BİRİNCİ FEN · İKİNCİ BÂB · SEKİZİNCİ FASIL · Üçüncü Madde
Article Three
It describes the epicycle of the planet Mercury, along with its form and movement.
O Noble One! Know that astronomical scholars, regarding the conditions of the planet Mercury, have not been content with merely determining the specified amount as with the other “confused planets,” but have ascertained the existence of a small sphere not included in the earth, which they have named the epicycle. This aforementioned epicycle is a small sphere not included in the earth within Mercury’s common-center sphere and is Mercury's fourth sphere. It also carries the body of the star.
It is situated on the belt of the third carrier sphere – that is, the eccentric sphere – between its two poles, such that the diameter of the epicycle is equal to the thickness of the carrier sphere, and the surface of the epicycle is tangent to the two surfaces of the carrier sphere at one point above and one point below.
The epicycle is a solid, spherical body enclosed by a single surface. Upon the body of the carrier sphere, it rotates around its own center with its specific movement, from west to east, as the signs rise, carrying Mercury along with it on one side. This sphere moves the star of Mercury approximately three degrees beyond its 360-degree belt in one day and one night, thus completing its cycle roughly every four months. This movement is referred to as “variant motion” or "specific motion."
The planet Mercury itself is a solid, luminous, spherical body enclosed by a single surface. It is situated upon the body of the epicycle such that it is found on one side, beside the belt, at the midpoint of the two poles of the epicycle’s surface, and touches the surface of the epicycle at a common point. That is to say, the body of the star has been entirely included within the body of the epicycle. The carrier sphere also, just as the epicycle rotates on one side, it has been observed through observations that the planet Mercury constantly turns around its own center, upon the side of the epicycle, in accordance with the rising of the signs. Observers have witnessed and confirmed this during solar eclipses (kusûf) which occur at midday (nısf-ı nehâr).