SECT, xxn.] DISCOVERY OF POLARIZATION. 219 



plate both rays will be reflected in the same plane, and 

 consequently will produce coloured rings by their inter- 

 ference. 



It is evident that a great deal of the light we see must 

 be polarized, since most bodies which have the power of 

 reflecting or refracting light also have the power of polar- 

 izing it. The blue light of the sky is completely polarized 

 at an angle of 74 from the sun in a plane passing through 

 his centre. 



A constellation of talent almost unrivalled at any period 

 in the history of science has contributed to the theory of 

 polarization, though the original discovery of that property 

 of light was accidental, and arose from an occurrence which, 

 like thousands of others, would have passed unoticed, had it 

 not happened to one of those rare minds capable of drawing 

 the most important inferences from circumstances ap- 

 parently trifling. In 1808, while M. Malus was accidentally 

 viewing with a doubly refracting prism a brilliant sunset 

 reflected from the windows of the Luxembourg Palace in 

 Paris, on turning the prism slowly round, he was surprised 

 to see a very great difference in the intensity of the two 

 images, the most refracted alternately changing from bright- 

 ness to obscurity at each quadrant of revolution. A phe- 

 nomenon so unlocked for induced him to investigate its 

 cause, whence sprung one of the most elegant and refined 

 branches of physical optics. 



