Palm-sized, hollow metallic ball with a manometer connected to it for demonstrating change of pressure in a closed volume of air when heated or cooled. Immersing the ball in a water bath at a specific temperature allows the relationship between pressure and temperature of the enclosed air to be investigated in order to demonstrate the behavior of an ideal gas. Approx. 80mm diameter Hollow ball. Dual scale - 0-18psi/0-1.25 x 105 Pa, with needle set at atmospheric pressure.