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1850 (MDCCCL)was a common year starting on Tuesday of the Gregorian calendar and a common year starting on Sunday of the Julian calendar, the 1850th year of the Common Era (CE) and Anno Domini (AD) designations, the 850th year of the 2nd millennium, the 50th year of the 19th century, and the 1st year of the 1850s decade. As of the start of 1850, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
- July – Taiping Rebellion: Hong Xiuquan orders the general mobilisation of rebel forces.
- July 1 – St. Mary's School for Boys (the future University of Dayton) opens its doors in Dayton, Ohio.
- July 9
- Mírzá 'Alí-Muhammad, known as the Báb, is executed by a firing squad in Tabriz, Persia, for claiming to be a prophet.
- Vice President Millard Fillmore becomes the 13th President of the United States, upon the death of President Zachary Taylor.
- July 10 – President Millard Fillmore is sworn in.
- August 28 – Richard Wagner's romantic opera Lohengrin (including the Bridal Chorus) premieres under the direction of Franz Liszt, in Weimar.
- September 4 – The Eusébio de Queirós Law is passed in the Brazilian Empire, to abolish the international slave trade.
- September 9
- September 13 – Piz Bernina, the highest summit of the eastern Alps, is first ascended.
- September 18 – The Fugitive Slave Law is passed by the United States Congress.
- September 29 – Papal bull Universalis Ecclesiae: The Catholic hierarchy is re-established in England and Wales, by Pope Pius IX and future Pope Pius X.
- Dost Mohammad Barakzai, emir of Afghanistan, captures Balkh.
- The first portion of the Oudh Bequest is transferred, from Oudh State in the British Raj, to the Shia Islam holy cities of Najaf and Karbala, in Persia.
- The American system of watch manufacturing is started in Roxbury, Massachusetts, by the Waltham Watch Company.
- Bingley Hall, the world's first purpose-built exhibition hall, opens in Birmingham, England.
- Allan Pinkerton forms the North-Western Police Agency, later the Pinkerton National Detective Agency, in the United States.
- Harriet Tubman becomes an official conductor of the Underground Railroad in the United States.
- The temperance organisation, International Organisation of Good Templars, is established in Utica, New York, as the order of the Knights of Jericho.
- The dry-goods store of Lehman Brothers, Montgomery, Alabama, predecessor of the bank, is so renamed.
- One of the original segments of The Historic Pacific Highway in Washington in Clark and Cowlitz counties is established.
- German physicist Rudolf Clausius publishes his paper on the mechanical theory of heat ("On the Moving Force of Heat") which first states the basic ideas of the second law of thermodynamics.
- Europeans make up 22% of the world population.
- The city of Manchester, England reaches 400,000 inhabitants.
- From this year until 1880, 144,000 East Indian laborers go to Trinidad and 39,000 to Jamaica.
беларуская (тарашкевіца): 1850
srpskohrvatski / српскохрватски: 1850