Jason Clarke Antiques has dated this piece to the 1850s.
The card dial has a compass magnet applied to the underside using gummed paper and is positioned upon the pin through the central ferrule to allow for self-levelling and free compass movement.
The top is provided with a brass gnomon and a black white dial showing both time and compass direction and with typical fleur de Lys decoration at the North position and a star motif running around the outer circumference.
The compass dial is protected with a dome-shaped brass lid with applied label to the inside which provides the user with an equation of time meant to allow the user to adjust the reading depending on the time of the year.
This example is unnamed making it somewhat difficult to date, but the style was developed during the Late Eighteenth Century and was popularised Samuel Porter in the 1820’s. Owing to the style, I suspect this example to be of slightly later age.
Circa 1845
Jason Clarke Antiques has dated this piece to the 1850s.
You can view the stock and full dealer information on the Jason Clarke Antiques Profile Page
Early Victorian Magnetic Compass Sundial or Porters Dial
