The Lunar Eclipse

The Annals of Clonmacnoise have an entry for 670 that reads "The Moone was turned into a sanguine collor this year." A red moon usually means a lunar eclipse. During a lunar eclipse, the Earth passes between the sun and Moon, causing the light on the Moon to appear sanguine, or blood-red.

The mechanics of eclipses were understood long ago. Babylonians over 3000 years ago had eclipses figured out, and even Isidore of Seville in the 7th century understood the process. (The illustration is a 14th century book showing the phases of eclipses.) Isidore knew that the lunar eclipse would only occur when the Moon was full.

Not everyone knew that this was a predictable and understandable phenomenon, however. A solar eclipse took place on 23 June 1191 in England, and the monk Richard of Devizes commented that those who saw it and did not know what scholars knew thought it was a sign of something ominous. Earlier, a lunar eclipse during the First Crusade showed a blood-red Moon over Jerusalem as the Crusaders approached. It was described as a sign of God's will. (This was reported later by Albert of Aachen, writing a history of an event he did not himself witness. Albert had no compunction against stating that a lunar eclipse portended a defeat for the Crusade's enemies, while a solar eclipse would have meant disaster for the Crusade.)

John of Salisbury warned against using eclipses as signs of future success or failure. Astronomy was fine, but using it to predict the future was as erroneous as soothsaying, astrology, and other such practices.

Bishop Thietmar of Merseburg also proclaimed that eclipses were not caused by evil incantations or the celestial bodies being eaten by demons or monsters. This is the only reference to the idea of the sun or Moon being "eaten" during an eclipse. We can't be sure if anyone really claimed this, or if Thietmar was just exaggerating the fears of the uneducated so that he could counter them.

An eclipse in 756 was described by Simeon of Durham in some detail:

Moreover, the Moon was covered with a blood-red color on the 8th day before the Kalends of December [i.e., November 24] when 15 days old, that is, the Full Moon; and then the darkness gradually decreased and it returned to its original brightness. And remarkably indeed, a bright star following the Moon itself passed through it, and after the return to brightness it preceded the Moon by the same distance as it had followed the Moon before it was obscured.

Simeon seems to be describing the occultation of a star during the eclipse.

John of Salisbury has been mentioned here before, but he said and did a lot that deserves attention. We'll look at him next time.

al-Farghani's Accomplishments

Despite the potentially reputation-damaging error in calculation made by al-Farghani in the case of a canal, he is better known for other accomplishments.

Abū al-ʿAbbās Aḥmad ibn Muḥammad ibn Kathīr al-Farghānī (c.800 - 870) was known as Alfraganus in Western Europe (see illustration, from a 1493 astronomical work). He was described as Arab and as Persian; there is a suggestion that his name comes from being born in Farghana in Uzbekistan.

His best-known work was Kitāb fī Jawāmiʿ ʿIlm al-Nujūm (Elements of astronomy on the celestial motions), a summary of Ptolemey's astronomical Almagest with revised calculations. He concentrated less on the mathematics and more on explaining the concepts in ways that were easy to understand. This work reached the West in translations by John of Seville and Gerard of Cremona. Dante's knowledge of astronomy came from al-Farghani.

One of his first recorded acts is being involved in a team that calculated the diameter of the Earth. This work influenced Columbus in his voyage across the Atlantic. Columbus, however, misunderstood the translation of al-Farghani's use of "mile." Columbus assumed al-Farghani was using the 4856-foot Roman mile; actually, al-Farghani used the 7091-foot Arabic mile. Columbus thought the diameter of the Earth was smaller.

In Cairo, al-Farghani wrote a treatise on the astrolabe earlier than al-Ashraf Umar II and Abd al-Rahman al-Sufi. Also while in Cairo he supervised the New Nilometer. The Nilometer, as you might guess, was designed to measure the height and clarity of the water of the Nile River.

The annual flooding of the Nile was crucial to Egypt's agricultural cycle, but it was unpredictable. Too heavy a flood was destructive; too light could lead to famine. Knowing what was coming was important. Nilometers come in different designs, but the simplest was a vertical column submerged in the river with markings to denote height of the water. Later, more elaborate versions involved shafts with steps that led down. Noting the height and comparing it to previous years helped predict whether the crops would be successful.

Speaking of flooding...next I want to tell you about a flood that killed thousands in more than one country. See you tomorrow.

Al-Farghani's Mistake

While expanding the urban settlements along the Tigris, the 9th century Abbasid caliph al-Mutawakkil needed a canal to bring water to a new city, al-Jaʻfariyya (after the caliph's birth name). He gave two courtiers the job of finding an engineer to design and build the canal. Two brothers, Muhammad and Ahmad ibn Musa, went for the expertise of al-Farghani (c.800 - 870).

al-Farghani was one of the most famous astronomers in the Muslim world in the 9th century. He had written a summary of Ptolemy's Almagest called Elements of astronomy on the celestial motions with more accurate data. Columbus used al-Farghani's calculations on his voyages across the Atlantic. Under a previous Abbasid caliph, al-Ma'mun, al-Farghani and a team had used the curvature between two points to calculate the diameter of the Earth.

He had also worked as an engineer, and for al-Mutawakkil had successfully created the New Nilometer in Old Cairo (more on that later). So designing a canal was not outside of his abilities. There was something wrong with the construction, however. A miscalculation made the entrance to the canal too deep. Water entering it would have to be abnormally high to be able to enter the rest and flow to its destination.

al-Mutawakkil was angered, and sent someone to figure out how culpable the two brothers were for the error. The investigator was not keen to see Muhammad and Ahmad punished, so he kept delaying his report. In fact, he delayed it long enough that it became a non-issue after the assassination of al-Mutawakkil, saving the lives of the brothers.

al-Farghani was not known for making mistakes, and tomorrow we'll look at some of his accomplishments, as well as explain the New Nilometer, which is exactly what you think it might be based on the name. See you then.

Armillary Spheres

The "wooden terrestrial spheres" mentioned here are what we now call "armillary spheres." An armillary is a spherical arrangement of rings designed to mimic the orbits of the sun and planets around the Earth—or around the Sun, depending on the prevailing theory at the time. If the Earth is the center, it is a Ptolemaic sphere; if the Sun is at the center, it is a Copernican sphere. China and Greece each invented them BCE. Hipparchus credited Eratosthenes (276 - 194BCE) as the inventor.

An early Christian philosopher, John Philoponus, wrote the earliest extant treatise on the armillary sphere and the astrolabe. The oldest example of one we have today dates to the 11th century.

Gerbert d'Aurillac (946 - 1003), who became Pope Sylvester II in 999, had brought the armillary sphere to Western Europe. He was also responsible for introducing Western Europe to the abacus, the Hindu-Arabic numeral system we use today, and (possibly) the mechanical clock.

Sylvester used the armillary sphere and sighting tubes to determine the definitive position of the pole star and to record measurements for the tropics and the equator. His work was improved upon in the Renaissance by Tycho Brahe (1546 - 1601). Public figures would have an armillary sphere incorporated into their portraits to indicate their wisdom and knowledge.

I've written about clocks before, but I don't recall learning that Gerbert d'Aurillac invented it. I want to check that out; I'll let you know what I find.

Al-Kindi

Abu Yūsuf Yaʻqūb ibn ʼIsḥāq aṣ-Ṣabbāḥ al-Kindī (801-873CE) is called the Father of Arab philosophy. Born in Kufa and educated in Baghdad, he was instrumental in the translation of many Greek scholarly texts into Arabic. (Remember that a lot of classical scholarly knowledge came to Western Europe via Arabic translations.) He is also credited with introducing Indian numerals (what we mistakenly think of as Arabic numerals) into the Arab and western world.

He was a polymath who contributed to many fields, although he did not always find the scientific truth.

In astronomy he followed Ptolemy's geocentric theory of the solar system, and he was certain the planets followed circular orbits in obedience to God.

He was a chemist who debunked the idea of alchemy turning base metals into gold or silver. He was the first to distill pure ethanol, with which he created several perfumes. He also created cosmetics and pharmaceuticals, and wrote a book on the chemistry of perfume.

A recently discovered book of his in Istanbul, entitled (in English) A Manuscript on Deciphering Cryptographic Messages shows that he was a pioneer in cryptography with the first known explanation of how to decipher encrypted messages by analyzing the frequency of letters.

He wrote on pollution, environmentalism, and meteorology, and explained tides as a result of heating and cooling.

He published 15 treatise on music theory—five of which have survived—including the first known written use of the term "music" (musiqia); he urged the use of music in therapy.

In optics, he explained that both the eye and the object seen must be linked by a transparent medium (air) filled with light. He criticizes Anthemius of Trailes for reporting that sunlight could be focused in war to cause opposing warships to burst into flame. Anthemius did not witness it himself. Al-Kindi performed experiments to be certain this would actually work.

His theory that time, space, motion, and bodies were not absolutes but relative to other objects and the observer puts him closer to Einstein than to Galileo and Newton.

Although his belief that philosophy could support theology was contested by many Arabic scholars who followed him, his writings laid the groundwork much of Arabic philosophy to come.

He also applied mathematics to pharmacology, which I'll talk about tomorrow.

Medieval Eclipses

[source]

Eclipses were a mystery for awhile, but eventually enough took place that astronomers could spot the patterns. European astronomers in the 1600s were able to publish books explaining how lunar and solar eclipses took place. Prior to that, however, they were mysterious occurrences whose importance was tied to whatever was happening on the ground.

In 632, an eclipse that was visible in Medina on 27 January coincided with the death of Ibrahim, the son of the Prophet Muhammad. Muhammad interpreted this as a sign for his followers to pray for Ibrahim.

On 2 August 1133, a total eclipse took place. When King Henry I of England died months later, it "confirmed" for the popular culture that eclipses were bad omens for rulers. They knew that the eclipse portended bad news; they just had to wait a long time to find out what the bad news was.

There's a stone in Ireland whose carvings are interpreted as the first recorded eclipse. You can see it above. The two sets of concentric circles colliding in the middle represent the eclipse. The circular carvings above it represent the other stars that appeared in the sky at the moment of totality. The overall pattern enabled astronomers to determine when the eclipse took place. So it is pretty well established that the earliest recording of an eclipse was made on the Loughcrew Cairn Megalithic Monument in Ireland; the eclipse took place on 30 November, 3340 BCE.

A Sultan's Observatory

The Ulugh Beg Observatory Museum, built in 1970

Ulugh Beg is the more familiar name of Mīrzā Muhammad Tāraghay bin Shāhrukh (22 March 1394 - 27 October 1449). "Ulugh Beg" is more of a nickname, meaning "Great Ruler."

He was a grandson of Tamerlane who became sultan in Samarkand while still a teenager. He decided to turn Samarkand into an intellectual center, building a university and inviting scholars to take up residence.

He also built the Ulugh Beg Observatory in 1420, where some of the finest Islamic astronomers worked and studied, but only those whom Ulugh personally approved. The picture here is a modern structure on the site of the original, which was destroyed by religious fanatics in 1449. An excavation uncovered its primary feature—a giant sextant:

The so-called "sextant" obviously would have extended well above the ground (as the drawing shows) and likely was closer to being a quadrant. As Krisciunas points out in his interesting discussion of the instrument, it "was by far the largest meridian instrument ever built." Fragments of the curved measuring track have survived with markings for around 20 degrees; this is about the highest point that observations likely would have been made. The "sextant" would have been used to measure the angle of elevation of major heavenly bodies, especially at the time of the winter and summer solstices. Light

from the given body, passing through a controlled opening, would have shone on the curved track, which is marked very precisely with degrees and minutes. "It could achieve a resolution of several seconds of arc--on the order of a six-hundredth of a degree, or the diameter of an American penny at a distance of more than half a kilometer" (Krisciunas). It is not clear whether more than the sun and moon could have been measured in this fashion, since planets, for example, would not have cast sufficient light. [link]

Building a giant permanent astronomical instrument was a unique idea at the time—remember that this was 200 years prior to the invention of a telescope. He created a catalog of over 1018 stars, discovering and correcting many inaccuracies in the star tables created by Ptolemy. Copies of these star charts are on display at the Ulugh Beg Observatory Museum; the originals are in the Bodleian Library in Oxford.

St. Dominic

The Dominicans have been mentioned many times, and their founder has been mentioned as a friend of Simon de Montfort, but his life deserves a little more attention.

St. Dominic is most often referred to (prior to canonization, that is) as Dominic Guzmán. He was born in 1170 in Castile, and was supposedly named for an earlier St. Dominic.* Nothing reliable is known of his family, since the earliest chroniclers had no interest in his parents and later chroniclers naturally tried to make his parentage sound impressive.**

In 1191, when Spain was suffering from famine, the young university student Dominic sold all he owned—including his clothes—for money to feed the starving poor. A few years later he joined the Canons Regular, who followed the rule of St. Augustine.

In 1215, the year of the Fourth Lateran Council (mentioned here and other places), Dominic and six disciples started their own house in Toulouse with some monastic rules, and were given permission by the local bishop to preach in Toulouse. That same year, Dominic and the bishop went to Rome to request permission for the founding of a new order to combat heresy; it was given by Pope Honorius III in the winter of 1216/17 and called Ordo Prædicatorum ["Order of Preachers"] (which is why, although referred to as "Dominicans," they have the initials "OP" after their names).

Interest in his order grew, and although his headquarters was in Rome where the pope had given the Dominicans a house, Dominic constantly traveled to keep in touch with the various chapters. We are told that he abstained from meat and excessive food and talking, and that he never allowed himself to sleep in a bed. The use of the rosary is attributed to him: it was known earlier, but he certainly promoted it as a guide for prayer.

His icons, seen in the picture above, are the lily for his chastity, the book and staff representing his authority to preach (supposedly granted to him by a vision of Saints Peter and Paul), and the star above his head. The star was seen by his mother in a vision before he was born; because of it, he is considered the patron saint of astronomers. The last symbol, also seen by his mother in a vision, is the dog with the torch in its mouth, representing that he was to "set fire to the earth" with his preaching. This ties directly to the Dominican connection to the Inquisition, which will get its own post in the near future.

Dominic died on 6 August 1221.

*St. Dominic of Silos (1000 - 1073), who had been abbot of a monastery a few miles from Dominic's birthplace.
**The name eventually given to Dominic's mother was Joan of Aza, and that name was beatified in 1828 by Pope Leo XII.


http://en.wikipedia.org/wiki/Saint_Dominic

Halley's Comet

Halley's Comet on the Bayeaux Tapestry

The nice thing about astronomy is that some celestial events are so predictably cyclical that they can help confirm dates in history, or be spotted in the historical record. Halley's Comet has appeared numerous times while human beings have been on Earth, and many of those appearances have been noted by record-keepers.

BCE records suggest Halley's was spotted as early as 467 BCE by the Greeks and the Chinese, but the first report detailed enough to be certain of Halley's pattern was in 240 BCE by a Chinese chronicle.

The 1493 Nuremberg Chronicles used many early sources, one of which mentioned the comet appearing over Europe in 684. The 837 approach—recorded by astronomers in Germany as well as across the Middle East and Asia—was the closest the comet ever came to earth: a mere 3.2 million miles away, and took place on 10 April. The Annals of Ulster—an Irish chronicle extending from 431 to 1540 CE—says of 912 "A dark and rainy year. A comet appeared."

1066 saw the appearance of an invading Norman army in England and the appearance of the comet in the Anglo-Saxon Chronicle, in the Irish Annals of the Four Masters, and later in the Bayeaux Tapestry.

Drawing and note from Eadwine Psalter

The Bayeaux Tapestry wasn't the only attempt to record visually what they saw in the sky. The 1145 appearance was drawn up by a monk, Eadwine, who was copying a psalter at Canterbury Cathedral. On the bottom of the page with the Fifth Psalm, Eadwine added a drawing and a note: “Concerning the star ‘comet’. The star ‘comet’ has a ray such as this, and in English it is called the long-haired star.* It appears rarely during the course of many years, and then as a portent.”

The next appearance of Halley's is scheduled for 28 July 2061.

*comet is from Greek and means "hair" or "long hair."

Abd al-Rahman al-Sufi, Astronomer

MS. Marsh 144, fol. 135v, Bodleian

The contributions of the Muslim world to astronomy are many, and I have only briefly touched on some of them (such as here). There were nine Muslim astronomers in particular who made major contributions. One of them was the Iranian Abd al-Rahman al-Sufi (7 December 903 - 25 May 986). His name indicates that he was a Sufi Muslim, like Rumi.

al-Sufi translated and expanded on the work of the Greeks, especially attempting to reconcile the Greek and Arabic star charts and constellations. In 964 he published Suwar al-Kawakib al-Thabitah, the "Book of Fixed Stars."* In it he gave the latitude and longitude of hundreds of stars for the year 964 from two views: from both the exterior and interior of a celestial globe. The oldest surviving manuscript known is in the Bodleian Library and was created about 1009 by al-Sufi's son. There was no English translation of this book until 2013.

Among the "firsts" that can be credited to al-Sufi's work are the following identifications:

Ursa Major

• "the little cloud" that we call the Andromeda Galaxy.
• the Large Magellanic Cloud*
• the Omicron Velorum star cluster
• a "nebulous object" in Vulpecula, now called "Al Sufi's Cluster"

He also describes the astrolabe and lists a thousand uses of it.

The significance of al-Sufi's work led the astronomical community to name other objects after him, such as a a lunar crater (Azophi) and 12621 Alsufi, a minor plant in the asteroid belt with a period of 2000 days.

*There is an argument that he could not have known of the Magellanic Cloud until the same time as Western European astronomers in the 15th century because of its position in the Southern Hemisphere.

Medieval Meteors

Woodcut showing meteorite coming to Ensisheim.

Today is the anniversary of the first meteorite the exact date of whose fall to Earth has been recorded. It was in 1492, around noon, when a young boy heard an explosion and observed a rock fall from the sky, burying itself in a wheat field outside the town of Ensisheim in what is now France (but was then Austria). The sound of the explosion was heard up to 150 kilometers away. Townspeople came to investigate and found a 127-kilogram triangular rock in a pit a meter deep. They retrieved it from its trench and immediately started chipping pieces from it, until a local authority stopped them, ordering the rock to be delivered to the steps of the local church and preserved pending an investigation.

But that was far from the first meteor or meteorite recorded.* The Journal for the History of Astronomy in 1978 published "Meteors, Meteor Showers and Meteorites in the Middle Ages: From European Medieval Sources." The article lists every meteoritic phenomenon it could find by carefully scouring historical texts, and includes items such as:

453 or 454 — Tres magni lapides (three big stones). Three meteorites fell in Thrace 

518 — Alius ignis . . . instar scintillarum (another fire sparklike). A meteor. Date uncertain. Theophanis Chronographia 

557 — Discursus stellarum (moving stars). A shower lasting the whole night that caused terror. Date uncertain. G. Cedrenus

There are several pages of entries. Meteoric phenomena could be seen as good or evil, often depending upon their proximity to events in the lives of the observers.

As for the Ensisheim Meteor, it currently resides in the Ensisheim museum and is toasted every year by The Brotherhood of Saint-Georges of the Guardians of the Meteorite of Ensisheim. Maximilian I (1459-1519), son of Holy Roman Emperor Frederick III, visited the rock shortly after its fall and declared it a wonder from Heaven. He took some chips for himself and a friend. After years of people taking parts of it away, the rock is now roughly spherical and has been reduced to about 56 kilograms. I guess everyone wanted to have their little piece of Heaven.

*A meteor (first coined in the 16th century, from a Greek word meaning "lofty") is a rocky object that streaks through the atmosphere, heating up via friction and creating a streak of light; a meteorite is a meteor that reaches the ground. A small percentage of meteorites are composed of nickel and iron.

Cross-referencing an Eclipse

Diagram of an eclipse from a modern translation of Hipparchus

It is not always easy to figure out dates from classical or medieval writings. Chroniclers did not necessarily strive for the kind of historical accuracy which 21st-century audiences expect. When they wanted to be precise, they often expressed themselves in ways that do not provide a proper context for the modern scholar.

Consider, for instance, Pappus of Alexandria, whom the Encyclopedia Britannica calls "the most important mathematical author writing in Greek during the later Roman Empire." [source] He wrote many important texts, but we knew little of his life.

I mentioned the other day how Suidas' Lexicon gives us data on works and events otherwise lost to history. The entry for Pappus reads:

Alexandrian, philosopher, born in the time of the elder emperor Theodosius, when the philosopher Theon also flourished, the one who wrote about Ptolemy’s Canon. His books [are] Description of the Inhabited World; Commentary on the 4 Books of the Great Syntaxis of Ptolemy; The Rivers in Libya; Dream-Interpretations. [source]

We know that Theodosius reigned from 372-395 CE, so it gives us a time frame for Pappus. This creates a small head-scratcher, however. Pappus claims to have calculated and observed an eclipse in the month of Tybi (the fifth month of the Coptic calendar). There is a problem with this dating: no eclipse occurred during the month of Tybi during the reign of Theodosius that Pappus could have observed! Could the Suidas be wrong? Certainly. But then... what is right?

There is, as it turns out, a 10th century copy of a work by Theon of Alexandria (the one mentioned in the Suidas entry) that has a marginal note next to an entry on the Emperor Diocletian (who reigned from 284-305 CE), stating "at that time wrote Pappus." Is it possible that the composer of Suidas had access to that work and assumed that it meant Pappus flourished when Theon did? If we look closer to the reign of Diocletian, we discover that there was an eclipse in the month of Tybi which would place it (using the modern method of dating) on 18 October 320 CE. If Pappus observed it himself in 320, it isn't likely that he was flourishing over 50 years later. This places him firmly in the earlier part of the 4th century.

Pappus is far more important than as an example of the care with which modern historians must date historical events. Some of his eight-volume work on mathematics is extant; and deals with many facets of geometry and carefully lays out the mathematical findings of his predecessors and how their work builds on each other over time. He also worked on several problems such as inscribing regular polyhedrons inside a sphere, conic sections, trisecting an angle, and many more. He has a theorem named after him, as well as the Pappus chain, the Pappus configuration, and the Pappus graph.

His commentary on Ptolemy provides us with insight into some lost works of classical astronomy, such as an astronomical work by Hipparchus on eclipses (illustrated in the above figure).

Nicholas Oresme

Nicholas Oresme (c.1325-1382) likely came from humble beginnings; we assume this because he attended the College of Navarre, a royally funded and sponsored college for those who could not afford the University of Paris. He had his master of arts by 1342, and received his doctorate in 1356. He became known as an economist, philosopher, mathematician and physicist.

One of his published works was:

Livre du ciel et du monde
(The Book of Heaven and Earth)
In this work he discussed the arguments for and against the rotation of the Earth.

• He dismissed the notion that a rotating Earth would leave all the air behind, or cause a constant wind from east to west, pointing out that everything with the Earth would also rotate, including the air and water.
• He rejects as figures of speech any biblical passages that seem to support a fixed Earth or a moving sun. (Keep in mind even today we unanimously speak about the beauty of the sun setting when it's really the Earth rising!)
• He points out that it makes more sense for the Earth to move than for the (presumably more expansive and massive) heavenly spheres and Sun to move.
• He assures his readers that all the movements we see in the heavens could be accounted for by a rotating Earth.
• Then he assures the reader that everyone including himself thinks the heavens move around the earth, and after all he has no real evidence to the contrary!

Years later, Giordano Bruno (1548-1600) wrote his theories out in a way so similar to Oresme's that it is assumed he had access to Oresme's writing.

Asking Questions

Image from Adelard's translation
of Euclid's Elements of Geometry

Being inquisitive is the first step to learning.* In the early Middle Ages, the presence of many classical authorities circulating in Latin, such as Aristotle and Plato, eliminated the need for inquiry in the opinions of many.

The 12th century saw an influx of more works, many of them Greek writings (preserved by Arabs) or Arab writings. The widening of philosophical and scientific horizons by this wave of knowledge caused many scholars to re-think what had been established.

Adelard of Bath (c.1080-c.1152) was an English philosopher who was in a position to translate into Latin for the first time many of the Greek and Arabic works becoming available to the West. After studying at Tours and teaching at Laon in France, he traveled for seven years through Italy, Sicily, Syria and Palestine. He translated Al-Kwarizmi's astronomical tables and Euclid's Elements of Geometry from Arabic, wrote works on the abacus and on his love of philosophy, and a book called Questiones Naturales (Natural Questions) in which he tackled, in dialogue form, 76 questions about the world. One of his themes is the choice of using reason rather than merely accepting authority.

For what should we call authority but a halter? Indeed, just as brute animals are led about by a halter wherever you please, and are not told where or why, but see the rope by which they are held and follow it alone, thus the authority of writers leads many of you, caught and bound by animal-like credulity, into danger. Whence some men, usurping the name of authority for themselves, have employed great license in writing, to such an extent that they do not hesitate to present the false as true to such animal-like men. [...] For they do not understand that reason has been given to each person so that he might discern the true from the false. [Questiones Naturales, VI]

To be clear: Adelard's science is not ideal: his periodic table of elements contains only four substances, which are mixed in various proportions to create all materials. Some animals see better by day or night because of either white or dark humor in their eyes. We see because an extremely light substance (Plato's "fiery force") is created in the brain, gets out of the brain through the two eyes, swiftly reaches an object and learns and retains its shape, then returns to the brain through our eyes so that we "see" what is in front of us. A mirror, whose surface is smooth, bounces back the fiery force, which on returning to us picks up our image on its way and allows us to see our reflection.

Still, his works were copied and distributed, and influenced much of what was to come. His assertion of reason over blind acceptance of classical authorities was an important milestone in scientific thought. Many of his ideas are seen again in the writings of Robert Grosseteste, Roger Bacon, and Hugh of St. Victor. Once the printing press was perfected, Adelard's translation of Euclid became a standard text for a hundred years.


*One of the followers of this blog is part of a group trying to promote inquiry-based learning in young people. Visit Prove Your World to learn more.

Pre-Inertia

Expositio & questiones manuscript

Jean Buridan (c.1300-c.1361) was a University of Paris scholar who was not afraid to tackle some of the big scientific and philosophical issues of the day. That meant, in some cases, taking a critical look at one of the most revered figures in science and philosophy, Aristotle. Buridan, like William of Ockham (c.1288-c.1348),  believed in the observable reality around him, and believed that observation of the world was the key to understanding it. Challenging Aristotle could be risky, but as more and more scholars observed the world around them, they realized that Aristotle's theories needed amendment. He wrote Expositio & questiones (Expoition and questions) to analyze Aristotle's work.

For example, Aristotle believed that an object set in motion—let's say, a rock thrown by a human hand—continues to move after it has left the hand because there must be some continuous external force exerted on it. He theorized that, in the same way a hand swished through water creates little eddies and swirls in the water around it, so the rock's movement is continued by eddies and currents of the air. If there were no movement in the medium that helped carry the rock forward, he believed, the rock would stop its forward course (and presumable drop the the ground). The currents eventually faded, allowing the rock to end its forward flight.

Buridan was not satisfied with this. Building on the work of others (such as John Philoponus and Avicenna, both of whom deserve their own entries some day), he believed that there must be a property in the rock itself that accounts for its action once it has left the motive force of the hand. He called this property of the object impetus (from Latin impetere, literally "to rush toward, to attack").

The property or quality of impetus was clearly changeable. To hurl a heavy rock required you to give it more impetus than to hurl a pebble. Also, impetus was obviously used up over time, allowing the rock to cease its movement and fall. He also explained that a falling object gained impetus the longer it fell (are you paying attention, Galileo?). Unlike Aristotle, who believed that the medium of air in which the object moves helps it along, Buridan saw the air as resistance, causing the object to use up its impetus.

He expanded this theory by looking up. A question had bothered some philosophers for ages: why don't the planets slow down? Will they move forever? Buridan extrapolated his theory to say that a thrown rock in a vacuum would experience no resistance and its impetus would last indefinitely. If the planets were moving in a vacuum...

Well, actually, he couldn't go that far. He agreed with Aristotle that a vacuum couldn't exist in space, since there was no container to keep matter from rushing into the empty area. If above our atmosphere were filled with quintessence, however, Aristotle's "fifth element" that was pure, unchangeable, and frictionless, then the impetus imparted to the planets by whatever initial agency would continue to move forever! The idea of an eternal universe was supportable by science!

Refuting Astrology

As attractive as astrology was in the Middle Ages, not everyone was willing to accept the premise that it was "easy" to use it for predictive purposes, or even that it was likely that the existence and movements of observable heavenly bodies had a direct influence on events and people on Earth.

We have seen how some sources, such as the University of Paris, spoke against astrology's predictive uses not because it believed they were in error, but because they were believed to contravene God's wishes for human beings. There were others who objected to the reliance on astrology because they could not believe that it was likely to work.

Ibn Qayyim Al-Jawziyya (1292-1350) was a Sunni Islam theologian and commentator on the Qu'ran. Not given to flights of fancy, and accustomed to arguing the details of the law, he put a critical lens on astrology. One of the lynch pins of his refutation of astrology came from the fact that hundreds of stars were not included in astrological calculations. Astrologers told him that the stars were too far away and to small to matter. To Al Jawziyya, this was an intolerable double-standard:

And if you astrologers answer that it is precisely because of this distance and smallness that their influences are negligible, then why is it that you claim a great influence for the smallest heavenly body, Mercury? Why is it that you have given an influence to al-Ra's and al-Dhanab, which are two imaginary points?

Astrologers accepted at the time, through their calculations, that the stars appeared small because they were far away, but were actually enormous compared to the world. They also knew that the Milky Way was "a myriad of tiny stars packed together in the sphere of the fixed stars"; Al-Jawziyya said that it was impossible to know what effect, if any, they would have. Astrology had too many variables, and was just so much guesswork.

What were the "two imaginary points" mentioned in the above quotation? He was referring to "orbital nodes," the imaginary point in space where the line of "an orbit crosses the plane of reference to which it is inclined." Astrologers made much out of these points, which had no physical existence, and yet ignored actual physical stars. They neglected stars as being too small to matter, and yet put all their attention on planets that were a ridiculously small fraction of the size of a star. To the keen legal and theological mind of Al-Jawziyya, this suggested that astrology was not, in fact, based on any kind of rational thinking.

Father of Arab Astrology

Abu Ma'shar, from his Introduction to Astronomy

Albertus Magnus, Robert Grosseteste, Geoffrey Chaucer—well-known names from the Middle Ages denoting a Dominican scientist, a university scholar and administrator, and a courtier and poet. One thing they had in common, besides a love of learning, was their attention to the art of astrology. And through their interest in astrology, they were all influenced by a 9th century Arab known in the West as Albumasar. His full name was Abu Ma'shar Ja'far ibn Muhammad ibn 'Umar al-Balkhi (787-886), and he was one of the most respected figures in the history of astrology.

Abu Ma'shar was of particular interest to Western Europe because he was a source for knowledge of and commentary on Aristotle when his writings reached Europe in the 12th century, brought back by the Crusaders. He offered so much more, however. His work blends knowledge of Greek science with Islamic doctrine, Persian chronology, Mesopotamian astrology, and hermetic traditions from Anatolia. He presented a unified approach to the knowledge of several cultures that lent weight to his work.

For instance, he uses the Biblical Flood as the focal point of his astrological tables. He calculates it at midnight on Thursday to Friday, 17-18 February 3101 BC. This date was not arbitrary, nor was it an indication that Abu Ma'shar believed in a short-lived Earth. He chooses the date because it is the start of the Hindu Kali Yuga (the "age of vice"; the last of four phases the world will go through). His knowledge and acceptance of Hindu chronology and its "Great Year" (composed of 360,000 years) is further shown when he calculated a grand conjunction of planets in 183,101 BC, and again in 176,899 BCE.

The Middle Ages loved "unified theories" that could reconcile different traditions to enhance understanding. Abu Ma'shar argued for the superiority of his chronological calculations because he made the year out to be 365.259 days long. Why was he so enamored of this number? Because "259" he explained was the minimum number of days for human gestation (8.6 months). It was obvious to him that he was onto something!

Unlike the hostility experienced by astrology from the University of Paris and others, who felt it was a way to contravene God's plan, or to know what should remain unknowable, Abu Ma'shar was able to give his astrology a veneer of respectability by acknowledging Islamic religious doctrine.

The Father of Modern Optics

For a long time, there were two competing theories about how the eyes see—both wrong.

Alhazen ibn al-Haytham

Aristotle believed in what is called the intromission theory: the idea that actual physical forms enter the eye to plant images in your head. Euclid and Ptolemy believed in the theory of extromission: the idea that rays from the eyes went out and "scanned" or "detected" objects. Scholars and philosophers for centuries came down on one side or the other. It wasn't until the 11th century that a better theory came along.

Alhazen ibn al-Haytham (965-c.1040) was a Muslim who wrote about many topics. Originally he was a theologian, trying to address and reconcile the issues between the Shi'ah and Sunnah sects. He made his most lasting contributions, however, in the fields of astronomy, mathematics and optics. His Kitab al-Manazir (Book of Optics) changed the study of optics forever. He rejected both previous theories, arguing that there was no time for the eye to emit rays that could travel to a distant star and back to the eye instantly the way they would have to when first opening the eyes. He also refused to believe there was any mechanism that allowed forms to enter the eye. Instead, he opted (ha ha) for light coming from external objects to enter the eye, carrying an image of the object being looked at.

His theory of light's involvement in sight came when he realized that bright and dim light both affected visual perception, and that bright light left after-images on the eye. Also, it was obvious that perceiving color depended upon having sufficient light. He even invented the camera obscura in order to learn more about how light worked.

...and he did it while in prison.

Alhazen's diagram of the eye, with terms we still use

Earlier in his career, he became overconfident in his knowledge and made the mistake of claiming it would be possible to devise a way to control the annual spring flooding of the Nile. (Although born in Basra, Iraq, he lived his adult life in Cairo.) Hearing this, Caliph al-Hakim bi-Amr Allah, the sixth ruler of the Fatimid dynasty, ordered him to do so. When al-Haytham realized he wasn't able to perform this enormous feat of engineering, he tried to simply retire from the profession. The angry Caliph sent his men for al-Haytham, who feigned madness in order to avoid a death sentence for disappointing his all-powerful ruler. He was placed under house arrest, and devoted the remainder of his life to the sciences for which he is now known. Because of the experiments he conducted in order to test his theories, mirroring what would be known as the scientific method, some think of him as the "first scientist."

Hermann of Reichenau

Hermann, with crutch & Salve Regina

Hermann of Reichenau (1013-1054) was born to Count Wolverad II and his wife Hiltrud in Upper Swabia. He was severely disabled at birth, and had to be carried around in a specially built chair. A 1999 article tried to diagnose him based on contemporary reports.

Using the biography written by his disciple Berthold, [an] unbiased analysis of the symptoms described [...] is worked out: [...] Intellectual functions were unaffected. [...] Muscle disease is considered possible, but motor neuron disease - either amyotrophic lateral sclerosis or spinal muscular atrophy - seems to be the most convincing diagnosis. [C Brunhölzl, Thoughts on the illness of Hermann von Reichenau]

Because of his condition, he was nicknamed "Contractus" or "the Lame." When he was seven years old, his parents handed him over to the cloister school of the nearby Benedictine monastery on Lake Constance, where he studied under Abbot Berno. Berno was a well-known figure at the time for, among other things, his reforms in liturgical music. Hermann became a monk in 1043 and, upon Abbot Berno's death in 1048, became Berno's successor as abbot.

Despite Hermann's extreme difficulty in moving and even speaking, he was considered a devoted monk and brilliant scholar. He wrote a great deal on music, mathematics, and astronomy. As well as a treatise on the science of music, he wrote two of the best-known of the medieval liturgical songs, the Alma Redemptoris Mater (Loving Mother of the Redeemer), and the Salve Regina (Hail Holy Queen).*

Among his other accomplishments, he is credited with speaking Arabic, because through his writings he made available to the Latin West many scientific discoveries that were previously only widely known in the Arab world. This knowledge of Arabic, however, is only an assumption. His biographer, Berthold, never mentions knowledge of Arabic, which would be unusual omission for such an accomplishment. The monastery was a center of learning in the area, and very likely held copies of works by Gerbert of Aurillac, who learned much from Arabic sources in Spain.

Hermann wrote two works on the astrolabe, previously unknown in Europe, and described a portable sundial. His works on mathematics used Roman numerals. Although this precluded the use of decimals, he still achieved some remarkable results. In his Epistola de quantitate mensis lunaris (Letter on measurement of lunar months), he tries to find the average length of a lunar month. In decimal notation, it is 29.530851 days. Hermann did not only not have decimal notation, he didn't have minutes and seconds. In his time, the hour was divided into "moments" and "atoms." He calculates the length of the lunar month to be 29 days, 12 hours, 29 moments, 348 atoms, which turns out to be exactly right.

He also wrote a history called Chronicon ad annum 1054 (Chronicle to the year 1054). The original is lost, but a 1529 edition saved the unique historical knowledge inside. After Hermann's death, it was continued by Berthold; Berthold died in 1088, but the duty was taken up by others up until 1175.

Hermann died on 24 September. In 1863, he was beatified (a step toward being recognized as a saint). As Blessed Hermann of Reichenau, he is considered the patron of unborn babies, and his Feast Day is celebrated on 25 September.

*A popular English version of Salve Regina was prominent in the Whoopi Goldberg film "Sister Act."

Autumnal Equinox Lightshow

Holy Trinity Church in Barsham, Suffolk

The equinox, from Latin aequinoctium (the time of equal days and nights), the day twice each year when the amount of daylight and darkness equalizes. We are used to marking the solstices, because the longest day of sunlight and the shortest day in winter carry real-life significance for us. But the equinoxes in spring and fall rarely get the same attention.

But in Suffolk, England, in Holy Trinity Church in the tiny town of Barsham, the equinoxes have provided a special show since the Middle Ages—if one knew where to look.

To be truthful, the "special show" was forgotten for a long time because of some changes. Holy Trinity is an early church, using stone from Caen that tells us it was built post-1066, although the round tower is by many considered to be an earlier Saxon style. The church suffered when Henry VIII broke with Rome and made changes consistent with the new Anglican Church. A rood screen, an ornate partition between the main part of the church and the nave behind the altar, was torn down, and the large crucifix that hung on it was eliminated. In 1870, however, the vicar of Holy Trinity decided to rebuild the rood screen and restore the crucifix to the same spot it hung in centuries earlier. Unfortunately, the vicar also decided to hang a large painting over a narrow west window whose significance he did not realize.

On the equinoxes, light strikes the crucifix for 4 minutes

Then, in 1979, a fire destroyed the nave roof. During the reconstruction, someone took the painting down. Years later, during a mass at dusk on the autumnal equinox, someone saw it. Now that the church was restored to its original configuration, the narrow western window throws a shaft of light for 4 minutes each equinox—and only on the equinox—right onto the crucifix near the top of the rood screen.

It was easy to miss for several years: it doesn't show when there is cloud cover at twilight, and you need to be looking up. Now that the phenomenon has been re-discovered, however, the church is filled each equinox by people waiting to see the fascinating result of an unknown medieval architect who decided to use light to illuminate his art.