The true size of the sun and stars, against Epicurus
Book 9 on perforated reservoir walls, then stars viewed through a pinhole and the sun's real magnitude
The leaf opens with the heading 'Book 9,' on water passing through a reservoir whose walls are riddled with spiracles of varying sizes, shapes and heights, matched by a dotted diagram of a perforated wall at the upper right. A section headed 'Praises of the sun' then turns to the heavens: viewing stars without rays through a fine pinhole held near the eye shows them extremely minute, their smallness caused by great distance even though many are far larger than the earth. Leonardo urges the reader to imagine how small our own earth would look at such a distance, and blames ancient thinkers, Epicurus among them, who claimed the sun is no larger than it appears.
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The sun and stars are far larger than they appear
Leonardo argues that the vast distance of the stars reduces them to points, though many are many times larger than the earth with its water. He invites the reader to imagine how small our own star, the earth, would look at such a distance, and how many stars fill the dark space by longitude and latitude. He blames ancients such as Epicurus who held the sun no larger than it shows, tracing the error to a nearby light that seems undiminished at any distance.
Seeing stars without rays through a pinhole
To strip the stars of their radiating glare, Leonardo describes looking through a small hole pricked with the fine point of a slender needle held almost touching the eye. Seen this way the stars appear so minute that nothing could seem smaller, revealing that their apparent size owes to distance rather than to true smallness.
Book 9: water through a perforated reservoir wall
The chapter-heading treats water passing through a reservoir whose walls are full of spiracles of various sizes, shapes and positions, set at differing heights that vary alternately from entrance to exit. The reservoir too varies in shape, depth, length and width, and the water in power, speed and volume. A dotted diagram at the upper right shows the perforated wall.