How long objects travel in a canal current
Studies of a floating bar aligning, drifting oblique or turning, and of an eddy (retroso)
Red-chalk (sanguigna) studies examine how a long object of even weight and thickness behaves when carried down a uniform canal. Placed in mid-channel it runs lengthwise with the flow; set between the middle and the bank it drifts obliquely; and lying nearer the side it turns round upon the surface. A final study of an eddy (retroso) compares the pull of the first current against the slower back-current where they meet, and marks where sand (a) and sweepings (n) collect.
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Long object in mid-channel runs with the current
A long object of equal weight and thickness passing through the middle of a uniform canal moves lengthwise, its length following the length of the water's course.
Object between mid-channel and bank drifts oblique (n, a)
The long object that moves along the canal between the middle and the neighbourhood of the bank will travel obliquely, no longer aligned with the flow. The rectangle is lettered n a.
Object nearer the bank turns on the surface (a, f)
An object that shares more of the side than of the middle of the channel will go turning round upon the water, spun by the uneven current. The rectangle is lettered a f.
Eddy (retroso): where sand and sweepings settle
In the eddy a-n the weight is heavier toward the first current than toward the slower back-current of the eddy where the two meet. Sand (a) and sweepings (n) are marked as the deposits that gather there.