BRADLE Y'S DA TA EXPLAINED. 1 23 



weary of our scientific or semi-scientific disquisition, that 

 the lunar nodes, i.e., the points of the Ecliptic through which 

 the moon passes when it proceeds from south to north (the 

 ascending node), and from north to south (the descending 

 node), are the analogues of the solar equinoxes ; the equa- 

 torial points through which the sun passes on its course from 

 south to north (the spring equinox), and in returning from 

 north to south (the autumn equinox), points of intersection 

 whose retrogradation constitutes, as we have seen, the pre- 

 cession of the equinoxes. Well, the moon's nodes retrograde 

 in a similar manner by a movement directed from east to 

 west ; only it is a much slower movement. While the equi- 

 noxes are displaced but fifty seconds (50") in a year, the 

 lunar nodes, during the same period, and in the same direc- 

 tion, move over a space of 19 20' 29" ; so that, in less 

 than nineteen years, they have made the complete circuit 

 of the heavens, to return to exactly the same point, after tra- 

 versing 360. 



Thus, then, we have explained the data on which Bradley 

 rested his prediction. It was confirmed by Le Monnier, who 

 observed, in fact, that the star y in Draco, and the neighbour- 

 ing stars, observed by Bradley from 1727 to 1736, moving 

 from south to north, occupied the same period of time, from 

 1736 to 1745, in accomplishing an equal excursion in a 

 contrary direction, from north to south. These observa- 

 tions enabled him to fix approximatively the quantity of the 

 nutation. 



