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BELL SYSTEM TECHNICAL JOURNAL 



through them because the second sheet can transmit none of the vibrations 

 transmitted by the first sheet. As we rotate the second sheet back from 

 complete extinction to "best transmission" the transmitted Hght increases 

 sinusoidally. In any such arrangement as Fig. 2.20 the first sheet is called 

 the polarizer, the second is called the analyzer. The name analyzer is 

 chosen because light that can be extinguished by means of a suitably ro- 

 tated analyzer must be plane polarized, and it must be vibrating at right 

 angles to the transmission vibration direction of the analyzer when set for 

 extinction. The transmission vibration direction of a polaroid plate will 

 hereafter be called its vibration axis. 



Let us go back to Fig. 2.19 and cut out from around the point p, the small 

 tangential crystal plate shown magnified in Fig. 2.21. Here p is the direction 

 of propagation as before, and z is parallel to the optic axis. Also s which is 



UNPOLARIZED 

 OR PLAIN 

 LIGHT 



POLARIZED 

 LIGHT VIBRATING 

 VERTICALLY 



Fig. 2.20 — -Light polarization 



in the plane of p and z, is the direction of slow vibration while / which is 

 perpendicular to this plane is the direction of fast vibration. The vibra- 

 tion frequency is really the same for both. "Slow vibration" means "vi- 

 bration direction for slow transmission." All directions of propagation 

 that have this vibration axis have the same velocity. 



In Fig. 2.22 we have placed this plate between " crossed polaroids" — that 

 is polaroids set for extinction. The slow direction makes an angle a with 

 the polarizer vibration axis. When this vertical-polarized ray of intensity 

 / enters the crystal it breaks up into components, one of intensity: 



and one of intensity 



/ cos a vibrates along s 



I sin a vibrates along/ 



(2.1) 



(2.2) 



as illustrated in Fig. 2.23. 



