Ber: 
215 
titled to assume henceforth a very high rank among the principles 
of physical optics. 
The method which Mr. Mac Cullagh has adopted may be said 
to be in general the method of mathematical induction, as distin- 
guished from dynamical deduction. He has not sought to deduce, 
from any pre-supposed attractions or repulsions, and arrangements 
of the molecules of the ether, any conclusions respecting the vibra- 
tions in the interior or at the boundaries of a medium, as necessary 
consequences of those dynamical principles or assumptions. But 
he has sought to gather from phenomena a system of mathematical 
laws by which those phenomena might be expressed and grouped 
together, be conceived in connexion with each other, and receive 
an inductive unity. He has sought to arrive at laws which might 
bear somewhat the same relation to the optical observations already 
made, as the laws of Kepler did to the astronomical observations of 
his predecessor Tycho Brahe, without seeking yet to deduce these 
laws, as Newton did the laws of Kepler, from any higher and 
dynamic principle. And though, no doubt, it is to such deduction 
that science must continually tend ; and though, in optics, some 
progress has been actually made, by Cauchy and by others, toa 
dynamical theory of light, as a system of vibrations regulated by 
forces of attraction and repulsion ; yet it may well be judged a 
matter of congratulation when minds are found endowed with 
talents so high as those which Mr. Mac Cullagh possesses, and 
willing to apply them to the preparatory but important task of dis- 
covering, from the phenomena themselves, the mathematical laws 
which connect and represent those phenomena, and are in a manner 
intermediate between facts and principles, between appearances and 
causes. : 
It was thus, that, in a former paper, Mr. MacCullagh proposed, 
as mathematical expressions for the phenomena of Quartz, a system 
of differential equations, which are indeed simple in themselves, 
and seem to agree well with observation, but have not yet been 
shewn to be consistent with dynamic views. And in that later 
memoir for which the present prize is awarded, he has, in like 
manner, adopted some hypotheses, and rejected others, without 
apparently regarding whether and how far it may seem possible 
