For the four elements of ancient philosophy modern chemistry now catalogues at least sixty-seven. Of these, earth generally contains eight; air is a mixture of two; water is a compound of two; and fire is the visible evidence of a combination between elements which produces light and heat. On the “elements” of the Greek philosophers vide Arist., Met. i. 3. Thales (†c. 550 b.c.) said water; Anaximenes (†c. b.c. 480) air; and Heraclitus (†c. b.c. 500) fire. To these Empedocles (who “ardentem frigidus Ætnam insiluit, c. b.c. 440) added a fourth, earth.