CONTENTS. XI 



CHAPTER XL 



STELLAR SYSTEMS AND NEBULAE. 



Life and work of John Herschel Binary stars Computation 

 of orbits Work of Wilhelm Struve Of Otto Struve Of 

 Burnham Satellites of Sirius and Procyon Astronomy 

 of the invisible Work of Pickering and Vogel Spectro- 

 scopic binaries Work of Be*lopolsky and Campbell Star- 

 clusters Nature of nebulae Spectroscopic work of 

 Huggins Of Copeland Nebular photography Work 

 of Eoberts, Barnard, Wolf Of Keeler . . .197 



CHAPTER XII. 



STELLAR DISTRIBUTION AND THE STRUCTURE OF THE 

 UNIVERSE. 



Work of John Herschel Researches of Wilhelm Struve 

 Extinction of light Madler's " central sun " Distribution 

 of nebulae Work of Proctor Aggregation of stars on the 

 Galaxy Work of Gore and Schiaparelli Studies of 

 Gould Researches of Kapteyn Of Newcomb Is the 

 Universe limited 1 Newcomb's argument Observations of 

 Celoria Researches of Seeliger External Universes 

 Gore's speculations . . . . . .214 



CHAPTER XIII. 



CELESTIAL EVOLUTION. 



Laplace's nebular hypothesis Helmholtz and solar con- 

 traction Theories of solar heat Objections to La- 

 place'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 227 



