Thales

tha'lez (about 640-546 B. C.), a learned Greek. He is known as one of the seven wise men of Greece. He was the first of the Ionian natural philosophers. He considered water the basis of all things, the universal principle of nature. He established the length of the year at 365 days. He predicted an eclipse of the sun for May 28, 585 B. C. He is considered the originator of several geometrical theorems. he discovered the truth that each angle inscribed in a semicircle is a right angle. This he regarded so important a mathematical truth that it is said he sacrificed an ox to the immortal gods. He is also said to have computed the height of an Egyptian pyramid by thrusting a stick into the ground. The shadow of this stick and the height of his stick, and the shadow of the pyramid, gave him three terms of a proportion, whereby he found the fourth term, namely the desired height of the pyramid. See Euclid; Pythagoras; Alchemy