REFRACTIVE POWER. ~ 189 
“To apply thus, without any limitation on its general- 
ity, calculation to phenomena ;—to deduce, from a single 
consideration of a very general kind, all the solutions 
which before were only obtained from particular consid- 
erations,—is truly to write a treatise on analytical optics, 
which, concentrating the whole science in a single point 
of view, cannot but contribute to the extension of its do- 
main.” 
The Academy decided (which is the highest degree of 
approbation it can bestow) that the memoir of Malus 
should be printed in the Recueil des Savants Etrangers.* 
MEMOIR ON THE REFRACTIVE POWER OF OPAQUE 
BODIES. 
On the 16th November, 1807, Malus presented to the 
Academy a memoir in which he treats a point of optics 
of great importance, a question, in fact, involving no less 
* Malus’s analytical theory contained in his Traité d’ Optique, is pre- 
fixed to his prize memoir on Double Refraction, Paris, 1810. 
The ordinary deviations by reflexion or refraction which rays un- 
dergo on impinging on given surfaces, may be investigated in all the 
simpler cases by means of elementary geometrical constructions, lead- 
ing to the theory of foci, caustics, &e. But more general investiga- 
tions of the same kind have been pursued by considering the algebraic 
equations of rays undergoing such deviations, This higher generaliza- 
tion leads to, and includes, the same results. An excellent discussion 
of the subject treated in this point of view will be found in Dr. Lloyd’s 
Treatise on Light and Vision. It is a still higher generalization of this 
kind which was followed out by Malus. The reader who is desirous 
of seeing a condensed abstract of the leading mathematical principles 
involved, is referred to a brief but luminous summary drawn up by 
the Rev. A. Neate, M. A., and inserted in Professor Powell’s Elemen- 
tary Treatise on Optics, p. 71, Oxford, 1833. But the entire subject 
has been treated by a far higher analysis with extreme generality, and 
by a new and powerful principle of his own, by Sir W. R. Hamilton, 
in his essay on the Theory of Systems of Rays. Mem. of R. Irish Acad- 
emy, vols. xv. and xvi., and Supplement, vol. xviii Translator. 
