# Mathematician:Thales of Miletus

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## Contents

## Mathematician

Greek mathematician, scientist, philosopher and astronomer, who (amongst other things) predicted a solar eclipse in 585 BCE.

An early source of the emergent philosophy of rationality.

Apparently the first Greek astronomer.

Visited Egypt and the Near East, where much knowledge was exchanged. Brought back to Miletus knowledge of Babylonian astronomy and Egyptian geometry.

Supposedly:

- Made a huge profit on renting out olive-presses because his meteorological studies gave him foreknowledge of a bumper harvest.
- Diverted the course of the river Halys so that King Croesus could pass more easily.
- Trained a mule out of suboptimal behaviour by an ingenious trick.
- Fell into a ditch while gazing at the stars when out walking.

Much of our knowledge of Thales comes from the writings of Proclus and Aristotle.

## Nationality

Greek

## History

- Born: c. 625 BCE, Miletus, Asia Minor (now Turkey)
- 585 BCE: Predicted the solar eclipse of 28th May
- Died: c. 547 BCE, Miletus, Asia Minor (now Turkey)

## Theorems and Definitions

The following are attributed to Thales:

- Circle is Bisected by Diameter
- Isosceles Triangle has Two Equal Angles
- Two Straight Lines make Equal Opposite Angles
- A triangle is completely determined if two angles and the included side are given
- Thales' Theorem: An angle inscribed in a semicircle is a right angle

All of the above are found in Euclid's *The Elements*.

Results named for **Thales of Miletus** can be found here.

## Notable Quotes

*All things are water.*- -- reported by Aristotle

## Critical View

*How do you expect to understand what's happening up in the sky, when you can't even see what's under your own feet?*- -- Thracian maidservant, pulling him out of the ditch he had fallen into

*Thales, who had traveled to Egypt, was the first to introduce this science to Greece.*

## Sources

- John J. O'Connor and Edmund F. Robertson: "Thales of Miletus": MacTutor History of Mathematics archive

- 1929: Herbert Westren Turnbull:
*The Great Mathematicians*: Chapter $1$ - 1992: George F. Simmons:
*Calculus Gems*... (next): Chapter $\text {A}.1$: Thales (ca. $625$ – $547$ B.C.) - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next): Entry:**Thales of Miletus**(c.525-c.547 bc) - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**Thales of Miletus**(about 585 bc)