You can see “shadows” of eddies on the ground!
As everybody who has ever watched a bath tub drain knows – eddies do lead to a deformation of the water’s surface. Here is an example of what that looks like in the real world:
In case you don’t see the eddies like pearls on a string coming off the edge of that rock in the picture above, watch the movie below – it’s much clearer when it is moving! Do you see the surface dipping where those little eddies are?
And in the movie below you can see how there is a shadow at the bottom underneath each of those eddies.
Why, you ask? Well, remember this from last weeks post?
The water droplet with the convex surface focusses the light. The eddies with a concave surface, on the other hand, does have the opposite effect: As the light enters the water, it is refracted away from its previous axis, leading to a “shadow” at the bottom underneath the eddy. How cool is that?