Aha! In "Pulvis et Umbra", I wrote, "The engineers were still trying to figure out the fountain at the bottom of the hill." This was based on something I had read about the development of Sanssouci, namely that Friedrich wanted a fountain spurting water into the air, but that it was a tricky problem before the 19th century and depended a lot on local topography, and engineers didn't figure out how to make it work at Sanssouci until the 19th century. (I like that they were still trying!)

You can see the product of their success in the picture I took when I was there. Oh, and this one, viewed from the top of the hill.

Well, what I didn't realize was that "engineers" included the great Euler! His Wikipedia page has this quote from Friedrich in a letter to Voltaire: "I wanted to have a water jet in my garden: Euler calculated the force of the wheels necessary to raise the water to a reservoir, from where it should fall back through channels, finally spurting out in Sanssouci. My mill was carried out geometrically and could not raise a mouthful of water closer than fifty paces to the reservoir. Vanity of vanities! Vanity of geometry!"

Engineering is hard, let's go shopping stick to math.

Likewise, in one of my comments on these posts, I mentioned the bit about the time the dogs started barking because there was a WOMAN in the room, but I had forgotten *which* woman, and never did know her life story. Fleshing out all these details is fun!