For Aristotle the identity of any object was hidden in its "essence." This meant objects in the world were not defined according to the attributes (like color, weight, etc.) which might change relative to other objects but by their immutable "essences. "

This view led to a flat and two-dimensional painting style until the 15th century, a style in which objects were painted regardless of their distance to the viewer since what mattered was the "essence" of an object and not its relationship to the viewer or the other objects in the painting.

For example, a Saint was painted always larger and in colors brighter than a Sinner or a Peasant regardless of his position in the painting. Why? Because a Saint had a more valuable "essence." There was no room for the concept of "visual perspective" in medieval art.

Al-Hazen (Courtesy of Wikipedia)

Then some time during the 14th century a book on optics written by the Arab philosopher Al-Hazen was translated to Latin (and then I believe into the kind of vernacular Italian spoken in Florence) thanks to the translators working overtime in Al Andalus, or the Muslim Spain.

What was so important about Al-Hazen's book? It debunked the ages-old theory that we saw objects thanks to the light rays emitting from our eyes!  

"On the contrary," Al-Hazen said, and proved that we see thanks to light coming from external sources and bouncing off of objects out there.

His proof: if the light with which we see things in the world originated from our eyes then we would never have any trouble looking into a very bright ray of light. But we can’t do that since the light is produced by a source other than our own eyes.

This simple fact is now so commonplace that it sounds moronic even to consider it as an "important" discovery but back then, in the depth of the dark Middle Ages, it really was a revolutionary idea indeed.

Al-Hazen said something else that was important: not all light rays that reach our eyes are equally important, he said. He distinguished the CENTRIC RAY that passed straight through the eye's pupil from all the others that arrived at more oblique angles. We'll shortly see why this was such an important distinction.

Al-Hazen's translation fell on fertile grounds in Florence, the Italian city-state blooming with a new wave of humanist revolution (Renaissance). This was the aftermath of the Black Plague which started in 1347 and within 40 years killed almost half of Europe. Now those who survived the catastrophe despite all odds wanted to celebrate their good luck and rejoice in the works of Man.

Filippo Brunelleschi (Courtesy of Wikipedia)

A Florence architect by the name of Filippo Brunelleschi, who erected the still-magnificent dome of the Santa Maria del Fiore church, was impressed by Al-Hazen's idea about rays reaching the eye from the outside and one center ray from which all other rays seemed to emerge.

With that inspiration, Brunelleschi drew the first PERSPECTIVE PICTURE ever recorded in Europe – that of a church in his home town. The drawing was so realistic that if the viewers looked at the real church through a hole he cut in the center of the drawing they could not tell the difference! This was a startling development and a turning point in Western Art. But it turned out to be a turning point in Western Science and Exploration as well.

Brunelleschi's close friend and Renaissance Architect Leon Battista Alberti had the formal education that Brunelleschi lacked. Soon after Alberti formalized the principle of PERSPECTIVE and transformed Al-Hazen's "centric ray" into the "Vanishing Point" concept.

Now for the first time in history all European artists had a technique, a concrete method with which they could draw perspective lines converging on a vanishing point and draw perfect-looking buildings and other objects that looked just like the "real life." And they could do it every time they wanted. 

Gone were the flat and distorted people and buildings that looked totally unrelated to one another. Now objects were not identified by their other-worldly "essences" but by their relative positions to one another in this-worldy space.

Now the HUMAN OBSERVER, and not an Aristotelian "essence," was at the center of the painting, thanks to the Perspective. Florence artists proudly trumpeted the arrival of the age of Humanism.

Leon Battista Alberti (Courtesy of Wikipedia)

Soon the awakened minds of Florence discovered something else: since perspective meant objects lined up along straight lines merging at a vanishing point, there were a lot of TRIANGLES in them paintings. And where there are triangles one could use the THALES's Law to measure the size of the objects in the distance -- even if one had never been at the other location! With this realization the Renaissance intellectuals felt more empowered than before.

How did all this lead to the discovery of America? Let me digress for a second…

15th century was also a time when the Ottoman Turks started to put pressure on the famous Spice Route that passed through Constantinople, today’s Istanbul. When Constantinople fell to Turks in 1453, the Portuguese were long in search of alternative routes to the "Spice Lands" of Far East through the Horn of Africa.

But navigating south of the Equator along the shores of Western Africa presented an unforeseen problem for the Portuguese sailors.

Sailors of the time were navigating by the Polar Star. Polar Star’s height from the horizon at certain hours of the day told the sailors when to "turn East" and head for Lisbon.

Yet the farther south they went harder it became to see the Polar Star until they couldn’t see it all together. At that point navigation became a problem since the Portugese ships began to get lost down the Equator. That was no way to find a new route to the Spice Lands and recapture the trade advantage lost to the Turks.

A crucial development was the introduction of Ptolemy’s world-map GEOGRAPHICA to Florence via Constantinople in 1400. This important map not only showed all the land mass between Spain and China, but also GRIDS! The map was neatly divided into longitudes and latitudes. This meant one could exactly measure the location of even UNKNOWN spots on earth. One could travel to places one had never been to before by following the grids.

Toscanelli's World Map  (Courtesy of Wikipedia)

Yet Ptolemy’s world-map did not cover the oceans, where the Portugese wanted to venture. By putting Ptolemy’s grid system and Brunelleschi’s perspective and “measuring at a distance” ideas together, a doctor and mathematician by the name of Toscanelli designed a grid-map of the Atlantic Ocean in 1474.

Actually, Toscanelli (wrongly) calculated that if one went 6,500 miles to the West of Lisbon one could land in China and Japan. With Toscanelli’s map in hand, Italian captains started to search for funds for the passage to China and Japan.

One such Italian captain was turned down by all financiers in Florence. So he went to the Spanish Court and he was turned down again. Just as he was heading for Paris to ask for the patronage of the French Court, the Spaniards changed their minds and sponsored the trip. In his attempt to find the Spice Lands of China (Cathay) and Japan, the Italian captain landed in the American continent in 1492. His name was of course Christopher Columbus...

A good resource to read on these fascinating connections is James Burke’s book The Day The Universe Changed.

Ugur Akinci is a history buff and a Fortune 500 writer who shares free writing tips and tutorials at http://www.how-to-write-anything.com