Geometrical Protractor Invented by John Pool

Even though American practitioners highly prized European craftsmanship, some Americans competed relatively early on in U.S. history with imported products by manufacturing, modifying, and marketing mathematical instruments. Between 1825 and 1828, brothers John (1796–1865) and Horace Minot (1803–1878) Pool established a firm in Easton, Mass. Using the name J. & H. M. Pool, they sold levels, compasses, and chains to surveyors, architects, and civil engineers. Within a few years, they had partnered with distributors in Massachusetts, Rhode Island, New York, New Jersey, Pennsylvania, Maryland, and Washington, D.C.
On June 16, 1830, John patented a "geometrical protractor" in the form of the instrument depicted here. Like all U.S. patents issued before 1836, the patent was not numbered and the record was lost to fire. However, Ed Hands and Bob Vogel reported that the Pool family retained a copy of the patent which survives. Although the firm apparently was financially successful and their products were of high quality, John and H. M. parted ways in 1841 and established separate instrument businesses. The brothers and their sons maintained personal and financial connections—at least one of John's sons worked for H.M.—but both businesses closed by the 1880s.
This quarter-circle brass protractor is graduated to quarter-degrees. The brothers devised their own form of a dividing engine to engrave the angle markings. The protractor is labeled by tens from 40° to 0° to 40° and from 50° to 90° to 50°, both in the clockwise direction. The left leg of the protractor is marked: J & H. M. POOL (/) EASTON, MASS. (/) PATENT; $8.00; 40. The protractor is mounted on a mahogany base that extends on either side as a rectangle with width 1-3/8". Unlike other Pool geometrical protractors, which have only the rectangle as backing, the wood on this instrument is cut in a wedge so that the back of the protractor is completely covered. A piece of brass is affixed to the lower edge of the wooden base.
A brass arm is affixed to the protractor's vertex with a wing nut. The portion that slides over the protractor's numbers, as a vernier would, resembles a belt buckle. A curlique and arrow are engraved, perhaps by hand, on the inside of this part of the arm. The number 40 near the wing nut almost aligns with the number 40 on the left leg of the protractor. The extending part of the arm, which is over 14" long, is marked with a diagonal scale. The portion of the scale for measuring to 1/100 of an inch is labeled by ones from 1 to 7, 9 to 1, and 1 to 9. The remainder of the scale is marked by tens from 10 to 90. Ten units correspond to one inch.
References: Donald and Anne Wing, "The Pool Family of Easton, Massachusetts," Rittenhouse 4 (1990): 118–126; United States Patent Office, A List of Patents Granted by the United States from April 10, 1790, to December 31, 1836 (Washington, D.C., 1872), 452; William Lincoln, "[Report from] Worcester Agricultural Society," The New England Farmer, ed. Thomas G. Fessenden, 9, no. 21 (10 December 1830): 164–165; Robert Vogel and Edmund Hands, The Pools of Easton, Massachusetts,
Currently not on view
date made
Pool, John
Pool, Horace Minot
place made
United States: Massachusetts, Easton
Physical Description
mahogany (overall material)
brass (overall material)
overall: 4 cm x 54 cm x 16.5 cm; 1 9/16 in x 21 1/4 in x 6 1/2 in
ID Number
accession number
catalog number
Credit Line
Gift of Timothy Trace
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center


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