Article of the month July

Altitude dial 2

The top hat

In Alsace, France, there are some old stone sundials shaped like an inverted a top hat.
These are altitude dials with the single horizontal gnomon replaced by a circular disk, which represents in fact infinitely many horizontal gnomons.

These are fixed sundials and do not need any adjustments.
The readout is the top of the curved shadow.
This point is difficult to determine, especially at lower solar altitudes.

Things improve with the addition of an azimuth measurement on top. The projecting part of the azimuth indicator provides a definite reading point in the shadow curve.

Below is a model of such a sundial with azimuth measurement, using the vertical rod and rotating indicator on top.

But would it not be preferable by far to sit under such a top hat, enjoying a cool drink? This is possible in Italy.
Unfortunately, I do not know where this top hat is.