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XIV. AN ESSAY TOWARDS A DYNAMICAL THEORY OF 

 CRYSTALLINE REFLEXION AND REFRACTION. 



[Transactions of the Royal Irish Academy, VOL. xxi, Read December 9, 1839.] 



SECT. I. INTRODUCTORY OBSERVATIONS. EQUATION OF MOTION. 



NEARLY three years ago I communicated to this Academy* the 

 laws by which the vibrations of light appear to be governed in 

 their reflexion and refraction at the surfaces of crystals. These 

 laws remarkable for their simplicity and elegance, as well as 

 for their agreement with exact experiments I obtained from a 

 system of hypotheses which were opposed, in some respects, to 

 notions previously received, and were not bound together by any 

 known principles of mechanics, the only evidence of their truth 

 being the truth of the results to which they led. On that occa- 

 sion, however, I observed that the hypotheses were not indepen- 

 dent of each other ; and soon afterwards I proved that the laws 

 of reflexion at the surface of a crystal are connected, in a very 

 singular way, with the laws of double refraction, or of propaga- 

 tion in its interior ; from which I was led to infer that "all these 

 laws and hypotheses have a common source in other and more 

 intimate laws which remain to be discovered ;" and that " the 

 next step in physical optics would probably lead to those higher 

 and more elementary principles by which the laws of reflexion 



* In a Paper "On the Laws of Crystalline Reflexion and Refraction." Trans- 

 actions of the Royal 'Irish Academy, VOL. XYIII. p. 31. (Supra, p. 87.) 



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