Amos Mendenhall

The practical calculator of Amos Mendenhall (© National Museum of American History, Washington, D.C.)
The practical calculator of Amos Mendenhall, perspective view (© National Museum of American History, Washington, D.C.)

On 13 August 1867, Amos Mendenhall, a merchant and amateur mechanic from Cerro Gordo, Randolph County, Indiana, patented an improved calculating machine (US patent Nr. 67786). The patent model of the device (up to 1880, the US Patent Office required inventors to submit a model with their patent application) is still preserved in the National Museum of American History, Washington, D. C. (see the nearby image).

The so-called practical calculator of Amos Mendenhall was described by the inventor himself as a machine by which figures of any desired magnitude may be readily added, subtracted, multiplied, and divided. It is made of brass and is placed in a square metal box with overall measurements: 5.4 cm x 13 cm x 13.8 cm (although Mendenhall stated that the device is not limited to a particular size or shape, and may be made of wood, card-board, or any other suitable material). The box has a boss in the center inside, in which the shaft of a cylinder with a graduated plate is to turn.

The practical calculator of Amos Mendenhall is an adder with a brass box that has a rotating disc inset on the top. There are 100 small holes around the rim of the disc. Outside the disc, on the top of the box, is a circular ring numbered from 01 to 99, with a gap at 00. Outside of this are three rings of holes, with 100 holes in each ring. These holes are to be used to hold markers indicating digits carried when the disc makes full rotations.

The practical calculator of Amos Mendenhall (© National Museum of American History, Washington, D.C.)
The practical calculator of Amos Mendenhall, side view (© National Museum of American History, Washington, D.C.)

On the side of the box is placed a rotating multiplication table (see the nearby image).

Amos Mendenhall proposed two methods for recording numbers over 99. The first was a set of 9 holes around the edge of the fixed disc, into which the operator could place a pin. Whenever the rotating disc moved a full turn, the operator moved the pin up to the next hundreds digit. Mendenhall suggested a mechanism that would count the number of times the upper plate rotated, and hence give the hundreds place. If the operator rotated especially energetically and arrived at higher numbers, he suggested a system of pins to be used to represent thousands and higher places.

Biography of Amos Mendenhall

Mendenhall family were descendants of the early settler John Mendenhall (1659-1743) from Wiltshire, England, who came to America in the early 1680s and settled in Chester County, Pennsylvania.

Amos Cowgill Mendenhall was born on 16 November 1828, in Clinton County, Ohio, to Hiram Mendenhall (20 Feb. 1801-30 Jun. 1852) and Martha Ann Hale (23 Jun. 1801-5 Aug. 1880). He was named after his uncle Amos Cowgill (1794-1856), who married Hiram’s sister Edith (1799-1888). Amos had two sisters (Rowena (1822-1887), and Martha Ann (1826-1862), and seven brothers (Joseph Hale (1824-1908), Nathan (b. 1830); Jacob Hale (1833-1885); John and William, twins, (born and died in 1835); Samuel H. (1836-1923), and James Hiram (1839-1909).

Hiram L. Mendenhall was a minister, extensive landowner, miller, and farmer by trade and a Hicksite Quaker and abolitionist in belief, one of the most outstanding figures to be found in the list of Quaker pioneers. In 1836 Mendenhall clan (Hiram together with his father Nathan and several of his brothers and their families) moved from Clinton County, Ohio, to Randolph County, Indiana, where he entered 400 acres of land (a wild forest), and opened a fine farm. Three years later he erected a sawmill, then two grist mills, and later on a woolen factory.

In 1837 Hiram Mendenhall laid out the town of Unionport, and in 1845 went on to pool his property with others to form the Unionport commune of the Society for Universal Inquiry and Reform. This social experiment soon collapsed (only one year later), leaving the Mendenhall’s financial situation hopeless. In 1850 during the California Gold Rush Hiram and Amos went to California to recoup the family fortunes in the gold fields. They didn’t find gold, but eventually erected a sawmill on the Sacramento river, and sold it for a goodly sum of money. In 1852 they embarked for home upon a steamer by way of Havana, Cuba, but Hiram died of cholera on 30 June on shipboard in the Gulf of Mexico.

Amos, his mother, and his siblings continued to live in the vicinity of Unionport (in Cerro Gordo), where Amos managed a farm, general store, manufactured goods, etc. He obviously was an imaginative man and very good mechanic, because, besides the above-mentioned patent for the calculator, Amos is the holder of several more patents in the USA and Canada for gold mining devices (US360713 and US540997), tricycle (US453151), and bicycle (US740156).

Amos Cowgill Mendenhall never married. He died on 10 April 1909, in Unionport, IN.