Communication
An optical telegraph using torches to signal from hilltop to hilltop operates in Greece. It uses combinations of 5 torches to indicate each letter of the Greek alphabet. See also 1792 ce Communication.
Earth scienceDemocritus of Abdera [b. Abdera, Thrace, c. 470 bce, d. c. 380 bce] is reputed to be able to predict the weather. See also 330 bce Earth science.
MathematicsHippocrates of Chios [b. Chios (Greek island), c. 470 bce, d. c. 410 bce] writes his Elements of Geometry, which predates Euclid's more famous Elements by more than a century. Since the work has been lost, it is not clear what it contained. However, his most famous discovery is the method of squaring a figure with two sides that are each segments of circles. The figure is called the lune because of its resemblance to the crescent Moon. He is also credited with introducing indirect proof, a method in which the opposite of what is to be proved is shown to be impossible. See also 585 bce Mathematics; 300 bce Mathematics. (See essay.)
PhysicsDemocritus of Abdera expands the concept, introduced by his teacher Leucippus, of the atom as an indivisible body and shows how every form of matter can be explained by his version of the atom. See also 450 bce Physics. (See essay.)
