Water Instruments: The Archimedean Screw
How drum thickness, number of coils and rise-height govern a screw's water-lifting
Continuing the 'Water instruments' series, this page sets out numbered propositions ('First,' 'Second,' 'Third') on the water-raising screw, with a sail-like coiled screw sketched at upper right, a diagonal wound screw below it, and a small section of a screw. Leonardo argues that among screws alike in every dimension the one wound around a thicker drum raises its water higher, and that equal quantities of water are lifted more easily by a screw that reaches a lesser height, because a thinner screw leaves less space between the drum's axis and the line of the weight. A further rule holds that among screws of equal length and obliquity, the one with more pipe-coils wound about the drum carries less water to the same height.
On this page
A screw on a thicker drum raises water higher
Among screws with pipes of equal width, water-discharge, obliquity and length from the lowest to the topmost mouth, the one whose pipe is wound around a thicker drum will raise its water higher. Marked as the 'Second' proposition and drawn as a coiled screw at upper right.
Equal quantities of water are lifted more easily to a lesser height
Of waters of equal quantity, the screw lifts more easily the one that reaches a lesser height; being thin, such a screw leaves less space between the central line of the drum and that of the weight. By the 'Third' proposition, among screws of equal length and obliquity, the one with more coils wound on the drum carries less water to the same height.