APPENDIX. 617 



delsohn says that if the concurrence has happened n times the 



probability that there is a causal connexion is ; but he gives 



no intimation of the way in which he obtains this result. He 

 takes the following illustration : suppose a person to drink coffee, 

 and to be attacked with giddiness ; the concurrence may be acci- 

 dental or there may be some causal connexion : if the concurrence 



has been observed n times the probability is that the o-id- 



diness will follow the drinking of coffee. 



If we apply the theorem of Bayes and Laplace, and suppose 



that an event has happened n times, the probability that it will 



?i + 1 

 happen at the next trial is ^ ; see Art. 848. It is certainly 



curious that Mendelsohn's rule should agi-ee so nearly with this 

 result when n is large, but it is apparently only an accidental 

 coincidence, for there is nothing in Mendelsohn's essay which 

 suggests that he had much knowledge of the subject or any great 

 mathematical power : we cannot therefore consider that he in any 

 way anticipated Bayes. 



Mendelsohn makes his rule serve as the foundation of some 

 remarks on the confidence which we repose on the testimony of 

 our senses, referring especially to the scepticism of Hume. Men- 

 delsohn also touches on the subjects of Free Will and the Divine 

 Foreknowledge ; but as it appears to me without throwing any 

 light on these difficult problems. 



I was aware that Mendelsohn had written on Probability from 

 the occurrence of his name in Art. 840, but I assumed that his 

 essay would not contain any matter bearing on the mathematical 

 theory, and so I omitted to examine it. I supply the omission 

 at the request of the late Professor Boole ; he had seen a reference 

 to Mendelsohn in some manuscripts left by Dr Bernard, formerly 

 teacher of Hebrew in the University of Cambridge, and, in con- 

 sequence of this reference, expressed a wish that I would report 

 on the character of the essay. 



1060. I take from Booksellers' Catalogues the titles of four 

 works which T have never seen. 



