DOUBLE REFRACTION. 127 



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 

 separated at its entrance into two component movements, which 

 will advance with different velocities. The two component vibra- 

 tions, 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 phe- 

 nomena, 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. Wollaston 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, appear- 

 ing 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.! Similar obser- 

 vations were afterwards made by M. Cordier and the Count de 

 Bournon. 



The next step of any importance in this new field of research 



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

 M. Lame 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 the spectrum. 

 Ann. Chim., torn. Ivii. 



t Phil. Trans. 1804. 



