xiv Preface to the Second Edition. 



otherwise; owing to my having endeavoured to avoid the 

 needlessly polemical tone which, as is often the case with 

 those who are making their first essay in writing upon any 

 subject, was doubtless too prominent in the former edition. 

 I have not thought it necessary, of course, except in one or 

 two cases, to indicate points of detail which it has seemed 

 necessary to correct. 



A number of new discussions have been introduced upon 

 topics which were but little or not at all treated before. The 

 principal of these refer to the nature and physical origin of 

 Laws of Error (Ch. II.); the general view of Logic, and con 

 sequently of Probability, termed the Material view, adopted 

 here (Ch. x.); a brief history and criticism of the various 

 opinions held on the subject of Modality (Ch. XII.); the 

 logical principles underlying the method of Least Squares 

 (Ch. xiii.); and the practices of Insurance and Gambling, 

 so far as the principles involved in them are concerned 

 (Ch. xv.). The Chapter on the Credibility of Extraordinary 

 Stories is also mainly new ; this was the portion of the former 

 work which has since seemed to me the least satisfactory, 

 but owing to the extreme intricacy of the subject I am far 

 from feeling thoroughly satisfied with it even now. 



I have again to thank several friends for the assistance 

 they have so kindly afforded. Amongst these I must promi- 

 neatly mention Mr C. J. Monro, late fellow of Trinity. It is 

 only the truth to say that I have derived more assistance from 

 his suggestions and criticisms than has been consciously ob 

 tained from all other external sources together. Much of this 



