Stanhope adding machine

The Englishman Charles, 3rd Earl Stanhope, Viscount Mahon (1753-1816), invented his 12-place adding machine in 1780 after successfully completing his two 4-species machines in 1775 and 1777 (both today in the Science Museum, London). The original version is today housed in the Old Ashmolean Museum, Oxford. Stanhope enlisted the help of the mechanic James Bullock to build it, as inscribed on the cover: ”Visc[oun]t Mahon Inv[enit] 1780 Ja[me]s Bullock Fecit“. The twelve setting discs are all arranged on the planar cover and four are labeled for English currency. The eight decimal discs are for hundred millions down to tens, while the four currency discs are for pounds, shillings, pence and farthings. The dials are turned by means of a stylus and are successively connected within the mechanism by wheels with just one cog. This has the unusual feature that a clockwise turning disc (from the lower row of dials) is followed by an anticlockwise turning one (from the upper row of dials) in a zigzag manner, as can be seen from the numbering. This makes the machine rather difficult to use. A particular problem is the transfer of forces: with the decimal wheels the lever ratio is 1:3 which means that only a third of the force is available for turning the next wheel. With the currency wheels the ratio is even worse. A detailed analysis revealed that the force applied at the beginning was reduced to less than one eightieth of its value in the sixth place, too little for the next transfer to take place, with a normal force applied at the start. Without additional “assistance” it would be totally fruitless to try to add a farthing to the number 999 999 999 999. This replica, with its 160 or so parts, was built by Ullrich Wolff, copying an earlier English replica, partly by hand and partly in the engineering workshop of the firm Klöckner-Möller, Bonn, under the supervision of Rolf Ludwig. The biggest problems were met in the production of certain springs which had to be manufactured from “solid blocks”, and it was also not always easy to procure the right material, e.g. the boxwood for the lid.