Sundial of the month January

The photograph above shows a very special sundial, or rather a triple sundial. It is barely visible on a buttress of the Large Church in Maassluis.
There are three vertical sundials, facing north-east, south-east and south-west.
This triple dial was probably made in the 17th century.
Each plate measures approximately 71cm x 71cm (28" x 28"). The photograph below shows a close-up.

The third photograph shows the southeast sundial in detail.
The sundial provides large hour numerals and heavy hour lines along its edge for daily use.
However, there is also a set of straight lines which, after a closer look, appear to indicate the hour angle directly, in increments of 10 degrees. That is not usually seen on sundials.
There are no numerals associated with these hour angle lines.

Further visible are curved lines resembling date lines, but covering a much larger range than the usual -23.5 to 23.5 degrees. The range is here from -40 to 80 degrees in increments of 10 degrees, and as before, there are no numerals.
Moreover, the three declination lines for start of summer, winter, and autumn/spring are drawn and annotated.

And as if that were not enough, azimuth and altitude lines were added.
The altitude of the sun is read from 0 to 60 degrees in increments of 10 degrees. Azimuth is indicated using the usual points of the compass.

It is not clear why the maker has arranged the three sundials in this particular way. It was possibly to demonstrate his knowledge of gnomonics. But it certainly made these three sundials into a unique set.

Fer J. de Vries