ALEXANDRIAN OR HELLENISTIC PERIOD 



tion after generation, since this alone of all the writ- 

 ings of the great astronomer has been preserved. 

 How widely the exact results of the measurements of 

 Aristarchus differ from the truth, we have pointed 

 out as we progressed. But let it be repeated that this 

 detracts little from the credit of the astronomer who 

 had such clear and correct conceptions of the relations 

 of the heavenly bodies and who invented such correct 

 methods of measurement. Let it be particularly 

 observed, however, that all the conclusions of Aris- 

 tarchus are stated in relative terms. He nowhere 

 attempts to estimate the precise size of the earth, of 

 the moon, or of the sun, or the actual distance of one 

 of .these bodies from another. The obvious reason 

 for this is that no data were at hand from which to 

 make such precise measurements. Had Aristarchus 

 known the size of any one of the bodies in question, he 

 might readily, of course, have determined the size of 

 the others by the mere application of his relative 

 scale; but he had no means of determining the size 

 of the earth, and to this extent his system of measure- 

 ments remained imperfect. Where Aristarchus halted, 

 however, another worker of the same period took the 

 task in hand and by an altogether wonderful measure- 

 ment determined the size of the earth, and thus brought 

 the scientific theories of cosmology to their climax. 

 This worthy supplementor of the work of Aristarchus 

 was Eratosthenes of Alexandria. 



ERATOSTHENES, "THE SURVEYOR OP THE WORLD" 



An altogether remarkable man was this native of 

 Cyrene, who came to Alexandria from Athens to be 

 VOL.I. 15 225 



