1808 followed by 1809
1808 (MDCCCVIII) was a leap year starting on Friday of the Gregorian calendar and a leap year starting on Wednesday of the Julian calendar, the 1808th year of the Common Era (CE) and Anno Domini (AD) designations, the 808th  year of the 2nd millennium, the 8th  year of the 19th century, and the  9th   year of the 1800s decade. As of the start of 1808, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.October–December
October 6 – English chemist Humphry Davy electrochemically isolates potassium from potash.
October 12 – Banco do Brasil, a major Financial group in South America, founded in Rio de Janeiro, Brazil.
November 8 – 1808 United States presidential election: James Madison defeats Charles C. Pinckney, winning 122 electoral votes to Pinckney's 47. Ten of the 17 states choose their electors by popular vote, the rest choose through state legislatures. George Clinton, who is separately elected as vice president, gets six electoral votes for president.
November 12 – Four large French frigates under the command of Jacques Félix Emmanuel Hamelin, including the Venus, are sent to operate from Isle de France (Mauritius) against British trade in the Indian Ocean, triggering the Mauritius campaign of 1809–11.
November 15 – Mahmud II (1808–1839) succeeds Mustafa IV (1807–1808), as sultan of the Ottoman Empire.
November 19 – A new truce at Olkijoki ends fighting in Finland, and Swedish troops concede that area to Russia.
November 23 – Battle of Tudela: French Marshal Lannes defeats a Spanish army.
December 1 – Tsar Alexander I of Russia proclaims Finland a part of Russia.
December 4 – Napoleon joins his army in Spain.
December 9 – At 20:34 UTC, Mercury occults Saturn (there are no observation records).
December 20
Peninsular War: Second siege of Zaragoza begins.
The original Covent Garden Theatre in London is destroyed by a fire, along with most of the scenery, costumes and scripts.
December 22 – Beethoven concert of 22 December 1808: Ludwig van Beethoven conducts and plays piano in a marathon benefit concert, at the Theater an der Wien in Vienna, consisting entirely of first public performances of works by him, including Symphony No. 5, Symphony No. 6, Piano Concerto No. 4 and Choral Fantasy.