Surveying Instrument Collection
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Maker |
Hilger & Watts Ltd., London, England |
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Model |
N/A |
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Serial Number |
93269 |
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Dimensions |
Telescope length 355mm, Height 190mm, Base width 120mm |
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Image |
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Description |
This tilting level by Hilger & Watts is a high precision, three footscrew, levelling instrument typically used in precise and geodetic levelling. The telescope of the instrument features an objective diameter of 50 mm and all the optical surfaces are specially coated to avoid internal reflection, thus ensuring maximum brightness combined with high resolution at a magnification of 38x. The instrument has a built-in parallel plate micrometer for precise levelling with invar staves (graduated in intervals of 0.02 foot). Its function is to determine the distance between the point where the line of collimation (line-of-sight) of the level intersects the staff and the next lower staff graduation, and thus eliminates the need for estimation. The micrometer has a range of 20 divisions (of 0.001 ft). The staff reading can be estimated to 0.0001 ft (0.03mm). The tubular spirit bubble is situated on the left-hand side of the telescope and is permanently attached to the telescope via a solid casting to ensure accurate adjustment. The telescope is supported at its centre by a pivot and may be tilted (up and down) by turning the "tilting screw" which is located on the stage component of the level between the telescope and the base. This tilting screw enables the telescope to be precisely levelled before each staff reading, without altering the height of the telescope. The screw carries a graduated drum working against an index, where one division corresponds to a gradient of 1 in 50,000. As opposed to the dumpy level, the tilting level allows rotations about both the horizontal and vertical axis, however the rotation about the horizontal axis is extremely minute. |
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History & comments |
In 1770, Johann Mayer of Göttingen invented the circular "bull's eye" level used for approximate levelling of instruments. The bubble of the level tube defines a horizontal plane, and, when the instrument is in adjustment, the line of sight which passes through the centre of the cross hairs and the optical centre of the telescope is parallel to this plane. |
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Conservation |
In a container |
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Condition |
Good |
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Dates |
Manufactured in 1950 (approx). Catalogued in 1997. |
