SEQUEL TO THE EPOCH OF HIPPARCHUS. 211 



tasks of a period of verification is to ascertain with 

 accuracy the magnitude of the quantities which 

 enter, as elements, into the theory which occupies 

 men during the period ; the improvement of instru- 

 ments, and the methods of observing and experi- 

 menting, are principal features in such periods. We 

 shall, therefore, mention some of the facts which 

 bear upon this point. 



The estimation of distances among the stars by 

 the eye, is an extremely inexact process. In some 

 of the ancient observations, however, this appears 

 to have been the method employed : and stars are 

 described as being a cubit or two cubits from other 

 stars. We may form some notion of the scale of 

 this kind of measurement, from what Cleomedes 

 remarks 4 , that the sun appears to be about a foot 

 broad ; an opinion which he confutes at length. 



A method of determining the positions of the 

 stars, susceptible of a little more exactness than 

 the former, is the use of alineations, already noticed 

 in speaking of Hipparchus's catalogue. Thus, a 

 straight line passing through two stars of the Great 

 Bear passes also through the pole-star: this is, 

 indeed, even now a method usually employed to 

 enable us readily to fix on the pole-star ; and the 

 two stars, j3 and a of Ursa Major, are hence often 

 called " the pointers." 



But nothing like accurate measurements of any 

 portions of the sky were obtained, till astronomers 



4 Del. A. A. i. 222. 



P2 



