PROCEEDINGS 



OF 



THE ROYAL IRISH ACADEMY. 



1841. No. 31, 



November 8. 



SIR Wm. R. HAMILTON, LL.D., President, in the Chair. 



John H. Jellett, Esq., F. T.C.D., w'as elected a member 

 of the Academy. 



A letter was read from Dr. Orpen, stating that increas- 

 ing ill health would not allow him to continue to discharge 

 his duties to the Academy, and tendering the resignation 

 of his office of Treasurer, and of his place as a member of 

 Council. 



Resolved, — That the Academy have heard Dr. Orpen's 

 communication with much regret, and that they deeply la- 

 ment the cause which deprives them of his valuable services. 



Professor Mac Cullagh read the following notes on some 



points in the Theory of Light. 



I. 



On a Mechanical Theory which has been proposed for the 

 Explanation of the Phenomena of Circular Polarisation 

 in Liquids, and of Circular and Elliptic Polarization in 

 Quartz or Rock-crystal ; with Remarks on the correspond- 

 ing Theory of Rectilinear Polariisation. 

 The theory ofelliptic polarization, which I feel myself called 



upon to notice, was first stated by M. Cauchy, and has been 



VOL. II. N 



