*In this same treatise Bacon elsewhere uses the figure once in every 130 years. The actual error is closer to once every 128 years.
Roger Bacon did not care. One of medieval Europe’s most original and curmudgeonly thinkers, he seemed to relish his role as a rebel--first as a master at the University of Paris in the 1240s and then as a priest after he joined the Franciscan order sometime during the 1250s, when he was in his forties. Insatiably curious and always willing to challenge orthodoxy, Bacon devoted his life to pondering what causes a rainbow, diagramming the anatomy of the human eye, and devising a secret formula for gunpowder. Two centuries before Leonardo da Vinci he predicted the invention of the telescope, eyeglasses, airplanes, high-speed engines, self-propelled ships and motors of enormous power. He drew these conclusions based on the then-radical notion that science offered objective truths regardless of dogma or what was written down in a book.
Bacon’s contemporaries were impressed by his intellect but frightened of his ideas. His own monastic brothers at Oxford and Paris may have held him under house arrest. Even worse, they banned him for long periods from writing and teaching, keeping him busy with the mundane chores of the monastery--tending the garden, reciting prayers, scrubbing the floors. Occasionally they punished him by withholding food.
This might have been the end of Roger Bacon’s story if not for a sudden interest in his ideas by a man named Guy Le Gros Foulques. In 1265 this former lawyer and advisor to King Louis IX of France became aware of Bacon and contacted him, asking the friar to send him a compendium of his thoughts. Like Bacon, Foulques had joined the priesthood later in life, in 1256, the year his wife died. He had then advanced with breathtaking speed from priest to bishop, archbishop and cardinal, his position when he approached Bacon. How Foulques heard about the long-cloistered friar is unknown, nor is it clear why this important cardinal was interested in Bacon’s ideas, nor if he agreed with them.
Whatever his reasons, Foulques’s interest was a dramatic turn of events for Roger Bacon. The long-suffering friar must have felt as if he were finally being allowed to bring fire back to the cave. And if this were not enough, just a few months later Guy Le Gros Foulques was elected supreme pontiff of the Catholic Church, taking the name of Clement IV. This led to a second notice sent to Bacon: a papal mandate delivered in June 1266 to forward the friar’s work as soon as possible to St Peter’s in Rome.
Bacon was elated but embarrassed, for after years of persecution by his own religious order, including at times a prohibition on writing, he had nothing complete enough to send to Rome. ‘My superiors and my brothers,’ a frustrated Bacon wrote to the pope, ‘disciplining me with hunger, kept me under close guard and would not permit anyone to come to me, fearing that my writings would be divulged to others than . . . themselves.’
Free at last to pursue his ideas, Roger Bacon promised to prepare a manuscript and send it as quickly as possible. For nearly two years he worked feverishly, finally dispatching an epic treatise to Rome in 1267 called
Opus Maius
(Major Work). In this book and two others, hand-carried by a faithful servant named John along the sometimes treacherous medieval highway across Europe, Bacon expounds on topics ranging from a study of languages and the geometry of prisms to the geography of the Holy Land.
His diatribe describing the flaws in the calendar falls in a long and rambling chapter on mathematics, in a section where he advocates using the objectivity of numbers and science to expose mistakes. He opens with an announcement that he is bringing up a matter ‘without which great peril and confusion cannot be avoided’, an error conceived out of ‘ignorance and negligence . . . [that is] contemptible in the sight of God and of holy men . . . The matter I have in mind,’ he says, ‘is the correction of the calendar.’
Bacon traces flaws in the calendar back to its originator, Julius Caesar, who launched the calendar used by Bacon--and by us today with some modifications--on 1 January 45 BC. ‘Julius Caesar, instructed in astronomy, completed the order of the calendar as far as he could in his time,’ writes Bacon:
But Julius did not arrive at the true length of the year, which he assumes to be in our calendar 365 days and one fourth of a day . . . But it is clearly shown . . . that the length of the solar year is not so great, nay, less. This deficiency is estimated by scientists to be about the one hundred and thirtieth part of one day. Hence at length in 130 years there is one day in excess. If this were taken away the calendar would be correct as far as this fault is concerned. Therefore, since all things that are in the calendar are based on the length of the solar year, they of necessity must be untrustworthy, since they have a wrong basis.
Bacon also condemns a second calendric mistake that comes out of the first. ‘There is another greater error,’ writes Bacon, ‘regarding the determination of the equinoxes and solstices. For . . . the equinoxes and solstices are placed on fixed day . . . But astronomers are certain that they are not fixed, nay, they ascend in the calendar, as is proved without doubt by tables and instruments.’
This second point was critical, Bacon notes, because the spring equinox--astronomically the point between winter and summer at which the sun strikes the equator--is the date used by Christians to determine Easter. According to Church rules, Easter is celebrated on the first Sunday after the first full moon after the spring equinox.* In Bacon’s day the equinox was permanently fixed on 21 March by order of the Church, as established by an important Christian council held at Nicaea in Turkey in AD 325. But since 325, as Bacon notes, the equinox had been ‘ascending in the calendar . . . and likewise the solstices and the other equinox’ by 1/130 of a day each year, or just over 11 minutes. He set the true date of the equinox for the year he was writing, 1267, on ‘the third day before the Ides of March’, or 12 March--a nine-day difference. ‘This fact cannot only the astronomer certify,’ says Bacon, ‘but any layman with the eye can perceive it by the falling of the solar ray now higher, now lower, on the wall or other object, as anyone can note.’
*The actual calculation of Easter is considerably more complicated than this, but this simplification will suffice for now.
He calculates that by 1361 the calendar would drop back another whole day, throwing the entire progression of dates and sacred days further into disarray. The friar concludes with an appeal to Clement to embrace the ‘truth’ offered by science, and to fix the mistake:
Therefore Your Reverence has the power to command it, and you will find men who will apply excellent remedies in this particular, and not only in the aforesaid defects, but in those of the whole calendar. ... If then this glorious work should be performed in your Holiness’ time, one of the greatest, best, and finest things ever attempted in the Church of God would be consummated.
Bacon’s own solution was to drop a day from the calendar every 125 years. But he adds a word of warning, noting that ‘no one has yet given us the true length of the year, with full proof, in which there was no room for doubt’--a reality that would continue to complicate a final solution for the calendar problem for centuries to come.
Roger Bacon was hardly the first to realize the calendar’s drift against the solar year. A millennium earlier the Greek astronomer Claudius Ptolemy (c. 100-178) had noted that the calendar year fell short against the true year, though his calculation differed substantially from Bacon’s. In
The Almagest,
a work on astronomy widely read (if not fully understood) during the Middle Ages, Ptolemy sets the drift at about one three-hundredth of a day, a slippage of an entire day every 300 years. This amounts to a five-minute shortfall, or a year of 365 days, 5 hours and 55 minutes, rather than Caesar’s year of 365 days and 6 hours (365 1/4 days). ‘And this number of days,’ writes Ptolemy, ‘can be taken by us as the nearest approximation possible from the observations we have at present.’ Considering that Ptolemy, like Bacon, had no telescope and believed that the sun revolved around the earth, this calculation was a reasonably close approximation, though less accurate than Bacon’s year of 365 days, 5 hours and 49 minutes.
Between Ptolemy and Bacon, scholars in Europe and Asia tinkered with solutions, attempting to refine earlier estimates of the true year--but always falling short (or long). These tinkerers included the great Indian astronomer Aryabhata (476-550); the mathematician Mohammed Ibn Musa al-Khwarizmi (c. 780-850) and others in the Islamic world; and a progression of mostly obscure monks and scholars in the West, the best-known being the Venerable Bede (673-735) of Britain. Using a sundial in a Northumbrian monastery, Bede suspected that the solar year was slightly off from the calendar but did not know by how much. In part this was because Europeans after the collapse of Rome either ignored or did not understand complex fractions. They tended to round off anything but a simple fraction such as one quarter or one half.
Other monks who tried, and failed, to calculate the true solar year include Notker the Stammerer, a Swiss priest-scholar who challenged the accuracy of certain saints’ days in a treatise written in about 896; the French ecclesiastic Hermann the Lame, who dared to suggest in 1042 that the Church-approved calendar might be misaligned with the heavens; and Reiner of Paderborn, who made his attempt in the 1100s. But none of these computists dared challenge the Church on a matter so fundamental as measuring time.
Then came Roger Bacon, who seized the opening offered him by Clement to plunge into this ancient puzzle. Dismissing with a wave of his quill centuries of reticence by fearful astronomers, Bacon declared that anyone who rejected the truth offered by science was a fool.
Clement’s reaction to Bacon’s pronouncements and appeals is unknown. On 29 November 1268, the pope suddenly died, probably before he had a chance to read Bacon’s just completed opus.
Nothing could have been more disastrous for the friar, who had just accused the Church of ignorance and wrongheadedness and demanded reforms that Vatican officials less sympathetic than Clement might have condemned as heresy. Instead the Holy See did something far more damning: they ignored him. Clement’s successor, Gregory X, never mentions Bacon or his books; nor does anyone else at St Peter’s.
But Bacon continued to speak his mind. In 1272 he penned a blistering attack on academics and what he considered the abysmal state of learning. It spared no one, including universities, kings and princes, lawyers and the papal court. He also began applying his standards for truth and objectivity to the practice of Christianity, joining a small but vibrant movement of monks scattered across Europe who believed that the Church had strayed from the original dictates of Christ by acquiring too much worldly wealth and power.
Ultimately Bacon’s radical talk landed him back in serious trouble. In 1277 he was denounced again by his own religious order, which charged him with espousing ‘suspected novelties’. This time they did not merely cloister him: they sent him to prison. According to Franciscan records of his trial, their high council ‘condemned and reprobated the teaching of Friar Roger Bacon of England’, forbidding anyone from studying his work. They also requested that Pope Nicholas III issue a decree commanding that the friar’s ‘dangerous teaching might be completely suppressed’.
For the next decade and a half Roger Bacon disappeared. Then in 1292 the elderly friar, now in his late seventies and apparently out of prison, emerged once more to pen yet another firebrand essay--his last. By then, however, the name Roger Bacon was so obscure that this unfinished and unpublished manuscript was noticed by no one. Nor did anyone bother to record the exact date of his death, possibly in that same year.
But Bacon’s passion for the truth endured. Centuries later Roger Bacon became a posthumous hero of late Renaissance and Enlightenment thinkers, who were astonished by the modernity of his ideas.
It took another three centuries before Bacon’s demands for calendar reform were heeded, when Pope Gregory XIII (1502-1585) finally fixed the calendar in 1582. By then scientists had been openly clamouring for a correction for several decades. Even Copernicus, a generation before Gregory’s correction, penned a section about the true length of the year in his
Revolutions of Heavenly Spheres,
published in 1543. This was the same treatise that offered a compelling theory overturning the age-old belief that the sun and the planets revolved around the earth.
Gregory’s reform came after he appointed a calendar commission in either 1572 or 1574, led by the Bavarian mathematician Christopher Clavius (1537--1612), one of two quiet heroes of the Gregorian correction. The other was an obscure Italian physician named Aloysius Lilius (1510-1576), who actually devised the solution Gregory issued as a papal bull on 24 February 1582. This came almost exactly 316 years--and two and a half additional lost days--after Roger Bacon’s appeal to Clement IV.
Today almost everyone takes the precision of our calendar for granted, unaware of the long threads spooling out from our clocks and watches backwards in time, running through virtually every major revolution in human science, all linked to the measurement of time. The thread largely runs through the West, since this is the source of the world’s civic calendar, but also casts lines of varying sizes and thickness outwards to China, India, Egypt, Arabia and Mesopotamia. Unwinding backwards, it pauses at Clavius and at Bacon; at the rush of knowledge coming from Islam and the East during the Middle Ages; at bloody wars fought over dates after Rome’s collapse; and at Rome at its height, when Julius Caesar fell in love with Cleopatra, an affair that gave the West its calendar. It moves back further still to the Egypt of the pharaohs, Babylon, Sumer and beyond, thousands of years before Roger Bacon penned his treatise to the pope, when an unknown man dressed in reindeer skins and clutching an eagle bone gazed at the sky and got an idea as radical in his day as anything Bacon thought of in his: to use the moon to measure time.