| 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. |
| 1810–1859 | USA [agriculture] | US cotton production, the vast majority of which is grown in the southern states, rises from 171,000 bales in 1810 to just under 5.4 million in 1859. |
| 1840–1850 | USA [farming] | Wheat becomes an increasingly important cash crop in the USA; production in 1839 is nearly 85 million bushels and climbs to over 100 million bushels in 10 years. |
| 1840–1860 | world [plagues and epidemics] | A cholera pandemic kills millions of people worldwide. |
| 1841–1850 | USA, UK [statistics and demography] | Emigration to the USA is 267,044 from Britain and 780,719 from Ireland. |
| 1842 | England [poetry] | The English writer Alfred, Lord Tennyson, publishes Poems, which contains revised versions of ‘The Lotus-Eaters’ and ‘The Lady of Shalott’, and new works such as ‘Morte d'Arthur’, ‘Locksley Hall’, and ‘Ulysses’. |
| 1842 | UK [newspapers] | The first photograph to be printed in a newspaper appears in the London, England, newspaper The Times. |
| 1842 | Italy, UK, USA [opera] | The opera Nabucodonosor (later known as Nabucco) by the Italian composer Giuseppe Fortunino Francesco Verdi is first performed, in Milan, Italy. It is first performed in Great Britain in 1846 (in London, England), and in the USA in 1848 (in New York City). |
| 1842 | Germany [orchestral music] | German composer Felix Mendelssohn completes his Symphony No 3 (Opus 56), the Scotch. He began work on it in 1830. |
| 1842 | Austrian Empire [physics] | Austrian physicist Christian Doppler publishes Über das farbige Licht der Doppelsterne/On the Coloured Light of Double Stars, in which he describes how the frequency of sound and light waves changes with the motion of their source relative to the observer – the ‘Doppler effect’. He also theorizes that the wavelength of light from a star will vary according to the star's velocity relative to Earth. |
| 1842 | Germany [astronomy] | The German astronomer Friedrich Bessel suggests that perturbations to the motion of Sirius are due to the existence of a companion star. |
| 1842–1845 | UK [astronomy] | Irish astronomer William Parsons (later Lord Rosse) builds the 180 cm/72 in reflecting telescope ‘Leviathan’. |
| 13 January 1842 | Afghanistan, UK [wars] | Most of General William Elphinstone's British forces are massacred by Afghan troops at Gandalak, Afghanistan, in the Second Afghan War. |
| 8 May 1842 | France [transport disasters] | The Paris–Versailles train jumps the track and catches fire trapping passengers inside the wooden carriages; 100 people die. It is the world's first serious train accident. |
| 13 May 1842 | England [births and deaths] | Arthur Seymour Sullivan, British composer of operettas with William Schwenk Gilbert, born in London, England (–1900). |
| August 1842 | UK [political events] | Strikes and riots in protest at economic conditions break out in the manufacturing areas of England and quickly turn into agitation in favour of the People's Charter of 1835. |
| 29 August 1842 | UK, China [treaties] | By the Treaty of Nanjing ending the First Opium War between Britain and China, Canton, Shanghai, and other Chinese ports are opened to Britain, which is permitted to establish consular facilities and obtains a large indemnity. |
| 10 October 1842 | Afghanistan, UK [wars] | The First Anglo-Afghan War, begun by a British invasion in 1839 to counter perceived Russian and Persian expansionism in the region, ends in British defeat. After the massacre of over 3,000 British and Indian troops retreating from a popular revolt in Kabul in January, a punitive expedition reoccupying the country is withdrawn by the British government. |
