432 



POLARIZATION. 



D 



with the reflecting surface an angle of 35 25' (angle of 

 incidence = 54 35'). 



612. Malus's Polariscope. This instrument has 



two reflectors made of 

 bundles of glass plates. 

 Of these, A is called 

 the polarizer and B the 

 analyzer. Both reflect- 

 ors turn upon horizon- 

 tal axes ; B also turns 

 upon a vertical axis by 

 means of the horizontal 

 circles CO. When A 

 and B are placed at the 

 polarizing angle with 

 the vertical axis, a beam 

 of light is made to fall upon the polarizer in such a direc- 

 tion that the reflected light will pass vertically upward to 

 B. This reflected light will be polarized. The polarized 

 light will be reflected by B when the second reflector is 

 parallel to the first (Fig. 343) ; it will be absorbed or 

 transmitted when B is perpendicular to A (Fig. 342). 



(a.) Place B as shown in Fig. 343. Throw a beam of light upon 

 A, the room being darkened. The light reflected from S will form 

 a white spot upon the side of the room. Turn the collar C slowly 

 around. The spot of light will move around the sides of the 

 room gradually growing fainter. When C has been turned a 

 quarter way around (Fig. 342) the spot has wholly disappeared. 

 Beyond this it grows brighter until C has been turned half way 

 around, when it is as bright as at the bginning. When C has 

 been turned three-quarters around, the spot again disappears, 

 again reappearing as C and B are brought to their original 

 positions. 



FIG. 342. 



FIG. 343. 



