Tower Clock Pendulum

The pendulum is the basic element of the clock! Everything else merely optically or acoustically displays the number of oscillations and thus the elapsed time. The pendulum determines how fast the driving weight of the clock unwinds and thus the speed of the entire clock mechanism. The length of the pendulum influences the accuracy of the clock’s operation. Theoretically, the mass of the pendulum does not determine the speed of oscillation, only the length does. However, a larger mass means a higher potential energy content, greater inertia, and thus smoother operation. Furthermore, a longer pendulum means slower rotation of the wheels and, consequently, less wear on the material of the rotating (shafts) and contact elements (gears, escapement).

All weights, both pendulum and driving, are made of the same porous stone, sandstone. The clock has four driving weights. The smallest and thus lightest weight drives the clock (going train) and weighs 44.8 kg. The other weights drive the hammer striking the bell, acoustically announcing the time. The first weight (if standing in front of the pendulum at the entrance, on the right) weighs 64.1 kg and drives the ringing every 15 minutes. This is followed by the described weight that drives the clock. The third drives the repetition of the full hour ringing and weighs 61.5 kg. The fourth drives the full hour ringing and weighs 62 kg.

The weights were likely dimensioned based on empirical values during the clock’s construction (the lighter the better, but it must work reliably…). By winding them, we lift them and thus add potential energy, which is the driving force of the clock itself and the associated ringing mechanisms. The right weight drives the quarter-hour ringing mechanism, the second (lightest) drives the clock, the third drives the full hour repetition mechanism, and the fourth drives the full hour. Today, the weights are hung on steel cables (certainly safer), whereas linen ropes once performed this role. A steel eyelet is inserted into the stone part of all weights from the top, allowing the weight to be hung. This eyelet is joined to the stone using lead. Lead was melted and poured into the hole with the steel eyelet. When the lead solidified, it formed a solid and reliable bond.

The stone for the pendulum bob (weight), which determines the lowest point of the pendulum and has a mass of 303 kg, is processed in the same way. It is connected to the wooden part of the pendulum by two threaded shafts. Their task is to keep the pendulum weight constantly at the same distance from the clock, despite material expansion due to temperature differences or fatigue. Whoever maintains the operation of the clock must therefore constantly adjust or equalize environmental influences on the pendulum and its length. Only in this way will the clock work accurately and reliably. The oscillation period of the pendulum is 8.9 seconds, which means the oscillating motion repeats about 404 times per hour. The amplitude (maximum displacement from the equilibrium position) is 60 cm.