REPORT ON PHYSICAL OPTICS. 393 



the ether is repulsive, M. Lam^ concludes also from the exa- 

 mination of the same case, that the retardation of the vibratory 

 motion, in penetrating into a dense body, will be greater, the less 

 the length of an undulation ; so that the refraction will be greater 

 for waves of shorter length. This he conceives to be the true 

 explanation of the phenomenon of dispersion. 



M. Lame has likewise endeavoured to connect the phenomena 

 of double refraction with an assumed constitution of the ethereal 

 fluid. He takes the case in which the ether is supposed to be 

 distributed round the molecules of the body in confocal ellip- 

 soidal shells ; and he concludes that a vibratory movement, 

 propagated from vacuum into a body so constituted, will be se- 

 parated at its entrance into two component movements, which 

 will advance with different velocities. The two component 

 vibrations, he finds, will be at right angles, and parallel to the 

 lines of greatest and least curvature of the elementary ellipsoids. 

 Thus, the bifurcation of a ray of light on entering a crystallized 

 medium, and the opposite polarization of the two pencils, are 

 found to be consistent with a molecular constitution such as that 

 described. 



These results are of the highest interest ; and will, no doubt, 

 receive an early examination from those engaged in the same 

 department of analysis. Their author seems to be persuaded 

 that his methods will lead him to the mathematical laws of other 

 phenomena, which he conceives to depend, in like manner, on 

 the motions of the ethereal fluid*. 



I cannot close this division of the present Report without 

 referring to the phenomena of absorption by crystallized media, 

 although the laws of these phenomena are as yet wholly without 

 the pale of theory. Dr. WoUaston seems to have been the first 

 who noticed any facts connected with this interesting subject. 

 The absorbing properties of crystals were found to vary with 

 the direction ; certain crystals of palladium, for example, ap- 

 pearing of a deep red colour when viewed along the axis, and of 

 a yellowish green in a transverse direction. Tourmalines were 

 observed also to possess analogous properties f. Similar observa- 



• In a continuation of this memoir, recently read to the French Academy, 

 M. Lam6 has considered particularly the mode of vibration of the particles of 

 the ether which are disposed round the ponderable particles of body in concentric 

 spherical shells of decreasing density. Transparent homogeneous bodies are 

 supposed to consist of a multitude of such particles distributed uniformly in 

 space, and at distances incomparably greater than their diameters; and he 

 conceives that the waves propagated from the particles adjoining to the surface 

 of emergence will, by their interference, give rise to phenomena resembling the 

 fixed lines in tlie spectrum. Ann. Chim., torn. Ivii. 



t Phil. Trans. 1804. 



