_B._ Upon the same centre A, draw a larger circle to stand for the ecliptic: for you know the sun is always in the plane of the ecliptic. _A._ There it is. The diameters of it at right angles are B Z. _B._ Draw the diameter of the equator. _A._ How? _B._ Through the centre A (for the earth is also always in the plane of the equator or of some of its parallels) so as to be distant from B twenty-three degrees and a half. _A._ Let it be H I: and let C G be equal to B H; and so C will be one of the poles of the ecliptic, suppose the north-pole; and then H will be east, and I west. And C A produced to the circumference in E, makes E the south-pole. _B._ Take C K equal to C G, and the chord G K will be the diameter of the arctic circle, and parallel to H I, the diameter of the equator. Lastly, upon the point B, draw a little circle wherein I suppose to be the globe of the earth. _A._ It is drawn, and marked with _l m_. And B D and K G joined will be parallel; and as H and I are east and west, and so are B and D, and G and K. _B._ True; but producing Z B to the circumference _l m_ in _b_, the line B _b_ will be in the diameter of the ecliptic of the earth, and B _m_ in the diameter of the equator of the earth. In like manner, if you produce K G cutting the circle, whose centre is G, in _d_ and _e_, and make an angle _n_ G _d_ equal to _b_ B _m_, the line _n_ G will be in the ecliptic of the earth, because G _d_ is in the equator of the earth. So that in the annual motion of the earth through the ecliptic, every straight line drawn in the earth, is perpetually kept parallel to the place from whence it is removed. _A._ It is true; and it is the doctrine of Copernicus. But I cannot yet conceive by what one motion this circle can be described otherwise than we are taught by Euclid. And then I am sure that all the diameters shall cross one another in the centre, which in this figure is A. _B._ I do not say that the diameters of a sphere or circle can be parallel; but that if a circle of a lesser sphere be moved upon the circumference of a great circle of a greater sphere, that the straight lines that are in the lesser sphere may be kept parallel perpetually to the places they proceed from. _A._ How? And by what motion? _B._ Take into your hand any straight line (as in this figure), the line L A M, which we suppose to be the diameter of the sun’s body; and moving it parallelly with the ends in the circumference, so as that the end M may withal describe a small circle, as M _a_. It is manifest that all the other points of the same line L M will, by the same motion, at the same time, describe equal circles to it. Likewise if you take in your hand any two diameters fastened together, the same parallel motion of the line L M, shall cause all the points of the other diameter to make equal circles to the same M _a_.