!9EW PROPE&Tif OF RE&LJECTED HGSTo §5 



iiL 



t)rt d P'ropeTtij of refiected Light : by Mr, Malus*. 



HEN a solar ray is reflected, or reTracted, it retains jj^j^g^^g^j ^^^ 



in general its phj'sical properties ; and if it be Subjected to retVacied ra^§ 



i .., ,^ .. . •. If. • it c -i generally sinii* 



ne,w trials, it comports itself in the same manner, as if »t fat to 'dire'ctj 



iisued directly from thelumiiibiis body. The prism, while 



It disperses the coloured rays, only changes their respective 



directions, without altering theii* nature. There are cir- buttiotalvriVgi 



cumstances however, in which the influence df certain bodies 



impriesses on the rays they reflect, or refract, characters and 



properties which they carry with them, and by which tliey 



4rie essentially distinguished from direct light. 



The property of light I am about to describe is a modifi- Douiiie fe- 

 cation of this kind. It had already been perceived in a fracuoii. 

 particular circumstance of the doubling of images exhibitied 

 h^ calcareous sp;ir: but, the phenomenon iesulting from it 

 having been ascribed to the properties of this crystal, rid 

 one suspected, that it niight be produced, not only by all 

 bodies that afford a double refraction, but by all other dia- 

 phanous substances, whether solid or liquid, and fcven by 

 bpake bodies. 



If a ray of light be received perpendicularly on the face ArayoHrgfil 

 of a rhomboid of calcareous spar, this ray is divided into ''^c^'^®^ o*^ ., , 

 IWo pencils, one continued in the direction of the incidental -^^ divided iritS 

 rays, the other making with it ah angle of a few degrees. The two^ 

 plane that passes through these two rays has several peculiar pjahe of the 

 prdperties, and is called the plane of thie principal section, principal set; 

 tt is always parallel to the axis of the integrant particles through thStil- 

 bf the crystal, and perpendicular to the natural and artificial 

 refractive surface. "When the incident ray is inclined to -j-hfe rays re- 

 the refractive surface, it is equally divided into ttvo pencils; fracied ordJ- 

 One refracted according to the ordinary law, and the other "raordinarU^i^ 

 according to an extraordinary law, which depend on the 

 angles that the incident ray forms with the refractive sur- 

 face and the principal section. When the face of emergence 

 is parallel to that of incidence, the two emergent rays are 



» M6in. de la Soc. tl' Arcueil, voL 11^ p. 143, 



parallel 



