PREFACE 
M Y book attempts to describe the present position of Cosmogony and 
of various closely associated problems of Astronomy, as, for instance, 
the physical state of astronomical matter, the structure of the stars, the 
origin of their radiation, their ages and the course of their evolution. 
In a subject which is developing so rapidly, few problems can be discussed 
with any approach to finality, but this did not seem to be a reason against 
writing the book. Many years have elapsed since the last book on general 
Cosmogony appeared, and the interval has seen the whole subject trans 
formed by new knowledge imported from observational astronomy and atomic 
physics. It has also witnessed the growth of an interest in the results of Cos 
mogony, which now extends far beyond the ranks of professional astronomers, 
and indeed beyond scientific circles altogether. 
With this in my mind, I have tried to depict the present situation in the 
simplest language consistent with scientific accuracy, avoiding technicalities 
where possible, and otherwise explaining them. As the book is intended to 
be, first and foremost, a rigorously argued scientific treatise, the inclusion of a 
substantial amount of mathematical analysis was inevitable, but every effort 
has been made to render the results intelligible to readers with no mathe 
matical knowledge, of whom I hope the book may have many. 
In a sense the book constitutes a sequel to my Problems of Cosmogony 
and Stellar Dynamics of ten years ago. So much has happened in the 
intervening decade that a new book seemed to be called for, rather than 
a new edition of the old. At any rate I allowed myself to be attracted by 
the idea of a big clean canvas on which I could paint a picture on a more 
comprehensive scale than had originally been possible in the publication of 
a Prize Essay. A considerable part of the present book is devoted to examining 
the consequences of the hypothesis, first put forward in the closing pages of 
the earlier book, that the energy of stellar radiation arises out of the annihi 
lation of stellar matter. The calculations of stellar ages given in the present 
book seem to shew that this is the only possible source of stellar energy, 
since nothing short of the complete annihilation of matter can give an 
adequate life to the stars. I have, however, tried to explain and discuss all 
reasonable hypotheses at present in the field, both on this and other subjects,