artificial horizon, for use with sextant
Date: late 19th century
Inventory Number: 5322
Classification: Artificial Horizon
Subject:
Maker: L. Casella (1860 - 1905)
Owner: Institute of Geographical Exploration (1929 - 1952)
Cultural Region:
Place of Origin:
Dimensions:
9 × 9 × 3 cm (3 9/16 × 3 9/16 × 1 3/16 in.)
case: 10 × 10 × 5 cm (3 15/16 × 3 15/16 × 1 15/16 in.)
Accessories: brown leather case with belt and buckle closure
Description:
Metal cylinder with optical glass lid, with mercury chamber inside.
The glass lid screws on and off. The cylinder itself is divided into two parts; the upper portion is about one-third as tall the lower portion. The upper portion may be turned to right or left to open or close the mecury chamber inside, as indicated by the arrow engraved on the top portion coming into alignment with the vertical lines next to the words "SHUT" (on the left) and "OPEN" (on the right) engraved on the lower portion.
When the chamber is opened, mercury runs into the trough on the top of the cylinder through a pinhole to one side of the trough; it runs back into the chamber through a slightly larger, sunken hole on the opposite side of the trough.
The instrument is stored in a circular brown leather case with a leather strap and buckle to hold the lid of the case closed.
The glass lid screws on and off. The cylinder itself is divided into two parts; the upper portion is about one-third as tall the lower portion. The upper portion may be turned to right or left to open or close the mecury chamber inside, as indicated by the arrow engraved on the top portion coming into alignment with the vertical lines next to the words "SHUT" (on the left) and "OPEN" (on the right) engraved on the lower portion.
When the chamber is opened, mercury runs into the trough on the top of the cylinder through a pinhole to one side of the trough; it runs back into the chamber through a slightly larger, sunken hole on the opposite side of the trough.
The instrument is stored in a circular brown leather case with a leather strap and buckle to hold the lid of the case closed.
Signedengraved on trough, top center: L. CASELLA / LONDON
Inscribedengraved on trough, bottom center: PATENT / No 521
engraved on side of bottom portion of cylinder: SHUT | | OPEN
engraved on side of bottom portion of cylinder: SHUT | | OPEN
FunctionFor use with a sextant. The artificial horizon serves as a point of reference to determine altitude when the actual horizon is obscured, as by fog.
The user first places the artificial horizon on a flat surface. He turns the cylinder to its open position to fill the trough with mercury. Next, he locates the reflection of the object to be sighted in the mercury; he then adjusts the sextant sights so that the object and its reflection coincide with one another.
The user first places the artificial horizon on a flat surface. He turns the cylinder to its open position to fill the trough with mercury. Next, he locates the reflection of the object to be sighted in the mercury; he then adjusts the sextant sights so that the object and its reflection coincide with one another.
Primary Sources"Artificial Horizons," List, with Notes, of Standard Meteorological and Other Instruments . . . , Manufactured by L.P. Casella, London: 1862, 51. Available online here.;
"Artificial Horizons," Surveying and Drawing Instruments, C.F. Casella & Co., Ltd., London: 1911, 35. Available online here.
"Artificial Horizons," Surveying and Drawing Instruments, C.F. Casella & Co., Ltd., London: 1911, 35. Available online here.