Note 33 — Chapter VI · THE STUDY OF NATURE. FUNDAMENTAL POSITIONS.

Besides the definitions of αἴσθησις in Diog. 52, and the remark that impressions are made on the organs of sense, but that the seat of feeling is in the ἡγεμονικόν (Plut. Plac. iv. 23, 1), the following statements may be mentioned: In the process of seeing, the ὁρατικὸν πνεῦμα, coming into the eyes from the ἡγεμονικόν, gives a spherical form to the air before the eye, by virtue of its τονικὴ κίνησις (on τόνος, see p. 128, 2), and, by means of the sphere of air, comes in contact with things; and since by this process rays of light emanate from the eye, darkness must be visible. Diog. 158; Alex. Aph. De Anim. 149; Plut. Plac. iv. 15. The process of hearing is due to the spherical undulations of the air, which communicate their motion to the ear. Diog. 158; Plut. Plac. iv. 19, 5. On the voice, called also φωνᾶεν, see Plut. Plac. iv. 20, 2; 21, 4; Diog. 55, and above p. 214, 2; 74, 6. Disease is caused by changes in the πνεῦμα, Diog. 158; sleep ἐκλυομένου τοῦ αἰσθητικοῦ τόνου περὶ τὸ ἡγεμονικόν, Diog. 158; Tertull. De An. 43; and in a similar way, death ἐκλυομένου τοῦ τόνου καὶ παριεμένου Iambl. (in Stob. Ecl. i. 922), who, however, does not mention the Stoics by name. In the case of man, the extinguishing of the power of life is only a liberation of rational souls. ↑