Circular Adders

A collection of adders including a Magic-Brain Calculator, an Exactus Mini-Add, a Troncet Arithmographe, and a Locke Adder.

On some adders, numbers were represented along an arc of a circle. People used their fingers or a stylus to enter numbers. On a few of these instruments, a mechanism allowed one to carry a single digit. These objects are described here as adders with carry. They blur the line between adders and adding machines.

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Hart's Mercantile Computing Machine

The instrument consists of three concentric brass discs, a brass marker, a steel stop, and a wooden handle (instrument must be removed from box to find handle). Each brass disc has the numbers from 0 to 99 stamped around the edge.
Description
The instrument consists of three concentric brass discs, a brass marker, a steel stop, and a wooden handle (instrument must be removed from box to find handle). Each brass disc has the numbers from 0 to 99 stamped around the edge. The two inner discs both have a circle of 100 holes just outside the numbers. The inner holes are used to add the last two digits of a number by rotation. Any hundreds value in the sum carries to the second set of holes, which are used to add hundreds and thousands places.
The machine is in a cylindrical wooden case with cover.
According to the Kirksville [Missouri] Democrat for August 2, 1888, by then Hart had sold 3500 of these devices and “he lately ordered one thousand more.”
References: U.S. Patent #199289
P. Kidwell, "Adders Made and Used in the United States," Rittenhouse, 1994, 8:78-96.
Kirksville [Missouri] Democrat, August 2, 1888.
Location
Currently not on view
date made
1878
patentee
Hart, William
maker
Scovill Manufacturing Company
ID Number
1993.0510.01
accession number
1993.0510
catalog number
1993.0510.01

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