54] Estimate of Grtek Astronomy 7$ 



definite by the aid of geometry, had been sufficiently 

 developed to be capable of comparison with observation, 

 rapid progress was made. The Greek astronomers of the 

 scientific period, such as Aristarchus, Eratosthenes, and 

 above all Hipparchus, appear moreover to have followed 

 in their researches the method which has always been 

 fruitful in physical science namely, to frame provisional 

 hypotheses, to deduce their mathematical consequences, 

 and to compare these with the results of observation. 

 There are few better illustrations of genuine scientific 

 caution than the way in which Hipparchus, having tested 

 the planetary theories handed down to him and having 

 discovered their insufficiency, deliberately abstained from 

 building up a new theory on data which he knew to be 

 insufficient, and patiently collected fresh material, never to 

 be used by himself, that some future astronomer might 

 thereby be able to arrive at an improved theory. 



Of positive additions to our astronomical knowledge 

 made by the Greeks the most striking in some ways is the 

 discovery of the approximately spherical form of the earth, 

 a result which later work has only slightly modified. But 

 their explanation of the chief motions of the solar system 

 and their resolution of them into a comparatively small 

 number of simpler motions was, in reality, a far more im- 

 portant contribution, though the Greek epicyclic scheme 

 has been so remodelled, that at first sight it is difficult to 

 recognise the relation between it and our modern views. 

 The subsequent history will, however, show how completely 

 each stage in the progress of astronomical science has 

 depended on those that preceded. 



When we study the great conflict in the time of Copper- 

 nicus between the ancient and modern ideas, our sympathies 

 naturally go out towards those who supported the latter, 

 which are now known to be more accurate, and we are apt to 

 forget that those who then spoke in the name of the ancient 

 astronomy and quoted Ptolemy were indeed believers in 

 the doctrines which they had derived from the Greeks, but 

 that their methods of thought, their frequent refusal to face 

 facts, and their appeals to authority, were all entirely 

 foreign to the spirit of the great men whose disciples they 

 believed themselves to be. 



