Finding a lodestone's north pole; problems of the screw
A lodestone floated in a cup turns to the pole star; four problems relating screw, lever, load and motive power
The upper part of the folio explains how to identify the north-seeking part of a lodestone: float it in a wooden cup set in a vessel of water, and its attractive virtue will turn it toward the northern star and carry it to the vessel's rim. A drawing shows the floating dish linked by a ray to a star. Below, under 'Problems of the screw,' Leonardo poses four reciprocal questions relating the motive power, the load, the thickness of a simple screw and the length of its lever, referring the reader to his book of Mechanical Elements. A screw-and-lever mechanism with a hanging weight is drawn in the lower margin.
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Finding the lodestone's north with a floating cup
To find the part of the lodestone that turns north, float it in a wooden cup within a wide vessel of water; the stone drifts like a boat and, by its attractive virtue, turns toward the northern star, then comes to rest at the rim of the vessel with that north-seeking part foremost.
Four problems of the screw, nut and lever
Labelled d - b a - c, this set poses four reciprocal problems: given any three of the motive power, the load, the thickness of the simple screw and the length of the lever, find the fourth. Leonardo refers the solution to the definition of the screw in his book of the Mechanical Elements.