Intelligence and Miscellaneous Articles. 40 1 



angles, the rings would be seen with centre white; when equal to 

 the other polarizing angle, the rings would disappear ,- and beyond 

 this the rings would again be seen witii centre black." The paper 

 now read, contained an account of experiments made with a lens 

 of glass placed upon a plate of diamond. A theoretical calculation 

 was given to show that the rings, when the angle of incidence was 

 between the two polarizing angles, must be extremely faint ; and 

 that the combination of a plate of tourmaline with a doubly-refract- 

 ing prism would be necessary to exhibit them in sufficient purity. 

 Other precautions would also be necessary for the destruction of 

 the light reflected at the upper surface of the lens, &c. The author 

 then described in detail the appearances which lie observed. While 

 the angle of incidence was less than the polarizing angle of the 

 glass, the centre of the rings was black; when equal to that angle, 

 the rings disappeared: beyond it their centre was white ; and be- 

 yond the maximum polarizing angle of the diamond their centre 

 was black. Tiie author considered that the agreement of these re- 

 sults with the theoretical anticipations aHordcd strong evidence of 

 the general correctness of Fresnel's theory of reflection, and its 

 perfect accuracy (as far as the senses can judge) with regard to 

 reflection from glass. But in one respect there was a very curious 

 deviation from theory. When the angle of incidence approached 

 the maximum polarizing angle of the diamond, the rings, though 

 very faint, did not disappear; but the white- centred rings were 

 changed into black-centred rings by the contraction of all the rings, 

 the first black ring contracting so far that the white spot disap- 

 peared, and the black ring became the central spot. This showed 

 that on increasing the angle of incidence by a few degrees, the 

 plane of undulation in the plane of reflection was retarded by nearly 

 180°. From this and other pha^nomena the author concluded, that 

 the nature of reflection from the surface of diamond is different 

 from that of any other reflection ; that up to a certain angle it most 

 resembles reflection from metals: through a small angle it has the 

 peculiar property d'jscribed above; and beyond this it does not 

 sensibly differ from reflection at the surface of glass. These con- 

 clusions, he observed, do not coincide witii those of Sir David 

 Brewster. 



LIX. Intelligence and Miscellaneous Articles. 



biei.a'.s comkt. 



THIS connt, who.se return was jjredicted in the present year and 

 in the present month, has created almost as mucli alarm in the 

 country as the dreadful ravages of the cholera, in consequence of the 

 publication o^' some wild s|)eculations relative to tlic probability of its 

 encountering the eai til in its progress, and involving us in one gene- 

 ral ruin. Tiie eyes of all the astronomers in Europe have been, for 

 this month past, directed towards that quarter of the heavens, in \\hich 

 it was ex|)ected to be first visible, but witiiout success, — if wc except 

 Third Series. Vol. 1 . No. 5. Nov. 1 832. 3 F 



