We all know how a thermostat works 2 different type of metal are attach together, when temperature changes 1 metal strap expands more than the other strap causing the straight metal strap to bend. 45 years ago when I was in college the professor brought a desk top heat engine to class. He told us the name of this heat engine and I wrote it down. In the past 45 years I have lost that information. It was not called a sterling engine but it might be a type of sterling engine. Here is how the engine is build and how it works. 2 different types of thin flat metal straps are made into a donut round circle shape about 3" diameter and connected together. The 3" round double strap is on rollers so it is free to rotate on rollers. I don't remember the details of the rollers, I think there were 3 rollers on the inside and 2 on the outside near the top. The 3" metal ring sets in a cup of cold or hot water when you give the ring a spin it keeps on rotating around the rollers as long as it continues to stay in the water. 1 roller is near the water surface left side of the cup while part of the 3" round ring is in the water. Water temperature makes the strap bend so the metal ring continuously pushes away from the roller and keeps rotating as long as the metal strap stays in the water. As the strap rotates near the top its temperature returns room air temperature the strap returns to its original shape near the top. If water is made colder the strap spins faster. I don't remember if it will rotate the other direction if put in hot water, teacher did not bring hot water, I don't recall he mentioned if the ring rotates the other direction in hot water. If I knew the name of this device I could do Google search and read about it. I might even be able to find a desk top model for sale. Does anyone know that this engine is called? I might be able to draw a picture with paint brush and post if here if anyone would like to see a picture. Is it possible to upload photos here or do they have to be posted some place different then linked here?