Maker

Baker, London, England

Model

N/A

Serial Number

93

Dimensions

Telescope length 350 mm, Height 190 mm, Base diameter 90 mm

Image

Description

This dumpy level by Baker is one of the two major types of levels available in the instrument collection. It is the simplest form of levelling instrument consisting of two main parts: the tribrach and the telescope. The tribrach has four foot screws which are used to give the telescope the required horizontal line-of-sight. The instrument has a vertical axis, around which the telescope can be rotated to sight to a staff. No other adjustment is possible between the telescope and the tribrach. 

The level is fitted with a long sensitive bubble tube attached to the top of the telescope which enables the line-of-sight (line of collimation), as defined by the cross hairs, to form a horizontal line which is perpendicular to the direction of gravity at that point. The levelling of this tubular bubble is carried out by manipulating the four foot screws.

There is also a smaller tubular bubble, which is perpendicular to the longer bubble and hence the line-of-sight of the telescope. This bubble provides the instrument with an additional adjustment in the direction perpendicular to the telescope's line-of-sight. Levelling the cross bubble reduces the cross-axis tilt.

In a dumpy level, there is only one axis of rotation - the vertical axis. The initial levelling of the dumpy level must be done very carefully. Any adjustment of the foot screws between sightings to the staff alters the height of the line-of-sight.

History & comments

More modern types of dumpy levels are still used by builders and contractors, but have been largely superseded for survey work. Before the introduction of 'digital levels' with electro-optical staff readings in the 1990s, a more common type of level was the 'automatic level' , which is constructed in a manner similar to the dumpy level, in that the telescope is rigidly fixed to the vertical axis of rotation. However, the difference between the two is that automatic levels feature an optical-mechanical 'compensator' suspended under gravity, which automatically adjusts the line of collimation without the need of a level tube.

Conservation

In container 

Condition

Good condition

Remarks

• Catalogued by T. Ko
• Updated by F. Pall

Dates

Manufactured in 1900 (approx). Catalogued in 1997 and 2010.