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.
-Alfred, Lord Tennyson, “The Holy Grail”
An old nautical superstition holds that waves become progressively higher until
the ninth wave (some say the tenth) and that then the progression begins all
over again. While waves sometimes form larger ones when they meet, there is no
fixed interval when a large one can be predicted.