HIPPARCHUS OF NICEA 



160-125 B.C. 



HiPPARCHUS was the first of the great observers of the 

 heavens who made actual measurements. Of him also no 

 portrait exists. He followed the movements of the sun, 

 moon, and planets by angular measurement, and deduced 

 from his results much improved values for the length of the 

 year, the inclination of the ecliptic and the eccentricity of the 

 moon's orbit. He discovered the very slight inequality of 

 the length of the apparent solar day, and the precession of the 

 equinoxes. He further recognised that the distances of the 

 sun and the moon from the earth are variable. He attempted 

 to determine these distances, expressed in semi-diameters of 

 the earth, and succeeded very well in the case of the moon. 

 In the case of the sun, however, he was not able to attain the 

 accuracy necessary for such great distances, and his result 

 was much too small, but he found correctly that it was very 

 much greater than the distance of the moon. His star cata- 

 logue gives the position of over a thousand fixed stars. He 

 was thus the actual founder of measurement in astronomy, 

 and was only surpassed much later by Tycho. He thus 

 provided the foundation upon which Copernicus built. His 

 life is unknown to us; even his achievements are almost all 

 known to us only through the later work of Ptolemy. 



These great men were followed by a period of more than 

 fifteen hundred years, which was practically barren of all 

 results for scientific investigation, and indeed, for the advance 

 of knowledge generally (about 150 B.C. to 1500 a.d.). In this 

 period no single name of equal importance can be mentioned. 

 Men had forgotten how to think of space and time,^ and the 



1 What comes to us from this period, mainly attributable to the Arabs, 

 does not concern us here, since we are only considering important and 

 essential progress in science. Art also passed through a completely 

 barren period; but architecture and poetry attained to high development 

 much sooner than science. 



