; the second was an order that in the observation of Easter all should “conform to the Romans”. This (in simple language) placed Easter on the first Sunday on or after the full moon after the vernal equinox (21 March)—that is, at some time between 22 March and 25 April.⁵ Easter was the central focus of Christianity and a five-month cycle of major fasts and feasts was subsequently tied to it, from the beginning of Shrovetide seven weeks before Easter Sunday to Corpus Christi sixty days after it.

Easter was thus from the very beginning a theological and not an astronomical event. In determining the date of Easter, astronomy was at best a useful witness; religion was the true guide. The method eventually adopted was first worked out by Dionysius Exiguus, the sixth-century monk best known for having instituted the system of dating from the birth of Christ whose date he (inaccurately) calculated for the purpose. His successors, notably Bede, developed a system of calculation known as the computus in order to find the date of Easter. The formula involved the use of the dominical letter (A-G) to indicate the day of the week upon which new year's day fell, and the golden number (1-19) to indicate which year of its 19-year cycle the moon was in. Reference had also to be made to a number of other cyclical variables, including the Roman indiction or tax year, needed to date the earliest events of the Christian era. There were numerous other complications to make allowances for: the Jewish method of finding the full moon by conting fourteen days after the new moon, which for technical reasons had to be incorporated but which for religious reasons could not be duplicated; inclusive and exclusive methods of counting the days; different Jewish and Christian customs of starting the day (sunset in Jewish lands, midnight, dawn or even noon elsewhere); and the four-yearly “slip and claw-back” cycle of leap days.

The computus relied not on science but upon complex rules and tables, formulated for theological ends. The moon of the heavens was not the moon of the church, and the moon of the church was indeed “a mean moon”.⁶ This theological approach to time reckoning had several implications. It defeated the Roman end of a universal time system, complicating pure solar time with lunar months and sabbath days. It distanced the Christian church from pagan reliance on the exact observation of natural time for discerning omens and destinies: as Augustine had put it, God “wanted to make Christians, not mathematicians”. Finally, it subordinated the calendar to ecclesiastical authority; the church was “the master and not the slave” of Easter, and Easter itself became the chief end and determinant of a correct Christian calendar.

In the eighth century the Christian system of dating and time reckoning was systematized by the Anglo-Saxon monk Bede who (as Borst explains) “brought together time reckoning, the liturgy, and historiography”. The use of the computus was extended from Easter to all time reckoning. A new martyrology was instituted with the allocation of no less than 114 days to the memory of different saints. Bede used chronicles and gospels to verify historical and Christian time, dating both the creation and the incarnation, and firmly establishing the use of the year of the incarnation (the “year of our Lord”) for dating in western Christendom. Bede's learning spread to the continent, and the first Holy Roman Emperor, Charlemagne, in the early ninth century ordered the universal adoption of Bede's computus. The result was to make of the ecclesiastical computus an arcane discipline, separate from common timekeeping. The computus thus became insulated from later waves of interest in time as a numerical discipline (as in the use of the abacus and in music) and as a system of codifying real, historical events. This wider discipline became known as the “great computus”; ecclesiastical time reckoning was simply the “small computus”.⁷

None of this mattered too much as long as the ecclesiastical measure of Easter commanded general agreement. It took time to establish the Nicene rule everywhere. The date of Easter was the main sticking point in Bishop Augustine's dispute with “the faithless Britons” in ad 603, and the conflict between Romanist and Scottish-influenced Christians in the British isles continued for much of the seventh century.⁸ Bede's account of the confusion at the court of King Oswy is well-known:

Queen Eanfled and her court, having a Kentish priest named Romanus who followed the Catholic practice, observed the customs she had seen in Kent. It is said that the confusion in those days was such that Easter was sometimes kept twice in one year, so that when the king had ended Lent and was keeping Easter, the Queen and her attendants were still fasting and keeping Palm Sunday.

All this was eventually resolved in favour of Rome at the synod of Whitby in 664, by appeal to Nicene authority and ancient practice rather than to any supposed true astronomical Easter.⁹ It was to be several centuries before the divergence between the ecclesiastical Easter and the apparent Easter of the heavens became great enough to reopen the issue.

The problem of Easter as it developed in the thirteenth century was twofold. Firstly, the method of determining the date of the full moon by the golden number had proved to be faulty; the lunar cycle did not repeat itself on a nineteen-year cycle as assumed, but rather it slipped one day in 308 years. This might not have mattered too much to a church accustomed to using a hypothetical moon to determine Easter, had it not been for the separate problem of solar drift, by which the date of the vernal equinox was moving apart from the natural equinox by one day every 134 years. Even this would not have mattered had the church fathers at Nicaea not anchored Easter to the date rather than to the equinox. It was a classic example of a “pole and punt” problem. As the pole of 21 March and the punt of the equinox drifted apart the church fathers chose the pole, and were left marooned as the true equinox floated away in the stream of time. Infrequently at first, but increasingly often over the centuries, the Easter of the church failed to take place on the Sunday indicated by observation of the heavens.¹⁰

Awareness of the dislocation of Easter coincided with dissatisfaction among clerics over the divergence between the ecclesiastical computus and the real-world science of natural time measurement. Jennifer Moreton has recently demonstrated how a concern for a more natural method of time reckoning lay behind the proposal for reform of the computus by Roger of Hereford in the twelfth century. She is able to show that Roger drew upon a west country Celtic method of calculating Easter which had survived the Romanizing campaigns of the seventh century; here again, the diffusion of calendars reflects that of cultures.¹¹ In the early thirteenth century Robert Grosseteste and Jean Sacrobosco sought to reform the computus, with ingenuity but without acceptance. A wider desire to reconcile ecclesiastical and natural time measurement motivated the English friar Roger Bacon to appeal to the pope in 1266 for a general reform of the calendar. His reasons were mainly religious: to divide up the time left to mankind with greater accuracy, and to avoid Christians appearing ignorant before Muslims when explaining ecclesiastical methods of time reckoning. Bacon, however, also believed that calendar reform would help “rationalize civic trade”—the first appearance of a long-running argument that a more accurate and natural method of time reckoning would be of economic benefit.¹²

The question of calendar reform was considered at papal level again in the 1340s, in the 1430s, and in the early sixteenth century. Each time it was shelved, partly because of the confusion it would cause in adjusting contracts and interest payments at the changeover, and partly because of lack of medieval interest in the precise measurement of anything, but above all because sufficiently accurate astronomical measurements were not available. The council of Basle went so far as to cancel a week at Whitsun in 1439, arguing that “since it is a movable feast, the general public [vulgus] does not think about what particular day it falls upon”.¹³ Early printed farmers' almanacs give the impression that this was still the case in the sixteenth century, their range of graphic symbols for astronomical, liturgical and seasonal events reflecting “an entire cosmos of deep-rooted time regulation, a mixture of faith and superstition, experience and prejudice, that could not be called into doubt by any science of mathematics”.¹⁴ The spread of printed almanacs in this period, however, can only have created an impression that there was something wrong with the calendar as their owners, uninitiated in the mysteries of the computus, found the official date of Easter inconsistent with the equinox and moon of the almanacs. The reform of the calendar may have been a result of the invention of printing.

THE GREGORIAN REFORM OF THE CALENDAR, 1582

If the fate of the reformed calendar in England and the rest of the protestant world is to be understood, it is essential to grasp the nature of the Gregorian reform. Measurement, the subject of most of the discussion, was only a means to an end. As Westman explains, “Both protestant reformers and catholic counter-reformers saw mathematics as a weapon in the overall conflict for the salvation of souls. The reform of the calendar … was symbolic of the church's power to shape social reality”.¹⁵ Although it drew upon some of the chronometrical advances of the age its purpose was not scientific but religious: it was “an act of the counter-reformation”.¹⁶ In North's words, “the real key to the movement for reform was the desire to celebrate Easter at the correct time”.¹⁷ The over-arching aim was to reconcile the ancient computus with astronomical advances while preserving the authority and traditions of the church of Rome. It was a reform of the computus as much as a reform of the calendar. At a time when advanced thinkers were coming to terms with the plurality of human time reckonings and beginning to see the computus as a vain and foolish pseudo-science, the Gregorian reformers made one last heroic attempt to shore up the entire edifice, and retain a single over-arching system of time reckoning set on a religious foundation.¹⁸

It would be tempting to equate the sixteenth-century reform of the calendar with the rise of modern, Copernican astronomy—tempting, but wrong. It is true that Copernicus's treatise De Revolutionibus began life as a response to a request of the Lateran councils of the early sixteenth century for more accurate information upon which to base a reform of the calendar. Indeed, Copernicus himself stated that his book “promises a reform of … the calendar”—he believed he had solved the age-old problem of the precession of the equinoxes, a discrepancy in the length of the year caused by the earth's wobble on its axis, inexplicable on the assumption that the earth was static.¹⁹ Copernicus's figures may even have been used in the Gregorian calculations, although thee is some doubt about this.²⁰ There, however, the case for seeing the Gregorian calendar reform in terms of the scientific revolution ends. While Rome's condemnation of Copernicus still lay in the future, it was keeping his ideas carefully quarantined. Clavius, the Jesuit astronomer behind the reform, was an anti-Copernican, and later (according to a recent biographer) “explained that the reformers deliberately avoided connecting the new calendar with specific astronomical hypotheses”.²¹ The reform of the computus required practical measurement, not cosmological theory.

The Gregorian reform involved an attempt to re-assert papal authority over a divided western Christendom. As contributors to the Vatican quatercentenary conference stressed, it was a religious act. “It cannot be said too often”, writes North, “that the calendar problem in the period under discussion was a church matter”; “from a scientific point of view, the calendar debate is disappointing”. For Ziggelaar, the Gregorian reform was “fundamentally a great act of religion, one of respect for tradition in the Church”; it was promulgated in a papal bull “as an ecclesiastical law”, “under the full authority of the Pope”, intended as “an ecumenical act”.²² This last point requires some explanation. The order for the reform to be made was given by the pope at the last session of the council of Trent in 1563. The council of Trent had been Rome's response to the protestant reformation, an attempt to convene another general council of the entire Christian church, east and west, Roman and protestant, to mend past schisms. Protestants refused to attend, but the council sat intermittently for 23 years with eastern representatives in attendance. The observance of a single agreed date for Easter was a deeply symbolic move. Behind the calendar reform lay, it may be inferred, a long-term vision of a reunited Christendom. A reformed Easter fitted perfectly the rationale of the counter-reformation, in that it would have involved practical adjustments to accommodate criticism without any theological concessions. More than this, it would have recapitulated one of the key achievements of the first general council at Nicaea, whose authority (now claimed by Rome) was recognized by virtually all Christians. The Gregorian reform was indeed “an act of the counter-reformation”.²³

The key question was the date of Easter. The order of the council of Trent had simply been to reform the breviary and missal; the need for calendar reform was implied, but its nature left entirely open. As an interim measure, the golden numbers were moved up in the 1568 breviary to cover up the four-day lunar slip.²⁴ The commission charged with framing a more durable reform met several years later, and even then took over a decade to report. The main inspiration and architect behind the reform was Christopher Clavius (1548-1612), the Jesuit astronomer and mathematician, professor at the Collegio Romano, and variously described as “the Euclid of his times” and “one of those dreadful exhausters of their subjects with whom the mathematical world abounds”.²⁵ Clavius and the commission were privately in no doubt that their church was “the master and not the slave” of Easter, and was entitled to make new rules to govern it. However, it was considered prudent and convenient to retain the old rules with their undisputed ecumenical status and seek to apply them more accurately.²⁶

The solution for Easter was as labyrinthine in motivation and execution as the original computus. The system of golden numbers was retained, even though the nineteen-year cycle had proved to be an inaccurate measure of lunar motions. Its application was refined by reference to yet another variable, the epact, a measure from one to thirty indicating the age of the moon at the start of the year. The epacts were, however, adjusted by one day, creating a deliberate discrepancy with the heavens in order to ensure that Easter would always fall late enough to avoid clashes with the Passover. Other complex measures were subtly manipulated; Clavius “relied more on tables than on rules”.²⁷ As for the calendar framework itself, most commentators had favoured a fourteen-day reform to the time of Caesar, when the Julian calendar was instituted, or at least to the time of Christ, whence it measured its epoch, for the council of Nicaea had been unaware of the drift in the calendar which had already taken place since Caesar's day. It was decided, however, to make only a ten-day reform, to the time of Nicaea, in order to satisfy the Greek churches and maintain respect for tradition and the first general council of the church.²⁸ The Gregorian reform was promulgated in a papal bull, Inter gravissimas, in February of 1582—the very year of the adjustment, and long after the almanacs for that year had been printed. Ten days were removed from October 1582—the deadest part of the liturgical year, chosen to avoid interfering with major festivals. A new catalogue of saints was published and a new rubric on Easter inserted in the missal, thus renovating Bede's original calendrical edifice.

The successful introduction of the Gregorian calendar, Owen Chadwick has remarked, was “one test of the progress of the counter-reformation”.²⁹ Roughly speaking, the Latin countries (Spain, Portugal, and parts of Italy), together with Poland, seem to have adopted it on time, deleting the recommended days in October 1582, though in every case adding civil decrees to the papal bull. France adopted the new calendar by civil decree in December 1582, preceded by the bishopric of Strasbourg in November. Flanders and much of the Netherlands also adopted it in December 1582, by order of the duke of Alençon, French defender of the low countries in their war against Spain.³⁰ Other catholic countries—Austria, the Swiss catholic cantons, Bohemia, and Moravia—adopted the reform at various stages in 1583-4, helped along by a decision of the emperor to adopt it in his own lands. Hungary followed in 1587. In Bohemia, and in Augsburg in particular, there were several years of strife between catholics and protestants over the issue, known as the kalenderstreit.³¹ Most protestant states—including large parts of Switzerland, Germany, the low countries, and Scandinavia—retained the Julian calendar for another century or more, creating a patchwork of calendrical practice throughout central Europe. One complaint was that the reform was against nature: birds no longer knew when to sing and when to fly away. This whimsical lament expresses the salient point that the calendar reform had disrupted the traditional relationship between the farming year and the familiar landmarks of the human calendar.³² It is a reminder that the Gregorian reform had been conducted entirely upon theological and astronomical grounds, with little consideration of the impact of this piece of chronological engineering upon the complex time patterns of everyday life.³³

CALENDAR REFORM IN THE PROTESTANT WORLD

The reform of the calendar in the protestant world has usually been seen as a straightforward adoption of the Gregorian calendar. According to this account, it was only a matter of time, depending on how long it took the religious prejudices of the age of the reformation to die down until they “at last became enlightened”.³⁴ Protestant astronomers and mathematicians had always acknowledged the superior accuracy of the Gregorian calendar, whatever their ideological objections to it; all that happened at the end of the seventeenth century was that protestant churchmen and statesmen found a “face-saving” formula to allow them to adopt it.³⁵ In place of the familiar whig/protestant vision of the rise of science and decline of religion we have (putting it crudely) a Roman catholic vision of the rise of science and decline of protestantism. There is force to both lines of argument, but a more thorough understanding involves going beyond them.

The Gregorian calendar received a mixed and largely hostile reception in the protestant world. The calendar reform provoked considerable argument. Catholic astronomers generally accepted it readily enough, although some went into print to suggest improvements—not surprisingly given that the dominant opinion before the reform had been for a calendar reform starting from the time of Christ. Appearing to accept papal authority was the greatest sticking point. As an anglican apologist later put it, “What hath once been established by an universal council [Nicaea], ought not to be altered by a provincial synod [Trent]”.³⁶ Luther had written that calendar reform was a matter for sovereigns. The Lutheran astronomer Michael Maestlin, Kepler's tutor, led the attack, fulminating against papal arrogance and error, and insisting that only an astronomically determined Easter was acceptable. In Bavaria, opinions among protestants on this point varied: some would accept the calendar provided it was enacted by the emperor, others would reject it even if it was enacted by the emperor.

Maestlin was unusual among protestant astronomers in rejecting the Gregorian reform completely. Tycho and Kepler were happy to disregard the papal origin of the reform on the grounds that it was accurate enough astronomically. Others, notably the chronologer Joseph Scaliger, criticized it but proposed improved versions. Scaliger emphasized the time of Christ as a baseline and wanted a more exact method than that offered by the papal cyclus, with Easter governed by the real vernal equinox; both these were to become common protestant tenets. Clavius in turn rebutted these criticisms in print, arguing that the Gregorian reform was both astronomically correct and theologically non-controversial, keeping in the background his private views about the final authority of the pope in such matters.³⁷

Kepler's line was the most conciliatory.³⁸ Around the turn of the century he had argued with his tutor Maestlin on the subject, and written an unpublished dialogue to summarize the arguments. In 1613, as court mathematician to the emperor, he was given the job of persuading the protestant princes of the diet of Regensburg to follow the imperial lead and adopt the Gregorian calendar. Kepler, for all his belief in the mathematical harmony of creation, was quite prepared to accept the Gregorian calendar with all its faults, and its papal fingerprints, on the grounds that it was the best available and that harmony was more achievable than exactitude in such matters. Many objections could be met if it were adopted by civil decree. Thus, it would be a good thing if the others in German countries would follow the large majority and accept the calendar reform in obedience to his majesty as the proper authority and in brotherly love toward all Christianity and finally for the sake of promoting orderly conditions within the German Empire.³⁹

Kepler's arguments failed to work in 1613, but they seem to have become more widely accepted in time. After the end of the thirty years' war in 1648, the protestant states were urged to accept the new calendar, but in vain. The peace of Ryswick in 1697 brought another opportunity, and the prospect of the two calendars moving a day further apart in 1700 added urgency to the discussions.⁴⁰ In Denmark, arguments about the need for harmony with other countries seem to have been persuasive; in the protestant states of the empire, further reasoning was needed. The crucial proposal came from the astronomer Erhard Weigel, whose solution was that the papal cyclus be rejected as the method of calculating Easter in favour of an astronomical Easter, using the Gregorian dates but calculated from Kepler's Rudolphine tables rather than those of Clavius. The result was that the diet of Regensburg agreed on 23 September 1699 to bring dating in the whole of the empire line with the Gregorian calendar: 18 February 1700 would be followed by 1 March. Easter would in future be decided astronomically, on the advice of “the evangelical mathematicians”. A public statement was issued, together with an explanation to be inserted in almanacs.⁴¹

The diet's explanations show how important was the role of religious criteria, at least in public. The sixth-century Dionysian calendar and the Gregorian were bracketed together as errors imposed by Rome, and the protestant rationale for the new calendar was emphasised. To ram the rationalist point home, the mathematicians were at the same time “ordered to Consider how for the future the Abuse of Judiciary astrology in the Almanacks may be abolished”. The calendar had departed from the movements of the sun and moon “and consequently from the appointed tymes of the observation of those feasts and holy days presented by the church”. “The Protestants Sundays, Feastdays, and other days of the week” were to be listed in a separate column in the almanacs, to be headed “the reformed almanack”. Easter and other feasts would be computed “according to the astronomical calculation, as they used to be, before the Nicene Counsell”, and “reduced to the course of the Sunn, and to what it was before the Nicene Counsell”.

This reversion “to an Ancient Rule and Practice of the Christian Church” meant that in the special case “when the Æquinoctial Full-Moon shall fall too near a Sunday”, Easter would have to be observed a week later in order to keep it away from the Jewish Passover. It was further emphasized that “this resolution proceeds from the power and authority of the protestant states, in sacris et profanis” and “cannot be interpreted as accepting the Gregorian calendar”. Rather, the different protestant Easter would be “a perpetual and annual Reall protestation” against the injunction of pope Gregory. In the end the Romanists “if they will not Transgress against the Canons, and the course of the Heavens … must comply with us”. Perhaps this is just the sound of protestants being led kicking and screaming into the eighteenth century. However, the protestant states of the empire were clear at the time that they were not simply adopting the Gregorian calendar.

The resolution of the diet of Regensburg in September 1699 left several loose ends. Late February had been chosen for the changeover in order to avoid obliterating any major feast days, but St Matthias on 24 February was lost for that year only. This did not matter, for it happened to fall on a Sunday, and it was simply moved for one year to the following Sunday, 1 March 1700, “so that it's all one whether it be Observed on the one or the other Sunday, 8 Days sooner or later”. The question of a revised leap year formula was not tackled: the Gregorian practice was tacitly followed. More significantly, no solution was found for Easter. Rather, it was resolved that “All the Protestant mathematicians shall be obliged diligently to confer, with the mathematicians of the King of Sweden [who was also considering reform], to try if and how their proposals relating hereunto, can be agreed to, and so the work be perfected”.

These efforts failed. A second resolution had to be passed on 10 January 1700 to allow the Rudolphine tables to be used until something better could be determined. It never was, but the Prussian astronomers at Berlin “and several other experienced Evangelical Mathematicians” were able to agree each year that the correct astronomical date happened to be that of the Gregorian Easter. In 1723, however, the diet had to face the problem that the protestant Easter in 1724 would fall a week earlier than the Gregorian, owing to the use of the pre-Nicene formula. This would happen again in 1744, 1778 and 1798. Furthermore, on the latter two dates Easter would fall on the Jewish passover “which however the Nicene Council has ordered to be carefully avoided”. The original resolutions were nonetheless ordered to be “strictly observed”: the early Easter would stand, and the most ancient known practice was preferred to the edict of Nicaea. Only in 1775—under the enlightened despotism of Frederick the Great, and with the first synchronous Passover-Easter for thirteen hundred years just three years away—was the distinctive protestant Easter dropped.⁴²

The German reformed calendar of 1699 was, like the Gregorian, part of a wider project: in this case, to ensure the adoption of the reformed calendar over the whole protestant world, giving it the same basic unity enjoyed by Roman catholicism, and to establish a scientific institution on the model of the Royal Society of London to oversee the changeover. As has been seen, Denmark adopted the Gregorian calendar at the same time; so too did the remaining provinces of the Netherlands and (in 1701) the northern Swiss Cantons.⁴³ This left Sweden, England and Scotland. Sweden proved unexpectedly difficult, despite its inclusion in the Easter discussions. It first adopted the Gregorian leap year convention and the protestant astronomical Easter but retained the Julian calendar in other respects. Omitting the leap day in 1700 kept it ten days out of step with the Roman catholic and reformed protestant calendars but now one day out of step with the Julian. In 1712 it picked up the leap day again, putting itself back in line with the other Julian countries over dating but out of line with the reformed protestant countries over Easter. Finally, in 1747, the Royal Swedish Academy of Sciences was given a monopoly on the publication of reformed almanacs in preparation for the adoption of the Gregorian calendar, which happened in 1753. The price of almanacs immediately tripled, and provided the Academy's main source of income well into the twentieth century—an early example of successful Swedish state enterprise.⁴⁴

The project to establish a scientific academy in Prussia was inspired by Leibniz, and both he and his scheme had English connections. Leibniz was a pupil of the astronomer Weigel, architect of the Regensburg solution. When the diet further resolved in January 1700 to use the Rudolphine tables to calculate Easter, Leibniz was specifically requested to approach the Royal Society for better information, which was eventually forthcoming despite the English lack of interest in joining the calendar reform. The elector Frederick founded the Prussian Academy of Sciences in Berlin in May 1700. Its immediate purpose was to oversee the production of the reformed almanacs in return for a monopoly on their sale; an observatory was to be built to provide the information. Leibniz was clearly hopeful that the new academy would enhance his status with London in particular; but his greater vision, according to McClellan, was of “the cultural union of all Germany and the West under the banner of science and a unified Protestant church”.⁴⁵ This vision, at once “universalist, patriotic and religious”, had a lot in common with those of the Gregorian reformers—and, as will be seen, of John Dee. In 1582, a Roman catholic reform of the calendar was on offer; in 1699, a protestant one. England was to reject both.

Notes

1. Among the numerous works explaining the calendar, four have been of particular value: Augustus de Morgan, On the ecclesiastical calendar, in Companion to the [British] almanac (London, 1845), pp. 1-36; Arno Borst, The ordering of time: from the ancient computus to the modern computer (Cambridge, 1993); J. D. North, The western calendar: “intolerabilis, horribilis, et derisibilis”; four centuries of discontent, in Gregorian reform of the calendar: proceedings of the Vatican conference to commemorate its 400th anniversary, 1582-1982, ed. G. V. Coyne, M. A. Hoskin, O. Pedersen (Vatican, 1983); and G. J. Whitrow, Time in history (Oxford, 1988).

2. Borst, Ordering of time, pp. 16-18.

3. North, Western calendar, p. 76.

4. Whitrow, Time in history, appendix 3.

5. To be exact, the formula is that Easter falls on “the Sunday next after (and not on) the fourteenth day of the Paschal moon”, which in turn is defined as “the calendar moon whose fourteenth day falls on, or is the next following, the vernal equinox, taken as 21 March”. This, however, was apparently not part of the Nicene decree, and has to be inferred from other evidence (North, “Western calendar”, p. 76; de Morgan, “On the ecclesiastical calendar”, p. 6).

6. de Morgan, “On the ecclesiastical calendar”, pp. 16-20.

7. Borst, Ordering of time, chs 5-9.

8. Bede, A history of the English church and people, revd edn (Harmondsworth, Middlesex, 1968), II:2, II:19, III:3-4, III:18.

9. Bede, III:25.

10. North, “Western calendar”, pp. 76-80.

11. Jennifer Moreton, Before Grosseteste: Roger of Hereford and calendar reform in eleventh- and twelfth-century England, Isis, 1995, pp. 562-86.

12. Borst, Ordering of time, pp. 78-80; North, “Western calendar”, pp. 82-4.

13. Borst, Ordering of time, pp. 89-99.

14. Borst, Ordering of time, pp. 101-3.

15. Robert S. Westman, The astronomer's role in the sixteenth century: a preliminary study, History of science, 18 (1980), p. 131.

16. Ziggelaar, The papal bull of 1582, in Coyne, Hoskin, Pendersen, Gregorian reform, at p. 227.

17. North, “Western calendar”, p. 76.

18. Borst, Ordering of time, pp. 103-12.

19. R. S. Westman, Proof, poetics and patronage: Copernicus's preface to De Revolutionibus, in D. C. Lindberg & R. S Westman (eds), Reappraisals of the scientific revolution (Cambridge, 1990), p. 181.

20. Thomas S. Kuhn, The Copernican revolution (Cambridge, Mass., 1957), pp. 125-6, 142-3; R. S. Westman, Proof, poetics and patronage, p. 181; North, “Western calendar”, 94-100.

21. de Morgan, “On the ecclesiastical calendar”, pp. 9-11; James M. Lattis, Between Copernicus and Galileo: Christopher Clavius and the collapse of Ptolemaic cosmology (Chicago, 1994), pp. 3-4. For this reason, Lattis's biography has curiously little to say about Clavius's best-known achievement.

22. North, “Western calendar”, pp. 105-6; Ziggelaar, Papal bull of 1582, pp. 201, 227-8, 230. The bull did not, however, carry the threat of excommunication, as some protestant critics assumed (p. 228).

23. Ziggelaar, Papal bull of 1582, p. 227.

24. North, “Western calendar”, 100-2.

25. Lattis, Between Copernicus and Galileo: Christopher Clavius, p. 3 & ch. 1; de Morgan, “On the ecclesiastical calendar”, pp. 9-11.

26. de Morgan, “On the ecclesiastical calendar”, pp. 9-11; Ziggelaar, “Papal bull of 1582”, pp. 218, 230.

27. Ziggelaar, “Papal bull of 1582”, pp. 209-10, 218-24; de Morgan, “On the ecclesiastical calendar”, pp. 19-30.

28. H. M. Nobis, The reaction of astronomers, in Coyne, Hoskin, Pendersen, Gregorian reform, at p. 245; North, “Western calendar”, p. 101; Ziggelaar, “Papal bull of 1582”, pp. 214, 218, 220-4, 230-1.

29. Owen Chadwick, The reformation (London, 1964), pp. 300, 313.

30. O. Gingerich, The civil reception of the Gregorian calendar, in Coyne, Hoskin, Pedersen, Gregorian reform, pp. 265-6, and see below, Chapter 4.

31. Gingerich, Civil reception, pp. 266-8; Nobis, Reaction of astronomers, p. 252 n. 3; K. Fischer, Appended note: on the calendar reform in Bohemia and Moravia, in Coyne, Hoskin, Pedersen, Gregorian reform, pp. 282-5; J. J. Bond, A handy book of rules and tables for verifying dates (London, 1875), p. 8. See also: H. Nicolas, The chronology of history (London, 1833), pp. 32-6; H. Spencer-Jones, The calendar, in C. Singer et al. (eds), A history of technology iii (Oxford, 1957); C. R. Cheney, A handbook of dates for students of history (revised edn, Royal Historical Society, London, 1991). Gingerich provides references to the literature, which is mostly in Latin and German; see also Borst, Ordering of time, n. 177 (pp. 156-7).

32. This point is taken up in Chapter 9 below with reference to the calendar reform in England.

33. Nobis, “Reaction of astronomers”, pp. 243-8; Hoskin, Reception of the calendar, pp. 259-60.

34. See Nobis, Reaction of astronomers, pp. 243-55; Hoskin, “Reception of the calendar”, pp. 259-60; Gingerich, “Civil reception”, pp. 266-8 (quotation at p. 268); Spencer-Jones, The calendar.

35. Gingerich, Civil reception, p. 267.

36. [John Willes], The judgement of the foreign reformed churches concerning the rites and offices of the Church of England (London, 1690).

37. Nobis, Reaction of astronomers, pp. 266-7.

38. Max Caspar, Kepler, 2nd edn (New York, 1959; corr. edn, New York, 1993), pp. 227-32.

39. Caspar, Kepler, p. 232.

40. Bond, Handy book of dates, p. 8.

41. MS English versions are to be found in the Royal Society's Classified papers, XVI, item 10, and in Lambeth Palace MS932, item 68. An abbreviated printed version is in Philosophical transactions (abridged), III, ed. J. Lowthorp (London, 1705), pp. 408-10. Most English people would have encountered the resolution in the summary published in The Monthly Mercury, Nov. 1699, pp. 406-7, and at greater length in March 1700, p. 97. The quotations which follow here come from the Royal Society MS and Lowthorp.

42. Royal Society, Classified papers, XVI, item 10; Gingerich, Civil reception, p. 267. Gingerich states that the astronomical calculation of Easter in the protestant lands also differed from the Roman catholic in 1704, but according to the resolution of 1723 Germany used the Gregorian date in that year.

43. The Swiss cantons began 1701 on 12 January, “but the old calendar was, nonetheless, retained in some parts of Switzerland”: Harris Nicolas, The chronology of history (London, 1833), pp. 32-6.

44. Gingerich, Civil reception, pp. 267-8; Arne Holmberg, The Royal Swedish Academy of Science, in A. Holmberg et al. (eds), Academies in Sweden (Gdynia, Poland, 1937), p. 309; James E. McClellan III, Science reorganized: scientific societies in the eighteenth century (New York, 1985), pp. 88-9.

45. McClellan, Science reorganized, pp. 68-71.