82 , Memoir on New Optical Vhenomena. [Feb. 



incident light. In the intermediate positions the reflection will be 

 more or less complete, according as the reflected ray approaches 

 more or less to the plane of the meridian. In these circumstances, 

 though the reflected ray acts so very different a part, it preserves 

 always the same inclination with respect to the incident ray. We 

 sec iiere, therefore, a vertical ray of light, which lulling upon a 

 diaphanous body acts in one way when the reflecting face is turned 

 to the north or south, and in a different way wlien that face is 

 turned towards the east or west, though these faces form always the 

 angle 35° 25' with the vertical direction of that ray. These obser- 

 vations lead us to conclude tliat the liglit acquires, in these circum- 

 stances, properties independent of its direction with respect to the 

 reflecting surface, and cormectcd solely with the sides of the vertical 

 ray, which are the same for the north and south sides, and different 

 for tlie east and west sides. Giving to these sides the name of poles , 

 I shall call the modification whicii gives to light properties relative 

 to these ^o\es polarizal ion. I have hitherto hesitated to admit this 

 term into the descriptions of tlie physical phenomena here de- 

 scribed. I did not venture to introduce it into the Memoirs in 

 which I published my first experiments ; but the varieties which 

 this new kind of phenomenon present, and the difficulty of de- 

 scribing them, oblige me to admit this new expression, which sig- 

 nifies simply the modification which light has undergone in 

 acquiring the new properties which are not relative to the direction 

 of the ray, but only to its sides considered at right angles, and in ai 

 plane perpendicular to its direction. 



I now pass to the description of the phenomenon which consti- 

 tutes the object of this memoir. Let us consider anew the appa- 

 ratus of which I have just spoken. If we present to the solar ray 

 which has traversed the first glass, and of which a part has been 

 reflected, a silvered mirroi which will reflect it downwards towards 

 the ground, we obtain a second vertical ray, which has properties 

 analogous to tiiose of the first, but in a direction exactly opposite. 

 If we present to this ray a glass forming with its direction an angle 

 of 35° 25', and if without changing this inclination we turn the 

 fitces alternately to the north, east, south, and west, we shall 

 observe the following phenomena. There will always be a certain 

 quantity of light reflected by the second glass ; but this quantity 

 will be much less when the faces are turned to the south and north 

 that! when they are turned to the east and west. In the first vertical 

 niy we observed exactly the contrary. The minimum of reflected 

 light was- when the second gla_-s was turned to the east aud west. 

 Therefore if we abstract in the second ray that portion which acts 

 -as ordinary light, and which is equally reflected in all directions of 

 the face, we see that this vay contains another portion of light 

 Tvhich is polarized exactly in the opposite way of the vertical ray 

 reflected by the first glass. In this experiment I employ a silvered 

 Hiirror merely to dispose the two rays parallclly, and in the same 



