CONTENTS xv 



CHAPTER XXX 



THE STRUCTURE OF THE UNIVERSE 



PAGE 



Lambert's vast reveries The evidence for the grindstone theory 

 The question of a central sun Probability that the structure of 

 the universe corresponds more to the modern kinetic theory of 

 gases Analogies . . . . . . .383 



CHAPTER XXXI 



THE BIRTH AND DEATH OF WORLDS 



The increasing evidence for the nebular hypothesis Ideas of Buffon, 

 Kant, Laplace, and their successors Evidence from the theory 

 of solar heat Evidence from photographs of the nebulae They 

 are sketches of worlds in the process of creation . . . 399 



CHAPTER XXXII 



THE COSMIC EXCHANGE OF MATTER AND LIFE 



Worlds and systems are not isolated as was formerly supposed 

 The incessant exchange of matter and energy implies a 

 more or less homogeneous universe Possible means of a 

 cosmic propagation of life Ideas of Kelvin, Helmholtz, and 

 Arrhenius ........ 427 



CHAPTER XXXIII 



THE LAST RIDDLE 



The problem of gravitation and the force or forces which hold the 

 universe together Gravitation seems insufficient The mystery 

 of an apparently inexhaustible outpour of attractive energy 

 Speculations of Newton Modern attempts at a solution . 443 



