VI PREFACE. 



unification would have to start. The following pages 

 contain the result of this survey. Like every survey, it 

 can claim to be merely an approximation. It gives outlines 

 which closer scrutiny will have to correct and fill up. 



My original intention was to complete this survey in 

 three volumes, corresponding to the three divisions of the 

 subject set out in the Introduction. 



Some of my friends, who desired that the publication 

 of the book should not be unduly delayed, considered that 

 the Introduction and the earlier chapters of the work would 

 give something intelligible in themselves, and urged the ad- 

 vantage of smaller volumes. I therefore decided to complete 

 the first part of the history, which deals with scientific 

 thought, in two volumes instead of in one. 



For the information of my readers, I mention here that 

 the two last chapters of this volume, which treat of the 

 astronomical and of the atomic views of Nature, will be 

 followed in the second volume by similar chapters on 

 the mechanical, the physical, the biological, the statistical, 

 and the psychophysical views of Nature, and that it is my 

 intention to close the first part of my subject by an attempt 

 to trace concisely the development of mathematical thought 

 in this century. 



My thanks are due to many friends who have supported 

 me with assistance and encouragement. 



I consider myself fortunate in having secured for the 

 revision of the whole volume the invaluable aid of Mr 

 Thomas Whittaker, B.A., whose profound erudition, know- 



