92 THE GREEK SCHOOL PHILOSOPHY. 



an appropriate Idea and the other did not, though I might judge one 

 to be true and the other to be false. For instance, in comparing the 

 emissive and the undulatory theory of light, we see that both involve 

 the same Idea ; the Idea of a Medium acting by certain mechanical 

 properties. The question there is, What is the true view of the mechan- 

 ism of the Medium ? 



It may be remarked, however, that the example of Aristotle's failure 

 in physics, given in'p. 8 7,' namely, his attempted explanation of the 

 round image of a square hole, is a specimen rather of indistinct than 

 of inappropriate ideas. ' 



The geometrical explanation of this phenomenon, which I have there 

 inserted, was given by Maurolycus, and before him, by Leonardo da Vinci. 



"We shall, in the next Book, see the influence of the appropriate gen- 

 eral Ideas, in the formation of various sciences. It need only be 

 observed, before we proceed, that, in order to do full justice to the 

 physical knowledge of the Greek Schools of philosophy, it is not 

 necessary to study their course after the time of their founders. Their 

 fortunes, in respect of such acquisitions as we are now considering, 

 were not progressive. The later chiefs of the Schools followed the 

 earlier masters ; and though they varied much, they added little. The 

 Romans adopted the philosophy of their Greek subjects ; but they were 

 always, and, indeed, acknowledged themselves to be, inferior to their 

 teachers. They were as arbitrary and loose in their ideas as the Greeks, 

 without possessing their invention, acuteness, and spirit of system. 



In addition to the vagueness which was combined with the more 

 elevated trains of philosophical speculation among the Greeks, the 

 Romans introduced into their treatises a kind of declamatory rhetoric, 

 which arose probably from their forensic and political habits, and which 

 still further obscured the waning gleams of truth. Yet we may also 

 trace in the Roman philosophers to whom this charge mostly applies 

 (Lucretius, Pliny, Seneca), the national vigor and ambition. There is 

 something Roman in the public spirit and anticipation of universal 

 empire which they display, as citizens of the intellectual republic. 

 Though they speak sadly or slightingly of the achievements of their 

 own generation, they betray a more abiding and vivid belief in the 

 dignity and destined advance of human knowledge as a whole, than is 

 obvious among the Greeks. 



We must, however, turn back, in order to describe steps of more 

 definite value to the progress of science than those which we have 

 hitherto noticed. 



