of the Equinoxes. 
67 
'MxSC 
force on the particle G, in the same direction, is as g^ 3 — , the 
disturbing force of the sun, by its action on the particle G is 
S - or M x S i- T — , for SG may be considered as 
equal to SC — GH. But as SC is indefinitely great with re- 
SC 
spect to GH, =======n, by actual division may be considered as 
SC — GH! 
equal to -f- and therefore the disturbing force on the 
sc 3 
3M x GH 
SC 3 ' 
SC 
particle at G is 
Let K be a particle in the meridian, but on the opposite side 
of DF to that on which G is situated. Let KN, parallel to 
SC, meet DF in N ; and suppose SK to be drawn. Then the 
force of the sun on K being for the same reasons as be- 
MxSC 
fore, its force upon it in the direction of SC or KN is 
r SC + KNI » 
and after a reduction similar to the foregoing, the sun's dis- 
turbing force on K is — ■ 3M ^ N -. 
Hence it is evident, supposing M and SC to be constant, that 
the disturbing force of the sun on any particle in the meridian 
PELO is as the distance of the particle from DF ; and that 
the sign of the force in the half DAF nearest to S is positive, 
but the sign of the force in the other half DBF is negative. 
This difference of the signs indicates that the particles on the 
opposite sides of DF have a directly opposite tendency, as to 
direction, in affecting the position of the axis PL, or equator 
EO ; and the same is evident from the following considera- 
tions. As the disturbing forpe is as its distance from DF, it 
has no effect on particles in DF, and therefore the inertia * of 
* By this expression that part of the inertia is meant which opposes the disturbing 
force of the sun ; and the same is to be understood in the following expressions', 
K 2 
