In 342 B. C., at the request of Philip of Macedon, Aristotle became tutor to Philip’s son, Alexander. He remained in Macedonia for seven years and about 336, when Alexander departed for the invasion of Asia, returned to Athens where he taught at the Lyceum and established his famous school afterwards called the Peripatetic. Most of his works were produced during this the closing period of his life between 335 and 323 B. C. After Alexander’s death in 323 and the break up of his empire, Aristotle, who was regarded as friendly to the Macedonian power, was placed in a difficult position. Regarded with enmity by the anti-Macedonian party, he withdrew from Athens and died soon after in 322 B. C. at Chalcis in Euboea at about sixty-two years of age. The scientific works to which Aristotle’s name is attached may be divided into three groups, physical, biological, and psychological. In size they vary from such a large treatise as the _History of Animals_ to the tiny tracts which go to make up the _Parva naturalia_. So far as the scientific writings can be distinguished as separate works they may be set forth as follows: _Physics._ φυσικὴ ἀκρόασις _Physics._ περὶ γενέσεως καὶ φθορᾱς _On coming into being and passing away._ περὶ οὐρανοῡ. _On the heavens._ μετεωρολογικά. _Meteorology._ [περὶ κόσμου. _On the universe._] [μηχανικά. _Mechanics._] [περὶ ἀτόμων γραμμῶν. _On indivisible lines._] [ἀνέμων θέσεις καὶ προσηγορίαι. _Positions and descriptions of winds._] _Biology in the restricted sense._ (a) _Natural History_. περὶ τὰ ζῳα ἱστορίαι. _Inquiry about animals = Historia animalium._ περὶ ζῴων μορίων. _On parts of animals._ περὶ ζῴων γενέσεως. _On generation of animals._ [περὶ φυτῶν. _On plants._] (b) _Physiology._ περὶ ζῴων πορείας. _On progressive motion of animals._ περὶ μακροβιότητος καὶ βραχυβιότητος. _On length and shortness of life._ περὶ ἀναπνοῆς. _On respiration._ περὶ νεότητος καὶ γήρως. _On youth and age._ [περὶ ζῴων κινήσεως. _On motion of animals._] [φυσιογνωμονικά. _On physiognomy._] [περὶ πνεύματος. _On innate spirit._] _Psychology and Philosophy with biological bearing._