CONFIRMATION OF THE UNDULATORY THEORY. 133 



The Homologous plagihedral faces of Quartz crystals are accompa- 

 nied by homologous circular polarization of .the same name. I do not 

 know that hcterologous circular polarization has been observed in any 

 crystal, but it has been discovered by Dr. Faraday to occur in glass, An-., 

 when subjected to powerful magnetic action. 



Perhaps it was presumptuous in me to attempt to draw such compa- 

 risons, especially with regard to living persons, as I have done in the 

 preceding pages of this Book. Having published this passage, how- 

 ever, I shall not now suppress it. But I may observe that the im- 

 mense number and variety of the beautiful optical discoveries which 

 we owe to Sir David Brewster makes the comparison in his case a very 

 imperfect representation of his triumphs over nature ; and that, besides 

 his place in the history of the Theory of Optics, he must hold a most 

 eminent position in the history of Optical Crystallography, whenever 

 the discovery of a True Optical Theory of Crystals supplies us with the 

 Epoch to which his labors in this field form so rich a Prelude. I cor- 

 dially assent to the expression employed by Mr. Airy in the P/> if. 

 Trans, for 1840, in which he speaks of Sir David Brewster as " the 

 F.-^ier of Modern Experimental Optics."] 



