Hairspring Compass with Lengthening Bar and Pen Point

This metal compass has a cylindrical scrolled handle. The upper parts of the legs have decorative grooves on either side. A thumbscrew on one leg may be used to finely adjust the angle of the leg (hence, the name "hairspring"). The lower parts of the legs are hinged and are attached by screws so that the pencil point and needle point may be replaced by the pen point or lengthening bar contained with the instrument. Small thumbscrews on the needle, pencil, and pen points allow for fine adjustments.
The donor of this object, William J. Ellenberger (1908–2008), studied electrical and mechanical engineering at The George Washington University between 1925 and 1934. He then worked for the Potomac Electric Power Company and the National Bureau of Standards. During World War II, he served in the U.S. Army Signal Corps. He was a civilian construction management engineer for the army from 1954 to 1968, when he became a private consultant. He may have acquired this instrument during his studies or early career.
Currently not on view
Object Name
compass, drawing
date made
early 20th century
Physical Description
metal (overall material)
steel (overall material)
overall: 1.5 cm x 16 cm x 2.5 cm; 19/32 in x 6 5/16 in x 31/32 in
ID Number
accession number
catalog number
Science & Mathematics
Drawing Instruments
Dividers and Compasses
See more items in
Medicine and Science: Mathematics
Dividers and Compasses
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of William J. Ellenberger

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