Fowler Adder Patent Model

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Some 19th-century Americans earned their keep as inventors and patent agents. One of them was George B. Fowler, inventor of this adder.
This U.S. patent model has a wooden frame with slots for 8 sliding bars. The frame is covered on the left and the right with black zinc plates. These hold the bars in place and also fold over the left and right edges of the device to form the sides. Each bar has a series of regularly spaced holes. The wooden pieces that form the slots are stamped from right to left 1 to 9. Numbers are entered by moving the bars from left to right. Totals are visible on the back of the device. There is no carry mechanism.
According to U.S. Census records, Fowler was born in Long Island in about 1834 or 1835. In 1863, when he patented this device, he listed himself as a resident of Chicago, Illinois. By 1864 he had settled in New York City, and at the end of the decade he was a patent agent in Brooklyn.
This small adder, patented July 14, 1863, was the subject of Fowler’s first patent (#39222). He went on to patent a variety of other devices, including a clothes and hat hook (#40923, December 15, 1863), wood-splitters (#53289, March 20, 1866), a game-box for ten-pins (#107030, September 6, 1870), a wagon-jack (#113285, April 4, 1871), an eggbeater and mixer (#256310, April 11, 1882), a picture cord and hook hanger (#357312, February 8, 1887), and an improved version of his adder (#432266, July 15, 1890).
Production models of Fowler’s instrument survive. Fowler charged $5.00 for the adder. He garnered testimonials from lumber dealers, bookkeepers, and insurance companies, and publicized the instrument in at least one circular and in Scientific American. Correspondence from 1863 suggests that Fowler hoped to find agents who would pay substantial sums to market his machine, but there is no indication that this occurred.
References: U.S. Patent 39,222, July 14, 1863.
Robert B. Otnes, “Sliding Bar Calculators,” ETCetera, #11, June, 1990, p. 7.
P. Kidwell, “Adders Made and Used in the United States,” Rittenhouse, May, 1994, p. 80.
Currently not on view
date made
Fowler, George B.
Fowler, George B.
place made
United States: Illinois, Chicago
place patented
United States: Illinois, Chicago
Physical Description
wood (overall material)
metal (overall material)
overall: 1 cm x 22.5 cm x 11.5 cm; 13/32 in x 8 27/32 in x 4 17/32 in
ID Number
catalog number
accession number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History


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