1804 in science
Astronomy and space science
- April 5 – High Possil meteorite, the first recorded meteorite to fall in Scotland in modern times, falls at Possil.
- September 1 – Karl Ludwig Harding discovers the asteroid Juno.
- March 7 – John Wedgwood founds the Horticultural Society of London.
- Jacques-Julien Labillardière begins publication of Novæ Hollandiæ Plantarum Specimen in Paris, the first flora of Australia.
- Publication in Paris of Nicolas-Théodore de Saussure's collected papers Recherches chimiques sur la végétation, outlining the basic reaction of photosynthesis.
- Publication in London of Maria Elizabetha Jacson's Botanical Lectures by a Lady.
- William Hyde Wollaston discovers how to make malleable platinum.
- German pharmacist Friedrich Sertürner first isolates morphine from opium, probably the first ever isolation of a natural plant alkaloid.
- May 14 – The Lewis and Clark Expedition departs from Camp Dubois and begin their historic journey by traveling up the Missouri River.
- Alexander von Humboldt discovers that the Earth's magnetic field decreases from the poles to the equator.
- October 13 – In Japan, Hanaoka Seishū (華岡 青洲) performs a partial mastectomy for breast cancer on a 60-year-old woman named Kan Aiya, using tsūsensan as a general anesthetic, generally regarded as the first reliably documented operation performed under general anesthesia.
- Publication of The Anatomy of the Human Body, vol. 3, Nervous System by Charles Bell.
- Antonio Scarpa publishes Riflessioni ed Osservazione anatomico-chirugiche sull' Aneurisma, a classic text on aneurisms.
- James Parkinson publishes the first volume of Organic Remains of a Former World, supporting belief in Catastrophism.
- February 21 – The Cornishman Richard Trevithick's newly built "Penydarren" steam locomotive operates on the Merthyr Tramroad between Penydarren Ironworks in Merthyr Tydfil and Abercynon in South Wales, following several trials since February 13, the world's first locomotive to work on rails.
- The first Burr Truss bridge is built by Theodore Burr across the Hudson River in Waterford, New York.
- William Congreve begins development of the solid-fuel Congreve rocket as an artillery weapon.
- The British Army first uses shrapnel shells ("spherical case shot"), invented by Major Henry Shrapnel, in action, against the Dutch in Suriname.
- February 12 – Heinrich Lenz, Russian-born Baltic German physicist (died 1865)
- February 18 – Baron Carl von Rokitansky, Bohemian pathologist (died 1878)
- March 8 – Alvan Clark, American telescope manufacturer (died 1887)
- April 5 – Matthias Schleiden, German botanist (died 1881)
- April 5 – Mary Philadelphia Merrifield, née Watkins, English fashion writer and algologist (died 1889)
- May 4 – Margaretta Riley, English pteridologist (died 1899)
- May 9 – Hewett Watson, English biologist (died 1881)
- May 13 – Janet Taylor, née Jane Ann Ionn, English mathematician and navigational instrument maker (died 1870)
- June 5 – Robert Schomburgk, German-born explorer (died 1865)
- July 20 – Richard Owen, English anatomist and paleontologist (died 1892)
- September 14 – John Gould, English ornithologist (died 1881)
- September 16 – Squire Whipple, American civil engineer (died 1888)
- October 1 – William Stokes, Irish physician (died 1878)
- October 24 – Wilhelm Eduard Weber, German physicist (died 1891)
- December 10 – Carl Gustav Jacob Jacobi, German mathematician (died 1851)
- February 6 – Joseph Priestley, English chemist (born 1733)
- March 26 – Wolfgang von Kempelen, Hungarian inventor (born 1734)
- August 30 – Thomas Percival, English reforming physician and medical ethicist (born 1740)
- September 20 – Pierre Méchain, French astronomer (born 1744)
- October 2 – Nicolas-Joseph Cugnot, French mechanical engineer (born 1725)
- Penguin Pocket On This Day. Penguin Reference Library. 2006. ISBN 0-14-102715-0.
- Serturner, F. W. A. (1806) J. Pharm. f. Arzte. Apoth. Chem. 14 47–93.
- Meyer, Klaus (2004). "Dem Morphin auf der Spur". Pharmazeutischen Zeitung (in German). GOVI-Verlag. Retrieved 2012-06-12.
- Izuo, M. (2004). "Medical history: Seishū Hanaoka and his success in breast cancer surgery under general anesthesia two hundred years ago". Breast Cancer. 11 (4): 319–24. doi:10.1007/BF02968037. PMID 15604985.
- Hyodo, M. (1992). "Doctor S. Hanaoka, the world's-first success in providing general anesthesia". In Hyodo, M.; Oyama, T.; Swerdlow, M. The Pain Clinic IV: proceedings of the fourth international symposium. Utrecht: VSP. pp. 3–12. ISBN 90-6764-147-2. Retrieved 2010-09-13.
- Perrin, Noel (1979). Giving up the gun: Japan's reversion to the sword, 1543-1879. Boston: David R. Godine. p. 86. ISBN 0-87923-773-2. Retrieved 2010-09-13.
- Matsuki, A. (2000). "New studies on the history of anesthesiology – a new study on Seishū Hanaoka's "Nyugan chiken roku" (a surgical experience with breast cancer)". Masui: the Japanese Journal of Anesthesiology. 49 (9): 1038–43. ISSN 0021-4892. PMID 11025965. Retrieved 2010-09-13.
- Jacyna, L. S. (2004). "Bell, Sir Charles (1774–1842)". Oxford Dictionary of National Biography. Oxford University Press. doi:10.1093/ref:odnb/1999. Retrieved 2011-04-06. (subscription or UK public library membership required)
- Richardson, Benjamin Ward (1886). "Antonio Scarpa, F.R.S., and Surgical Anatomy". The Asclepiad. London: Longmans, Green and Co. 4 (16): 128–157. Retrieved 2008-06-10.
- Bevan, Michael (2004). "Parkinson, James (1755–1824)". Oxford Dictionary of National Biography. Oxford University Press. doi:10.1093/ref:odnb/21371. Retrieved 2010-04-11.
- Rattenbury, Gordon; Lewis, M. J. T. (2004). Merthyr Tydfil Tramroads and their Locomotives. Oxford: Railway and Canal Historical Society. ISBN 0-901461-52-0.
- "The Burr Truss". Truss Styles of Covered Bridges. New York State Covered Bridge Society. January 2006. Archived from the original on 2006-09-08. Retrieved 2011-12-13.
- Hogg, O. F. G. (1970). Artillery: its origin, heyday and decline. London: Hurst. p. 180. ISBN 0-900966-43-2.