geer'ing, in machinery, the parts, collectively considered, by which motion communicated to one portion of a machine is transmitted to another, generally a train of toothed wheels. There are two chief sorts of wheel gearing, spur gearing and beveled gearing. In the former the teeth are arranged round either the concave or convex surface of the wheel, and are of equal depth throughout. In beveled gearing the teeth are placed upon a beveled surface round a wheel, which, if the slope of the bevel were continued, would form a cone the teeth sloping similarly. Spur gearing is used when the axles of the wheels are parallel, and beveled gearing is used when the axles are at right angles to each other.