Thales
[pic]Thales
Born: about 624 BC in Miletus, Asia Minor. Died: about 547 BC in Miletus |Thales seems to be the first known Greek philosopher, scientist and mathematician although his occupation was that of an engineer. However, none of his writing survives so it is difficult to determine his views or to be certain about his mathematical discoveries. Indeed it is unclear whether he wrote any works at all and if he did they were certainly lost by the time of Aristotle who did not have access to any writings of Thales. On the other hand there are claims that he wrote a book on navigation but these are based on little evidence.
Proclus, the last major Greek philosopher, who lived around 450 AD, wrote:- Thales first went to Egypt and thence introduced this study geometry into Greece. He discovered many propositions himself, and instructed his successors in the principles underlying many others, his method of attacking problems had greater generality in some cases and was more in the nature of simple inspection and observation in other cases. | |
|Heights of pyramids |Thales measured the height of pyramids. He succeeded in measuring the pyramids by |
| |observation of the length of their shadow at the moment when our shadows are equal to our|
| |own height. |
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This is based on the idea of similar triangles, that at the instant when the length of the shadow of one object coincides with its height, then the same will be true for all other objects.
| |In many textbooks on the history of mathematics Thales is credited with five theorems of|
| |elementary geometry:- |
|Elementary geometry |(i) A circle is bisected by any diameter. |
| |(ii) The base angles of an isosceles triangle are equal. |
| |(iii) The angles between two intersecting straight lines are equal. |
| |(iv) Two triangles are congruent if they have two angles and one side equal. |
| |(v) An angle in a semicircle is a right angle. |
| |About 300 years later Euclid was to develop these ideas in his great work The Elements. |
Now test yourself !
1. Was Thales only a mathematician ?
2. Is it sure that Thales wrote a book on navigation ?
3. What does “AD” mean ? What is the opposite abbreviation ?
4. Can you explain what similar triangles are, according to Thales’ works ?
5. Make a drawing for each theorem credited to Thales in many textbooks.
6. a. State Thales’ theorem as you know it in french.
b. Does it correspond to any previous theorem credited to Thales ?
c. How can you explain this ?
7. Find on Wikipedia who Euclid was. Have you already heard of him before ?
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