Imagine that we stand on any ordinary seaside pier, and watch the waves rolling in and striking against the colums of the pier. Large blue waves pay little attension to those columns - they divide right and left and unite after passing each column, much as a army of soldiers would if a tree stood in their path: it is almost as though the columns had not been there. But the short waves and ripples find the columns of the pier a much more formidable obstacle. When the short waves impinge on the columns, they are sent back and spread as new ripp ....