ifyjtiTl 



PROCEEDINGS 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 



February 9, 1857. 



Prof. Challis gave an account of his Observation of the Occupa- 

 tion of Jupiter on Jan. 2, 1857. 



February 23, 1857. 



A paper was read " On the Theory of Polarized Fasciculi, com- 

 monly known as Haidinger's Brushes." By the Rev. J. Power, 

 M.A., Librarian of the University. 



In this paper the view taken of the subject is similar to that 

 which had occurred to M. Jamin, and which will be found in Pog- 

 gendorfFs Annalen, 1849, p. 145, and in the Comptes Rendus, tome 

 xxvi. p. 197. The author arrived, however, at the present theory 

 quite independently in the course of last summer, and before he had 

 acquainted himself with the literature of the subject. M. Jamin 

 had taken as an essai de calcul the particular semi-visual angle 20°, 

 which lies far beyond the limits within which the phsenomenon is 

 visible ; and he has not attempted to give the general law for small 

 angles, which was the real problem to be solved. 



This is what the author has attempted in the present communica- 

 tion, availing himself of the experimental researches of Chossat 

 given in the Bulletin de la Soc. Philomatique, 1818, p. 94. 



The subject was rendered more complicated by the circumstance 

 that the formulae for the intensities of the refracted pencils are given 

 differently by Neumann, Airy, and the author of this paper. Instead 

 of taking any one set of formulae, the author managed to take them 

 all into consideration by previously showing that Airy's formulae 



result from Neumann's by multiplying them by ', which is equi- 



valent to - . ; while his own result from the same by multi- 



jj. cos d t 



No. XIII. — Proceedings of the Cambridge Phil. Soc. 



