The Stanhope Demonstrator was the first machine to solve problems in logic. It was designed by

Charles Stanhope, 3rd Earl Stanhope Charles Stanhope, 3rd Earl Stanhope, aka Charles Mahon, 3rd Earl Stanhope, FRS (3 August 175315 December 1816), was a British statesman, inventor, and scientist. He was the father of Lady Hester Stanhope and brother-in-law of William Pitt the ...

to demonstrate consequences in logic symbolically. The first model was constructed in 1775. It consisted of two slides coloured red and gray mounted in a square brass frame. This could be used to demonstrate the solution to a

syllogistic A syllogism (, ''syllogismos'', 'conclusion, inference') is a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two propositions that are asserted or assumed to be true. In its earliest form (define ...

type of problem in which objects might have two different properties and the question was how many would have both properties. Scales marked zero to ten were used to set the numbers or proportions of objects with the two properties. This form of inference anticipated the numerically definite

syllogism A syllogism (, ''syllogismos'', 'conclusion, inference') is a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two propositions that are asserted or assumed to be true. In its earliest form (defin ...

which

Augustus De Morgan Augustus De Morgan (27 June 1806 – 18 March 1871) was a British mathematician and logician. He is best known for De Morgan's laws, relating logical conjunction, disjunction, and negation, and for coining the term "mathematical induction", the ...

laid out in his book, ''

Formal Logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure o ...

'', in 1847.

Construction

The device was a

brass Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

plate about four

inches The inch (symbol: in or ) is a unit of length in the British Imperial and the United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelfth"), the word ''inch'' is also sometim ...

square which was mounted on a piece of

mahogany Mahogany is a straight- grained, reddish-brown timber of three tropical hardwood species of the genus ''Swietenia'', indigenous to the AmericasBridgewater, Samuel (2012). ''A Natural History of Belize: Inside the Maya Forest''. Austin: Universit ...

which was three-quarters of an inch thick. There was an opening with a depression in the wood about one and a half inches square and half an inch deep. This opening was called the ''

holon Holon (, ) is a city in the Tel Aviv District of Israel, located south of Tel Aviv. Holon is part of the Gush Dan, Gush Dan metropolitan area. In , it had a population of , making it the List of cities in Israel, tenth most populous city in Isra ...

'', meaning "whole", and represented the full set of objects under consideration. A slide of red translucent glass could be inserted from the right across the holon. A slide of gray wood could be slid under the red slide. When the device was used for the "Rule for the Logic of Certainty", the gray slider was inserted from the left. When it was used for the "Rule for the Logic of Probability", the gray slider was inserted from above. The red and the gray sliders represented the two affirmative propositions which were being combined. Stanhope called these ''ho'' and ''los''. At least four of the devices with this square style were built. In 1879, Robert Harley wrote that he had one which he had been given by Stanhope's great-grandson,

Arthur Arthur is a masculine given name of uncertain etymology. Its popularity derives from it being the name of the legendary hero King Arthur. A common spelling variant used in many Slavic, Romance, and Germanic languages is Artur. In Spanish and Ital ...

, who had kept one. The other two were owned by Henry Prevost Babbage – the son of

Charles Babbage Charles Babbage (; 26 December 1791 – 18 October 1871) was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer. Babbage is considered ...

, who continued his work on the Analytical Engine. One of the devices was donated to the

Science Museum, London The Science Museum is a major museum on Exhibition Road in South Kensington, London. It was founded in 1857 and is one of the city's major tourist attractions, attracting 3.3 million visitors annually in 2019. Like other publicly funded ...

by the last Earl in 1953. Other styles, such as circular models, were constructed, but these were less convenient.

References

{{authority control Automated reasoning Computer-related introductions in the 18th century English inventions History of logic Mechanical calculators Mechanical computers One-of-a-kind computers

Construction

See also

References