The Calendar

by David Ewing Duncan

  In 1200 Conrad of Strasbourg wrote that the winter solstice had fallen behind by 10 days since Caesar’s time. Conrad’s estimate established the figure of 10 days as gospel among reform-minded time reckoners, though they argued about whether one should calculate the drift from Caesar’s founding of the calendar in 45 BC or from the time of the Council of Nicaea in 325, when time reckoners fixed the equinox on 21 March.

  A few years after Conrad, the English scholar Robert Grosseteste (c. 1175-1253) recalculated Reiner’s lunar-solar slip and amended it to the gain of a day every 304 years--closer to the actual drift against the Julian year of a day every 308.5 years. He also proposed a solution: that one day be dropped from the lunar calendar every three centuries. Grosseteste, chancellor of Oxford University and later a bishop, also closely studied measurements of the solar year, confirming once and for all that the values arrived at by Hipparchus, Ptolemy, al-Battani and other Arabs and Greeks were superior to those worked out by Bede and centuries of computists. This led him to suggest a new starting point for the Easter calculation--a spring equinox of 14 March instead of 21 March--to compensate for the centuries-long drift in the calendar against the calendar year. Grosseteste is also remembered because of the standards he set for science. Known for his work in geometry and optics as well as astronomy, he was an early advocate of using experimentation and observation to verify theories. This was an idea years ahead of its time. For while most intellectuals were trying to reconcile contradictions between the new knowledge and the old dogma, Grosseteste was taking the next step and trying to reconcile the contradictions between reason and experience--between the new knowledge as written in books and empirical evidence.

  By Grosseteste’s time few serious time reckoners were denying that the errors existed in the lunar and solar calendars. But this hardly meant they were all for reform. Another Englishman, John of Sacrobosco (c. 1195-1256), proved the errors down to the minutes and seconds using an astrolabe and a deep knowledge of Arab, Greek and Indian mathematics and astronomy. Yet he was able to offer only one modest reform in the solar calendar: that the calendric order be restored by cancelling the leap day every 288 years. Otherwise John stuck with Bede’s admonition to follow the ‘universal custom’ of accepting the errors, insisting that the Church was the final authority. Referring to the Council of Nicaea in 325, he wrote: ‘Since the General Council forbade any alterations to the calendar, modern scholars have had to tolerate errors ever since.’ John’s reticence must have resonated with scholars. For three hundred years his textbook on time reckoning remained a standard in universities. Even Protestants republished it in 1538, soon after they changed the university at Wittenberg to a Lutheran institution.

  Into this mix in the mid-1200s came Roger Bacon, another firebrand visionary along the lines of Abelard. He not only took up the cause of Robert Grosseteste in pushing for reform of the calendar but he also became a staunch advocate of Grosseteste’s championing of empiricism and the objectivity of science. Even further ahead of his time than Grosseteste--centuries further--Bacon demanded that scholars stop talking and debating and start doing. In his Opus Mains--written in the 1260s, the same decade that Thomas Aquinas was labouring over his Summa Theologica--Bacon writes:

  The Latins have laid the foundations of knowledge regarding languages, mathematics, and perspective; I want now to turn to the foundations provided by experimental science, for without experience one cannot know anything fully.

  In possibly Bacon’s most famous passage he vividly illustrates his point:

  If someone who has never seen fire proves through reasoning that fire burns, changes things and destroys them, the mind of his listener will not be satisfied with that, and will not avoid fire before he has placed his hand or something combustible on the fire, to prove through his experience what his reasoning had taught him. But once it has had the experience of combustion the mind is assured and rests in the light of truth. This reasoning is not enough--one needs experience.

  As passionate and arrogant about his cause as Abelard was about the use of logic a century and a half earlier, Bacon argued that nature had been established by God and therefore needed to be explored, tested, and absorbed to bring people closer to God. He warns that a failure to embrace science is an affront to God and an embarrassment to Christians, who were forced to acknowledge the superiority of Arab science.

  A prime example of this embarrassment, he said, was the habit of Christian time reckoners and mathematicians to round off numbers rather than trying to calculate them precisely. This was an intentional jab at time reckoners such as Bede and Bacon’s contemporary John of Sacrobosco--those who admitted to calendric errors but settled for approximations rather than challenge the Church. This had led, writes Bacon, to a calendar that in that very year (1267) was causing havoc for devout Christians.

  The errors I have mentioned are terrible in themselves, yet they bear no comparison to those which follow from the facts now stated. For the whole order of Church solemnities is thrown into confusion by errors of this kind respecting the beginning of the lunation according to the Calendar, as well as by the error in determining the equinoxes. And not to refer to other years for evidence of this error, I shall state the case in this present year.

  Which he does in detail, explaining what this meant for pious Christians, in terms much starker than Reiner of Paderbom or Robert Grosseteste would have dared:

  Wherefore the feast of Easter, by which the world is saved, will not be celebrated at its proper time, but there is fasting this year through the whole true week of Easter. For the fast continues eight days longer than it should. There follows then another disadvantage that the fast of Lent began eight days too late; therefore Christians were eating meats in the true Lent for eight days, which is absurd. And again then neither the Rogations nor the Ascension nor Pentecost are kept this year at their proper times. And as it happens in this year 1267, so will it happen the year following.

  Bacon’s ardour for correcting obvious errors came in part from a belief that the Antichrist was about to arrive on earth; shortly after this event would come the end of the world. This left Christians little time to use science to bring order to civic life and to perfect the Christian way of life, or so Bacon argued in his strange amalgam of science and spiritualism.

  Bacon did not stop with condemnations, however. He demanded a change--taking his case directly to the papacy when given his surprise opening in 1265 from Guy Le Gros Foulques, the soon-to-be Pope Clement VI.

  But Bacon was not after a simple mechanical solution. He framed his argument philosophically by dividing time into three categories: that which is ‘designated by nature, ... by authority, and ... by custom and caprice’. He defined natural time as the measurable passage of years, seasons, months and days; authoritative time as that used in civil and ecclesiastic calendars; and time by custom as when people arbitrarily impose periods of time, such as months that number 28, 29, 30 or 31 days.

  Bacon derived his three-part definition from Bede, though the venerable monk had concluded that the authority of God’s time superseded the others. Bacon argued the opposite: that natural time was God’s time, and that time as interpreted by an authority such as the Church can be mistaken. This provided the philosophical underpinning that in Bacon’s view gave Rome the right and the responsibility to correct the calendar, both as Europe’s only authority capable of ordering a change and as God’s authority on earth.

  But Rome was still grappling with what to do about Abelard and the onslaught of reason, and it hardly seemed prepared to move several steps ahead to embrace Bacon’s essential idea--that human intellect through experimentation and observation could correct and negate core Church teachings. This leaves us with a mystery as to whether or not Clement IV shared Bacon’s ideas--or would have been receptive to his demand for reform had he lived.

  One thing is sure: Clement’s advisors, those who received and presumably glanced at the friar’s opus, were not receptive. Aft
er the pontiff’s death no one at St Peter’s so much as mentioned Bacon. Years later the French lawyer and bishop Guillaume Durand (c. 1230-1296), who joined the papal service under Clement, wrote an entire volume on time reckoning without so much as mentioning Roger Bacon.

  Yet change was in the air as the year 1300 arrived, much of it coming not from the endless debates and scholasticism of the universities or the gilded basilicas of Rome but more than ever from the rising merchants, traders, bankers, kings, generals, shipowners and other practical-minded people. They who felt a keen need not only to measure time accurately but also to find better ways to build ships, plant millet, fashion swords and construct battlements. By the 1290s the word computus itself had shifted its meaning to something more familiar to us today. Indeed, back in 1250 the Italian conto still meant time reckoning, while just a generation later a young Dante Alighieri (1265-1321) was writing love poems in which conto describes the relationship between two lovers--not physically, but in terms of economics and accounting, that is, how lovers reckon and balance income and expenditure. The word computare was becoming closely connected with finance, with conto in Italian, cuenta in Spanish and, later, Kanto in German, all meaning to count or reckon not stars and epacts of lunar cycles but money.

  At the same time a civic calendar of sorts was beginning to take shape along with the renewed sense of linear time crucial to conducting on-going business and government. This new age was signalled by Pope Boniface VIII’s declaring 1300 to be a ‘century’ year, which he marked with a jubilee to celebrate thirteen centuries of Christendom--starting a tradition that continues to the present, with jubilees now held every quarter century. Boniface’s affair attracted 20,000 pilgrims drawn by the spectacle and by the pope’s offer of special indulgences. The event also signalled a new awareness of the calendar and the final triumph of Dionysius Exiguus’s system of counting years from the supposed birth of Christ.

  It also was an effort by Boniface to emphasize the primacy of Rome in an age when the papacy was being challenged by the power and authority of kings, dukes and counts, and by what would become modern state governments replete with ministers, lawyers, tax and spending authorities and bureaucrats. The jubilee recalled the lavish feasts held by ancient Roman emperors on special anniversaries, and was meant to demonstrate the supremacy of Rome and papal rule then and for ever. This sentiment was made more starkly clear two years later when Boniface issued a papal bull that ordered all Christians to recognize the supremacy of the pope in all matters. Directed primarily at Boniface’s enemies of the moment, Edward I of England and Philip IV of France, the pope wrote: ‘Therefore we declare, state, define and pronounce that for every human creature to be subject to the Roman pope is altogether necessary for salvation.’

  It says a great deal about change in Europe that a pope even needed to issue such a proclamation just one hundred years after Pope Innocent III reigned over the papacy’s unchallenged supremacy. It says even more that Philip, who had been feuding with Rome over his right to tax and regulate the clergy, plotted to kidnap Boniface and bring him to Paris. Storming a palace where the pope had gone to write an order excommunicating Philip, the king’s henchmen held the pope three days, until Boniface was rescued. The pope died a month later, reportedly from shock over the incident.

  Another seminal moment in European history, this soap-opera affair symbolized the rising power of secularism in politics just as Abelard and Bacon signalled the start of a new secularism of the intellect. It also would trigger a century of chaos in the papacy, as it was drawn into the struggles and power-plays among the emerging great powers of Europe. In 1309 a French-sponsored pope was crowned in Lyons, and established residence at Avignon in Provence, launching a 68-year absence from the holy city that nearly split the Church in two.*

  *Between 1378 and 1417, rival popes resided in Avignon and in Rome.

  Still, in the years immediately after Boniface’s jubilee the overall attitude of Europeans remained positive, with trade increasing, the population growing and frequent outbreaks of original thinking. The early 1300s was the age of Dante, who finished the Divine Comedy in 1321--a work filled with allusions to time, which by then was becoming a subject not just for ecclesiastics, traders and scientists but also for poets. In his canto on paradise, Dante’s narrator (also named Dante) describes the source of time--what he calls the primum mobile, a ring of heaven situated above all the heaven-planets. This, he says, is the invisible, unmoving force of the divine mind that directs the daily revolutions of the planets around the earth, which is of course in the centre:

  The nature of the universe which stills

  The centre and revolves all else, from here,

  As from its starting-point, all movement wills.

  This heaven it is which has no other ‘where’

  Than the Divine Mind; ‘tis but in that Mind

  That love, its spur, and the power it rains in here . . .

  As in a plant-pot, then, time has its roots

  Herein, and where the other heavens trace

  Their course, thou mayst behold its shoots.

  This is a poetic version of Aquinas’s complementary truths: of Plato’s universal, unmoving mover situated in an Aristotelian hierarchy where cause and effect are clear. The reader is invited to ‘behold’ the inner workings of the heavens (and, in earlier cantos, hell and purgatory), and to join Dante the pilgrim in his quest to understand them as part of the great natural scheme of God’s universe.

  This also was the age of the poet Petrarch, the painter Giotto and the sculptor Nicola Pisano; when dozens of universities opened; when clockmakers built the first public bell towers in major cities across Europe and Genoan sailors set foot on the Canary Islands in the first step toward the European exploration of Africa and westward into the Atlantic Ocean.

  For the calendar, however, little of interest happened during the first four decades of the 1300s. Then in 1345 the newly installed pope at Avignon, the French nobleman Clement VI (1291-1352), abruptly decided the calendar needed to be reformed.

  It is not entirely clear why, though Clement seems to have been motivated by the age-old problem with Easter, and perhaps by Bacon’s arguments that such an obvious error was an embarrassment to a Christendom increasingly worried over what outsiders thought about it. Whatever his reasons, this pope, known for his pomp, his extravagant living and his patronage of the arts, dispatched letters to calendar experts on 25 September 1344, asking them to come to Avignon to consider and advise on the correction of the calendar. In his mandate the pope ordered the scholar’s expenses to be paid by their local bishops.

  The most important of these scholars was Jean de Meurs, an Aristotelian at the University of Paris who wrote two works in the 1320s touching on how to measure time. In one he compared the passage of time to what happens when someone plays or sings a musical piece, with its beginning and ending. Jean called this natural time, which interacts with abstract or mathematic time, which is how music is subdivided according to measures, notes and other breaks.

  In his 1345 response to Clement, titled Epistola super reformatione atitiqui kalendarii (Letter about the reform of the ancient calendar), Jean and another time reckoner named Firmin told the pope that their ideal solution for realigning Caesar’s calendar with the sun was to remove the appropriate number of days from a single year’s calendar. They insisted that determining this was relatively easy, given the accuracy of the latest star charts that built on Arab and Greek texts, and on observations of Reiner, Grosseteste and others.

  Jean warned, however, that removing days from the calendar might cause turmoil for governments and commerce: quarrels about payments and contracts, and perhaps riots. He also pointed out that if the Catholics changed their calendar, they would be celebrating fixed holy dates such as Christmas on different days than Christians in the East and in other schismatic sects, setting back the still important Catholic goal of a truly universal church.

  Jean and Firmin were
more optimistic about reforming the 19-year lunar calendar. Recalculating Grosseteste’s value for the error, they came up with a day gained every 310 years--just one and a half years off from the true Julian value of about 308.5 years. By 1345, Jean wrote, this error had accumulated to a slip of four days. They suggested that the pope restore the lunar calendar to its proper alignment by removing these days from the 19-year cycle, and order that a day be dropped thereafter every 310 years. The best year to start the reform, they said, would be 1349--the year after a leap year and the first year in the next 19-year Metonic cycle. Jean and Firmin drew up a calendar incorporating their proposed changes.

  Clement VI did not formally respond to the proposal, but it seems likely that he agreed with the reforms. Indeed, this modest correction seemed well on its way to being implemented as the 1349 date approached--possibly to be followed by a reform of the solar calendar.

  But it was not to be. For as 1345 passed into 1346 and 1347, the future of calendar reform--and of Europe itself--was being decided not in glittering Avignon but in a remote Genoan outpost on the Crimea, where a small fleet of trading vessels was setting sail to cross the Black Sea and then the Mediterranean. Heading off just before the winter winds at the end of the sailing season, the sailors and merchants on board these ships and others departing various Eastern ports were transporting more than spices and cloth. For in their blood a microscopic cargo was growing and spreading that would kill most of these men before they reached their destination. And with them would die what appeared to be in the time of Clement VI a nascent renaissance, one that might have solved the calendar conundrum two centuries before Gregory and Clavius.

  12 From the Black Death to Copernicus

  When the calendar was under discussion ... no solution was found for the sole reason that the length of years and months and solar and lunar motion were not yet considered to be sufficiently well determined. Since that time, in fact, I have turned my attention to the observation of these phenomena.