The container of fluid sits in a temperature regulated water bath. The temperature is stable to better than one ten thousandth of a degree. The container is composed of two very flat plates about four inches in diameter, a silver disk for the bottom plate and a single crystal sapphire for the top plate, and a plastic ring about a quarter inch high separating them. The height is uniform to better than three millionth of an inch over an area of seven and a half square inches.
To visualize the fluid motion we use a shadowgraph method, which utilizes the fact that light is bent differently by the hot and cold fluids (i.e. convection rolls act as little lenses). For the curious: the light spots in the image correspond to cooler, downflowing fluid, and the darker regions to the hotter, upflowing fluid. We can quantify the shadowgraph signal on the computer and compare the data with theory.