367 



numbers of favourable and unfavourable cases or hypotheses, their 



compound force is properly expressed by - — -• 



Under both of these conditions, the second given probability in- 

 creases or diminishes the force of the first, according as the fraction 

 expressing the second is greater or less than that expressing the first. 

 When the ratios only are given, then the increase or diminution is 

 indefinite. \Mien the actual numbers are given it is definite. 



In conclusion, it was questioned whether ^ was a proper expres- 

 sion for the probability derived from total ignorance, and whether 

 this would not be more properly expressed by the indefinite fraction 



vj. It was shown that such a priori probability had no effect upon 

 the force of a subsequently admitted probability. 



The following Gentleman was duly elected an Ordinary 

 Fellow : — 



Thomas Cleghoun, Esq., Advocate. 



The following Donations to the Library were announced : — 



Exhibition of the Works of Industry of all Nations, 1851. Reports 



by the Juries on the Subjects in the Thirty Classes into which 



the Exhibition was divided. 4 vols. fol. — From H. F. Talbot, 



Esq. 

 Journal of the Proceedings of the Linna?an Society. Vol. i.. No. 



1. 8vo. — From the Society. 

 American Journal of Science and Arts. Vol. xxi., No. 61. Bvo. 



— From the Editors. 

 Journal of the Statistical Society of London. Vol. xix., Part 1. 



8vo.— From the Society. 

 Quarterly Journal of the Geological Society. Vol. xii.. Part 1. Bvo. 



— From the Society. 

 Die Fortschritte der Physik im Jahre 1852. Dargestellt von der 



Physikalischen Gesellschaft zu Berlin. 2"^ Abtheil. 8vo. — 



From the Society. 

 Annalen der Koniglichen Sternwarte bei Miinchen. B^ 8. 8vo. — 



From the Observatory. 



