Stanhope stepped drum machine

In 1775 Charles, Third Earl Stanhope, Viscount Mahon (1753-1816), built the first of three mechanical calculating machines. As engineer, writer, scientist and politician the construction of such a machine was very dear to him, not only from the scientific and engineering point of view, but also because it would enable him to demonstrate the size of Great Britain’s state debt very graphically in parliament. His three machines were based on different systems. The last one is just an adding machine. The first is somewhat special: for each of the twelve places there is a horizontal rotatable metal cylinder inscribed with the numbers 0 to 9 around its front edge and, corresponding to these, longitudinal rows of that number of teeth. When a number is entered by turning these cylinders, in each place the corresponding number of teeth ends up facing downwards and engages a set of coaxial cogwheels, thus transferring the number into the result mechanism. When multiplying, the movable carriage is pulled towards one and then pushed away again. This first transfers the entered number into the result mechanism and then does the tens-carry steps. The multiplier is set at the beginning and when 0 is reached, the multiplication is complete. This facilitates subtraction and division, as the counter now rises from 0 to the answer. To prepare the machine for this, a toggle lever at the side is moved until a “D” appears in the window to right instead of an “M”. This, however, reverses the process during the push-and-pull of the carriage: the transfer to the result mechanism now takes place in the second step, with all rotations reversed, and the tens-carry steps are performed in the first step. This, however, has the disadvantage that the tens-carry steps arising in the second step are not carried out. Stanhope solved this by incorporating an additional small white-handled crank at the left with which any outstanding tens-carry steps can be done. The machine also features a place-shift mechanism to allow multi-digit multipliers and to facilitate division. The machine is made of brass, steel, ivory and mahogany. It was built in 1996 and is an exact copy of the original housed in the Science Museum, London. It is fully functional.