Sect. i. Of the SOLAR SYSTEM. z

the Ecliptick ; and this the Astronomers Edipthh.make the Standard to which the Planesof the other Orbits are judged to incline.

The right Line passing thro’ the Sun, andthe common Intersection of the Plane ofthe Orbit of any Planet and the Ecliptick,is called the Line of the Nodes of that Nodes.Planet; and the Points themselves, whereinthe Orbit cuts the Ecliptick, are called theNodes.

The Inclinations of the Orbits of thePlanets to the Plane of the Ecliptick, are asfollows, viz. the Orbit of Mercury makesan Angle with it of almost 7 Degrees; thatof Venus something above 3 1 Degrees; ofMars , a little less than 2 Degrees; of Ju-piter , i y Degree; and of Saturn, about 2| Degrees. The Orbits of the Planets arenot Circles, but Ellipses or Ovals. Whatan Ellipsis is, may be easily understood fromthe following Description. Imagine twosmall Pegs fixed upright on any Plane, andsuppose them tied with the Ends of a Threadsomewhat longer than their Distance fromone another : Now if a Pin be placed in theDouble of the Thread, and turned quiteround, (always stretching the Thread withthe same Force) the Curve described by thisMotion is an Ellipsis. The two Pointswhere the Pegs stood (about which theThread was turned) are called the Loci ofthat Ellipsis; and if, without changing theB 2 Length