Reflexion and Refraction . 137 



quence of those experiments, and by which it was brought to 

 its present simple form.* 



* Two or three months after this correction had heen published in the Philoso- 

 phical Magazine, a notice of it was inserted in Poggendorff's Annals, vol. xl. 

 p. 462. Up to that time, I helieve, nothing had been published in Germany on 

 the general theory of crystalline reflexion ; at least the writer of the notice (whom 

 I take to be M. Seebeck) does not seem to have heard of any other theory, or any 

 other principles than mine. But in the next number of Poggendorff, vol. xl. 

 p. 497, there appeared a letter from M. Neumann, in which the writer speaks of 

 a theory of his own, founded on principles exactly the same as those which I had 

 already announced, and refers to a Paper which he had communicated on the 

 subject to the Academy of Berlin. The Paper has been printed in the Transactions 

 of that Academy for the year 1835 ; and through the kindness of the author I have 

 received a copy of it, just in time to acknowledge it here. On casting my eye over 

 it, I recognize several equations which are familiar to me in particular, the equa- 

 tions (vn.), (vin.), (rx.), (x.), which I discovered independently in November last. 

 M. Neumann's Paper is very elaborate, and supersedes, in a great measure, the 

 design which I had formed of treating the subject more fully at my leisure ; nor 

 can I do better than recommend it to those who wish to pursue the investigations 

 through all their details. 



TKISITY COLLEGE, DUBLIN, March, 1838. 



