192 THE GREEK ASTRONOMY. 



are inexact, "a long period and the continued 

 efforts of many industrious men are requisite to 

 produce good instruments, but energy and assiduity 

 depend on the man himself." 



Hipparchus was the author of other great dis- 

 coveries and improvements in astronomy, besides 

 the establishment of the Doctrine of Eccentrics and 

 Epicycles; but this, being the greatest advance in 

 the theory of the celestial motions which was made 

 by the ancients, must be the leading subject of our 

 attention in the present work ; our object being to 

 discover in what the progress of real theoretical 

 knowledge consists, and under what circumstances 

 it has gone on. 



Sect. 2. Estimate of the Value of the Theory of 

 Eccentrics and Epicycles. 



IT may be useful here to explain the value of the 

 theoretical step which Hipparchus thus made ; and 

 the more so, as there are, perhaps, opinions in 

 popular circulation, which might lead men to think 

 lightly of the merit of introducing or establishing 

 the Doctrine of Epicycles. For, in the first place, 

 this doctrine is now acknowledged to be false ; and 

 some of the greatest men in the more modern his- 

 tory of astronomy owe the brightest part of their; 

 fame to their having been instrumental in over- 

 turning this hypothesis. And, moreover, in th< 

 next place, the theory is not only false, but ex- 



