The subject for this month is a marble clock. Well mass-produced marble clocks are common enough, but this one is out of the common run.

For a start, it is made by Pons. That is the Honore Pons de Paul who reorganised the production of clockmaking at St. Nicholas-d’Aliermont, near Dieppe. The clock has a pinwheel escapement, of which more later, it has centre seconds and a temperature compensated pendulum with an inset thermometer.

The general appearance is shown in Figure 1. It is about 660mm in height

The date of the clock is probably prior to 1850.

The shape of the escape wheel is interesting. On first inspection, it looks like a conventional pinwheel, but, if you look more closely, you can see that there are also teeth on the edge of the wheel. Could it have been that the original intention was to use an escapement similar to that shown in Saunier "Treatise on Modern Horology" Plate XIII Figure 7 but that this was found to be unreliable so the design was changed to a straight-forward pinwheel?

Another point of interest is that the pendulum is suspended well below the escapement pivot.

The pendulum construction is complex. There are outer steel supports and a central steel rod extending from the calibrated adjuster at the bottom to the suspension hook at the top. Surrounding this is a zinc, or zinc alloy tube, enclosed at the top by a brass tube, the height of which can be adjusted by the knurled nut midway.

The centre of the pendulum bob is fitted with a finely made, bi-metallic strip thermometer, the pointer being driven by a rack arc connected to one end of the strip.

All together a clock out of the common run of those in marble cases.