348 Mr. P. Cooper on the Connexion between 



ous founder: no essential part of it has been invalidated by- 

 subsequent experiment ; nor has it received much accession 

 of strength by the filling up of the intervals, which, it 

 must be admitted, is required to give it support from con- 

 nexion. It still remains, like an unfinished magnificent 

 building, with valuable materials for its completion scat- 

 tered around it. Refraction, reflexion, inflexion, polariza- 

 tion and other branches into which the science of optics 

 has been divided, though so evidently united in the opera- 

 tions of nature, are still unconnected in theory, and remain 

 distinct objects of investigation. 



This want of connexion in the material theory of light 

 has laid it open to various attacks ; and such has been the 

 recent success of a rival theory, that some of its most zeal- 

 ous supporters appear to be wavering. 



The following quotations from Sir David Brewster's life 

 of Sir Isaac Newton will shew the importance, as it relates 

 to this question, of establishing a connexion between the 

 theories of refraction and diffraction, or inflexion ; and it 

 is with this object in view that I now claim your indulgence. 



" By this mode of observation, he (Fresnel) made the re- 

 markable discovery, that the inflexion of light depended on 

 the distance of the inflecting body from, the aperture, or from 

 the focus of divergence, the fringes being observed to dilate 

 as the body approached that focus, and to contract as it 

 receded from it, their relative distances from each other, 

 and from the margin of the shadow continuing invariable," 

 p. 104. 



" The various phenomena of inflexion, which had so long 

 resisted every effort to generalize them, having thus re- 

 ceived so beautiful and satisfactory an explanation from the 

 undulatory doctrine, they must, of course, be regarded as 

 affording to that doctrine the most powerful support, while 

 the Newtonian hypothesis of the materiality of light is pro- 

 portionally thrown into the shade. It is impossible, indeed, 

 even for rational partiality to consider the views of Newton 

 as furnishing any explanation of the facts discovered by 

 Fresnel," p. 105. 



If we look through a prism at an unclouded sky, it pre- 

 sents a white surface, bounded by red and yellow fringes on 

 one side, and blue and violet, fringes on the other. These 



