702 



DARBYSHIBE 



[CHAP. 20 



(a) 



J L 



(b) 



(c) 



1 L 



(d) 



Fig. 2. Diagram showing various stages in a stationary wave cycle. (After Longuet- 

 Higgins, 1953.) 



Fig. 3. Diagram showing various stages when two progressive waves meet head on. 

 (After Longuet-Higgins, 1953.) 



