NUTATION OF THE EARTH'S AXIS, &c. 6i 



In applying the nutiuion in ri^ht afcenflon, obferve this 

 general rule, that when a noint 3 before the Ion ;ffude of the 

 Moon's afcendin-^ node, falls on the riajht fide of the meridian 

 of the flar, the point A or ri2;ht afcenfion being held from you, 

 the nutation will be pofitive for liars having north declination, 

 but negative for fouth : — the contrary is to be obferved when 

 a point 3' before the Moon's afcending node, falls on the left 

 fide of the meridian. Agreeably to thefe directions, the foro- 

 going equations when tabled will Itand as follows. 



Longitude of Moon's I Longitude of Moon's 

 Afcending node | Afcending node 



The next equation is that of the equinoftial points, which is 

 common to all the ftars, and occafioned by the poles of the 

 Earth inclining to, and receding from the celeftial equator. — 

 Suppofe the Moon's afcending node to be at 9', then the pole 

 of the Earth will be at o in the ellipfe, and the diftance C 

 will be its inclination towards •". — This inclination for any 

 point in the ellipfe will be a perpendicular let fall upon the 

 tranfverfe axis, which will be to the alteration of the equinoc- 

 tial points, as the tangent of the obliquity of the ecliptic, is to 

 radius ; — hence thefe deviations from the tranfverfe axis of the 

 ellipfe being multiplied by the nat. co-tangent of the obliquity 

 of the ecliptic, will give the equations required. 



The quantity C o ::: 7. 1 f foro' and 6'in theprojecfUonbut 



Mult, by nat. Co-tang' of 23° 28' — X ^-3 = l6"-3 tfor 3' and 9 of the long, of ]) 'snode. 



For any other points in the ellipfe add the log. of 9.55, to 

 the log. fine of the arc C 0, and from that fum deduft 10 for a 

 conftant log. to which add the log. fine of any arc from 3, or 

 9, and from that fum deduft 10, the remainder will be the log. 

 of a perpendicular let fall from the termination of tlaat arc to 

 the tranfverfe axis. 



I To 



