Automatic Machinery—The second great contribution of America to watchmaking after the establishment of the principle of interchangeability of parts, and making possible the effective execution of that principle.
Auxiliary—A device attached to a compensation balance to reduce what is known as the "middle temperature error." Some are constructed to act in high temperatures only—as Molyneux's; and some in low temperatures only—as Poole's.
Balance—The vibrating wheel in a watch or chronometer which with the aid of the balance spring (hair-spring) regulates the rate of travel of the hands. The balance is kept in vibration by means of the escape wheel. See [Compensation Balance].
Balance Arc—In detached escapements, that part of the vibration of the balance in which it is connected with the train. The remainder is called the drop.
Balance-Clock—A form of clock built before the pendulum came into use. The regulating medium was a balance on the top of the clock made with a verge escapement. See [Foliot].
BALANCE COCK
Balance Cock—The standard which supports the top pivot of the balance. In old watches often elaborately pierced and engraved.
Balance Spring—In America usually called the "hair-spring." A long slender spring that governs the time of vibration of the balance. One end of the balance spring is fastened to a collet fitted friction-tight on the balance staff, the other to a stud attached to the balance cock or to the watch plate. The most ordinary form is the volute, or flat spiral. The other form used is an overcoil. See Bréquet Spring. The principle of the isochronism of a balance spring was discovered by Hooke, and first applied to a watch by Tompion. The name hair-spring comes from the fact that the first ones are said to have been made from hog bristles.