THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



MARCH 1481. 



XXXII. On certain points in the Theory of Undulations, re- 

 lated to the Hypothesis of the Symmetrical Arrangemejit of 

 the Molecules. By the Rev. Baden Powell, M.A., F.R.S.y 

 4'c.y Savilian Professor of Geometry, Oxford*. 



(1.) AMONG the numerous and important accessions 

 '^^*- which have of late yeai's been made to our know- 

 ledge of the theory of light, and the chief of which have from 

 time to time found a place in the pages of this Journal, not 

 the least valuable have arisen out of the free discussion of 

 points of difficulty or objection, whether affecting the stability 

 of the theory itself, or referring to the structure of some of its 

 subordinate parts. 



Among such topics, my present remarks relate to one 

 which some time since struck me as of peculiar importance ; 

 originating in the first instance in the researches of Mr. Tovey 

 on elliptic polarizationf, and further illustrated by several 

 communications from Sir J. Lubbock if, yet involved in some 

 difficulties, from which I do not think anything hitherto pub- 

 lished has completely relieved it. 



(2.) More precisely: Mr. Tovey's investigation § involves an 

 important principle, viz. the existence of a relation betw^een 

 the peculiar supposed arrangement of the molectdes of the 

 oetherial medium in space, and the nature of the vibration as 

 elliptic or rectilinear. The character of such arrangement is 

 indicated mathematically by the presence or evanescence of 

 certain terms in the differential equations. These terms had 



• Coniinunicated by the Author. 



t L. & E. r^liil. Mag. vol. xii. No. 71. Jan. 1838. 



X Vol. xi. No. m. Nov. 18:57; Vol. xii. No. 71. Jan. 1838; Vol. xv. 

 No. 97. Nov. 1839. 



§ While this sheet was passing through the press I have been infonnetl 

 by a friend, that Eresnel adverts to a similar principle, but the time docs 

 not allow of my referring to it now more particularly. 



Phil. Mag. S. 3. Vol. 18. No. 1\6. March 1841. M 



