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Sundial Scale

Sundial Scale

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The scales on this three-foot wooden rule are drawn in red and black ink on paper attached to both sides of the instrument. The left end of one side is marked: A DiALLiNg SCALE [sic]. A brass hanger is screwed into the left end. This side has an hour line, a line of latitude, a line of chords, a scale of inches divided to 1/8" and numbered by ones from 1 to 12, another line of chords, another line of latitude, and another hour line. The last three scales are approximately 3/4 the length of the first three scales. For example, the first hour line is 18" long and the second is almost 13" long.
The middle of this side has two diagrams for calculating the gnomon rods of sundials. Next are two more sets of three scales (hour line, line of latitude, and line of chords). These scales are shorter than the first two sets of scales, with the hour line for the third set measuring 6-3/8" and the fourth hour line measuring 7-3/4". Drawings of a sun and a sundial are at the right end of this side. The side is covered with brass studs for affixing pins while making up gnomons.
The other side has diagrams for a line of inclination; a line of chords; an hour line; lines of chords and latitudes; lines of longitude, chords, latitude, and rhumbs; and an hour line. Two drawings of sundial platforms are at the right end. An oak and pine case is fastened with a metal hook. Presumably a craftsman used this rule to make sundials. The Smithsonian acquired this object in 1961.
Currently not on view
Object Name
scale, sundial
scale rule
date made
mid 18th century
place made
United Kingdom: England
Physical Description
wood (overall material)
paper (overall material)
brass (overall material)
overall: 95 cm x 13.8 cm x 3.4 cm; 37 13/32 in x 5 7/16 in x 1 11/32 in
ID Number
catalog number
accession number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Scale Rules
Data Source
National Museum of American History
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