Humidity and wooden pendulums
The tempo of a pendulum depends on its length. Shorter is faster.
4 June My experimental pendulum → is a plain pine-wood lath (5 x 27mm) and about a metre long. The pendulum weight is a steel tube 34 x 27 x 250 mm. 0.66kg. The tempo is regulated with an M3 (3mm) nut on a long threaded rod that positions the weight so the clock does one tick a second.
5 June I adjusted the pendulum so that it is running about the same as a nearby uncompensated clock of similar construction.→
6 June Now both clocks are adjusted according to the DCF77 time signal from Frankfurt.
14 June During the first week's run the 10cm wood block followed the humidity readings quite nicely and over-compensated, as expected. I cut the block down to 5cm - carefully saving the cut-off piece - and had readjusted the clock to DCF77 again by the morning of the 15th June.
22 JuneThe changes in rate are still related to humidity, not as wild as previously but far from even so I cut the block to half its previous size; it is now 2.5 cm long.
5 July There has been some improvement with smaller variations. The kinks in the clock and humidity graphs still change in the same direction so it is still over-compensating slightly. That means when the humidity increases the clock goes faster. So the block should be even shorter.
11 July I started recording again with a shorter wood block, see below.
19 July After an excellent start the pendulum became erratic. It seems that the wood block, currently 12mm high, is now too short. I will let it run a few more days and see what happens.
July 27 I added an 8 mm slice to the wood block so that it is now 20 mm high
August10 The two clocks are side by side on the same wall with a door between them. For the last week this door has been kept shut. Maybe this caused an improvement.