Notes on some Points in the Theory of Light. 201 



incline to think I did ; but I have a distinct recollection of having* 

 done so on the second occasion, in reply to questions that were 

 asked me by some Members of the Association.* Now, my first 

 attempt to explain those equations, which was made almost as soon 

 as I discovered them, actually turned upon the very idea which 

 about the same time found entrance into the mind of M. Cauchy 

 I mean the idea of an unsymmetrical arrangement of the ether. 

 For as it was generally believed, at that period, that the hypothe- 

 sis of ethereal molecules symmetrically distributed had led, in the 

 hands of M. Cauchy, to a complete theory of rectilinear polari- 

 zation in crystals,f the notion of endeavouring to account for the 

 phenomena of elliptic polarization, by freeing the hypothesis from 

 any restriction as to the distribution of the ether, would natu- 

 rally occur to anyone who was thinking on the subject, no less 

 than to M. Cauchy himself. And though, for my own part, 

 I never was satisfied with that theory, which seemed to me to 

 possess no other merit than that of following out in detail the 

 extremely curious, but (as I thought) very imperfect, analogy 

 which had been perceived to exist between the vibrations of the 

 luminiferous medium and those of a common elastic % solid (for 



* At the period of this meeting, M. Cauchy's letter on Elliptic Polarization had 

 been published for some months ; but I was not then aware of its existence. Indeed 

 the letter appears not to have attracted any general notice ; for the theory which it 

 contains was afterwards advanced in England as a new one, and M. Cauchy has 

 been lately obliged to assert his prior claim to it, through the medium of Professor 

 Powell. See notes, pp. 196, 202-3. 



t See his Exercises de Nathematiqites, Cinquieme Annee, Paris, 1830, and the 

 Memoires de I'lnstitut, torn. x. p. 293. 



J The analogy was suggested by the hypothesis of transversal vibrations, which, 

 when viewed in its physical bearing, was considered by Dr. Young to be "perfectly 

 appalling in its consequences," as it was only to solids that a "lateral resistance" 

 tending to produce such vibrations had ever been attributed. (Supplement to the 

 Encyclopaedia Britannica, VOL. vi. p. 862, Edinburgh, 1824.) He admits, how- 

 ever, that the question, whether fluids may not "transmit impressions by lateral 

 adhesion, remains completely open for discussion, notwithstanding the apparent 

 difficulties attending it." As far as I am aware, Fresnel always regarded the 

 ether as & fluid. M. Poisson affirms that it must be so regarded, and attributes its 

 apparent peculiarities to the immense rapidity of its vibrations, which does not 



