Sound in a Pipe and Marine Shells That Raise the Mountains
Why wind through a pipe makes a sharper or graver note, and how sea-shells prove the earth has changed
Under the heading 'On the voice', with a small drawing of two pipe segments, Leonardo explains that wind through the same pipe sounds graver or sharper according to whether it is slower or swifter, citing valveless trumpets and horns and the whistling of drafts through door and window chinks. The lower note, 'On the sea that changes the weight of the earth', argues that shells and oysters born in sea mud prove the earth's change: turbid rivers wear away their beds and banks, uncover the layered steps of buried shells, and build old sea-floors into hills and high mountains. As the lightened side of the earth rises, he adds, the antipodes draw nearer the world's centre.
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Why wind through a pipe makes a sharp or grave sound
Wind passing through one and the same pipe makes its note graver or sharper according as the wind is slower or swifter, as heard in valveless trumpets and horns and in drafts whistling through the chinks of doors and windows. The sound arises in the air the note penetrates, which dilates more or less as it is driven with greater or lesser power.
Sea-shells testify that the earth has changed
Shells, oysters and similar animals born in sea muds testify to the change of the earth about the centre of the elements. Buried in layered muds and walled up dead, they now lie in beds raised so high they have become hills or high mountains, whose sides the rivers wear away to uncover the steps of shells.
Turbid rivers wearing away their beds
The great rivers always run turbid because of the earth raised by the friction of their waters on the bottom and along the banks. This continual wearing-away uncovers the fronts of the layered steps of shells and, over time, lets the lightened side of the earth rise while the ancient sea-bottoms become mountain ridges.