no 



and, notwithstanding its being partially anticipated by Poinsot, is 

 well worthy of publication-. 



" In his course of lectures on Attractions he gave some very 

 beautiful theorems respecting the attraction of a body of any nature 

 and form, on a point distant a long way in comparison of its own 

 dimensions; by an original and very ingenious method, he deduced 

 the beautiful theorem of Chasles on the attractions of any two con- 

 focal ellipsoids on the same external point; and subsequently apply- 

 ing his results to the problem of the figure of the earth, he deduced 

 with ease the well-known and celebrated theorem of Clairaut. 



" In the same course of lectures he gave also some most simple 

 and elegant geometrical methods for finding the laws of attraction 

 of an homogeneous ellipsoid on any internal point, with several 

 other ingenious and beautiful theorems, which it would be tedious 

 to particularize. The subject of attractions seems indeed to have 

 been a favourite one with him ; on several previous occasions in 

 the course of his lectures he gave new and beautiful theorems in 

 it, and in many important respects improved the existing theories, 

 keeping always in advance of the knowledge of his time. . . . 



" I now come to his great course of lectures on ' The Dynamical 

 Theory of Light,' the unaided creation of his own surpassing ge- 

 nius, and to the statement of the single and simple hypothesis 

 upon which, as a basis (to borrow the language of Dr. Lloyd 

 when speaking of Fresnel's beautiful theory of double refraction), 

 Professor Mac Cullagh ' has reared the noblest fabric which has 

 ever adorned the domain of physical science, Newton's system of 

 the universe alone excepted.' When I say that I think Professor 

 Mac Cullagh ranks as a "philosopher higher than Fresnel in the 

 region of Light (and if that be admitted he will certainly rank 

 inferior to none on that subject), I do not at all institute any com- 

 parison between labours so different in their nature as those of 

 these two great men. Professor Mac Cullagh, I conceive, stands 

 to Fresnel in the same relation as Newton to Kepler. The latter, 

 undoubtedly, discovered all the elegant laws of the propagation 

 and double refraction of light in crystallized media, as well as 

 those of ordinary with some of those of total reflection at the 

 bounding surfaces of ordinary media, but he did not account for 



