Thales of Miletus

 624-546 BC, Thales is recognized by Aristotle as the first philosopher in the Greek Tradition. He Seven Sages of Greece, he was the first to define general principles and set forth hypotheses, and as such has been called the "Father of Science."

made a shift from the popular thought in his day, in that he attempted to explain natural phenomena, without reference to mythology. One of the

 No writings of Thales exist today, so all we have in regards to his work is from fragments written by others.  And while it is legend, the tale is told of how Thales first acquired wealth by Aristotle.

"For when they reproached him because of his poverty, as though philosophy were no use, it is said that, having observed through his study of the heavenly bodies that there would be a large olive-crop, he raised a little capital while it was still winter, and paid deposits on all the olive presses in Miletus and Chios, hiring them cheaply because no one bid against him. When the appropriate time came there was a sudden rush of requests for the presses; he then hired them out on his own terms and so made a large profit, thus demonstrating that it is easy for philosophers to be rich, if they wish, but that it is not in this that they are interested."

As a mathematician, five Euclidean theorems have been attributed to Thales. The most famous of which is known as the  Thales Theorem, and the Intercept Theorem.

PROPOSITION I.26: ‘If two triangles have the two angles equal to two angles respectively, and one side equal to one side, namely, either the side adjoining the equal angles, or that subtending one of the equal angles, they will also have the remaining sides equal to the remaining sides and the remaining angle equal to the remaining angle’ (Proclus, 347.13-16).

 It was through the use of the intercept theorem that Aristotle credits the following to Thales.

"Hieronymous says that he [Thales] actually measured the pyramids by their shadow, having observed the time when our own shadow is equal to our height."

The following description illustrates the use of the intercept theorem to compute the height of the Cheops' pyramid, it does however not recount Thales' original work, which was lost. With the  following data to work with:

• height of the pole (A): 1.63m
• shadow of the pole (B): 2m
• length of the pyramid base: 230m
• shadow of the pyramid: 65m

Thales could have computed

Knowing A,B and C he was now able to apply the intercept theorem to compute

 The Primary Principle to Thales was water. This was brought about by the problem of the nature of matter, and its transformation into the myriad things of which the universe is made. Aristotle writes,

"Most of the first philosophers thought that principles in the form of matter were the only principles of all things; for the original source of all existing things, that from which a thing first comes-into-being and into which it is finally destroyed, the substance persisting but changing in its qualities, this they declare is the element and first principle of existing things, and for this reason they consider that there is no absolute coming-to-be or passing away, on the ground that such a nature is always preserved"

 He continues,

"Thales, the founder of this type of philosophy, says that it is water (and therefore declared that the earth is on water), perhaps taking this supposition from seeing the nature of all things to be moist, and the warm itself coming-to-be from this and living by this (that from which they come-to-be being the principle of all things) -- taking the supposition both from this and from the seeds of all things having a moist nature, water being the natural principle of moist things." (R, 9)

-- Aristotle, Metaphysics (1.3 983b18-27), PP, p. 89.

 The rationale for this theory Aristotle also explains.

"For moist natural substance, since it is easily formed into each different thing, is accustomed to undergo very various changes; that part of it which is exhaled is made into air, and the finest part is kindled from air into aether, while when water is compacted and changes into slime it becomes earth. Therefore Thales declared that water, of the four elements, was the most active, as it were, as cause." (R, 8)

-- PP, p. 92.

 While today we know that this theory is incorrect, Thales was not so far off from the state of the universe. Hydrogen, is the simplest of all elements, consisting of one electron and one proton. As such hydrogen is the most abundant element in the universe, and accounts for about 75% of its mass. This is the foundation for creating H2O, which is perhaps the most fundamental building block for life itself, the human body being comprised of about 70% water content.

 This lead Thales to the conclusion that the Earth rests on a body of water, as described by Aristotle.

"Others say that the earth rests on water. For this is the most ancient account we have received, which they say was given by Thales the Milesian, that it stays in place through floating like a log or some other such thing (for none of these rests by nature on air, but on water) -- as though the same argument did not apply to the water supporting the earth as to the earth itself." (R, 9)

-- Aristotle, On the Heavens (2.13 294a28-34), PP, p. 85.

 This also lead Thales to his theory of Earthquakes.

"He [Thales] said that the world is held up by water and rides like a ship, and when it is said to 'quake' it is actually rocking because of the water's movement."

-- PP, p. 93

 As an astronomer, Thales is acclaimed for having predicted an eclipse of the sun which occurred on 28 May 585 BCE The earliest extant account of the eclipse is from Herodotus:

‘On one occasion [the Medes and the Lydians] had an unexpected battle in the dark, an event which occurred after five years of indecisive warfare: the two armies had already engaged and the fight was in progress, when day was suddenly turned into night. This change from daylight to darkness had been foretold to the Ionians by Thales of Miletus, who fixed the date for it within the limits of the year in which it did, in fact, take place’ (Hdt. I.74).

 This was later also noted by Diogenes Laertius

‘[Thales] seems by some accounts to have been the first to study astronomy, the first to predict eclipses of the sun, and to fix the solstices; so Eudemus in his History of Astronomy. It was this which gained for him the admiration of Xenophanes and Herodotus and the notice of Heraclitus and Democritus’ (D.L. I.23).

A report from Theon of Smyrna ap. Dercyllides states that:

‘Eudemus relates in the Astronomy that Thales was the first to discover the eclipse of the sun and that its period with respect to the solstices is not always constant’ (DK, 11 A 17).

From Diogenes Laertius we have the report:

‘[Thales] is said to have discovered the seasons of the year and divided it into 365 days’ (D.L. I.27).

Because Thales had determined the solstices, he would have known of the number of days between say, summer solstices, and therefore have known the length of a solar year. It is consistent with his determination of the solstices that he should be credited with discovering that 365 days comprise a year. It is also a fact that had long been known to the Egyptians who set their year by the more reliable indicator of the annual rising of the star Sirius in July. Thales may have first gained the knowledge of the length of the year from the Egyptians, and perhaps have attempted to clarify the matter by using a different procedure. Thales certainly did not ‘discover’ the seasons, but he may have identified the relationship between the solstices, the changing position during the year of the sun in the sky, and associated this with seasonal climatic changes.
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 Thales ultimately concluded, that while he removed mythology from  science, that even still, as Aristotle writes,

"And some say that it [soul] is intermingled in the universe, for which reason perhaps, Thales also thought that all things are full of gods."

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