Anthemius of Tralles

Anthemius of Tralles (c.474-c.557) was mentioned as one of the builders (along with Isidore of Miletus) of the new Hagia Sophia. We know much more about him than that, however, both about his talents...and his annoying pranks.

We have an anecdote about how he avenged himself on his neighbor, Zenon, by fashioning leather tubes that he ran to the joists of an upper room of Zenon's house, where Zeno used to entertain guests. We are told that Anthemius would, by running steam through the tube, create loud noises and vibration in he room, frightening the guests into thinking there was an earthquake. Also, he would flash incredibly bright light into Zenon's eyes with a concave mirror.

Possible? Well, he did write a treatise "On burning-glasses"; we don't have the treatise anymore, but enough of it existed in 1777 to be included in a work called Concerning wondrous machines by an L. Dupuy. He apparently studied and wrote on properties of mirrors and lenses, and supposedly described a camera obscura. He explained how to construct an ellipse using string, and he wrote a book on conic sections.

This intellectual excellence ran in the family. His father, Stephanus of Tralles, was a physician with five sons. Two of them followed in their father's footsteps, Dioscorus staying in Tralles and Alexander finding fame in Rome.  The rest pursued different professions. Metrodorus became a grammarian in Constantinople; Olympius became an expert in Roman jurisprudence.

Anthemius' knowledge of conic sections and parabolas would have supported both his work on optics (known to the later "Second Ptolemy" Alhazen ibn al-Haytham) and his architectural aspirations when designing the dome of the new Hagia Sophia. He was able to create what is called a "pendentive": a design that allows a dome to be built onto a square base.

His success with Hagia Sophia led to him being also chosen—probably by Emperor Justinian—to design flood defenses at Dara in northern Mesopotamia.

Figuring out the Sun

[DailyMedieval is on semi-hiatus for the holidays, and I am re-cycling some older posts. For Christmas I received A Short History of Nearly Everything by Bill Bryson. I have just read the section on the brilliant Lord Kelvin, who estimated the age of the Earth at as high as 400 million years. Interestingly, he kept revising his estimate, from 400 million to 100 million to 50 million and, finally, to 24 million. The difficulty in adhering to his longer estimates, for him and others in the burgeoning field of geology, was not that they could not imagine the Earth being older, but that for the Earth to be that old, the Sun would have to be around—and their best estimates of how the Sun worked could not imagine the nuclear forces that would allow it to produce heat continuously for hundreds of millions of years. This reminded me of the post for 10 June 2012.]

How Does the Sun Work?

Robert Grosseteste (c.1175-1235) is considered by some to be the founder of modern English intellectualism. Among other topics, he focused (pun intended) on light. One of his works sought to explain how the sun produced heat.

He first explained the three methods of heat generation:

1. An object that is hot
2. Motion/Friction
3. The scattering of rays

He determined that Method 1 cannot apply here. For heat to transfer from a hot object, there must be a medium through which it travels, and that medium will heat up during the transfer of heat. Clearly everything between the sun and us does not heat up.

He decided that Method 2 was also insufficient to explain the heat, because the motion that creates heat is caused by two substances moving in opposite directions—for instance, rubbing your hands together to warm them up—and the sun's circular motion does not act upon a second substance moving in an opposite direction: everything up there moved from east to west.

Method 3, he decided, must pertain. He reminds his reader that Euclid explained how a concave mirror can focus the sun's rays to cause a fire. He stated that the sun's rays falling upon the earth are scattered, but reflection by a mirror or refraction by a (clear) spherical body can change the direction of the rays, focusing them via the medium of the dense air and generating heat. For him, this had much to do with the denseness of the medium: he stated that the same amount of light falls on a mountaintop and scattering can be observed there, but the thinness of the medium of air disallows the generation of heat.

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."

The Rainbow Connection

Check this out, then come back.

Theodoric (or Thierry, or Dietrich) of Freiberg (c.1250-c.1310) was a Dominican, a philosopher, and a physician. His name is often written with the title magister (master), so we know he had an advanced university education, almost certainly at Paris. In 1293 he was named Provincial of the Dominican Order, Albertus Magnus' old post.

Freiberg's description of the geometry of the rainbow.

We have 21 works written by him, although a list of works by Dominican authors compiled in 1330 lists 31 under his name. Somewhere between 1304 and 1310, Theodoric produced De iride et radialibus impressionibus (Concerning the rainbow and impressions of radiance). In it, he presents the correct explanation for the rainbow. He explains the primary rainbow, the secondary rainbow and why the colors are reversed, and the path light takes to make the rainbow.

That last is important, especially if you've read the link I gave you above and are aware of the competing theories for refraction and reflection, and the place of water droplets versus clouds. Freiberg accurately describes how the path of sunlight is refracted when it enters the droplet, reflected off the other side of the droplet, and refracted again when it leaves the droplet and becomes visible to the observer. Freiberg determined much of this by experimenting with glass spheres filled with water, an extraordinary act in itself in the history of scientific experimentation.

Perhaps, however, the mechanics of the rainbow was an idea whose time had come. In one of those examples of synchronicity that crop up in history from time to time, there was another scientist who came to some of the same conclusions as Frieberg. His name was Kamal al-Din al-Farisi, and he and Freiberg had no contact—although they did have one thing in common: they both knew the 11th century seven-volume work called The Book of Optics by Ibn al-Haytham. But that's for another day.

Reasoning Wrong

Nicholas of Cusa (c.1400-1464) believed in using reason to determine how the universe worked. He did not exactly take a "scientific" approach: he argued from his understanding of metaphysics and, in some cases, numerology. His guesses, however, were better than some early scholars' observations.

Because he could not accept that God was finite, and since God is not separate from the entirety of the universe, he argued that the universe must by necessity be infinite. Also, because God must provide the center for His own totality, the Earth cannot be at the center of the universe—that would mean Earth was the center of God. Not being at the center of the universe, the Earth cannot be immovable, and it, along with the Sun, must be in motion just like every other observable heavenly body. This idea influenced Giordano Bruno.

Again, denying perfection for anything but God, he would not accept planetary orbits as perfectly circular, paving the way for Kepler (who referred to Nicholas as "divinely inspired") to design elliptical orbits in his planetary theory.

Cusa's thoughts on what we now call infinitesimals in his De Circuli Quadratura (On Squaring the Circle) helped Kepler out when trying to calculate the area of a circle, by picturing it as an infinite series of triangles. Cusa's reasoning for this was that the circle encompassed all other forms. Cusa's and Kepler's work was later important to  Leibniz' Law of Continuity.

Tomorrow: his views on bringing religions together.