 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Plumb bob" – news ·newspapers ·books ·scholar ·JSTOR(November 2023) (Learn how and when to remove this message) |
Aplumb bob,plumb bob level, orplummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as avertical direction as a reference line, orplumb-line. It is a precursor to thespirit level and used to establish a verticaldatum. It is typically made of stone, wood, or lead, but can also be made of other metals. If it is used for decoration, it may be made of bone or ivory.
Theinstrument has been used since at least the time ofancient Egypt[1] to ensure that constructions are "plumb", or vertical. It is also used insurveying, to establish thenadir (opposite ofzenith) with respect togravity of a point in space. It is used with a variety of instruments (includinglevels,theodolites, andsteel tapes) to set the instrument exactly over a fixedsurvey marker or to transcribe positions onto the ground for placing a marker.[2]
Theplumb inplumb bob derives from Latinplumbum ('lead'), the material once used for the weightedbob at the end.[3] The adjectiveplumb developed by extension, as did the nounaplomb, from the notion of "standing upright".
Until the modern age, plumb bobs were used on most tall structures to provide verticaldatum lines for the building measurements. A section of the scaffolding would hold a plumb line, which was centered over a datum mark on the floor. As the building proceeded upward, the plumb line would also be taken higher, still centered on the datum. Many cathedralspires,domes andtowers still have brass datum marks inlaid into their floors, which signify the center of the structure above.
A plumb bob and line alone can determine only a vertical reference. However, if they are mounted on a suitable scale the instrument may also be used as aninclinometer to measure angles to the vertical.
Ancient Egyptians used a plumb line attached to the top outer part of a tool resembling a letterE; when placed against a wall, the plumb line would indicate a vertical line. Anarchipendulum, anA-frame level with a plumb line hung from the vertex was also used to find horizontal; these were used in Europe until the mid–19th century. A variation of this tool has the plumb line hung from the top of an invertedT shape.[3]
The earlyskyscrapers used heavy plumb bobs, hung on wire in their elevator shafts.[further explanation needed]
A plumb bob may be in a container of water (when conditions are above freezing temperatures), molasses, very viscous oils or other liquids to dampen any swinging movement,[4] functioning as ashock absorber.
Students offigure drawing will also make use of a plumb line to find the vertical axis through thecenter of gravity of their subject and lay it down on paper as apoint of reference. The device used may be purpose-made plumb lines, or simply makeshift devices made from a piece of string and a weighted object, such as ametal washer. This plumb line is important for lining up anatomical geometries and visualizing the subject'scenter of balance.
| International | |
|---|---|
| Other | |
