ASTRONOMY. 113 



recedes from the vernal equinox 62", or by DE 

 LAMBRE'S Tables 6l".9 annually. 



a. This motion includes the precession of the equi- 

 noctial points, which is in the opposite direction, 

 and amounts to 0".25 ; so that the real motion 

 of the apsides eastward, in respect of the fixed 

 stars, is 1 1".65 a-year, or 19' 4/'.^ in a century. 



b. Hence there is a difference between the Tropical 

 Year, or the time of the sun's revolution from e- 

 quinox to equinox, and what is called the Anoma- 

 listic Year, or the time of the sun's revolution from 

 either apsis to the same apsis again. As the apsis 

 has gone in the same direction with the sun over 

 62" in a year, the sun must come to the place 

 where the apsis was at the beginning of the year, 

 and must move over 6 C 2" more before the anoma- 

 listic year is.completed. The time required to this 

 is.0l74?8 of a day, which, added to the tropical 

 year, gives 365 d .2:>9744, or 3654 6 h 14ni2s for 

 the anomalistic. BIOT, Astron. torn, n 91. 



c. The line of the apsides thus continually moving 

 round, must at one period have coincided with the 

 line of the equinoxes. The lower apsis or perigee 

 in 1750, was 278. 6211 from the vernal equinox, 

 according to LA CAILLE ; and the higher apsis was 

 therefore at the distance of 98.6211. The time 

 required to move over this arch, at the rate of C2" 

 annually, is about 57?2 years, which goes back 

 nearly 4000 before our era, a period remarkable 



VOL. II. H for 



