Remarks on the Lunar Theory. 



409 



But to proceed. The Chaldean period is the most perfect and 

 •shortest of any, in which the sohir and kmar motions, and the 

 motions of their perigee and nodes, are nearly coincident. The 

 other periods, which I before stated, show the analogy which 

 subsists between the solar years and the lunar periods. But if 

 the O and ]) were in conjunction at the beginning of those pe- 

 riods, the hke circumstance would not take place in a series of 

 consecutive returns, owing to the J) 's perigee and nodes not 

 being in conjunction also. The conjunction would likewise be 

 affected by the J) 's acceleration. In reference to the period of 

 39512 solar years (and not 36512 as stated at page 356), con- 

 taining 4S8695 lunations, wanting only live seconds of the line 

 of conjunction of the © and }) ; this calculation is founded on 

 the mean motion of the luminaries (see note, p. 14), and is given 

 in order to show the absurdity of instituting such long periods, as 

 the D 's accel. amounts to nearly 760 degrees ! It is a matter 

 of surprise to me, that Mr. Yeates could view it in any other 

 light, it being actually so expressed. In regard to the period 

 alluded to in Ferguson's Astronomy, as revised by me, viz. of 

 13700 years, it n)ay be necessary to observe, that the lunar 

 motions are arrived at a degree of perfection of which Mr. Y. 

 appears tn he totally ignorant. They did not attain their present 

 elevation from data and proceedings similar to those of yoin- 

 correspondent, but from an accumulated mass of astronomical 

 observations; viz. of transits, and zenith distances, ike. mado 

 during a period of many years, and the subse(|uent results com- 

 pared with ancient observations and eclipses : so that, if the falling 

 back of the line of the nodes can be ascertained during the space 

 of about a century only, it is surely no great presumption to 

 calculate their period, as is done in respect to the revolution of 

 the earth's perigee, and the ecjuinoctial points : some have even 

 gone so far as to calculate when the time will arrive when the 

 eeliptic w'lW coincide with the equator, and a universal spring pre- 

 vail all over the earth. But this idea is erroneous, as the rovoln- 

 tions of the fcjrmcr appear to be consecutive, while that of the 

 latter is only vibratory. Mr. Yeates admits that it was by the 

 aid of a period of 600 years, that i:^/p/j<7rc//«A' extended his science 

 in calculating ephemeridcs of the sun and moon, as he is related 

 to have done, and that with suHicient exactness for the regu- 

 lating of their calendar. — Fide p. 358. As I before rcnuukcd, 

 in the time of Sir Isaac Newton, the lunar tables gave tlie 



}) 's long, to within iive miimtes of a degree from the trutii ; 

 whereas they now give it to within ten seconds, and generally 

 nnich nearer. So that, embracing the lunar motions at the pre- 

 sent day, and applying them to a jjcriod <>f 13/00 years, the ad- 

 Vol. 56, No. 272. Du. 1820. o V ' vantage 



