Jules Dupuit (18 May 1804 – 5 September 1866) was a
FrenchFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
civil engineerA civil engineer is a person who practices civil engineering, one of the many professions of engineering. Originally a civil engineer worked on public works projects and was contrasted with the military engineer, who worked on armaments and defenses...
and
economistAn economist is an expert in the social science of economics. The individual may also study, develop, and apply theories and concepts from economics and write about economic policy...
.
He was born in
FossanoFossano is a town and commune of Piedmont, Italy, in the province of Cuneo. It is the fourth largest town of the Province of Cuneo, after Cuneo, Alba and Bra.It lies on the main railway line from Turin to Cuneo and to Savona, and has a branch line to Mondovì....
,
ItalyItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
then under the rule of Napoleon Bonaparte. At the age of ten he emigrated to France with his family where he studied in
VersaillesVersailles , a city renowned for its château, the Palace of Versailles, was the de facto capital of the kingdom of France for over a century, from 1682 to 1789. It is now a wealthy suburb of Paris and remains an important administrative and judicial center...
— winning a Physics prize at graduation. He then studied in the
Ecole polytechniqueThe École Polytechnique is the foremost French engineering school. Known for its extremely competitive entrance exam, it produces graduates that occupy outstanding positions in industry and research...
as a civil engineer. He gradually took on more responsibility in various regional posts.
Jules Dupuit (18 May 1804 – 5 September 1866) was a
FrenchFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
civil engineerA civil engineer is a person who practices civil engineering, one of the many professions of engineering. Originally a civil engineer worked on public works projects and was contrasted with the military engineer, who worked on armaments and defenses...
and
economistAn economist is an expert in the social science of economics. The individual may also study, develop, and apply theories and concepts from economics and write about economic policy...
.
He was born in
FossanoFossano is a town and commune of Piedmont, Italy, in the province of Cuneo. It is the fourth largest town of the Province of Cuneo, after Cuneo, Alba and Bra.It lies on the main railway line from Turin to Cuneo and to Savona, and has a branch line to Mondovì....
,
ItalyItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
then under the rule of Napoleon Bonaparte. At the age of ten he emigrated to France with his family where he studied in
VersaillesVersailles , a city renowned for its château, the Palace of Versailles, was the de facto capital of the kingdom of France for over a century, from 1682 to 1789. It is now a wealthy suburb of Paris and remains an important administrative and judicial center...
— winning a Physics prize at graduation. He then studied in the
Ecole polytechniqueThe École Polytechnique is the foremost French engineering school. Known for its extremely competitive entrance exam, it produces graduates that occupy outstanding positions in industry and research...
as a civil engineer. He gradually took on more responsibility in various regional posts. He received a
Légion d'honneurThe Légion d'honneur or Ordre national de la Légion d'honneur is a French order established by Napoleon Bonaparte, First Consul of the First Republic, on 19 May 1802...
in 1843 for his work on the French road system, and shortly after moved to Paris. He also studied flood management in 1848 and supervised the construction of the Paris
sewer systemA sanitary sewer is a type of underground carriage system, , for transporting sewage from houses or industry to treatment or disposal...
. He died in
ParisParis is the capital of France and the country's most populous city. It is situated on the river Seine, in northern France, at the heart of the Île-de-France region...
.
Engineering questions led to his interest in economics, a subject in which he was self-taught. His 1844 article was concerned with deciding the optimum
tollA toll bridge is a bridge over which traffic may pass upon payment of a toll, or fee.- History :The practice of collecting tolls on bridges probably harks back to the days of ferry crossings where people paid a fee to be ferried across stretches of water. As boats became impractical to carry large...
for a bridge. It was here that he introduced his curve of diminishing marginal utility. As the quantity of a good consumed rises, the marginal utility of the good declines for the user. So the lower the toll (lower marginal utility), the more people who would use the bridge (higher consumption). Conversely as the quantity rises (people allowed on the bridge), the willingness of a person to pay for that good (the price) declines.
Thus, the concept of diminishing marginal utility should translate itself into a downward-sloping demand function. In this way he identified the demand curve as the marginal utility curve. This was the first time an economist had put forward a theory of demand derived from marginal utility. Although not the first time that the demand curve had been drawn, it was the first time that it had been proved rather than asserted.
Dupuit's logic was suspect in that it skipped over the fact that marginal utility is particular to an individual, while market demand is an aggregate. Nothing was said on the interpersonal comparability of utility in order to connect personal marginal utility to aggregate demand. Dupuit, however, did not draw a supply curve and thus did not get price-determination into his story.
Dupuit went on to define "relative utility" as the area under the demand/marginal utility curve above the price and used it as a measure of the welfare effects of different prices -- concluding that public welfare is maximized when the price (or bridge toll) is zero. This was later known as
Marshall'sAlfred Marshall was an English economist and one of the most influential economists of his time, being one of the founders of neoclassical economics...
"consumer surplus".
Dupuit's reputation as an economist does not rest on his advocacy of
laissez-faireThe general meaning of Laissez-faire is to allow events to take their own course, or to let people do what they choose. The term is a French phrase literally meaning "let it be" or "leave it alone"....
economics (he wrote "Commercial Freedom" in 1861) but on frequent contributions to periodicals. Wanting to evaluate the net economic benefit of public services, Dupuit analysed capacities for economic development, and attempted to construct a framework for
utility theoryIn economics, the marginal utility of a good or of a service is the utility of the specific use to which an agent would put a given increase in that good or service, or of the specific use that would be abandoned in response to a given decrease...
and measuring the prosperity derived with public works. He also wrote on
monopolyIn economics, a monopoly exists when a specific individual or an enterprise has sufficient control over a particular product or service to determine significantly the terms on which other individuals shall have access to it...
and
price discriminationPrice discrimination exists when sales of identical goods or services are transacted at different prices from the same provider. In a theoretical market with perfect information, no transaction costs or prohibition on secondary exchange to prevent arbitrage, price discrimination can only be a...
.
Dupuit also considered the
groundwater flow equationUsed in hydrogeology, the groundwater flow equation is the mathematical relationship which is used to describe the flow of groundwater through an aquifer. The transient flow of groundwater is described by a form of the diffusion equation, similar to that used in heat transfer to describe the flow...
, which governs the flow of
groundwaterGroundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in...
. He assumed that the equation could be simplified for analytical solutions by assuming that groundwater is hydrostatic and flows horizontally. This assumption is regularly used today, and is known by hydrogeologists as the
Dupuit assumptionThe Dupuit assumption holds that groundwater moves horizontally in an unconfined aquifer, and that the groundwater discharge is proportional to the saturated aquifer thickness...
.