CHAPTER XIII. 227

CELESTIAL EVOLUTION. Laplace’s nebular hypothesis—Helmholtz and solar contraction—Theories of solar heat—Objections to Laplace’s theory—Faye’s hypothesis—Ball’s exposition—The meteoritic theory of Proctor—Its extension by Lockyer—Evolution of the stars—Vogel’s order of evolution—Tidal friction: work of Darwin—See’s explanation of double stars—Future of the Universe

A CENTURY’S PROGRESS IN ASTRONOMY.