OUTLINES OF NATURAL PHILOSOPHY. 



123. The position of the nodes is found, by 

 observing the longitude of the moon, when she 

 has no latitude ; and it appears, by a compari- 

 son of such observations, that the line of the 

 nodes is not fixed, but has a slow retrogade mo- 

 tion, at the rate of 3' 10",64 in a day ; so as to 

 complete a revolution relatively to the fixed 

 stars in 6793.421 days. 



BIOT, Astron. Phys. vol. n. p. 351. 2d edit. 



As the moment of the moon being in the ecliptic 

 may not be actually observed, yeU from several 

 observations, taken before and after, the exact 

 time, by the method of interpolations, may be 

 found. 



124. By comparing places of the moon, ob- 

 served at very remote periods, it is found that 

 the secular mean motion of the moon, relative- 

 ly to the fixed stars, is 1336 circumferences plus 

 306. 48763, which gives for the time of a side- 

 rial revolution 27 d ,32l66l. 



In the same Way, the tropical revolution, (taking in 

 the precession of the equinoxes), is found to be 

 2^d.321582 ; and the diurnal motion relatively to 

 the tropics 13. 18636. 



It also has been found, on making these comparisons 

 for very remote ages, that the secular mean motion 



was 



