Xll PREFACE. 



nient to include a full account of all his researches in the present 

 volume. There is ample scope for a continuation of the work 

 which should conduct the history through the period which has 

 elapsed since the close of the eighteenth century ; and I have 

 already made some progress in the analysis of the rich materials. 

 But when I consider the time and labour expended on the present 

 volume, although reluctant to abandon a long cherished design, 

 I feel far less sanguine than once I did that I shall have the 

 leisure to arrive at the termination I originally ventured to pro- 

 pose to myself 



Although I wish the present work to be regarded princijDally as 

 a history, yet there are two other aspects under which it may 

 solicit the attention of students. It may claim the title of a com- 

 prehensive treatise on the Theory of Probability, for it assumes 

 in the reader only so much knowledge as can be gained from 

 an elementary book on Algebra, and introduces him to almost 

 every process and every species of problem which the literature of 

 the subject can furnish; or the work may be considered more spe- 

 cially as a commentary on the celebrated treatise of Laplace, — 

 and perhaps no mathematical treatise ever more required or more 

 deserved such an accompaniment. 



My sincere thanks are due to Professor De Morgan, himself 

 conspicuous among cultivators of the Theory of Probability, for 

 the kind interest which he has taken in my work, for the loan of 

 scarce books, and for the suggestion of valuable references. A 

 similar interest was manifested by one prematurely lost to science, 

 whose mathematical and metaphysical genius, attested by his 

 marvellous work on the Laws of Thought, led him naturally and 

 rightfully in that direction which Pascal and Leibnitz had marked 

 with the unfading lustre of their approbation; and who by his 

 rare ability, his wide attainments, and his attractive character, 

 gained the affection and the reverence of all who knew him. 



I. TODHUNTER. 



Cambridge, 

 May, 1865. 



