102 



NEW PROPERTY OV REFLECTED liTGHT. 



Light f.om 

 the partial re- 

 flection of 

 opake bodies. 



Reflection 



frcm TnetalUc 

 mirrors. 



liP^akes a sensible angle wiih the principal section. If the 

 ray jubt mentioned be made to fall in this plane, under an 

 angle of 56" 30', or near it, it will comport itself at the 

 first surfdce as hi the precedmij caae, it will traverse it 

 without any reflection : but at the second surface it will be 

 reflected in two pencils, which will attain their maximum 

 of intensity, when the plane of incidence is perpendicular 

 to the principal section. 



■ ''It is obvious, that the light reflected at the second face 

 does not comport itself here as in the preceding case, be- 

 cause in the first experiment the incident ray refracted and 

 reflected is still in the same plane, while in the last the 

 repulsive force, that produces the extraordinary refraction, 

 turns the light away from the plane of incidence, so that it 

 ceases to be similarly circumstanced with respect to tht; 

 forces that act on it. 



Jf we examine the light that proceeds from the partial 

 reflection of opake bodies, as black marble, ebony, &c., we 

 shall equally find an angle, at which this light enjoys the 

 properties of that which has traversed a crystal of Iceland 

 spar. Polished metals appear to be the only reflecting 

 substances, that do not seem capable of producing this 

 phenomenon: but, if they do not impress this p^icuiiar 

 disposition on luminous rays, they do not alter it, when they 

 have already acquired it by the influeuce of another sub-r 

 stance. -* 



This property is preserved also by penpils, that traverse 

 substances which refract light siiigly. 



In the second part of this paper* I shgll describe the 

 circumstances, under which, by means of reflection frona 

 metallic mirrors, the mutual disposition of the particles of a 

 ray, either ordinary or extraordinary, may be so changed, 

 that some shall always be refracted ordinarily, while the 

 others are rtfracted extvaordlnafijy. The examination of 

 these different circumstances m\[ lead us to the law of these 

 phenomena, which depends on a general, property of the 

 fepulsive forces that act on light. 3 . 



This will appear in our next, C. 





Bii: .•jivav-v-fi.- 



IV, 



