Semi-columnar and unequal columnar waves
How a wave flattens and speeds as it travels, and how unequal waves override
A first note with the labels a-b states that a semi-columnar wave, the further it travels, the more it lowers, spreads and speeds up. A second considers two unequal columnar waves born at different times: the greater, having risen first, has already flattened and lowered by the time the later, still-high lesser wave reaches it, so the lesser overrides the greater and breaks on the far side, keeping its impetus. A third case reverses the geometry, and the folio closes with the principle that a wave is the same whether the obstacle moves against still water or the water moves against a still obstacle. Marginal figures illustrate the plume-like waves.
On this page
A travelling wave lowers, spreads and quickens (a-b)
The semi-columnar wave, the more it moves, the more it lowers, the more it dilates, and the more it becomes swift.
The later, higher wave overrides the earlier, flattened one
Of two unequal columnar waves, the greater arises first and, when the lesser reaches it, has already spread and lowered; the still-high lesser wave strikes that lowness, finds no equal obstacle, runs over the greater and breaks on the opposite side, keeping its impetus.
Moving obstacle equals moving water
If instead the lesser wave rises higher in the river than the greater, the greater keeps its natural course and the lesser follows it. The wave is the same whether the obstacle moves against still water or the water moves against a still obstacle.