BALANCE, SPRING

a form of weighing machine in common § use, consisting of a spirally wound steel spring usually inside a frame or case fitted with a ring for hanging from a support. One end of the spring is fastened to the upper end of the case, while the other end terminates in‘a rod ending in a hook, which protrudes from the case. In some balances a pointer is fastened directly on the movable end of the spring, or its rod, and slides over a calibrated scale. In other forms of spring balances, the rod carries a small rack which meshes with a pinion on a small shaft carrying a pointer. This pointer moves over a graduated dial. Both these methods serve to indicate the extent to which the spring is stretched by any force or weight applied to the movable end. According to Hooke’s law, the amount of deflection of the spring is directly are a to the weight or magnitude of the force applied to the hook; thus the scale is uniform, and may be calibrated in any system of units of weight desired. Spring balances are usually used where rapid and clear indications, rather than accurate measurements are required.,