Of the waters: no body weighs within its own element
Why a stone rebounds at equal angles once it is outside its element
Folio 84v opens a section headed 'Of the waters' with a compact physical principle: no part of an element has weight while within its own element. From this Leonardo derives that a stone rebounds between equal angles after striking its object, precisely because in rebounding it is outside its own element. A faint pencil outline of a large U-shaped form and a small pen flourish at upper right are also present on the sheet but are not covered by the transcription.
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No part of an element weighs within its own element
Leonardo lays down that no part of an element has weight while it remains within that same element. The principle is offered as the ground for the behavior of a body that has left its element.
The stone rebounds between equal angles
Because of that principle, the stone rebounds between equal angles after the percussion of its object. The equal-angle rebound follows from the stone being outside its own element at the moment of impact.