A River Whirlpool and an Anemometer (Wind-Vane)
A scouring whirlpool, and a vane device with notes on how compressed air strikes harder
The page combines a small spiral sketch of a whirlpool with a larger drawing of a framed vane device, labelled in the source as an anemometer or 'ventola.' Of the whirlpool, Leonardo notes that it scours the whole cavity and bottom beneath it. Of the vane and wind, he explains that air can be compressed, and the more it is compressed the more it weighs among the surrounding air and the harder it strikes its object—as with winds forced from a broad expanse through a narrow mountain gorge. He adds that without an opening above, such wind could not hold up so many things before it.
On this page
A whirlpool scours the cavity and bed beneath it
Under the heading 'retroso' (whirlpool), Leonardo notes that this whirlpool scours out the whole cavity and the bottom in its depths. A small spiral at the upper left of the sheet illustrates the eddy.
Anemometer or vane and the weight of compressed air
Beside a framed vane device labelled as an anemometer or 'ventola' (with the note 'passage of wind'), Leonardo argues that air can be compressed, and the more it is compressed the more it weighs among the rest of the air and the greater the impact it delivers to the object it strikes.
Wind forced from a broad expanse through a narrow gorge
As is seen in winds, air is forced from a great width to pass through a narrow mountain gorge, gaining force by compression. Leonardo remarks that if such wind had no opening above, it would not hold up so many things before it.