BALANCE, and BALANCE-SPRING. The balance of a watch is a wheel finely poised on its axis; the pivot-holes in which it turns being fre quently—in chronometers and clocks, as well as in watches—jeweled, or made of small rubies, diamonds. etc., for the sake of durability. The natural effect of an impulse given to such a wheel would he a complete rotation on its axis. This, however, is convertible, by the escapement (q.v.), and by the balance-spring, into a vibra tory motion. The balance-spring is held to be a crowning invention in the mechanism of the watch; and the honor of its first suggestion has been claimed for no less than three very eminent men—Hooke, an Englishman; AbbC. Hautefeuille, a Frenchman; and Huygens, the Dutch astrono mer. The honor, however, is thought to belong to Hooke, who applied for a patent for the inven tion in IG5S or MO.
The balance-spring consists of a coil of fine steel wire which determines the time of vibration of the balance. One of its extremities is fastened
to a point independent of the balance, while the other is attached near its axis. When the bal ance is at rest. the spring is not under tension, its position being called the point of rest; but when an impulse is given to the balance by the crown-wheel of the escapement, the balance moves around just so far as the impulse given is able to overcome the elastic resistance of the spring. When that resistance becomes equal to the impulse given, the balance stops for a mo ment, and then is driven back by the elastic recoil of the spring, and continues thus to vibrate so long as the impulse is repeated or the watch is in motion. The subject of balances and bal an•e•springs and their adjustment is treated at considerable length in Britten, Watch and Clock makers' HandboOk (London, ISM). For a gen eral description of watchmaking and for illus tration of the balance wheel. see WATCH.