Surveying Instrument Collection
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Maker |
A. Tornaghi |
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Model |
N/A |
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Serial Number |
S. G. O. No. 12 |
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Dimensions |
Length 313mm, Width 45mm, Height 190mm |
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Image |
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Description |
This trough compass, unlike the surveyor's and prismatic compasses, does not form a complete surveying instrument. The needle of this trough compass consists of a long (30 cm), narrow, magnetised bar of steel, pointed at both ends, with the usual agate bearing at its centre. It is mounted in a narrow rectangular box carrying a pivot at its centre. This box features a tongue or lever, worked from a small stud or handle outside, which enables the needle to be lifted off and kept clear of the pivot when the instrument is not in use. At each end of the box, which is closed by a glass cover, is a block of metal, the top of which is at the same level as the tip of the needle, and on which is engraved a zero line, the magnetic meridian, and a very short graduated arc extending about 5 degrees on either side of the zero mark. The instrument can be screwed onto a tripod and levelled by four levelling screws. It is used in navigation and surveying to assist in locating and describing stations and in orientating reconnaissance sketches. This trough compass carries the inscription "Standard Needle", S.G.O. (Surveyor General's Office) and was used for the calibration of the "Box Compasses" used by surveyors in the field . |
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History & comments |
First instruments are dated 1030-1093 ( Encyclopaedia of Shon-Kua China ). The Compass was introduced to Europe by Marco Polo in 1260. |
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Conservation |
In a fine wooden box |
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Condition |
Good condition, well maintained |
| Remarks |
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Dates |
Manufactured in 1860 (approx.). Catalogued in 1997. |
