292 POPULAR SCIENCE MONTHLY. 



be the form of the hole, the bright image, if formed at any con- 

 siderable distance from the hole, is circular. This, of course, is 

 easily seen to be a necessary consequence of the circular figure of 

 the sun, if we conceive light to be diffused from the luminary by 

 means of straight rays proceeding from every point. But Aristotle 

 attempts to explain the fact by saying that the sun's light has a 

 circular nature which it always tends to manifest. He employs the 

 vague and loose conception of a circular quality instead of the dis- 

 tinct conception of rays " (Whewell). 



It is a kind of reasoning which may be applied with great show 

 of success to everything, but which really proves nothing. 



And so, as a matter of fact, Aristotle did not leave one single 

 scientific generalization of value to succeeding ages. 



Did not the Greeks then do anything in the way of physical sci- 

 ence that was to stand? Yes, there was a little work that was exact, 

 and therefore lasting. Archimedes established the fundamental 

 principle on the one hand of the lever, on the other of pressure in 

 fluids — that is to say, laid the stable foundation of the sciences of 

 statics and hydrostatics. Euclid developed, if he did not discover, 

 the law of the reflection of light. Pythagoras discovered, and his 

 followers developed, some of the fundamental principles of har- 

 monics. Greater than any of the others in genuine scientific work 

 was Hipparchus, who, with many erroneous theories, yet really laid 

 the permanent foundation of the science of astronomy. Only one 

 more name need be mentioned among the ancients — that of Ptolemy, 

 who seemed possessed of a genuinely scientific spirit. He accom- 

 plished little original work, made no broad generalization (what is 

 known as the Ptolemaic system was in reality the system of Hip- 

 parchus), but more than any other of the ancients he is the type 

 of the true scientist in these respects — the accuracy of his observa- 

 tions, the thoroughness of his work at every point, and the really 

 great additions that he made to science in the way of verifying, 

 correcting, and extending the theory he received. He lived in the 

 early part of the second century a. d. 



And the next name to attract our notice is that of Copernicus, 

 more than twelve hundred years later. What is the meaning of 

 that lapse of time? After such noble foundations had been laid, 

 was there no great scientific work built thereon in all those cen- 

 turies? Absolutely none. It will be well for us to think for a 

 moment of what were the reasons for that barrenness, for the same 

 causes are more or less at work at all times to hinder the growth 

 of science and the extension of scientific method. 



1. And what strikes us most forcibly at the outset is a lack of 

 the sense of the importance of physical science. Through most of 



