vi Preface 



It is hoped that the book will be read in the spirit of the remarks of 

 Darwin just quoted. The main object of the essay is to build a framework 

 of absolute mathematical truth ; the backbone of the structure is the 

 theoretical investigation into the behaviour of rotating masses. Of this my 

 own contribution forms only a small part ; the book contains also an account 

 of general dynamical theory, and of the researches of Darwin, Poincare and 

 others, in so far as they relate to the main problem in hand. This part 

 of the book has been made as concise as possible, and I have ventured to hope 

 that it will prove of value to those who are embarking on a study of the 

 general problem of cosmic evolution. 



I have tried not only to build a skeleton but also to clothe it. When a 

 firm theoretical framework had been constructed, it seemed permissible and 

 proper to try to fit the facts of observational astronomy into their places. If 

 ever a complete mathematical theory is achieved, it will probably be an easy 

 task to trace out the order of evolution of stellar objects, but at present our 

 theoretical knowledge is so incomplete that a large element of speculation 

 must necessarily enter into every attempt to connect up theory and observa- 

 tion. I have tried throughout to keep speculation within reasonable limits, 

 and have applied as many checks and tests as I could to the various con- 

 jectural hypotheses brought forward. Many astronomers necessarily will 

 disagree with a number of these conjectures; it is in this way that science 

 advances. To any critic who may think the conjectures ought not to have 

 been brought forward at all, I would reply in the words of Herschel : 



"If we indulge a fanciful imagination and build worlds of our own,... 

 these will vanish like the Cartesian vortices, that soon gave way when better 

 theories were offered. On the other hand, if we add observation to observa- 

 tion, without attempting to draw not only certain conclusions but also con- 

 jectural views from them, we offend against the very end for which only 

 observations ought to be made. I will endeavour to keep a proper medium ; 

 but if I should deviate from that I could not wish to fall into the latter 

 error." 



The more speculative chapters fall naturally together at the end of the 

 book. Many readers may find these the most interesting, and I have tried 

 to arrange the book so that they will prove intelligible to those readers who 

 prefer to take mathematical investigations as read. In the present state of 

 our knowledge any attempt to dictate final conclusions on the main problems 

 of cosmogony could be nothing but pure dogmatism; I should not have 

 ventured even to suggest a conclusion except that the various theoretical 

 results obtained seemed to point with considerable unanimity in one parti- 

 cular direction. Consequently a definite scheme of cosmogony has been 



