Thirdly, From many Observations of the polar Points, and the Obliquity of the Earth's Equator to the Plane of her solar Orbit compared together, the Sun is very justly suspected to have changed his sidereal Situation; and this must either arise from a Change in the Position of the Earth's diurnal Axis, or from a Removal of the Sun himself, out of the primitive Plane of the _Orbis Magnus_. I believe you are so much of a Mathematician, as to know that if either of these Facts be allowed, the Consequence I want will follow. I shall not therefore here enter into any farther Dispute about it; but I think it will be necessary to submit some Observations to your Consideration, that may convince you that there is a Motion somewhere to be thus discovered, and whether in the Sun, or in the Stars, or in both, I leave to your own Determination, but to assist your Imagination, I refer you to PLATE XVIII. The Globe S is here supposed to represent the Sun, having changed its Situation by a local Motion from A to C, and B represents the Globe of the Earth in a permanent Position, with its principal Points and Circles, respecting the primitive Plane A, B, K. Now in Consequence of the Angle of Variation, A, B, C, it evidently appears that a new ecliptic Plane, will be produced, as C, B, and also a Variation in the greatest Declination of the Sun, North and South from the Line of the _Equator_ D, L. Hence, as in this Figure, the Obliquity of the Poles P, N, and G, F, will naturally decrease, and is shewn in Quantity by the Line of Aberration H, I. Here follows a Table of the Change observed in the Obliquity of the Ecliptic by Astronomers of different Ages. [Illustration: Plate XVIII.] _A Table of the Obliquity of the Ecliptic._ _Ante Christi_ ° ′ 124 Arato 24 00 ---- Hiparchus 23 51⅓ 127 Eratosthenes 23 51½ _Anno Dom._ ° ′ 140 Ptolomy 23 51⅓ 749 Abategnius 23 35½ 1070 Airahel 23 34 1140 Alomean 23 33 1300 Profatiograd 23 32 1458 Purbacchio 23 29½ 1490 Regiomontaus 23 30 1500 Copernicus 23 28½ 1592 Tycho Brahe 23 21½ 1656 Cassini 23 29½ Now sure, if we consider this continual Decrease of the Sun's Declination, which can proceed from no other Cause than that of his having moved out of the primitive Plane; we need make no great Difficulty thus far, to think our Conjectures not irrational. The following is a Citation from Dr. _Edmund Hally_, Astronomer-Royal. See _Philosophical Transactions_, N^o. 355. p. 736.