134 OUTLINES OF KATUKAL PHILOSOPHY. 



which the spectator describes a circle parallel to 

 the equator, in the course of the diurnal revo- 

 lution of the earth. 



. ' . 



Hence, when the moon rises, a spectator sees some 



spots toward the upper limb of the moon, which 

 he would not see at the centre. As the moon be- 

 comes more elevated, these points approach more 

 to the upper edge, while others, on the inferior 

 limb, come in sight. This order is reversed as the 

 moon descends to the horizon. This is called the 

 Diurnal or Parallactic Libratwn. 



136. From an attentive observation of the 

 lunar spots, it has been found, that the equator 

 of the moon is inclined to the plane of the 

 ecliptic, at an angle of 1 30' ; and that the line 

 in which its plane cuts the plane of the eclip- 

 tic, is parallel to the line of the nodes, or to 

 that in which the moon's orbit cuts the same 

 plane. 



BIOT, torn. n. p. 411. 72. 



a. Suppose three planes to pass through the centre 

 of the moon, one representing the equator of the 

 moon, another the plane of her orbit, and let the 

 third be parallel to the ecliptic. This last will lie 

 between the two others, and will intersect them in 

 the same Jine in which they intersect one another. 



With 



