PHYSICAL AND LITERARY. 201 



the coinman centre of gravity of the fua 

 and Jupiter, which we may confider as 

 the centre of the earth*s orbit, becaufe of 

 the minutenefs of the earth compared 

 with thefe, T the folflitial point, PT/* 

 the axis of the earth, IS the right line 

 joining the centres of the fun and Jupi- 

 ter, which we fuppofe perpendicular to 

 the orbit of the earth, while the earth is 

 m the folftice T. Then, if Jupiter be at 

 t, and the fuin at S, the angle PTS will 

 be the complement of the fun's greateft 

 declination, or of the angle contained by 

 the ecliptic and equator: But, if Jupiter 

 be at if and the fun at f, the angle PTf 

 will be the complement of this declina- 

 tion, and thefe would differ by the angle 

 STyj which, (becaufe GS is nearly equal 

 to a femidiameter of the fun), might a- 

 mount to 32'. 



But, becaufe the angle contained by 

 the orbits of Jupiter and the earth is 

 fmall, the right line CS is feen very ob^- 

 liquely from the earth, and the variation 

 of the obliquity thence ariling is fmall. 

 The a'ngle GTS is nearly to' the inclina- 

 tion of Jupiter's plane to the ecliptic, as 

 Vol. I. C c: the » 



