The different theories of vision among the ancient philosophers anterior to Aristotle are thus enumerated by E. H. von Baumhauer (De Sententiis Veterum Philosophorum Græcorum de Visu, Lumine, et Coloribus, Utrecht, 1843, p. 137):--"De videndi modo tres apud antiquos primarias theorias invenimus: et primam quidem, emanatione lucis ex oculis ad corpora externa, ejusque reflexu ad oculos (Pythagorei, Alcmæon): alteram emanationibus e corporibus, quæ per oculos veluti per canales ad animum penetrent (Eleatici, Heraclitus, Gorgias): quam sententiam Anaxagoras et Diogenes Apolloniates eatenus mutarunt, quod dicerent pupillam quasi speculum esse quod imagines acceptas ad animum rejiciat. Tertia theoria, orta è conjunctione duarum priorum, statuebat tam ex oculis quam corporibus emanationes fieri, et ambarum illarum concursu visum effici, quum conformata imago per meatus ad animum perveniat (Empedocles, Protagoras, Plato). Huic sententiæ etiam Democritus annumerari potest; qui eam planè secundum materiam, ut dicunt, exposuit." The theory of Plato is described in the same treatise, pp. 106-112.] [Side-note: Principal advantages of sight and hearing. Observations of the rotation of the Kosmos.] Such are the auxiliary causes (continues Plato), often mistaken by others for principal causes, which the Gods employed to bring about sight. In themselves, they have no regularity of action: for nothing can be regular in action without mind and intelligence.[60] But the most important among all the advantages of sight is, that it enables us to observe and study the rotations of the Kosmos and of the sidereal and planetary bodies. It is the observed rotations of days, months, and years, which impart to us the ideas of time and number, and enable us to investigate the universe. Hence we derive philosophy, the greatest of all blessings. Hence too we learn to apply the celestial rotations as a rule and model to amend the rotations of intelligence in our own cranium--since the first are regular and unerring, while the second are disorderly and changeful.[61] It was for the like purpose, in view to the promotion of philosophy, that the Gods gave us voice and hearing. Both discourse and musical harmony are essential for this purpose. Harmony and rhythm are presents to us, from the Muses, not, as men now employ them, for unreflecting pleasure and recreation--but for the same purpose of regulating and attuning the disorderly rotations of the soul, and of correcting the ungraceful and unmeasured movements natural to the body.[62] [Footnote 60: Plato, Timæus, p. 46 D-E.] [Footnote 61: Plato, Timæus, pp. 47 B-C, 90 C.] [Footnote 62: Plato, Timæus, p. 47 D-E. [Greek: ê( de\ a(rmoni/a . . . xu/mmachos u(po\ Mousô=n de/dotai; kai\ r(uthmo\s au)= . . . u(po\ tô=n au)tô=n e)do/thê.] Here we see Plato, in the usual Hellenic vein, particularising the functions and attributes of the different Gods and Goddesses.]