570 The Bight Eon. Lord Bayleigh on Polish. [March 29, 



A is supposed to be the original surface ; B, C, D, E surfaces formed 

 by corrosion, being constructed by circles having their centres on A. 

 In B the ridges are still somewhat rounded, but they become sharp in 

 D and E. The general tendency is to sharpen elevations and to smooth 

 off depressions. 



