Blows, the rounding cube, quicksilver and rising fire
Why beaten cubes turn round, mercury grains are spherical, and flame rises as a wedge
Folio 178v continues the study of deformation under blows: a square cube pressed by a blow grows more in its lateral than its angular diameter, and a cube struck by many blows is transformed into a circular figure. Leonardo then poses two questions of natural philosophy — why a grain of quicksilver is always spherical and the rounder the smaller it is, and why fire rises in the form of a wedge through the air though born of a flat fuel. A closing rule restates the balance: the fixed weights on an angular balance stand in the same proportion as the spaces between the central line and the middle of their gravity, with a small balance sketch at the lower right.
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A cube beaten by many blows turns round
A square cube of equal angles and sides pressed by the power of a blow grows more in its lateral diameter than its angular, the more the angular exceeds the lateral; and a cube struck by many blows is transformed into a circular figure.
Why quicksilver grains are spherical
Leonardo asks why the grain of quicksilver is always spherical, its surface equidistant from its center, and the smaller it is the rounder it becomes. The question is left open, posed as natural inquiry.
Why fire rises in the form of a wedge
A further question asks why fire mounts through the air in the form of a wedge (cone) even though it is born of a flat fuel. It is grouped with the quicksilver query among problems of natural motion.
Proportion of weights on the angular balance
Weights fixed on the angular balance stand in the same proportion as the spaces between the central line and the middle of their gravity. A small balance-and-triangle diagram appears at the lower right.