[ 4° 8 J 
Forming, therefore, the redangle P M p R, the 
motion of the pole according to P p will be refolved 
into two, according to P R and P M. 
The motion of the pole according to PR is pa- 
rallel to the plane of the ecliptic, and to the line of 
the nodes T Ca. This motion tends to move the 
pole P about the axe of the ecliptic, and in a parallel 
to the ecliptic, and caufes the equinodial point T to 
recede, and the point vp, and the node «&, to advance 
towards the fun ; which produces a preceftion of the 
equinox equal to the angular motion of the pole P 
about the axe of the ecliptic ; for it is indifferent 
whether the pole P of the earth moves about the axe 
of the ecliptic, whilft the plane y s - v remains fix’d; 
or the fame be fuppofed to be fix’d, and the plane of 
the ecliptic T $ & yr to turn about its centre C, and 
the axe of the ecliptic. 
If we take another place S z of the fun at the fame 
diftance from the folftice s, but on the fide contrary 
to S , the diredion of the pole P will be, by Art. io. 
according to Pp z , perpendicular to the plane PCS Z D Z P^ 
and confequently to the line P D z ; and the fun’s de- 
clination being the fame in D z as in D, the motion 
P p z will be equal to the motion P p. 
Refolving the motion according to P p z into two, 
according to P K and P M', the motion according to 
P R produces the fame preceftion, and with the fame 
fign, or the Fame diredion, as when the fun was on 
the other fide of the folftice ®, and in D; and the pre- 
cefilon is ever the fame at every quarter revolution of 
the fun. 
The motion according to C P M caufes the fame 
variation in the inclination of the earth’s axe to the 
ecliptic, 
