Dipleidoscope dial for latitude 52° North, used to measure the time of true noon as the Sun crosses the local meridian.

It has a square base set on three small feet, one of which is also a levelling screw. A steel compass needle is set in a glazed rectangular box along one edge. The needle can be locked in position by an arm operated by a lever on the side of the box. This box has a degree scale at one end and a bubble level on the base. An inclined brass pillar supports the body of the dial. This consists of a squat cylinder, in the upper face of which is a glass aperture behind which are set two mirrors. Below the cylinder is a silvered hour arc. Both of these parts are attached to a pillar which can rotate within the main pillar, but which can also be locked in position.

The dial has a wooden box with a broken hinged lid, lined with red velvet. It contains a lens, two microscope slides and a folded postcard, dated 1913, giving a description for the use of the dipleidoscope. The microscope slides are wrapped in a sheet from a society's journal detailing the Annual Registry of Deaths by Drowning. The last year entered is from 1916.

This instrument carries no serial number but was probably made in the 1850s, judging by its similarity to AST0243. On the hour-scale, it is stamped 'E.I. DENT PATENTEE LONDON'.

For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.