168 [June 19, 



some part or other of the long spectrum a band of absorption, or 

 maximum of opacity, occurs ; and the position of this band affords 

 a highly distinctive character of the substance which produced it. 



Among natural crystals, besides the previously known yellow 

 uranite, the author found that in adullaria, and felspar generally, a 

 strong fluorescence is produced under the action of the rays of high 

 refrangibility, referable not to impurities, but to the essential con- 

 stituents of the crystal. A particular variety of fluor-spar shows 

 also an interesting feature, though in this case referable to an im- 

 purity, exhibiting a well-marked reddish fluorescence under the 

 exclusive influence of rays of the very highest refrangibility. This 

 property renders such a crystal a useful instrument of research. 



With some metals broad, slightly convex electrodes were found to 

 have a great advantage over wires, exhibiting the invisible lines far 

 more strongly, while with some metals the difference was not 

 great. 



The blue negative light formed when the jar is removed, and the 

 electrodes are close together, was found to be exceedingly rich in 

 invisible rays, especially invisible rays of moderate refrangibility. 

 These exhibited lines independent of the electrodes, and therefore 

 referable to the air. This blue light has a very appreciable duration, 

 and is formed by what the author calls an arc discharge. 



The paper concludes with some speculations as to the cause of the 

 superiority of broad electrodes, and of the heating of the negative 

 electrode. 



XI. " On the Reflexion of Polarized Light from Polished Sur- 

 faces." By the Rev. SAMUEL HAUGHTON, M.A., F.R.S., 

 Fellow of Trinity College, Dublin. Received June 9, 1862. 



(Abstract.) 



When a plane-polarized beam of light is incident on a polished 

 surface at a certain angle of incidence, and polarized in a certain 

 azimuth, the reflected beam of light is circularly polarized. 



The tangent of this angle of incidence is called by the author the 

 Coefficient of Refraction, and upon it appears to depend the brilliancy 

 of a polished surface. 



