This “creeping” will cause the temperature compensation to jam up and become less effective.

But zinc is a ductile metal and the tube deforms with time under the heavy load of the 321kg pendulum bob. A similar construction is described for the clock in Trinity College Cambridge and near perfect temperature compensation can be achieved.

In the Westminster clock, the pendulum shaft is made of concentric tubes of steel and zinc. He came up with the solution of using metals of differing temperature expansion coefficient so that the pendulum doesn’t change in length as the temperature changes with the seasons. This was yet another of John Harrison’s genius ideas (you probably know him from longitude fame). The clock derives its remarkable accuracy in part from the temperature compensation which is built into the construction of the pendulum. The pendulum needs to be lifted out of the clock so that the spring can be closely inspected. Like any metal, it has the potential to suffer from fatigue. That’s nearly 8m times a year, bending the pendulum spring. The pendulum swings back and forth 21,600 times a day. Pendulum suspension from a Smith of Derby clock. The resulting damage took months to repair. In 1976 the speed regulator for the chimes broke and the mechanism sped up to destruction. In its 162-year history it has only had one major breakdown. The clock mechanism itself is remarkable. There are plumbing and electrical works to be done for a lift to be installed in one of the ventilation shafts, toilet facilities and the fitting of low-energy lighting. There is water damage to the masonry and condensation problems will be addressed, too. There is corrosion damage to the cast iron roof and to the belfry structure which keeps the bells in place. But a clock just doesn’t stop – especially not a clock as iconic as the Great Clock at the Palace of Westminster. It is convenient to choose a day when we’re out of the house to paint the doors, or when we don’t need the car to repair the brakes. The Illustrated News of the World December 4 1858Īny building or machine needs regular maintenance – we paint our doors and windows when they need it and we repair or replace our cars quite routinely.

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