1801

1730–1807	UK [newspapers]	The Daily Advertiser is launched in London, England. With its dependence on advertisements, this may be regarded as the first modern newspaper.
1799–1825	[maths]	The French mathematician and physicist Pierre-Simon Laplace publishes the five-volume Traité de mécanique céleste/Celestial Mechanics, which applies calculus to the motions of celestial bodies and Isaac Newton's theories of the Solar System to show how its stability is implicit in the law of gravitation.
1800–1850	USA [consumer products]	A revolution in retail and wholesale trade occurs: specialization transforms the urban retail market, replacing the general store with individual stores for hardware, groceries, dry goods, furnishing, books, tobacco, and so on. Cash-only sales policies are instituted around 1806.
1801	Italy, Spain, UK, Ireland, USA, France, Austria, Germany [statistics and demography]	The first accurate censuses, taken in 1800 and 1801, provide population statistics for: Italy, 17.2 million; Spain, 10.5 million; Great Britain, 10.4 million; Ireland, 5.2 million; the USA, 5.3 million; also for London, England, 864,000; Paris, France, 547,756; Vienna, Austria, 231,050; Berlin, Germany, 183,294, and New York City, 60,515.
1801	China, India, Japan, France, Germany, UK, Spain, USA [statistics and demography]	Populations in millions: China, 295; India, 130; Japan, 15; France, 27; the German states, 14; Britain, 10; Spain, 10; USA, 5.
1801	England [physics]	English physician and physicist Thomas Young discovers the interference of light when he observes that light passing through two closely spaced pinholes produces alternating bands of light and dark in the area of overlap. He thereby establishes the wave theory of light.
1801	USA [popular culture]	Frontier culture evolves in the western USA. Forms of entertainment – logrolling, barbecuing, whiskey drinking, gambling on horses or card playing, hunting, shooting, and dancing country reels and jigs – reflect the character of the frontier.
1801	UK [everyday life]	The Act of Union, formally uniting Britain and Ireland, is marked with the incorporation of the cross of St Patrick into the design of the British flag.
1801	Germany [maths]	German mathematician Carl Friedrich Gauss publishes Disquisitiones Arithmeticae/Discourses on Arithmetic, which deals with relationships and properties of integers and leads to the modern theory of algebraic equations.
1801	England [chemistry]	English chemist and physicist John Dalton formulates the law of partial pressure of gases.
1801	France [energy]	French engineer Philippe Lebon lights the Hotel Seignelay in Paris, France, with ‘thermolampes’. It is the first public building to be lit with gas.
1 January 1801	UK [legislation]	The Act of Union creates the United Kingdom of Great Britain and Ireland, bringing Ireland under direct control of the Parliament in Westminster.
9 February 1801	France, Austria, Belgium, Luxembourg, Italy [treaties]	The Treaty of Lunéville, following the French defeat of Austria in Napoleon Bonaparte's campaign of 1800–01, marks the virtual destruction of the Holy Roman Empire. France gains all territory west of the Rhine, including Belgium and Luxembourg. The grand duchy of Tuscany is ceded to the duchy of Parma to form the new kingdom of Etruria, and recognition is given to the Batavian, Cisalpine, Helvetian, and Ligurian republics.
14 March 1801	UK [political events]	William Pitt the Younger steps down as prime minister of Britain over King George III's refusal to consider the question of Catholic Emancipation (the removal of legal restrictions on voting and holding political office by Catholics). He is replaced by fellow Tory politician Henry Addington.
21 March 1801	France, Spain, Portugal, UK, North America [treaties]	The Treaty of Aranjuez is signed between France and Spain, formalizing their ultimatum to Portugal to break its traditional allegiance to Britain. Spain also agrees to cede the North American territory of Louisiana to France.
23 March 1801	Russian Empire [political events]	Tsar Paul I of Russia is assassinated by military officers concerned by his dangerous mental instability. He is succeeded by his son, Alexander I.
2 April 1801	UK, Denmark [wars]	British vice admiral Horatio Nelson is victorious against the Danish fleet in the Battle of Copenhagen, fought in retaliation for Danish actions against Britain in closing the River Elbe.
May 1801	USA [ships and shipping]	US inventor Robert Fulton completes the submarine Nautilus. It has enough air for four passengers for three hours and is driven by a hand-turned propeller while submerged, and a collapsible mast and sail while on the surface. Despite sinking several ships neither the British nor the French support it.
1 June 1801	USA [births and deaths]	Brigham Young, US religious leader of the Mormon Church who leads converts to colonize the US West and establishes a base at Salt Lake City, born in Whitingham, Vermont (–1877).
6 June 1801	Spain, Portugal, UK [treaties]	The Treaty of Badajoz formally ends the war between Spain and Portugal over Portugal's traditional allegiance to Britain. Portugal cedes the province of Olivenza and agrees to close its ports to British ships.
17 June 1801	UK, Russian Empire, Prussia, Sweden, Denmark, Prussia, France [treaties]	The Armed Neutrality of the North (the confederation of Russia, Sweden, Denmark, and Prussia, formed to defend their right to export goods to Napoleonic France) breaks up with the signing of the Treaty of St Petersburg between Britain, Russia, and Prussia, which recognizes British right of search of merchant vessels.
15 July 1801	France, Italy [political events]	A concordat with the papacy drawn up by Napoleon Bonaparte effectively places the church in France under state control. The pope is allowed to keep the Papal States, with the exception of Ferrara, Bologna, and Romagna, which are annexed by France.
2 September 1801	Egypt-Ottoman, France, UK [French Revolutionary Wars (1792–1801)]	French forces in Egypt under General Jean Menou surrender to the British and are immediately offered free passage home, ending Napoleon Bonaparte's hopes of oriental conquest.
12 September 1801	Russian Empire [political events]	Tsar Alexander I of Russia announces the annexation of the kingdom of Georgia and George XIII, Regent of Georgia, recognizes the Russian decision instead of accepting the traditional suzerainty of Persia.
1 October 1801	UK, France [treaties]	Preliminaries of peace are signed between Britain and France; Britain is to restore all maritime conquests, except Trinidad and Ceylon, to France, Spain, and the Netherlands; France agrees to evacuate Naples and the Papal States; the integrity of Portugal is recognized; the independence of the Ionian Islands is agreed upon; both French and British armies are to evacuate Egypt, which is to be restored to the Ottoman Empire, and Malta is to be restored to the Knights of St John by Britain.
24 December 1801	UK [railways]	English engineer Richard Trevithick builds a steam-powered carriage, which he successfully drives up a hill in Camborne, Cornwall, England.