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(Original Caption) : Sheet 9A : Leonardo devotes the text and illustrations of folio 28v to practical hydraulics, particularly pile driving. On folio 9r he begins his water notes, using a 1348 source to account for the gap at the rock of Gonfolina. He concludes that some seashells are swept by rivers from mountaintops to the sea. 28V SYNOPSIS: The illustrated discussion on this page is devoted to practical applications of hydraulics. Leonardo describes how to drive piles with a device that employs a man as a counterweight to raise the ram and then describes how to arrange the slope of a weir so that it will not be subject to erosion. Concerning weir construction, Leonardo says: "In front of river dams made of hollow and spaced-out piles, a lower dam ought always to be made to a height just above water level, so that water falling from it at flood time comes to dig out the bottom (Photo by Seth Joel/Corbis/VCG via Getty Images)