200 ESSAYS AND OBSERVATIONS 



different declinations at the time of the 

 folftice: And, as the obliquity of the e- 

 cliptic is determined always from the 

 declination of rae fun at the folflice, it 

 will 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 with- 

 in fmall limits, and its variation will 

 principally depend on the pofition of Ju- 

 piter and Saturn to the fun and earth, 

 and will nearly return to the fame mag- 

 nitude, when thefe return to the fame po- 

 fition with refpeclH: to one another and to 

 the folftice. Jupiter has moft effedl in 

 producing this variation ; and, if it be 

 found to have a connexion or depen' 

 dence on his pofition to the fun and earth, 

 it will be an indication that this is the 

 true caufe of the phaenomenon. 



Was the orbit of the earth perpendicu- 

 lar to the orbit of Jupiter, this variation 

 would be much more confiderable than 

 it is, and might amount to above half a 

 degree, or a diameter of the fun. Sup- 

 pofe [Tab.'cL. Fig. i8.] BET to reprefent 

 the orbit of the earth in fuch a cafe, C 



the 



