Demonstrates conversion of light into mechanical energy and the concept of radiant heat. Evacuated glass bulb with a delicately-balanced, fine rotor pivot at its centre on which are supported. Spring control and magnetic damping. Long, pointer, needle, with thick arrowhead for clear visibility from a distance, moves on hardened and polished steel pivots and jeweled bearings. Mounted is sturdy, plastic frame with transparent front and back windows. One side of frame has color-coded for locking pointer needle. Any one removable, large scale with graduations on both sides can be selected from demonstrates meter.