Читать книгу The Modern Clock. A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair онлайн

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Pendulum Suspension Springs.—Next in importance to the pendulum is its suspension spring. This spring should be just stiff enough to make the pendulum swing in all its vibrations in the same time; that is, if the pendulum at one time swung at the bottom of the jar 1¼ inch each side of the center, and at another time it swung only 1 inch each side, that the two should be made in exactly one second. The suspension springs are a point in the construction of a fine pendulum, that there has been very much theorizing on, but the experiments have never thus far exactly corroborated the theories and there are no definite rules to go by, but every maker holds to that plan and construction that gives his particular works the best results. A spring of sufficient strength to materially influence the swing of the pendulum is of course bad, as it necessitates more power to give the pendulum its proper motion and hence there is unnecessary wear on the pallets and escape wheel teeth, and too weak a spring is also bad, as it would not correct any inequalities in the time of swing and would in time break from overloading, as its granular structure would finally change, and rupture of the spring would follow. The office of a spring is to sustain the weight without detriment to strength and elasticity, and if so proportioned to the weight as to be just right, it will make the long and short swings of the pendulum of equal duration. When a pendulum hung by a cord or knife edge instead of a spring is regulated to mean time and swings just two inches at the bottom, any change in the power that swings the pendulum will increase its movement or decrease it, and in either case the rate will change, but with a proper spring the rate will be constant under like conditions. The action of the spring is this: In the long swings the spring, as it bends, lifts the pendulum bob up a little more than the arc of the normal circle in which it swings, and consequently when the bob descends, in going to the center of its swing, it falls a little quicker than it does when held by a cord, and this extra quick drop can be made to neutralize the extra time taken by the bob in making extra long swings. ssss1. This action is the isochronal action of the spring, the same that is attained in isochronal hair springs in watches.