142. If you remove about six or seven yards from the candle, and place yourself so that it’s flame may be just about the height of your eye, and then desire the other person to move the ball slowly round the candle as before, keeping it as near of an equal height with the flame as he possibly can, the ball will appear to you not to move in a circle, but rather to vibrate backward and forward like a pendulum; moving quickest when it is directly between you and the candle, and when directly beyond it; and gradually slower as it goes farther to the right or left side of the flame, until it appears at the greatest distance from the flame; and then, though it continues to move with the same velocity, it will seem to stand still for a moment. In every Revolution it will shew all the above Phases § 141; and if two balls, a smaller and a greater, be moved in this manner round the candle, the smaller ball being kept nearest the flame, and carried round almost three times as often as the greater, you will have a tolerably good representation of the apparent Motions of Mercury and Venus; especially, if the bigger ball describes a circle almost twice as large in diameter as the circle described by the lesser. [Sidenote: Fig. III. The elongations or digressions of Mercury from the Sun. PLATE II.] 143. Let _ABCDE_ be a part or segment of the visible Heavens, in which the Sun, Moon, Planets, and Stars appear to move at the same distance from the Earth _E_. For there are certain limits, beyond which the eye cannot judge of different distances; as is plain from the Moon’s appearing to be no nearer to us than the Sun and Stars are. Let the circle _fghiklmno_ be the Orbit in which Mercury _m_ moves round the Sun _S_, according to the order of the letters. When Mercury is at _f_, he disappears to the Earth at _E_, because his enlightened side is turned from it; unless he be then in one of his Nodes § 20, 25; in which case, he will appear like a dark spot upon the Sun. When he is at _g_ in his Orbit, he appears at _B_ in the Heavens, westward of the Sun _S_, which is seen at _C_: when at _h_, he appears at _A_, at his greatest western elongation or distance from the Sun; and then seems to stand still. But, as he moves from _h_ to _i_, he appears to go from _A_ to _B_; and seems to be in the same place when at _i_ as when he was at _g_, only not near so big: at _k_ he is hid from the Earth _E_ by the Sun _S_; being then in his superiour Conjunction. In going from _k_ to _l_, he appears to move from _C_ to _D_; and when he is at _n_, he appears stationary at _E_; being seen as far east from the Sun then, as he was west from him at _A_. In going from _n_ to _o_ in his Orbit, he seems to go back again in the Heavens, from _E_ to _D_; and is seen in the same place (with respect to the Sun) at _o_ as when he was at _l_; but of a larger diameter at _o_, because he is then nearer the Earth _E_: and when he