Eddies at the bottom and crossing wave-circles
Why an eddy reverses below, and how circles from two stones pass through each other
Folio 61r pairs two diagrams of circular water-motion with Leonardo's reasoning about eddies and waves. An overhead sketch of a powerful eddy accompanies the claim that at the bottom the eddy turns contrary to its motion above, as its wide upper circles narrow to a point and submerge. Below, a diagram of two overlapping sets of seven concentric circles illustrates the argument that circles spreading from two stones thrown on still water meet and cross one another without breaking, each keeping its own center, because the water only trembles in place rather than travelling — as floating straws that stay put reveal. He draws the analogy to voices spreading through the air in circles.
On this page
At the bottom an eddy turns contrary to its surface
The circles that are wide above reduce to a point and submerge; following their begun motion, the eddy comes to move at the bottom contrary to its motion above as it separates from its center.
Two stones on still water: circles that cross but never break
Throw two small stones at once onto motionless water and two sets of circles form around the two impacts; growing, they meet and merge, one circle crossing another, yet each keeps the struck place as its center. The water does not leave its site — the opening the stones make closes at once — so floating straws stay put though a wave passes beneath them.
Wave-circles pass through one another like voices in the air
Voices penetrating the air start from their causes in circular movements, and circles from different beginnings meet without impediment, passing one into another while each keeps its cause as its center. Because water conforms closely to air in motion, its crossing circles are a proof: the motion is a tremor passed from part to part, so the circles cannot break one another when they meet.