## Stanhope adapting segment machine

The second 4-species machine designed by Charles, Third Earl Stanhope, Viscount Mahon, was built by the mechanic James Bullock in 1777. It is based on a special adapting segment mechanism. For each place there is an adapting segment which is a device with nine cogs that is set to the corresponding position when a certain digit is entered in this place. At a certain point, all the adapting segments are made to engage a set of transfer-cogwheels in the result mechanism, thus transferring the entered number into the latter. Stanhope, who used an adapted stepped drum mechanism in his first machine for all four operations of arithmetic in 1775, now tried to overcome its imperfect tens-carry mechanism when subtracting. He achieved this in his adapting segment machine by using so-called “double horns” for the tens-carry steps. Before entering a number, the cylinder with the setting discs is pushed to the left. Then an arresting stylus must be withdrawn and is then used to enter the number by turning the relevant discs. The number is shown in the middle row of windows. Then the arresting stylus is replaced, the setting mechanism moved to the right again, and the crank turned through one revolution. This transfers the entered number to the result mechanism. Before the crank is turned, the cogs of the adapting segments are not yet engaged with those of the transfer-cogwheels of the result mechanism. While turning the crank, the curved edge of each adapting segment engages them at just the right moment. If, for example, 5 is entered in a particular place, then the first four cogs of the adapting segment are turned past the corresponding transfer-cogwheel, leaving only the remaining five to engage it. Thus, 5 will appear in the corresponding window of the result mechanism. The double horns are placed in a staggered formation, so the tens-carry steps are performed successively. Their alignment is reminiscent of a double helix, so that in each place one double horn is in the right place after an addition step and another after a subtraction step. With this machine Stanhope demonstrated that he was not only able to build a fully functional 4-species machine based on a totally different principle from that of his first one, but was also able to eliminate the subtractive tens-carry faults of the latter. Thus he counts as one of the most innovative inventors of mechanical calculating machines of the 18th century. Multiplication and division are performed by repeated addition and subtraction with intermediate carriage movements. The cylindrical nine-place setting mechanism moves along a rod of square cross-section, behind it is the result mechanism and in front of it the revolution counter. The nine adapting segments have the digits 0 to 9 inscribed along a quarter of their edge and opposite these there are nine cogs. All nine segments are fixed in position by a rod on the left which must be removed before entering the number, which rotates the segments so that the correct number of cogs will engage later with the result mechanism. Then the arresting rod has to be replaced. Turning the crank through one revolution does three things: 1) the tens-carry mechanism gets turned. 2) The setting mechanism moves a short way to the right and engages the result mechanism. A quarter of one revolution has taken place. Then the number appears in the result mechanism, after which the setting mechanism moves back to the left again. 3) The tens-carry mechanism turns. These steps are all performed by the large cogwheel at the right. It has two segments of fourteen cogs each and engages a wheel with fifteen cogs in the tens-carry mechanism, which thus gets turned once round. In going from 9 to 0, one of the tens-carry teeth turns a lower cogwheel one cog on. This cogwheel features a “tripple horn”, a cog of which will, if required, turn the wheel of the next place on by one cog. Below all this is the axle of the tens-carry mechanism with eleven double horns. These are aligned like a double helix, one for multiplication and the other for subtraction. They perform the tens-carry steps by moving any tripple horns that have been moved into position, after which the respective tripple horn returns to its usual position. The other 14-cog segment of the driving wheel is needed for the tens-carry operations when the crank is turned in the other direction for doing subtraction and division. A 12-place revolution counter is placed closest to the user and is operated by a lever connected to the setting mechanism.