the greatest elongation of the Earth from the Sun, if the Earth be observed from the respective Planets, when the line G ♄ ♃ ♂ A, touches the Earth’s orbit in A. The nearer any of the superior Planets is to the Sun, the greater is the Parallax of the annual Orb, or the angle under which the semidiameter of the Earth’s orbit is seen from that Planet. In _Mars_ the angle ♂ S, (which is the visible elongation of the Earth seen from _Mars_, or the Parallax of the annual Orb seen from that Planet) is about 42 degrees, and therefore the Earth is always to the inhabitants of _Mars_ either their Morning or Evening Star, and is never seen by them so far distant from the Sun as we see _Venus_. The greatest elongation of the Earth seen from _Jupiter_, being nearly equal to the angle A ♃ S, is about 11 degrees. In _Saturn_ the angle A ♄ S is but 6 degrees, which is not much above ¼ part of the greatest elongation we observe in _Mercury_. And since _Mercury_ is so rarely seen by us, probably the astronomers of _Saturn_ (except they have better Optics than we have) have not yet discovered that there is such a body as our Earth in the Universe. The Parallax of the annual Orb, or the greatest elongation of the Earth’s orbit seen from any of the superior Planets, being given; the distance of that Planet from the Sun, in respect of the Earth’s distance from him, may be found by the same methods as the distances of the inferior Planets were. Thus, to find the distance of _Mars_ from the Sun, it will be as the Sine of the angle S ♂ A is to the _Radius_, so is the distance AS (the distance of the Earth from the Sun) to S ♂, the distance from the Sun to _Mars_. After the same manner the distances of _Jupiter_ and _Saturn_ are also found. The mean distance of the Earth from the Sun being made 1000, the mean distances of the superior Planets from the Sun are, _viz._ the mean distance from the Sun of { ♂ 1524 } { 141 } { ♃ 5201 } and the Excentricity { 250 } { ♄ 9538 } { 547 } To which, if you add or subtract their mean distances, we shall have the greatest or least distances of those Planets from the Sun. There are other methods by which the relative distances of the Planets might be found; but that which hath been here illustrated, is sufficient to evince the certainty of that Problem. [Sidenote: How the absolute distances of the Planets from the Sun are computed.] [Sidenote: _Parallax_ of the _Earth’s Semidiameter_.] [Sidenote: _Fig. 7._]