(1772-1823) English economist, author of Principles of Political Economy 1817. Among his discoveries were the principle of comparative advantage (that countries can benefit by specializing in goods they produce efficiently and trading internationally to buy others), and the law of diminishing returns (that continued increments of capital and labor applied to a given quantity of land will eventually show a declining rate of increase in output).

(1885-1974) English engineer who played a leading role in the development of the internal-combustion engine. During World War I and World War II, his work enabled British forces to fight with the advantage of technically superior engines. His work on combustion and detonation led to the octane-rating system for classifying fuels for gasoline engines.
Ricardo was born in London. At the age of 12 he built a steam engine, and as a student at Cambridge he designed and built a motorcycle, with its power unit. In 1905 he designed and built a two-cylinder, two-stroke engine and a four-cylinder version to power his uncle's large automobile. During World War I, Ricardo worked on aircraft engines and designed the engine for the Mark V tank. In 1917 he set up a research and consultancy company, which worked on engine development and categorization of fuels according to their ease of detonation.
Ricardo designed an effective combustion chamber, which was also used in his aircraft engines during World War II.