INTRODUCTION. 13 



to ultimate principles (the elements, as it were, of the ele 

 ments), Plato exclaims, with modest diffidence 1 , " God alone, 

 and those whom he loves among men, know what they are." 

 Such a mathematical mode of treating physical phenomena, 

 together with the development of the atomic theory, and the 

 philosophy of measure and harmony, have long obstructed the 

 development of the physical sciences, and misled fanciful in- 

 quirers into devious tracks, as is shown in the history of the 

 physical contemplation of the universe. " There dwells a 

 captivating charm, celebrated by all antiquity, in the simple 

 relations of time and space, as manifested in tones, numbers, 

 and lines."* 



The idea of the harmonious government of the universe re- 

 veals itself in a distinct and exalted tone throughout the writ- 

 ings of Aristotle. All the phenomena of nature are depicted 

 in the Physical Lectures (Auscultationes Physicce) as mov- 

 ing, vital agents of one general cosmical force. Heaven and 

 nature (the telluric sphere of phenomena) depend upon the 

 " unmoved motus of the universe."! The " ordainer" and the 

 ultimate cause of all sensuous changes must be regarded as 

 something non-sensuous and distinct from all matter.^ Unity 

 in the different expressions of material force is raised to the 

 rank of a main principle, and these expressions of force are 

 themselves always reduced to motions. Thus we find already 

 in " the book of the soul" the germ of the undulatory theory 

 of light. The sensation of sight is occasioned by a vibration 



* Cosmos, vol. ii., p. 351, note. Compare also Gruppe, Ueber die 

 Fragmente des Archytas, 1840, s. 33. 



t Aristot.,Poto., vii., 4, p. 1326, and Metapk., xii., 7, p. 1072, 10, Bekk., 

 and xii., 10, p. 1074-5. The pseudo-Aristotelian work, De Mundo, 

 which Osann ascribed to Chrysippus (see Cotmot, vol. ii., p. 28, 29), 

 also contains (cap. 6, p. 397) a very eloquent passage on the world-or- 

 derer and tcorld-sustainer. 



t The proofs are collected in Ritter, History of Philotophy (Bohn, 

 1838-46), vol. iii., p. 180, et seq. 



Compare Aristot., De Anima, ii., 7, p. 419. In this passage the 

 analogy with sound is most distinctly expressed, although in other por- 

 tions of his writings Aristotle has greatly modified his theory of vision. 

 Thus, in De Insomniis, cap. 2, p. 459, Bekker, we find the following 

 words : " It is evident that sight is no less an active than a passive 

 agent, and that vision not only experiences some action from the air 

 (the medium), but itself also acts upon the medium." He adduces in 

 evidence of the truth of this proposition, that a new and very pure me- 

 tallic mirror will, under certain conditions, when looked at by a woman, 

 retain on its surface cloudy specks that can not be removed without 

 difficulty. Compare also Martin, Etudes sur le Timfe de Platun., torn 

 ii. p. 159-163. 



