14 COSMOS. 



a movement of the medium between the eye and the object 

 seen and not by emissions from the object or the eye. Hear- 

 ing is compared with sight, as sound is likewise a consequence 

 of the vibration of the air. 



Aristotle, while he teaches men to investigate generalities 

 in the particulars of perceptible unities by the force of reflect- 

 ive reason, always includes the whole of nature, and the in- 

 ternal connection not only of forces, but also of organic forms. 

 In his book on the parts (organs) of animals, he clearly in- 

 timates his belief that throughout all animate beings there is 

 a scale of gradation, in which they ascend from lower to high- 

 er forms. Nature advances in an uninterrupted progressive 

 course of development, from the inanimate or " elementary" 

 to plants and animals; and, "lastly, to that which, though 

 not actually an animal, is yet so nearly allied to one, that on 

 the whole there is little difference between them."* In the 

 transition of formations, " the gradations are almost imper- 

 ceptible, "f The unity of nature was to the Stagirite the great 

 problem of the Cosmos. " In this unity," he observes, with 

 singular animation of expression, " there is nothing unconnect- 

 ed or out of place, as in a bad tragedy.''^ 



The endeavor to reduce all the phenomena of the universe 

 to one principle of explanation is manifest throughout the 

 physical works of this profound philosopher and accurate ob- 

 server of nature ; but the imperfect condition of science, and 

 ignorance of the mode of conducting experiments, i. e., of 

 calling forth phenomena under definite conditions, prevented 

 the comprehension of the causal connection of even small 

 groups of physical processes. All things were reduced to the 

 ever-recurring contrasts of heat and cold, moisture and dry- 

 ness, primary density and rarefaction even to an evolution 

 of alterations in the organic world by a species of inner divis- 

 ion (antiperistasis), which reminds us of the modern hypothesis 

 of opposite polarities and the contrasts presented by + and . 



* Aristot., De partibus Anim., lib. iv., cap. 5, p. 681, lin. 12, Bekker. 



t Aristot., Hist. Anim., lib. ix., cap. 1, p. 588, lin. 10-24, Bekker. 

 When any of the representatives of the four elements iu the animal 

 kingdom on our globe fail, as, for instance, those which represent the 

 element of the purest fire, the intermediate stages may perhaps be found 

 to occur in the moon. (Biese, Die Phil, des Aristoteles, bd. ii., s. 180.) 

 It is singular enough that the Stagirite should seek in another planet 

 those intermediate links of the chain of organized beings which we find 

 in the extinct animal and vegetable forms of an earlier world. 



% Aristot., Metaph., lib. xiii., cap. 3, p. 1090, lin. 20, Bekker. 



$ The uv: nrepicTCLOis of Aristotle plays an important part iu all hia 



