The pupil of the eye and percussion in dilatable material
A cube of extensible matter struck evenly turns from square to round
The opening lines observe that among bodies smaller than the pupil of the eye, the one nearest the light is the least discernible, and then head a new section 'On percussion made in dilatable material.' A lettered figure states that a cube of extensible matter, when struck uniformly, moves its extremities out evenly and so passes from square to circular. In this transmitted-light view a large eye-like diagram with converging rays and smaller figures accompanies the text.
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Small bodies before the pupil
Among bodies smaller than the pupil of the eye, the one nearer to the light is the less discernible. The remark introduces the eye and its threshold of vision, alongside a heading announcing a study of percussion in dilatable material.
A cube dilated by uniform percussion
A cube of extensible material, dilated by percussion, will — if the percussion is uniform — move its extremities out uniformly from its centre and pass from square to circular form. The claim ties an impact to a change of shape.