Artificial or mercury roof horizon, rectangular black-lacquered cast iron trough with pouring hole and brass-framed roof-shaped cover with clear glass panels. Round iron bottle filled with mercury with stopper and iron funnel, in fitted wooden carrying box, signed and made by H. Hughes & Son, London. With certificate of Examination from april 1895.
The artificial horizon is used to establish the elevation of the sun or a star when the horizon is not visible. The vertical angle between the celestial body and its reflection in the mercury was mesured. This has to be halved to establish the angle of elevation above the horizon.

Catalog: NM.5-17
Date: ca. 1850
HWL case: 13.5×19.5×15.5 cm
Label: H. Hughes & Son, Opticians, 59 Fen Church Street, London
Roof: same as on the label, No. 601, patent 95 and the name of the owner (?) V. Poole
Origin: England
Condition: perfect
Mercury is poisonous, please pay attention!