Motion, Voice, and the Blow: Mechanics Demonstrations
Wine jets, the carrying of the voice, a loaded support, and the three effects of a hammer blow
This folio turns from optics to a cluster of demonstrations gathered under the headings "Motion," "Voice," "Force and motion," and "Blow." Leonardo relates the reach of wine jets to the falling level in a vat, considers how a voice reaches a listener in a courtyard closed on three sides, analyses the inward twisting of a loaded wooden support, and dissects the three instantaneous effects of a hammer blow. Paired small devices show an iron wedge driven either out of or into a block depending on where the hammer strikes, and a separate note explains how the illuminated threads of falling rain are perceived against a dark background.
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The three effects of a single hammer blow
In an axle struck between two hammers with a nail, the blow makes three effects: first its swift contact, which makes the sound; second the entering of the nail's point; third the rebound of the hammer. The point of the nail is driven in before the hammer behind rebounds.
Wine jets gauge how much is left in the vat
The proportion of b-c to a-c equals that of the two quantities of wine in the vessel. If a full vessel pours at c and a nearly empty one at a, then when it pours at the midpoint b the vessel is exactly half full.
How the voice carries to a listener in an enclosed courtyard
If the voice is at m and its listener at n, the voice will appear to him at S, provided the courtyard is closed on at least three sides toward that listener.
The air-angles at the ends of a loaded support
The angles the surrounding air makes at the ends of a support never change in size however the support moves; as the acute angles at a diminish and the obtuse angles f-b grow, the sustaining wood twists inward.
Seeing the threads of rain against a dark background
To tell whether rain is beginning, men look at the air between the eye and some dark place, where the thin illuminated threads of the little drops are easily seen. But they mistake the nearest threads for the farthest, not realizing the dark place may be so distant that a nearby tower could not be seen there.
Striking a wedged iron out of or into a block
In the paired devices, striking with the hammer o on the square q makes the iron m jump out, whereas striking with the hammer p on the square r drives the iron n into the block.