9

of the Solar System.

earth at T, through the planet at e, is atangent to the orbit of the planet.

22. As an inferior planet moves from itsgreatest: elongation at a, fig. 5. through e,its superior conjunction, to e, its greatestelongation on the other side of the fun, itsgeocentric motion is direct.

23. When the earth is at T, Venus ata,a spectator at T sees the planet at a, in theline T a A among the fixed stars at A:when the planet is come to b, it appears inthe line T b B, or amongst the stars at B;at c, it is in its superior conjunction, and seenamong the stars at C; at d, it appears amongthe stars at D) and when it arrives at e, itappears among those at E. In this motion,Venus appears to describe the arc ABCDE,in the concave sphere of the heavens: andas these letters are in the same direction withabede, which express the planets mo-tion round the fun, its apparent motion seenfrom the earth is therefore direct, fromwest to east, or according to the order of thesigns. r

24. An inferior planet pasting from e, itsgreatest elongation, through f, its inferiorconjunction, to a, its greatest elongation on

the