CIRCULAR POLARIZATION. 



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other means by which to produce circular polarization ; 

 and, as usual, a remarkable discovery was the reward of 

 these efforts. This discovery may be announced in two 

 words ; there is a partmdar kind of double refraction 

 which communicates to rays circular polarization, as the 

 double refraction of Iceland spar communicates the com- 



The mechanical conception of two rectilinear vibrations at right 



angles compounded, giving an elliptical or circiilar vibration, may be 

 illustrated by a very simple contrivance, which may be described as 

 follows : — 



On any convenient support, there projects an arm terminating in 



