Caged Archimedean Screw and Cone for Draining a Marsh
A four-thread screw: two threads keep it turning, two raise water from the marsh to the needed height
Two studies occupy the leaf, figures 39 and 40: a caged cone and a caged Archimedean screw. Leonardo notes that this screw is made in four threads - two used to maintain the motion and the other two to carry water drawn from the marsh up to the necessary height. The drawings belong to his series of self-driving water-lifting machines.
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Four-thread screw draining a marsh
A caged Archimedean screw wound in four threads: two of the threads carry the water taken from the marsh up to the height required. Its purpose is to drain standing water and lift it where needed.
Two threads that maintain the motion
Of the four threads of the screw, Leonardo assigns two to maintaining the motion while the other two do the lifting - an attempt at a self-sustaining working cycle.
Caged cone (fig. 40)
At the upper right stands a caged cone, one of the recurring gridded solids that serve across these folios as housings for the screw-pumps.