per itn 
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 
Reflexion and Refraction,” 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, 1 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 
