Dialogue. I.
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ment that they generate and dissolve; for if without generating or corrrupting, they should appear there by onely local motion, they would all be seen to enter,A conclusive demonstration, that the spots are contiguous to the body of the Sun. and pass out by extreme circumference. The other observation to such as are not situate in the lowest degree of ignorance in Perspective, by the mutation of the appearing figures, and by the apparent mutations of the velocity of motion is necessarily concluding, that the spots are contiguous to the body of the Sun, and that touching its superficies, they move either with it or upon it, and that they in no wise move in circles remote from the same.The motion of the spots towards the circumference of the Sun appears slow. The motion proves it, which towards the circumference of the Solar Circle, appeareth very slow, and towards the midst, more swift; the figures of the spots confirmeth it,The figure of the spots appears narrow towards the circumference of the Suns discus, & why. which towards the circumference appear exceeding narrow in comparison of that which they seem to be in the parts nearer the middle; and this because in the midst they are seen in their full luster, and as they truly be; and towards the circumference by reason of the convexity of the globous superficies, they seem more compress'd: And both these diminutions of figure and motion, to such as know how to observe and calculate them exactly, precisely answer to that which should appear, the spots being contiguous to the Sun, and differ irreconcileably from a motion in circles remote, though but for smal intervalls from the body of the Sun; as hath been diffusely demonstrated by our* Under this word Friend, as also that of Academick, & Common Friend, Galilœus modestly conceals himself throughout these Dialogues. * Friend, in his Letters about the Solar spots, to Marcus Velserus. It may be gathered from the same mutation of figure, that none of them are stars, or other bodies of spherical figure; for that amongst all figures the sphere never appeareth compressed, nor can ever be represented but onely perfectly round; and thus in case any particular spot were a round body, as all the stars are held to be, the said roundness would as well appear in the midst of the Solar ring, as when the spot is near the extreme: whereas, its so great compression, and shewing its self so small towards the extreme, and contrariwise, spatious and large towards the middle, assureth us,The Solar spots are not spherical, but flat like thin plates. that these spots are flat plates of small thickness or depth, in comparison of their length and breadth. Lastly, whereas you say that the spots after their determinate periods are observed to return to their former aspect, believe it not, Simplicius, for he that told you so, will deceive you; and that I speak the truth, you may observe them to be hid in the face of the Sun far from the circumference; nor hath your Observator told you a word of that compression, which necessarily argueth them to be contiguous to the Sun. That which he tells you of the return of the said spots, is nothing else but what is read in the forementioned Letters, namely, that some of them may sometimes so happen that are of so long a duration, that
they
