Butterfield Sundials

The Butterfield dial is a type of semi-universal horizontal dial, which was first produced in the second half of the 17th century. It owes its name to the British-born instrument maker, Michael Butterfield, who spent his working life in Paris. However, this type of instrument was available before he established his workshop in Paris, and it was probably only the distinctive bird index that was his innovation.

Butterfield dials are generally either octagonal or oval in shape and almost always carry three or four different hour scales. Each of these hour scales will be marked with a latitude for which that scale can be used - the hour angles change for different latitudes, and therefore one scale will not do for all. Usually, these hour scales are set for latitudes 3-5 degrees apart; for latitudes lying between those specified, the nearest hour scale is used, it being judged that the difference in hour angles is sufficiently small for there to be no significant difference. In order for the dial to be used in different latitudes, the angle of the gnomon must be adjustable. The gnomon proper is marked with a latitude scale and it can be moved within an index, which marks the latitude angle against the scale. By far the most common type of index was that in the form of a bird whose beak acted as the pointer. The form of the bird changed very little over the 120 years or so during which this type of dial was popular. It appears not to have been made beyond the end of the 18th century.

Technical details for a standard Butterfield dial:

Octagonal dial-plate with three or four concentric hour-scales reading clockwise. The compass is set into the dial-plate at the South-end, supporting the plate in conjunction with a single leg at the opposite end. It has cardinal points indicated by French initials and North is further marked by a fleur-de-lys. North is offset 5° West of North to allow for magnetic variation. The needle is blued, with an open circle indicating North, and is surmounted by a brass pyramidal pivot. The gnomon is hinged, folds flat when not in use and is adjustable for latitudes 40°-60°. A bird index marks the latitude. On the reverse side, the compass base is decorated with acanthus decoration. The remainder of the reverse contains a list of towns with their latitudes.

Thanks to the National Maritime Museum