Equatorial sundial

Description

Philipp Matthäus Hahn (1739-1790) invented this particular type of table sundial in 1763. The disc at the socket has a wind rose; from the socket an iron arc rises on which a brass ring calibrated for setting the latitude for the location is suspended. Two signatures, "Hahn 1782" and "Hahn / Echterdingen / 1782", are engraved on the disc and on the brass ring. An open brass box moves round on the diameter of the ring and engages through a gear with the dial on the inside bottom of the box. Hahn's invention consists in the fact that instead of a shadow cast by a gnomon the rays of sunlight themselves, passing through two tiny holes in the wall parallel to the axis, strike the time scale on the inside of the box. Thus either the mean time or the real local time can be read off the dial. Two hands indicate the hours in Roman (I-XII) and the five minutes in Arabic numerals.