PHYSICAL anp LITERARY. 181 
therefore appear to vary, but not in a manner 
that will accrefce and produce any fenfible 
change in our feafons; but it will increafe 
and decreafe a little within {mall limits, and 
its variation will principally depend on the 
pofition of Fupiter and Saturn to the fun and 
earth, and will nearly return to the fame ma- 
gnitude when thefe return to the fame pofi- 
tion, with refpect to one another and to the 
folftice. “fupiter has moft effect in produ- 
cing this variation; and, if it be found to have 
a connexion or dependence on his pofition 
to the fun and earth, it will be an indication 
that this is the true caufe of the phenome- 
non. 
Was the orbit of the earth perpendicular 
to the orbit of ‘fupiter, this variation would 
be much more confiderable than it is, and 
_ might amount to above half a degree, ora 
diameter of the fun. Suppofe[ Tad. 2. Fig. 18.] 
BET to reprefent the orbit of the earth in 
fuch a cafe, C the common center of gra- 
vity of the fun and ‘fupiter, which we may 
_ confider as the center of the earth’s orbit, be- 
— ufe of the minutenefs of the earth compa- 
fed with thefe, T the folftitial point, PTp 
4 the axis of the earth, IS the right line join- 
ing 
