The year 1804 in science and technology included many events, some of which are listed here.

See also: 1803 in science, other events of 1804, 1805 in science, list of years in science

Chemistry

• William Hyde Wollaston discovers palladium, and how to make malleable platinum
• Jons Jacob Berzelius discovers cerium

Exploration

• May 14 - The Lewis and Clark Expedition departs from Camp Dubois and begin their historic journey by traveling up the Missouri River

Geology

• Alexander von Humboldt discovers that the Earth's magnetic field decreases from the poles to the equator

Meteorology

• Joseph Louis Gay-Lussac and Jean Baptiste Biot study the atmosphere from a hot-air balloon

Technology

• Richard Trevithick produces his first railway locomotive

Awards

• Copley Medal: Smithson Tennant

Births

• July 20 - Richard Owen, anatomist and paleontologist (died 1892)
• September 14 - John Gould, zoologist (died 1881)
• October 24 - Wilhelm Eduard Weber, physicist (died 1891)
• December 10 - Carl Gustav Jakob Jacobi, mathematician (died 1851)
• Robert Schomburgk, explorer (died 1865)
• William Stokes, physician (died 1878)
• Heinrich Lenz, physicist (died 1865)
• Matthias Schleiden, biologist (died 1881)

Deaths

• February 6 - Joseph Priestley, chemist (born 1733)
• October 2 - Nicolas-Joseph Cugnot, engineer (born 1725)
• Pierre Méchain, astronomer (born 1744)