BRADLE Y'S DISCO VER Y. 121 



abnuere). This is scientifically denominated the nutation of 

 the earth. 



Who was the fortunate mortal to discover a phenomenon 

 so singular? Bradley, the English astronomer; the same 

 who discovered the aberration of light. It was in the 

 course of his researches to determine the annual parallax 

 or distance of the stars that, at an interval of nineteen 

 years, he made, in 1728, the discovery of the aberration of 

 light, and, in 1747, that of nutation. 



The reader may not be displeased to know under what 

 circumstances he accomplished the latter discovery. While 

 observing, for several successive years, the circumpolar stars, 

 and notably the star 7 in Draco, a constellation situated 

 between Ursa Major and Ursa Minor (see Fig. 2, p. 9), 

 Bradley noticed that this star changed its position by a move- 

 ment constantly directed towards the north, from 1727 to 

 1736, or for a period of nine years. When it had reached the 

 latter limit the star appeared stationary for a moment, and 

 then retraced its course in a southerly direction. Would it 

 also occupy a period of nine years to arrive at the limit of 

 this contrary excursion ? Bradley affirmed that it would, and 

 communicated his prediction to a French astronomer, Le 

 Monnier. 



How was Bradley led to appear in the new character of a seer? 



By two special circumstances the universality, and the 

 duration of the phenomenon. 



If the star 7 in Draco had been the only one to direct its 



