Birds in the Wind, Reflection in a Sphere, and Circle Diagrams
Flight, the geometry of reflected rays, and small squared figures
The sheet mixes a study of how a bird spreading its wings is overturned by the wind unless it gains weight with an optical construction of a ray reflected from a spherical mirror to the eye. The lower half is filled with many triangle-and-circle diagrams working out the geometry of incidence and reflection, while small figures at the right assign a value of "one square" to a labelled part. A stray marginal note reads simply "fire beneath the table."
On this page
A bird overturned by the wind unless it gains weight
Leonardo pairs two propositions: among bodies of equal weight, the one that spreads over greater breadth shows itself less heavy; and a bird sustaining itself on the wind with outspread wings will be flipped upside down unless it acquires more weight. He notes this is taught by the converse shown above, from a to b.
Reflection of a ray from a spherical mirror to the eye
The triangles a c e and b d c are said to be similar, with right angles at d and e, and the line d c touching the circle at the image-point c. The line a b runs from the eye to the light b as the first of the incident and reflected rays, while a e touches the mirror at c in rectangular tangency, meeting the sphere's surface perpendicular above its centre f.
Triangle-and-circle constructions filling the sheet
The lower two thirds of the leaf are covered with repeated diagrams of triangles inscribed in or touching circles, the geometric scaffolding for the reflection argument. Each carries pointed vertices and chords drawn to the circle. No measurements accompany them in the transcription.
Small figure worth "one square"
A small figure labelled b a is annotated that a is worth one square. Two further companion figures repeat the labels b-a and a-b. The relation is stated without further calculation.