22 HISTORY OF SCIENCE. 



ing and fleeting shadows of certain eternal and unchangeable realities, 

 which possessed in a higher sphere of being an existence independent 

 of the things of sense. These realities, which alone could be the 

 objects of true knowledge, and could be taken cognizance of by the 

 mind only, Plato called 77/6' Ideas. By ideas Plato meant not mere 

 thoughts, or images of the things in the mind, but substantive existences 

 that were in being before matter, or man, or the objects of sense came 

 into existence, and that constitute the patterns or archetypes to which 

 the sensible objects, more or less, conform. Things, according to Plato, 

 are perceived to be what they are only by their participation in the 

 Ideas, and it is only so far as they participate in these unchangeable 

 realities that phenomena are contemplated by the philosopher. As 

 an illustration of the manner in which this theory of Plato's reconciled 

 the notions of change and permanence, consider the diversities pre- 

 sented by the individuals of the human race, in age, conformation, sex, 

 and numberless other particulars. Yet in the midst of the endless 

 diversity we recognize the possession of something in common, by 

 which each individual appears to more or less agree with a certain 

 model, which in ordinary language is sometimes called our idea of 

 humanity. The word idea, as here used, would express simply the set 

 of qualities which we consider as essentially human, or, expressed in 

 words, it would be the definition of humanity. But Plato conceived 

 of ideas as things existing absolutely, apart altogether from the world 

 of phenomena. 



In the dialogue of Plato's called the " Timseus " we have the earliest 

 account of a physical theory of the universe, which lias reached us in 

 it's author's own words. To the modern reader, whose view of nature 

 is very different from that which presented itself to the minds of the 

 older Greeks, the "Timseus" appears a confused and bewildering spe- 

 culation. In this dialogue, theological, philosophical, mathematical, and 

 physical considerations, which now are clearly separated and treated 

 apart, run together without distinction. These speculations carry us 

 back to a period at which the intellectual domain had not yet been 

 parcelled out into distinct fields, or, to borrow a phrase from tfee lan- 

 guage of the evolutionists, the now recognized classes of notions had 

 not as yet become differentiated. It may be here remarked, in order to 

 guard readers unacquainted with Plato's writings from obtaining a 

 false impression concerning them, that Plato's philosophy does not 

 turn upon physical science, to which, indeed, he attaches little import- 

 ance, apparently regarding it rather as a recreation than a serious or 

 profitable study. 



Inquiries into facts of natural science presented no attractions for 

 Plato, and he seems to have believed that no certain results were attain- 

 able. It is noticeable that he makes Timseus speak with a diffidence and 

 hesitation, contrasting strongly with the confident manner in which the 

 interlocutors in other dialogues expound such doctrines as those of the 



