Station Pointer

Description:

To determine where one is going, it is necessary to know where one is currently located. Beginning in the 17th century, navigators combined multiple triangulations to ascertain the position of their ships. With a sextant and a station pointer, sailors in the 19th century could plot locations from three data points as long as they were within view of land.

Navigators employed a sextant to measure the angles between their position and each of three known landmarks. They then placed the station pointer on their chart and set its arms to the observed angles. The center of the protracting circle on the station pointer would then show the position of the ship. Station pointers were also useful for surveying the geographical features of coastlines, either from the water or on land, in order to create accurate maps.

This station pointer consists of a brass circular protractor divided by single degrees and marked by tens from 0° to 180° to 0°. Three black-coated anodized brass arms meet in the open center, which has a brass pricker for positioning on the chart. Three brass and blackened anodized brass legs are screwed to the center piece by rings on one end of each arm. Each leg has a thumb screw for tightening in position and an arrow for pointing to the angle measurement. The number 602 is engraved near the top of the center leg.

The rectangular wooden case has wood built-ins and green fabric lining to support and cushion the instrument. The case is fastened with two brass hooks. It is cracked in the left front corner, and there are several dirt and paint marks. This station pointer was probably mainly used for charting a ship's position, since it lacks the verniers that were typically found on the arms of station pointers employed in surveying.

Ursula N. Forbes donated the instrument in 1986.

Compare this station pointer to ID Number MA.333663.

References: National Maritime Museum, "Charting Instruments—Station Pointer," http://www.nmm.ac.uk/collections/search/listResults.cfm?name=Station%20pointer&category=90488; William John Macquorn Rankine, A Manual of Civil Engineering, 5th ed. (London, 1867), 120–121.

Date Made: 20th century

Location: Currently not on view

Subject: MathematicsProtractorNavigation

Subject:

See more items in: Medicine and Science: Mathematics, Science & Mathematics, Protractors

Exhibition:

Exhibition Location:

Credit Line: Gift of Ursula N. Forbes

Data Source: National Museum of American History

Id Number: 1986.0316.07Accession Number: 1986.0316Catalog Number: 1986.0316.07

Object Name: protractor

Physical Description: felt (overall material)hardwood (overall material)brass (overall material)Measurements: overall: 5.6 cm x 60.7 cm x 18.2 cm; 2 7/32 in x 23 29/32 in x 7 5/32 in

Guid: http://n2t.net/ark:/65665/ng49ca746a7-2b7a-704b-e053-15f76fa0b4fa

Record Id: nmah_904347

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