Reaction Wheel

—A device for illustrating the effect of the discharge of electricity from points. If slender metal needles, radiating from a center like a wheel with their points all bent at right angles in the same direction, be supported upon a pivot and placed upon the positive pole of an electrostatic machine, the force of the electricity discharged from the points acting against the surrounding air will cause the wheel to rotate in a direction opposite to that in which the points are bent. It is often called an electric fly. 2. In hydraulics, an enclosed wheel into which water enters under head or pre ure and escapes from it tangentially; the force being derived from the reaction of the weight thrown off at the edge of the wheel.