268 



A Short History of Astronomy 



[C'H. X. 



had some scientific correspondence. Maupertuis appears 

 to have told others, but Bradley himself waited patiently 

 for the completion of the period which he regarded as 

 necessary for the satisfactory verification gf his theory, and 

 only published his results definitely at the beginning of 

 1748. 



214. Bradley's observations established the existence of 

 certain alterations in the positions of various stars, which 



FIG. 77. Precession and nutation. 



could be accounted for by supposing that, on the one 

 hand, the distance of the pole from the ecliptic fluctu- 

 ated, and that, on the other, the precessional motion of 

 the pole was not uniform, but varied slightly in speed. 

 John Machin (? -1751), one of the best English mathe- 

 maticians of the time, pointed out that these effects would 

 be produced if the pole were supposed to describe on the 

 celestial sphere a minute circle in a period of rather less 



