- Explorations of the highlands of the Brazil; with a full account of the gold and diamond mines. Also, canoeing down 1500 miles of the great river São Francisco, from Sabará to the sea. By Captain Richard F. Burton, F.R.G.S. etc. Vol II.
- Sphere (Wikipedia)
A sphere (from Greek σφαῖρα, sphaîra) is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. Formally, 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 r is the sphere’s radius. The earliest known mentions of spheres appear in the work of the ancient Greek mathematicians.