XVII.] THE LAW OF ERROR. 396 



basis of probability and of related questions concerning 

 causation, belief, desi^i^n, testimony, &c. ; but I cannot 

 always agree with Mr. Venn's opinions. No mathematical 

 knowledge beyond that of common arithmetic is required 

 in reading these works. Quetelet's Letters form a good 

 introduction to the subject, and the mathematical notes 

 are of value. Sir George Airy's brief treatise On tlie 

 Algebraical and Numerical Theory of Errors of Ohserva- 

 tions and ihc Comhination of Observations, contains a 

 complete explanation of the Law of Error and its prac- 

 tical applications. I)e Morgan's treatise " On the Theory 

 of Probabilities " in the Encyclopaedia Metropolitana, 

 presents an abstract oi' the more abstruse investigations 

 of Laplace, together with a multitude of profound and 

 original remarks concerning the theory generally. In 

 Lubbock and Drinkwater's work on Probability, in the 

 Library of Useful Knowledge, we have a concise but 

 good statement of a number of important problems. The 

 Eev. W. A. AVhitworth has given, in a work entitled 

 (Jhoice and Chance, a number of good illustrations of 

 Giilciilations both in combinations and probabilities. In 

 j\Ir. Todhunter's admirable History we have an exhaustive 

 critical account of almost all writings upon the subject of 

 probability down to the culmination of the theory in 

 Laplace's works. The Memoir of Mr. J. W. L. Glaisher 

 has alieady been mentioned (p. 375). In spite of the 

 existence of these and some other good English works, 

 there seems to be a want of an easy and yet pretty com- 

 plete mathematical introduction to the study of the theory. 

 Among French works the Traite Elementaire du Calcul 

 des Frobabilites, by S. F. Lacroix, of which several editions 

 have been published, and which is not difiicult to obtain, 

 forms probably the best elementary treatise. Poisson's 

 llecherches sur [a ProbabiUte des Juyements (Paris 1837), 

 commence witli an admirable investigatinn of the grounds 

 and methods of the theoiy. While Laplace's great Thcurie 

 Aiialytique des Probabilitds is of course the " Principia " 

 of the subject ; his Essai Philosophique sur les Probabilitis 

 is a popular discourse, and is one of the most prolound 

 and interesting essays ever published. It should be 

 familiar to every .student of logical method, and has lost 

 little or none of its importance by lapse of time. 



