Iceland Spar in Electricity History

[Ya Sam]

1669 a transparent crystal from Iceland was sent Erasmus Bartholin 
(1625-1698) who noted that objects seen through it appeared double.  A 
century later Thomas Young suggested that two light rays polarized at right 
angles to each other must be refracted at different angles.  It is currently 
understood that such materials as Iceland Spar (sample at left) have 
electric charge distributions in their crystal lattices which slow light 
waves of polarity aligned with one dimension by a different amount than 
light waves with perpendicular polarity.  As a result half of the light is 
refracted at one angle while the remainder of the light is refracted in a 
different direction.  Notice light from the text is split different 
directions by the Iceland Spar making duplicate new and speak.  This 
provides evidence that light must be a transverse wave.

William Nicol (1768-1851) found that two crystals of Iceland Spar attached 
together could be used to measure the angle of polarization of compounds.  
But such devices were very expensive.  Edwin Land, (1909-1991) when a 
Harvard freshman, conceived the idea that a comparable polarizer might be 
made by aligning tiny crystals (iodoquinine sulphate) embedded in 
transparent plastic, an idea which he patented in 1929.  Light of one 
polarity is absorbed while that perpendicular passes through.  Such film 
made by Land's Polaroid Corporation can be obtained in Polaroid sun glasses. 
  (Land and his Polaroid Corporation later invented cameras that produce 
self-developing photographs and ultra-sonic range finders used for 
self-focusing cameras.  Land trailed only Thomas Edison in the number of 
patents;  Land received 535.)

http://homepage.mac.com/dtrapp/ePhysics.f/labIV_5.html

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