The ninth sphere rotates on two poles, which are absolutely fixed, “fermi e fissi e non mutabile, secondo alcuno rispetto,”[589] the eight within it have each two poles which are only relatively fixed (for they move with the movement of the Primum Mobile), and every sphere has an equator, every point on which is equally distant from the two poles of rotation, as anyone may see who will turn round an apple, or any other spherical thing. Any point on the equator moves more quickly than any other point on the sphere, and each part moves more quickly the nearer it is to the equator, more slowly as it is far from it and nearer to the pole, since all the circling is done in the same time, and some parts have a greater, and some a less distance to go, according to their distance from the equator. Dante adds that the nearer any part of a heaven is to its equator, the nobler it is compared with its poles, for it has more movement, and more actuality, more life, and more form, and it touches more of the heaven just above, and in consequence is more noble.[590] ------------------------------------------------------------------------ [589] “Firm and fixed and not moveable, from any point of view.” _Conv._ II. iv. 50, 51. [590] _Conv._ II. iv. 68-75. ------------------------------------------------------------------------ Besides these ten heavens there are others which, strictly speaking, should be included in the number: these are the little spheres which are called “epicycles” by astronomers, and they also have equators and poles of rotation, and are fixed on the large spheres, or heavens. Dante does not enter into any particulars about these, but only mentions (as belonging specially to the subject in hand) that the brilliant star of Venus is carried “on the back” of an epicycle, which is itself fixed on the back of the third Heaven.[591] The apparent movement of Venus is therefore compounded of no less than four movements: that of her epicycle, of her whole heaven (the “deferent” Dante does not name, probably as introducing too technical a word), of the west to east motion of the star sphere (precession), and the diurnal. The epicycle of Venus is also called in this treatise, as we have already seen, “quello suo cerchio che la fa parere serotina e mattutina, secondo i due diversi tempi,”[592] and the “terzo epiciclo”[593] is referred to in _Par._ viii. 3. ------------------------------------------------------------------------ [591] _Conv._ II. iv. 78-104. [592] “That circle of hers which makes her appear as evening and morning star, according to the two different periods.” _Conv._ II. ii. 3-5. [593] “Third epicycle.” ------------------------------------------------------------------------