Rotational Optical Activity in Isotropic Media. 999 

 o£ — ; while the second, in' which E Z2 — iE^=0, is propa- 



gated with a velocity equal to the real part of — . The 



result is that at a depth z into the medium from the place 

 of entry of this beam the amplitudes in the respective 

 components are 





E . 



-2 



in(t- 



~Ee K 



£15) 



Ez/i 



-~ 2 * 



and 



%r 



=1 



Ee 



> 



^ 



as >•»(<- f) 



so that 



in all 

















E, 



-2^ 



m(#- 



?i«\ 



> 



and 





E, 



~~ 2 



(/ 



(, si* 



v c 



> 



and therefore 



















e 



Q2 Z 

 -in ~^~ 



■ Q-2Z 

 c 



— *» O 



+ e 



c 



— e 











= tan 



/■«;- 



■«*«v 



2c 



This shows that, if the imaginary parts of ft and ft are the 

 same, then the beam of light is still plane polarized even at 

 this depth, but the plane of polarization has been turned 

 through an angle 



nz , . 



This is the case when the absorption of the two beams is the 

 same, which in reality only occurs when there is no absorp- 

 tion at all. In every other case the light is elliptically 

 polarized, but the rule of rotation of the major axis is always 

 verv approximately determined by the real part of (ft — ft) • 

 We need not here enter further into the details of this 

 analysis, which are fully dealt with in most text-books *. 

 In any case the complete circumstances are determined when 

 we know (ft — #2) andean effect its separation into real and 

 imaginary parts. 



* See for example Voigt, ' Magneto- u. Elektro-optik,' pp. .32-34. 



3U2 



