Surveying Instrument Collection
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Maker |
J. W. Handley |
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Model |
N/A |
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Serial Number |
721 |
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Dimensions |
Length 250mm, Height 230mm |
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Image |
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Description |
This instrument measures vertical angles and is used in conjunction with the plane-table in topographical work as a means of obtaining differences of height between the observed points and the plane-table. The instrument consists of a peep-hole carried on a short vertical arm, which is hinged at it's lower end to one end of a fairly heavy, long, narrow, metal stand, a long vertical arm, with a central vertical slit, being hinged to the other end of the stand. A slide, provided with a small window, in the middle of which is a horizontal wire, can be moved up and down the longer vane by a rack and pinion fitted with a milled head. The stand is fitted with two feet at its forward end, and a tilting levelling screw at the other end, and it also carries a level tube for indicating when the instrument is properly levelled. The window and cross hair in the slide can be seen from the peep-hole in the short vane through the slit in the long vane, the latter having a scale of degrees on its inside face at one side of the slot and a scale of natural tangents at the other. In this way, sights to distant objects can be taken and the angle of inclination, or its tangent, read on one of the scales. Usually, it is the tangent scale which is read, as this reading, multiplied by the distance of the object as scaled from the map, gives the difference of elevation between object and plane-table. When the instrument is not in use, the vanes fold down over the stand and the whole apparatus is carried in the leather case. When it is to be used, the instrument is laid on the plane-table and levelled by the levelling screw after the vanes have been lifted to the upright position, and the instrument sighted at the object whose elevation is required. |
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History & comments |
No historical information is available |
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Conservation |
In a fine leather case |
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Condition |
Good, mild rust on surface |
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Remarks |
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Dates |
Manufactured in 1942. Catalogued in 1997 |
