PHENOMENA OF DIPOLARIZED LIGHT. 83 



perty, which seemed to require for its very conception a crystalline 

 structure in the body, belonged nevertheless to several fluids, and in 

 different directions for different fluids. Oil of turpentine, and an 

 essential oil of laurel, gave the plane of polarization a rotation to the 

 left hand ; oil of citron, syrup of sugar, and a solution of camphor 

 gave a rotation to the right hand. Soon after, the like discovery was 

 made independently by Dr. Seebeck, of Berlin. 



It will easily be supposed that all these brilliant phenomena could 

 not be observed, and the laws of many of the phenomena discovered, 

 without attempts on the part of philosophers to combine them all 

 under the dominion of some wide and profound theory. Endeavors 



1 / 



to ascend from such knowledge as we have spoken of, to the general 

 theory of light, were, in fact, made at every stage of the subject, and 

 with a success which at last won almost all suffrao-es. We are now 



o 



arrived at the point at which we are called upon to trace the history 

 of this theory ; to pass from the laws of phenomena to their causes ; 

 from Formal to Physical Optics. The undulatory theory of light, the 

 only discovery which can stand by the side of the theory of universal 

 gravitation, as a doctrine belonging to the same order, for its irene- 



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rality, its fertility, and its certainty, may properly be treated of with 

 that ceremony which we have hitherto bestowed only on the great 

 advances of astronomy ; and I shall therefore now proceed to speak of 

 the Prelude to this epoch, the Epoch itself, and its Sequel, according 

 to the form of the preceding Book which treats of astronomy. 



[2nd Eel.] [I ought to have stated, in the beginning of this chapter, 

 that Malus discovered the depolarization of white light in 1811. He 

 found that a pencil of light which, being polarized, refused to be 

 reflected by a surface properly placed, recovered its power of being 

 reflected after being transmitted through certain crystals and other 



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transparent bodies. Malus intended to pursue this subject, when his 

 researches were terminated by his death, Feb. 7, 1812. M. Arago, 

 about the same tune, announced his important discovery of the depo- 

 larization of colors by crystals. 



I may add, to what is above said of M. Biot's discoveries respecting 

 the circular polarizing power of fluids, that he pursued his researches 

 so as to bring into view some most curious relations among the ele- 

 ments of bodies. It appeared that certain substances, as sugar of 

 canes, had a right-handed effect, and certain other substances, as gum, 

 a left-handed effect ; and that the molecular value of this effect was 

 not altered by dilution. It appeared also that a certain element of the 



