213 



to deliver on the occasion of first taking the chair of this Academy : 

 the only difference, indeed, so far as science is concerned, being 

 the subsequent adoption of a suggestion of Professor Lloyd, re- 

 pecting a change of distribution of those subjects which were in- 

 cluded by me under the two great heads of Physics and Physio- 

 logy, but by him under those of Experimental and Observational 

 Science, or Physics and Natural History. The time for acting 

 upon this modification has not, however, as yet arrived; and be- 

 fore the suffrages of your Council were collected, at its last meet- 

 ing, on the question of the absolute and relative merits of the 

 various communications which have lately been made to our Trans- 

 actions, it was resolved to postpone, till after the recess, the con- 

 sideration of all scientific or other awards, except only that which 

 should be made for the most important paper in pure or mixed 

 mathematics, communicated during the three years which ended 

 in March 1837, and already actually printed. The papers coming 

 within this definition were few ; the authors of them were only two, 

 Professor Mac Cullagh and myself. The decision, which in theory 

 is a decision of the President and Council, and which did in fact 

 receive my cordial and previously expressed concurence, was in 

 favour of Mr. Mac Cullagh's paper " On the Laws of Crystalline 

 Keflexion and Eefraction," contained in the just published part of 

 the eighteenth volume of the Transactions of this Academy. 



It may happen that upon future occasions of this sort, if it shall 

 again become my duty to present from this Chair those Medals 

 which may hereafter be awarded, for papers of other triennial cycles, 

 and upon other subjects, I may not think it necessary or expedient 

 to occupy your time by any but the briefest statement of the 

 grounds on which those future awards may have been made. But 

 on the present occasion, which is (to me at least, and in relation 

 to our new plan) the first occasion of its kind ; while the subject 

 is one of a class to which my own inquiries have been much di- 

 rected, and upon which, therefore, I may speak with a less risk of 

 impropriety than upon many others ; and while we, as an Aca- 

 demy, by extra hours and extra nights of attendance, during that 

 busy session which is now about to close, have earned for ourselves 

 a little leisure, on this last night of meeting, without interfering (as 



