Dollond Rolling Parallel Rule in Case

Description
This ebony ruler has ivory edges divided to 1/12" and numbered by ones from 1 to 6. Ivory rollers at each end of the ruler's interior are numbered by sixes from 6 to 18 and within brass housings. The rollers are connected by a metal rod that runs through a brass and paper counting dial numbered by ones from 1 to 12. A metal pointer or index attached to this dial shows the number of inches the rule has rolled. The rod is covered with ebony. The right end of the rule is marked: DOLLOND (/) LONDON. A wooden case is covered with black leather and lined with green velvet.
The Dollond family began to make eyeglasses, telescopes, and scientific instruments in London in the mid-18th century. A. George Eckhardt invented a rolling parallel ruler in 1771 and gave the patent to the firm. In the late 18th century, brothers and partners Peter and John Dollond advertised four forms of parallel rulers: an ebony rule with unnumbered brass rollers; a rule adding ivory scales on the rollers; a rule adding ivory scales along the edges; and a rule adding the measuring dial with index. This object is a 6" example of the fourth type of rule and sold for 1 pound, 6 shillings. The firm merged with Aitchison & Co. in 1927 and was purchased by Boots Opticians in 2009.
References: Deborah J. Warner, “Browse by Maker: Dollond,” National Museum of American History Physical Sciences Collection: Surveying and Geodesy , http://amhistory.si.edu/surveying/maker.cfm?makerid=10; Maya Hambly, Drawing Instruments: 1580–1980 (London: Sotheby's Publications, 1988), 111–113; A Catalogue of Retail Prices of Optical, Mathematical and Philsophical Instruments made by P. and J. Dollond, Opticians to His Majesty in St. Paul's Church-Yard and St. James Haymarket (London, [1780–1805]); accession file.
Location
Currently not on view
Object Name
parallel rule in case
parallel rule
date made
late 18th century
maker
Dollond
Physical Description
wood (overall material)
fabric (overall material)
leather (overall material)
ebony (overall material)
brass (overall material)
ivory (overall material)
glass (overall material)
Measurements
overall: 1.8 cm x 17.8 cm x 5 cm; 23/32 in x 7 in x 1 31/32 in
place made
United Kingdom: England, London
ID Number
MA*323499
catalog number
323499
accession number
250508
subject
Parallel Rules
Science & Mathematics
Mathematics
Drafting, Engineering
See more items in
Medicine and Science: Mathematics
Parallel Rules
Data Source
National Museum of American History, Kenneth E. Behring Center
Additional Media

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