But it is well known to all Mathematicians, that the first of these Comets moved in so eccentric a Trajectory, that the least Error in its almost incredible Proximity to the Sun will produce a very sensible Difference in the Area of the Orbit: And accordingly, if we moderate the Perihelion Distance of this Comet, by making it but 1000 instead of [L]612, which is but increasing it a 1/35000th Part of the great Radius of the Orbit, (which is an Error every Astronomer will readily grant is very easily made) and we shall find the Orbits of the said two Comets to be exactly equal. [Footnote L: The Number in Dr. _Hally's_ Synopsis.] Further, I must inform you, that the Comet of 1682, which the above is compared with, seems to have been so accurately observed, that it does not appear to have altered its Perihelion Distance half a 68th Part in one intire Revolution. Now, if we can with any Show of Reason, and a Probability on our Side, bring the Areas of these two extream Comets, as I may call them, to an _Equality_, sure we may conclude, it is a Subject highly worthy to be more considered and enquired into. PLATE VI. Is a true Representation of the satellite Systems, proportionable to one another, and to the Orb of the Sun's Body, that a just Idea of the Distances of those secondary Planets, may be easier had from their respective primary ones. S represents the solar Body with its Atmosphere. _Fig._ 1. is the System of _Saturn_ from the same Scale. _Fig._ 2. that of _Jupiter_ from _ditto_. And _Fig._ 3. the Orbit of the Moon round the Earth, in the same Proportion. But as you can have but a very imperfect Idea of the Magnitude of these last Circles, with regard to the Body of the Earth or Moon, PLATE VII. Is a true Projection of their real Globes, at their proper Distance from each other, with their common Center of Gravity, and the Point and Line of equal Suspension betwixt them, _viz._ A, represents the Globe of the Earth. B, that of the Moon. C, Point, and C D, Line of equal Suspension betwixt them. E, Common Center of Gravity, which describes the _Orbis Magnus_. E, F, and B, G, is the Orbit of the Moon. Farther, that nothing may be wanting to give a true Notion of the whole together, PLATE VIII. Is a proportional Drawing of all the primary and secondary Planets together, distinguished by their Characters, proper to attend a Globe of twelve Inches Diameter, such a one being supposed to represent the Sun. PLATE IX.