Oct. 24, 1878] 



NATURE 



671 



5" the " mean sun." 



K for diurnal tide, a star whose right ascension is 90°. 



^for semi-diiu-nal tide, the "first point of Aries," or T. 



O a point moving with angular velocity 20-, and having 270° 

 of right ascension when M is in T. 



Q a point moving with angular velocity 2<r - a, and 270° 

 before M in right ascension when the longitude of M is half the 

 longitude of the perigee. 



P a point moving with angular velocity, 2r\ having 270° cf 

 right ascension when .S" is in T. 



N a point moving w ith angular velocity, \a — \<ii, and passing 

 alternately throug;h the perigee and apogee of the moon's orbit 

 when iT/ is in perigee. 



L a point moving with angular velocity, \(r + \w, and passing 

 alternately through 90° on either side of the perigee of the 

 moon's orbit when M is in perigee. 



