Long case clock, astronomical regulator, sidereal time, metal / mahogany, Thomas Earnshaw, London, England, 1791. The Thomas Earnshaw precision astronomical regulator clock consists of timber clock casing and an internal mechanism. The mahogany case can be divided into two sections, the trunk and the hood, while the internal mechanism is made up of of the movement, clock face, pendulum and weight.
The trunk of the case is made from mahogany, with a dark polished surface. It has a flat top and back, but swells slightly to bombe sides near the pendulum. A rectangular door at the front is hinged on one side and has a small key hole on the left and a window at the bottom for viewing the swinging pendulum. When opened, the clocks pendulum and weights are revealed, as well as four labels on the interior. The base of the trunk is square, with cornice edges, a decorative square relief on the front and sits on four bracket feet.
The hood of the clock is also made from mahogany, with a smooth polished finish. It is flat-topped, with a moulded cornice, reeded edges and canted corners, edging a glazed square window at the front, revealing the clock face. This brass hinged window has a small keyhole on the left hand side. The sides are panelled, with the hood sliding forward for removal, only being held in place by a wooden swivel catch inside the door. An admiralty mark, consisting of a broad arrow below an asterisk, can be found on the door of the hood.
The weight driven movement is made from polished brass and consists of a series of plates, supports and gears, which are turned by the constant swaying of the pendulum below. The movement is mounted on a wooden block, which sits atop the trunk and is protected by the hood and can be screwed in place using four wood screws. At the front of the the movement is the clock face. It is square, and made from silvered brass and features three separate dials. The first is a large outer minutes ring with black markings and numerals in 5 second increments. Within this are the two smaller, internal, dials, one for seconds and one for 24 hours, each also inscribed with markings and numerals in black. 'Earnshaw/ London' is engraved in the centre of the hours dial. Each dial has a, blue, steel hand, with the square winder hole on the right.
The pendulum for the Earnshaw clock is a separately suspended, Harrison's, grid-iron pendulum. It consists of nine temperature compensated parallel rods, in brass and steel, with a spherical lenticular bob at the bottom and a graduated regulation nut at the top with numerals, '5:30' in increments of 5 engraved on the surface.
The drive weight for the going train of the regulator clock is a cylindrical, brass, prism with a small metal ring at the top, used for attaching it to a pulley which is connected to the movement by a metal wire, through the underside of the hood.
The winding key is made from metal and has a wooden handle. The key is shaped at a right angle and has 'XII' engraved on the metal.
The two keys for the long case regulator clock consists of a large bi-metallic key, used for the main door in the trunk of the clock and a smaller, silver, key, which is used for the clocks hood door.