228 



Magnetische und Meteorologische Beobachtungeii zu Prag. 1841, 

 1842, 1843, 1844, 1845, 1846, 1847, 1848. 4to. 



Magnetische und Geographische Ortsbestimmungen Bohnien in dem 

 Jahren 1843-5. Von Karl Kreil. 4to. 



Magnetische und Geographische Ortsbestimmungen in Osterreichisch- 

 en Kaiserstaate. Erster Jahrgang. 1846. 4to. — By the Ob- 

 servatory of Prague. 



Monday, March 19, 1849. 



The Right Rev. Bishop TERROT, Y. P., in the Chair. 



The following Communications were read: — 

 1. An Attempt to compare the Exact and Popular Estimates 

 of Probability. By Bishop Terrot. 



The author began by defining probability as being that state of 

 mind in which we are inclined to believe a proposition, without be- 

 ing absolutely convinced that it is true. Objectively, every propo- 

 sition is either true or false ; subjectively, it may be certainly true, 

 probable, or impossible. 



The measure of probability he shewed to be the same as the mea- 

 sure of the cause producing it ; that is, the ratio of the reasons in- 

 clining us to believe a proposition, to the whole number of reasons 

 bearing upon it, whether for or against ; all of which reasons are 

 founded, either upon necessary inference from experience, or from 

 testimony. 



How inference from experience may lead to a definite expectation 

 of an event different fi'om that which has been experienced, was 

 shewn in the case of an urn, containing two balls, white or black, 

 and from which a white has been drawn. There is then a probabi- 

 lity of \ that the remaining ball will be black ; and if a witness as- 

 serts that at a second drawing black was drawn, his credit must be 

 very low indeed, if his assertion does not raise this probability from 

 I to above ^, that is to say, render it more likely that the event in 

 the second drawing was different from, though not contradictory, to 

 that observed in the first drawing, than that it was not different. 



