64 NUTATION of the EARTH's AXIS, Lc 



In applying the equations for nutation in declination obfei-ve, 

 that when a point y before the longitude of the Moon's amend- 

 ing node falls on the fame fide of a diameter at right angles to 

 the meridian of the ftar with its point of right afcenfion, the 

 nutation will be additive for ftars having north declination, but 

 negative for thofe having fouth declination ; the contrary is to 

 be obferved when a point 3' before the longitude of the Moon's 

 afcending node falls on the other fide of the diameter. The 

 above equ.itions for nutation in declination will be properly ex- 

 preffed in the following table. 



The foregoing calculations as combined with the projeftioQS, 

 may be rendered fomewhat more fimple, by numbering the figns 

 of the Sim's place in the ellipfe for aberration 3* fliort of the 

 true figns ; and the figns for the place of the Moon's afcending 

 node in the ellipfe for nutation 3* forwaj-d, by which the cal- 

 culations will coincide with the figns for which they were made, 

 and fo much of the rules for the application of the equations 

 as depend upon a point y behind the place of the Sun for aber- 

 ration, and 3' before the place of the Moon's afcending node 

 for nutation, will become unnecefi"ary. 



There is yet one other equation which, in very nice opera- 

 tions, fuch as determining the lengths of meridians, &c. may 

 require fome attention. It is the eifeft of the inequality of the 

 aftion of the Sun between the folftices and equinovcs, on the 

 equatorial diameter of the earth, by which the poles are carried 

 annually, twice round the mean poles in a fmall circle, whofe 

 diameter is i . By which the equinoftial points, the obliquity 

 of the ecliptic, the right afcenfion, and declination of the 

 ftars, are affe(fi:ed in a fmall degree. The maximum of the al- 

 teration 



