To illustrate this primitive Motion of the Stars, and at the same time to show that the Variety which appears in the Quantity of Motion can be no Objection to it, See PLATE XVIII. _Fig._ 2. Where A represents the Eye of an Observer, and B, E, F, H, various Systems, moving in different Directions thro' the mundane Space; it is evident that the Sphere B, having moved from C, and that of E, not having appeared to move at all, there must be a sensible Change in the new Position of these two Systems to one another, and so of the rest; and tho' the apparent Motion of H, be much more than that of F, from the Point A, yet from C, they will appear less different, and from B, they will appear nearly equal. And farther, as the Direction from H, is in the Line I, H, and that of F, in the Line K, G, those two Systems will appear to approximate, and the Magnitude of the Star in the first will be increased, and in the latter diminished. Thus, many of the Stars in the oldest Catalogues, which were said to be of the second Magnitude, are now become of the first, and several of the first are now judged to be of the second, &c. But as this apparent Motion of the Stars at the Earth, must, from its Nature, be very small, so as scarce to be discovered in some of them in less than an Age, with any Instrument by the nicest Observer, I judge it will be extremely proper in this Place to propose some Method, by which, in process of Time, the Truth of the Theory may be ascertained. The Way I think most likely to succeed is this. PLATE XIX. Is a Plan of the principal Stars that form the Pleiades, correctly taken by a Combination of Triangles, as in the Figure, from whence it will naturally follow, all the whole Form being comprehended in much less than one Degree. That the most minute local Motion in any one of those Stars in a very few Years, will be made sensible to an Eye at the Earth. For Instance, if any of the Stars that form the Letter A, or T, within the Term of ten or twenty Years, be found in the least to deviate from the Lines of their present Position and Direction, it will be evident beyond a Contradiction, that they have a Motion amongst themselves, and since at such a Distance they cannot possibly be affected by the Earth, it must be a Motion of their own; and thus if any one can be proved, to change its Situation, with regard to the rest, we can have no new Difficulty in concluding that they all may do the same. Thus if any of the regular Triangles M B Z, Z P H, A Z M, Y A Γ, or Π Ο I, &_c._ in due Time be carefully noted, we may venture to say with great Safety, that the thousandth Part of a Degree will be plainly discovered. PLATE XX.