Anti-de Sitter space bell. It might be described as being the "opposite" of the surface of a sphere, which has a positive curvature. General relativity is a theory of the nature of time, space and gravity in which gravity is a curvature of space and time that results from the presence of matter or energy. Energy and mass are equivalent (as expressed in the equation "E" = "mc"), and space and time can be translated into equivalent units based on the speed of light ("c" in the "E" = "mc" equation). A common analogy involves the way that a dip in a flat
Southern Pacific class MC-2 the tender. of air pressure was sufficient to get the oil to the fire. The two MC-1 locomotives built in May 1909 were rebuilt in 1923 as MC-2 class with uniform cylinders measuring diameter × stroke; these rebuilt locomotives weighed , like the as-built MC-2 class, but with on the drivers. Most of the rest of the MC-2 class were "simpled" to the same size cylinders by 1931. Except for numbers 4011 and 4013 which were both scrapped by 1936, all of the MC-2 and the two former MC-1 locomotives were rebuilt again into class AC-1 with a higher boiler