Centre, and 17.68 deg (as at d,) and where it Orbit of MARS, make 8; for that is the place of his Orbit at that time. Fontbly, Draw the Right-Lines,, tuting the Right-lined Triangle and d The Theory thus finished, I come now to shew 1. To find the Sun's true Place in the Ecliptick, proposed. Lay a Ruler upon the Line, and it will cut Circle in bb, in 5. 51 deg. of Scorpio; and that Longitude (or Place in the Ecliptick) at the time pro II. To find the Longitude (or true Place in the l Through the Point in the Centre, draw a Right lel to the Line, as the short Line a da, whi the Ecliptick Circle in 25.00 deg of Libra, wh Character of M ARS; for that is his true Place of the Ecliptick, for the time proposed. Mark now the Triangle, made upon th the Centre, and the Point of and in their O that Triangle, The Sideis is the distance of off from the 205 All which are to be Measured upon -Proper Scales ral Planets. The Angle And is the An- Sunthor : Com 20oSgle at the PlanetS 2 Pare For of Elon These Angles may be Measured (very near the help of yoar Scale of Chords; but more accur the Sides are known) by Trigonometrical Cal which hereafter. But for the measuring of the Sides, Proper Scales must be made Fig. for each Planet, and the Earth. And, The Proportions between the Length of the Aphelial Lines of the feveral Planets, (taken from the Center of the Theories, to the Aphelial Points) and the Scales by which to measure their Diftances from the Sun or Earth; are these exhibited in this, Table, viz. LXXVI: Which Numbers will make Proper Scales for measuring the DiAances in each Theory. And the Scale for the Earth, will ferve, alfo, for the Theories of Venus and Mercury. And note farther, That all Distances meafured upon these Proper Scales, are And these Products shall Reduce the Distances measured upon the Proper Scales, into Semidiameters of the Earth. III. To find the Distance of MARS from the Sun and from the Earth, for the Time propofed. Take in your Compasses the length of the Aphelial Line Ap. ,, and opening the Sector in the Points 56.73 and 56.73. The Secter, as fo opened, shall be the Scale whereby to measure the Distances in the Theory of MARS. Wherefore, if you take in your Compaffes (out of the Theory) of Mars. IV. To find the Angle of Commination,, of Angle at the Sun) Lay a Ruler to the Centre, and the Point in its Orbit ; and it will cut the Ecliptick Circle in the Pointc: Also lay a Ruler upon the Centre, and the Point Mars in its Orbit, and it will cut the Ecliptick in the Point d; then will the Degrees of the Ecliptick, intercepted between c and d, be the quantity of the Angle , the Angle at the Sun (or of Commination) and will be found to be 162.00 deg.. V. To find the Angles of Elongation and Parallas of the Orb (or the Angles at the Earth and Planet) ♂ and These (as I faid before) may be measured upon the Theory by the assistance of the Scale of Chords: But the Angle of Commination and the distance of the Earth and Mars being known, they may more exactly be found by Trigonometrical Calculation: Thus; As the Sum of the Sides and 0.90.25-3.954447 3.317018 So is the Tang. of half the Angles at 8 and 0, 9.00 d. 9.199712 .. 12.516730 To the Tangent of 2.09 deg, 8.5.62283 Which added to 9.00 deg. gives 11.09 deg. for the Angle at the Earth (or of Elongation) - And substracted from 9.00 deg. leaves 6.91 deg. for the Angle at Mars (or of the Parallax of the Orb. VL Ta |