"A sphere is a solid figure described by the revolution of a semicircle about its diameter, which remains fixed.The axis of a sphere is the fixed straight line about which the semicircle revolves.The centre of a sphere is the same with that of the semicircle.The diameter of a sphere is any straight line which passes through the centre, and is terminated both ways by the superficies of the sphere."
A sphere is a surface analogous to the circle, a curve. In solid geometry, a sphere is the set of points that are all at the same distance r from a given point in three-dimensional space. That given point is the center of the sphere, and the distance r is the sphere's radius. The earliest known mentions of spheres appear in the work of the ancient Greek mathematicians.
"This is as I have said in my Arithmetic:—The area of a circle is equal to the product of the circumference by one-fourth of the diameter [πr²]. That result multiplied by 4 gives the surface of the sphere [4πr²], which is like the net surrounding a hand ball; the same (surface of a sphere) when multiplied by the diameter and divided by six [4/3πr³] becomes invariably the volume of the sphere."
Sphere