Use this apparatus to conveniently demonstrate the laws of refraction and reflection. The circular water tank, 25cm in diameter, is permanently mounted on a stand, and has a movable arm carrying a lamp housing with a 6V straight filament lamp. The sharp beam of light produced by the lamp is clearly visible on the printed degree scale, and can be adjusted to pass through the center of the tank for reliable angle readings. Fill the tank to the marked centerline with water, and adjust the lamp to any position around the tank. Size: 25cm x 35cm high. Requires a 6V/2A power supply (AC or DC).