Thales of Miletuswas the first known Greek philosopher and mathematician who introduced the basic concepts of geometryto the Greeks. A man of many talents, Thales was a successful merchant and founded his own school of philosophy in Miletus, which included teachings in mathematics and astronomy. Notably, Thales emphasis on "natural" rather than "supernatural" explanations for phenomena marks the beginning of scientific methodology and theoretical reasoning. Honored and revered as a man of knowledge and wisdom in his own time, Thales was named one of the Seven Wise Men of Greece.
Thales was born circa 640 B.C. to 620 B.C. in Miletus, a Greek island along the coast of Asia Minor. Since Thales left behind no writings, little is known about his life. As with many ancient thinkers, fact, fiction, and myth have become intermixed. His father was Examius and his mother Cleobuline. Growing up in a strategic caravan route from the East, Thales first made his mark as a highly successful merchant. According to one account, Thales made a fortune when he foresaw a good season for the olive crop and bought all the local olive presses, monopolizing olive oil market.
With his financial success, Thales traveled to Egypt, either to pursue business opportunities or to study Egyptian science and philosophy. Certainly, Thales learned the fundamentals of geometry while in Egypt. His aptitude for deductive reasoning is illustrated through the story of Thales' ability to calculate the height of the pyramids. According to legend, Thales was observing the Great Pyramid one day when the Pharaoh and his entourage came by. Intrigued by the foreigner's reputation as a man of wisdom, the Pharaoh asked Thales if he could calculate the pyramid's height. Thales may have accomplished the feat by using the "magic" of the Egyptian shadow stick, which, when placed in the ground, one could use it to calculate the height of an object by establishing a relationship between the height of the stick's shadow and the shadow of the object to be measured. A more plausible explanation is that Thales measured the pyramid's shadow at the exact time when his own shadow appeared to be the same length as himself, thus ensuring that the Great Pyramid's shadow accurately represented its true height.
Thales may also have traveled to Babylon and studied geometry and astronomy. He eventually returned to Miletus (possibly around 590 B.C.) and established a school where he taught science, astronomy, mathematics, and other subjects. Eventually, the philosophy of Thales became known as the Ionian School of Philosophy.
Introduces Geometry to Greece
Thales' reputation as one of the founders of mathematics and applied geometry stems not only from his introduction of geometry to Greece, but in his establishing the need for deductive reasoning and proofs for demonstrating a statement or theorem's validity. The first written account of Thales' mathematical acumen comes from Proclus, who wrote a famous commentary on Euclid's Elements. Prior to Thales, geometry was concerned primarily with measuring surfaces and solids. Thales developed geometry in both a practical and theoretical way by focusing on lines, circles, and triangles. Proclus credits Thales with five basic theorems of elementary geometry: (1) The circle is bisected by its diameter; (2) the base angles of an isosceles triangle are equal; (3) pairs of vertical angles formed by two intersecting straight lines are equal; (4) an angle inscribed in a semicircle is a right angle; (5) two triangles are congruent if they have two angles and one side that are equal.
Whether or not Thales actually proved geometrical theorems is unknown. Of his first three theorems, historians debate whether Thales developed them through intuition or whether he discovered and demonstrated them scientifically. However, Proclus indicates that Thales did prove theorem number two even though by the time Euclid wrote his Elements this theorem was accepted as obvious and needed no proof. As for theorem number four, it is not known whether Thales developed a proof or demonstrated the theorem empirically.
Many scholars believe that Thales made practical use of his fifth, or congruence, theorem in his renowned ability to measure the distance of a ship from shore. One theory of how Thales accomplished this remarkable measurement for his day says that Thales used a tower of known height on shore, a plum line, and a carpenter's square (known as a gnomon). Driving a nail in the tower that corresponded to a line of sight to the ship, Thales determined the distance from the right-angled base of the gnomon to where it intersected the line of sight, thus creating an easily measured right triangle. Then, by dropping a plum to the ground and determining the height of the tower, he was able to calculate the size of a larger right triangle that was proportional to the smaller triangle. The distance to the ship would equal the calculated length of the larger right triangle's base. To accomplish this feat, it is assumed that Thales knew that the sides of equiangular triangles are proportional.
Predicts Solar Eclipse
In addition to his interest in geometry and mathematics, Thales was fascinated by astronomy. A famous story concerning Thales' love of astronomy has him falling into a well while gazing at the stars. He is soon discovered by a slave girl who wryly comments that Thales was "so interested in the heavens he could not see what was in front of his own feet."
Thales may have developed his interest in astronomy during his reported travels to Babylon and studies under the Chaldean magi. He is reported to have written works focusing on the equinoxand the solstice and is sometimes attributed with explaining solar eclipses. He is also reported to have written on nautical astronomy and to have advised navigators to depend on Ursa Minor (Little Bear) rather than Ursa Major (Great Bear) for accurately navigating their destinations.
In his own time, Thales' most noted feat of astronomical observation was his prediction of a solar eclipse in 585 B.C. as reported by Herodotus. Thales possibly learned the secret of predicting such events through the Babylonians, who had kept detailed records of astronomical events for many centuries. With these records, Thales may have been able to calculate that an eclipse might occur in that year. No matter how Thales made his famous prediction, he had a tremendous amount of luck, not the least of which was the fact that the eclipse happened to be visible in Miletus. Regardless, this prediction bolstered Thales' fame to new heights.
Becomes One of the Seven Greek Sages
While he is remembered today primarily for his efforts in geometry and astronomy, Thales was also the first great Greek philosopher. In his Ionian school, philosophy, or the love of wisdom, took precedence over all other studies. Thales was renowned for his intimate knowledge of human nature and his humor. For example, the maxim "know thyself" is purported to originate with Thales. Other sage advice credited to Thales include his counsel that people could lead righteous lives by "refraining from doing what we blame in others" and his pronouncement that the strangest thing he had ever seen was "an aged tyrant."
Like most of his contemporaries, Thales mistakenly believed that the Earth was a flat disc on an infinite ocean. His belief that water was the origin of all life and matter was probably based on the knowledge that water is the essential element needed for the growth and nurturing of all organisms. Still, his belief that supposedly supernatural occurrences could be explained by natural events profoundly influenced the thinking and scientific explorations of those scholars who came after him. His most famous pupil was Anaximander, who was the first natural philosopher in the Milesian school of philosophy.
As a wealthy and learned man, Thales also played a vital role as a political counselor and statesman. Thales is reported to have convinced the Greek colonies (or Ionian city-states) to form an alliance to fight off Persian invaders. As a military advisor, he used his mathematical and engineering skills to help a Greek army cross a river by constructing a channel and diverting the river into it. Since the "Seven Wise Men of Greece" were predominantly statesmen, Thales was probably named one of the seven for these efforts. According to some accounts, Thales, who died circa 546 B.C., was the only one of the seven to be declared a Wise Man twice by the Oracle at Delphi, the second time for his prediction of the solar eclipse.
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