The calculating machines of Charles Stanhope
The British statesman and versatile scientist Charles Stanhope (see biography of Charles Stanhope) devoted considerable part of his time and money to the developing of three calculating devices of an original design, and a logic machine (see The Demonstrator of Charles Stanhope).
The calculating machines (at least the first two devices) were manufactured by the skilful mechanic James Bullock, the first machine—in 1775, second in 1777 and the last in 1780.
The last machine (from 1780) is the simplest of the 3 devices (see the photo below).
The adding machine of Stanhope from 1777 (Courtesy Nico Baaijens, www.calculi.nl)
It is an adding device with 12 digital positions (dials). The first eight (leftmost) dials are decimal and are labelled HM for hundred millions, XM for ten millions, M for millions, HT for hundred thousands, XT for ten thousands, T for thousands, H for hundreds, and X for tens. The next four dials are labeled L for pounds, S for shillings, D for pence and F for farthings. This is the old English system of money, used until 1971 (4 farthings = 1 penny, 12 pennies = 1 shilling, 20 shillings = 1 pound sterling). The rotating of the dials and entering of the numbers is done by means of a stylus, which can be put in the openings in the periphery of dials. The machine has also a tens carry mechanism.
The other two machines are more complex devices and can be used for the four arithmetical operations. In the machine from 1775 (see the photo below) is used the stepped drum of Leibniz, which teeth however are not smooth, but actually are teeth-strips (strips with 1 to 9 teeth).
The machine of Stanhope from 1775
The calculating mechanism contains 12 stepped drums (see the photo below), mounted on axes in a special movable carriage. To the axes are attached digital wheels (dials), and to the each digit of the dial corresponds a strip of the drum with the appropriate number of teeth (i.e. to digit 0 corresponds the smooth surface of the drum, to 1—a strip with 1 tooth, etc.).
The stepped drum of Stanhope
During the calculations the carriage is moved, and during this movement teeth-strips will be engaged with the gear-wheels of the main counter and will rotate them according to the teeth of the strip. There is also a secondary counter, which counters the number of the moving of the carry and is used during multiplication/division.
The tens carry mechanism is rather complex and innovative. Actually Stanhope is the first inventor, who separated the tens carry operation to two phases: a preparation phase, which is done when the digital wheel rotates from 9 to 0, and the execution phase, which is done during the movement of carriage. Some 100 years later on this 2-phase operation of tens carry will be widely accepted by the mechanics, because this mode of operation removes the very nasty effect of accumulation of strength in the mechanism.
The machine from 1777 (see the photo below) is some kind of improvement of this from 1775.
The machine of Stanhope from 1777, made by James Bullock
In this machine (made by: brass, iron, ivory, and wood; with overall measurements: 70 x 230 x 80 mm) the linear movement of the first machine is replaced by the more convenient and fast rotating movement.
The prototypes of calculating machines of Stanhope were eventually acquired by Charles Babbage, passed down to his son Henry P. Babbage, and given by him to the Victoria and Albert Museum in London.