I remember being on the coast with friends. Being a flatlander myself, I marveled at this bit of arcana, to wit, that every seventh wave coming off the ocean onto the shore is bigger than the others. I remember counting and thinking that this was clearly so. Or was it?
Is it so, that every seventh wave is bigger?
And more important, why?
While maybe not every seventh wave is always bigger, it is true that oscillation waves, which are created by winds blowing from the sea toward the land, often come in groups of seven, with the highest waves in the middle of the group. I wish I could find the diagram our professor showed us in Geology - his big area of expertise was wave development and beach erosion.
Sorry, no cites, this is just off the top of my head.
This from E. Cobham Brewer’s "Dictionary of Phrase and Fable (1912):
The ninth wave. A notion prevails that the waves keep increasing in regular series till the maximum arrives, and then the series begins again. No doubt when two waves coalesce they form a large one, but this does not occur at fixed intervals. The most common theory is that the tenth wave is the largest, but Tennyson says the ninth. 1
“And then the two
Dropt to the cove, and watch’d the great sea fall,
Wave after wave, each mightier than the last,
Till last, a ninth one, gathering half the deep
And full of voices, slowly rose and plunged
Roaring, and all the wave was in a flame.”
Tennyson: The Holy Grail.
(Tennyson wrote “The Holy Grail” between 1842 and 1855 as part of a muchlarger work, “The Idylls of the King.” The poem served as the inspiration for Kate Bush’s song suite “The Ninth Wave,” side II to her 1989 album “The Hounds of Love.” The passage above is reprinted on the album sleeve.)