Water speed on a slope, and the height of waves
Faster at the surface than the bottom; waves from a blow versus from wind
Two red-chalk semicircles at the top indicate different 'obliquities' (slopes), illustrating that water moving down an equal slope runs faster at the surface than at the bottom. A canal drawing below carries two rules on waves: a wave caused by a blow is higher at its beginning than in its middle, whereas a wave caused by wind is higher in the middle than at the beginning — the fourth wave higher than the first.
On this page
On an equal slope, surface flow is faster than bottom flow
Water that moves along an equal obliquity (slope) will be faster at the surface than at the bottom of the channel.
Waves from a blow versus waves from wind
A wave produced by a blow is higher at its beginning than in its middle; a wave produced by wind is higher in the middle than at the beginning — that is, the fourth wave is higher than the first.
Two semicircles marking different obliquities
Two graduated semicircular arcs, drawn like protractors, are used to indicate different obliquities (slopes) of the flow.