This demonstration helps emphasize the relationship between temperature and pressure. Clouds form when the pressure is suddenly reduced inside the chamber. The water vapor is condensed and forms a cloud around the smoke particles. The thermometer is used to measure the change in temperature when pressure is introduced. This unit is mounted on an acrylic base, with two upright steel rods and a crosspiece to hold the stopper in place when air in the cloud chamber is under pressure. (6" x 4" base x 8-1/4"; 2Ibs).