Water-screws: a helical and a conical lifting screw
How water circulates through an Archimedean screw and its 'equidistant lever'
Two studies of the coclea (Archimedean water-screw) trace the path of water as it is raised. In the upper detail a helical screw carries water to its head, where it falls at a, forms an 'equidistant lever' as far as b, then drops to c and takes up its rising motion again through the eight-turn thread. The lower figure shows a flat screw joined to a pyramidal (conical) one, with the water climbing to d and returning by a circular path to a; both mechanisms are noted as having eight spokes and eight turns.
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Water falling and rising through the helical screw
When the water reaches the head of the screw it falls at the point a and forms an equidistant lever as far as b. From b it drops to c, and there it begins to take up its motion again at the rise of the screw, which has eight turns with eight spokes.
Flat screw joined to a conical screw
Once the water arrives by the screw at point a it at once runs to b, and from b to c it makes an equidistant lever. It then rises through the flat screw as far as d, from which it returns by a circular path to a. The letter b is marked as having eight spokes and eight turns.