ON LIGHT. 347 



then, that the glass makes one entire revolution, the reflected 

 light will have two maxima answering to the positions N. and 

 S. and two absolute minima answering to the positions E. and 

 W, The transmitted light, and that which is refracted in the 

 ordinary manner by the rhomboid, have two minima answering 

 to the positions N. and S. and two maxima answering to the 

 positions E. and W. but the light refracted extraordinarily has 

 four absolute minima answenng to the positions N. S. E.and 

 W. and four maxima answering to the positions NW. SE. NE. 

 and SW. 



In the place of the moveable glass, but under exactly the A metallic 

 same circumstances, let a metallic mirror be substituted, ^f ™"^[jjgj" J,^'" 

 which the plane or incidence constantly makes an angle of A5'^ of the second 

 with that of the meridian. When this mirror is inclined only S'^^*- 

 a few degrees witii regard to the horizon, the light which it 

 reflects is entirely polarised, like the incident light with regard It polarises the 

 to the plane of the meridian. Jf the inclination be auginented, stri'idn^e \liU 

 it reflects, first, a certain quantity of light polarised with regard ations, govern- 

 to the plane of the meridian 5 secondly, another quantity cf^j. eflgai'oa* 

 light polarised with regard to the plane of incidence j and, ■' 



lastly, a certain inclination may be attained, by which the light 

 is completely polarised with regard to the plane of incidence. 

 Beyond this limit, the light polarised with regard to the piano 

 of the meridian begins to reappear, and the intensity of the 

 light polarised with regard to the plain of incidence, diminishes 

 until the mirror becomes vertical. Metallic bodies act, there- 

 fore, exactly in the same manner as transparent bodies on the 

 light which they reflect; but tran'^paient bodies totally trans- 

 mit the light which they polarise in one direction or manner, 

 and reflect that which is polarised in a contrary manner, while 

 metallic bodies reflect the light which they have polarised in 

 both directions or manners. 



The facts contained in this memoir point out the methods to 

 be followed, in order to obtain, in the dilTerent cases, an exact 

 measure of the phenomena. They resolve all that is proble- 

 matical in this theory, and establish, in a decided manner, the 

 following consequences — 



That all bodies in nature, without exception, polarise com- All bodies pa- 

 pletely the light which they reflect under a determined angle. LmThe'efffc^t'^*- 



That is governed hy 



