Made by Queen & Co., Philadelphia, PA
Artificial Horizons were used by navigators in conjunction with a conventional sextant. The sextant has a split image and views two objects at the same time, and measures the angle between them. This is commonly the horizon and a star. The horizon is used to provide a level surface in place of a bubble tube since the sextant has no tube level. When on land there is no level horizon and on a rolling ship at sea there is no level horizon so the navigator or a surveyor uses an artificial horizon. The tray is filled with mercury, which assumes a level position. The mercury being highly reflective acts as a level mirror. The navigator selects a star in the sky and also locates its position in the mercury surface. The measurement of the angle is made between the actual star position and the reflected image in the mercury. The result is divided by two and that gives the value corresponding to the star's elevation above the horizon. The glass cover is used to protect the mercury from disturbance by air currents. The brass container holds the mercury used in the instrument.
