Moon Spots, the Levelling Earth, and Canal Waves
Against vapor-clouds as the moon's spots; will convex and concave waves travel far?
Under four short headings Leonardo gathers a set of questions about the physical world. He rejects the idea that the moon's spots are vapors rising like clouds, since such vapors would shift and change shape as the moon is seen from different angles, whereas the spots stay fixed. He then reasons that because every heavy thing tends downward, in time all heights descend, the world becomes spherical, and the earth is covered by water, closing with the same claim in Latin; two further notes ask whether a convex wave and a concave wave (the latter from water dropping below a sluice) travel far in a canal of uniform width and depth. A margin diagram shows concentric ripples and a plumb line.
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Against vapors as the cause of the moon's spots
Some held that the moon's spots are vapors rising like clouds between the moon and our eyes. Leonardo objects that if this were so, the spots would never be stable in place or shape, and would appear to change figure as the moon is seen from different aspects, the way any object looks different from several directions; yet the spots stay fixed.
In time all heights descend and the earth becomes a sphere covered by water
Every heavy thing tends downward, so high things cannot keep their height and all will in time descend. Leonardo concludes that the world will therefore become spherical and be entirely covered by water, while the underground veins remain immobile; he restates the point in Latin, that the whole earth would already have been made spherical.
Will a convex wave travel far in a uniform canal?
Under the heading of the convex wave, Leonardo asks whether the wave made by water falling into the water of a canal of uniform width and depth will be of long motion or not.
Will a concave wave from a sluice travel far?
Under the heading of the concave wave, he asks whether the concave wave made by water dropping suddenly from the canal open below the sluice will be of long motion in a canal of uniform length and depth.
Diagram of spreading ripples
At the upper right a small drawing shows concentric ripples spreading in a rounded double form, illustrating the waves discussed in the wave notes.