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→Thales the scientist: Thales' geometrical work
In the field of astronomy, Thales is credited by [[Herodotus]] with having predicted a [[solar eclipse]], later identified as one which occurred in the year 585 BC. Although, in the absence of Thales' actual writings, there is currently some doubt as to the authenticity and nature of this prediction, it seems certain that he knew the causes of solar (and lunar) eclipses. He is also credited with having determined the length of the solar year and the dates of the solstices, as well as the diameters of the [[Sun]] and [[Moon]]. In each case, detailed observations over lengthy periods of time are necessary as well as the conception of how to carry out the tasks.
In the field of astronomy, Thales is credited by [[Herodotus]] with having predicted a [[solar eclipse]], later identified as one which occurred in the year 585 BC. Although, in the absence of Thales' actual writings, there is currently some doubt as to the authenticity and nature of this prediction, it seems certain that he knew the causes of solar (and lunar) eclipses. He is also credited with having determined the length of the solar year and the dates of the solstices, as well as the diameters of the [[Sun]] and [[Moon]]. In each case, detailed observations over lengthy periods of time are necessary as well as the conception of how to carry out the tasks.
Thales, who had travelled to [[Egypt]] where he observed the practical usage of geometrical measuring techniques, took the first steps in placing geometry on a theoretical basis. He is credited with having demonstrated several basic propositions of geometry. Thales' method of "proof" was based on repeated, empirical measurements and induction.
Among the propositions which he demonstrated in this manner are: 1) that a circle is bisected by a diameter; 2) the angles at the base of an isoceles triangle are equal; 3) the angle of a semi-circle is a right angle; 4) if two straight lines intersect each other, the opposite angles are equal, and; 5) he demonstrated certain properties of similar triangles, including the principle of ratio, or proportionality. It is this latter property (of simiilar triangles) which Thales used to measure the previously unknown height of the pyramids as well as the distance of ships at sea.
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