xvi PREFACE TO THE SECOND EDITION. 



(4). Page 509. Mr. Airy's explanation of the 

 phenomena termed by Sir D. Brewster a new pro- 

 perty of light, is completed in the Philosophical 

 Magazine for Nov. 1846. It is there shown that 

 a dependence of the breadth of the bands upon the 

 aperture of the pupil, which had been supposed to 

 result from the theory, and which does not appear 

 in the experiment, did really result from certain 

 limited conditions of the hypothesis, which condi- 

 tions do not belong to the experiment; and that 

 when the problem is solved without those limita- 

 tions, the discrepance of theory and observation 

 vanishes : so that, as Mr. Airy says, " this very 

 remarkable experiment, which long appeared inex- 

 plicable, seems destined to give one of the strongest 

 confirmations to the Undulatory Theory." 



TRINITY COLLEGE, CAMBRIDGE, 



November 7, 1846. 



