1904 in science

• Johannes Franz Hartmann discovers the interstellar medium.{{cite book|authorlink=Isaac Asimov|first=Isaac|last=Asimov|title=Asimov's Biographical Encyclopedia of Science and Technology|edition=2nd}}
• Edward Walter Maunder plots the first sunspot "butterfly diagram".
• Notable asteroid 522 Helga is discovered by Max Wolf in Heidelberg.
• December 3 – The sixth moon of Jupiter, later called Himalia, is discovered at Lick Observatory.

• Van der Grinten projection proposed.

• Henri Poincaré discovers the Poincaré homology sphere, leading him to formulate the Poincaré conjecture.
• Helge von Koch describes the "Koch snowflake", one of the earliest fractal curves described."Sur une courbe continue sans tangente, obtenue par une construction géométrique élémentaire".{{cite book|last=Addison|first=Paul S.|title=Fractals and Chaos: An Illustrated Course|publisher=Institute of Physics|location=Bristol|year=1997|isbn=0-7503-0400-6|page=19}}
• Charles Spearman develops his rank correlation coefficient.{{cite book|first=Tony|last=Crilly|title=50 Mathematical Ideas you really need to know|location=London|publisher=Quercus|year=2007|isbn=978-1-84724-008-8|page=145}}
• Ernst Zermelo formulates the axiom of choice to formalize his proof of the well-ordering theorem.{{cite journal|first=Ernst|last=Zermelo|year=1904|url=http://gdz.sub.uni-goettingen.de/no_cache/en/dms/load/img/?IDDOC=28526|format=reprint|title=Beweis, dass jede Menge wohlgeordnet werden kann|journal=Mathematische Annalen|volume=59|issue=4|pages=514–16|doi=10.1007/BF01445300|s2cid=124189935}}

• September 17 – An early study on the relationship between alcohol and cardiovascular disease is published in the United States.{{cite journal|last=Cabot|first=Richard C.|authorlink=Richard Clarke Cabot|title=The relation of alcohol to arterioscleroisis|journal=Journal of the American Medical Association|year=1904|volume=43|issue=12|pages=774–775|doi=10.1001/jama.1904.92500120002a|url=https://zenodo.org/record/1447273|accessdate=2019-10-04}}
• Epinephrine first artificially synthesized by Friedrich Stolz.
• Antoni Leśniowski presents to a meeting of the Warsaw Medical Society a surgical specimen of an inflammatory tumour of the terminal ileum with a fistula to the ascending colon, consistent with what will later become known as Crohn's disease.Reported by him in Pamiętnik Towarzystwa Lekarskiego Warszawskiego. {{cite journal|first=W. |last=Bartnik |date=December 2003 |title=Inflammatory bowel disease – Polish contribution |journal=Journal of Physiology and Pharmacology |volume=54 |issue=S3 |pages=205–210 |publisher=Polish Physiological Society |location=Kraków |pmid=15075474 |url=http://www.jpp.krakow.pl/journal/archive/1203_s3/articles/14_article.html |accessdate=2008-03-28 }}{{dead link|date=June 2017 |bot=InternetArchiveBot |fix-attempted=yes }}

• Vacuum tube invented by John Ambrose Fleming.
• James H. Jeans's [https://archive.org/details/dynamicaltheoryo00jeanrich The Dynamical Theory of Gases] is published in Cambridge.
• J. J. Thomson proposes the plum pudding model for the atom.
• Hantaro Nagaoka develops the Saturnian model for the atom.

• July 4 – Piero Ginori Conti demonstrates the use of geothermal power to generate electricity, at Larderello in Italy.
• July 23 – A continuous track tractor is patented by David Roberts of Richard Hornsby & Sons of Grantham in England.British Patent No. 16,345. {{cite book|first=Peter|last=Robinson|title=Lincoln's Excavators: The Ruston years 1875–1930|year=2003|location=Nynehead|publisher=Roundoak|isbn=1-871565-42-1}}
• November 16 – John Ambrose Fleming patents the first thermionic vacuum tube, the two-electrode diode ("oscillation valve" or Fleming valve).{{cite book|title=The Hutchinson Factfinder|publisher=Helicon|year=1999|isbn=978-1-85986-343-5}}
• November 24 – A continuous track tractor is demonstrated by the Holt Manufacturing Company in the United States.
• The first diesel engined submarine, the Z, is built in France.
• The Heckelphone variety of oboe is invented by Wilhelm Heckel and his sons.
• The sleeve valve is invented by Charles Yale Knight.
• The turbine-powered Bliss-Leavitt torpedo, designed by Frank McDowell Leavitt and manufactured by the E. W. Bliss Company of Brooklyn, is put into service by the United States Navy.{{cite book|last=Newpower|first=Anthony|url=https://books.google.com/books?id=eFZb_BqP10UC&q=%22Frank+McDowell+Leavitt%22&pg=RA1-PA18|title=Iron Men And Tin Fish: The Race to Build a Better Torpedo During World War II|location=Westport, Conn.|publisher=Greenwood Publishing Group|year=2006|page=18|isbn=0-275-99032-X}}
• Lucien Bull produces the first successful chronophotography (of insect flight), working in France.Reported by him in "Motional mechanism of the insect wing", Comptes rendus de l'Académie des sciences 138:590–592 (29 February); "Application of the electric spark to the chrono-photography of rapid motions", Comptes rendus 138:155–157 (21 March); "Chronophotography of rapid motions", Bulletin de la Société Philomathiclue (Paris) (June 11); Synthesis in chronophotography, Bulletin de la Société Philomathiclue (November 12).
• Rue Franklin Apartments, Paris, are completed by Auguste Perret and his brother Gustave, an early example of an exposed reinforced concrete frame building.{{cite web|url=http://www.greatbuildings.com/buildings/Rue_Franklin_Apartments.html|title=Rue Franklin Apartments|work=GreatBuildings|accessdate=2012-05-29}}

• First identification and last confirmed sighting of the Choiseul pigeon in the Solomon Islands.{{cite journal|last=Rothschild|first=Walter|authorlink=Walter Rothschild, 2nd Baron Rothschild|title=Microgoura, n. gen.|journal=Bulletin of the British Ornithologists' Club|volume=14|issue=CVII|date=1904-05-20|url=https://www.biodiversitylibrary.org/item/114181#page/565/mode/1up|pages=77–78|accessdate=2015-09-29}}

• Nobel Prizes
• Physics – John William Strutt, 3rd Baron Rayleigh
• Chemistry – Sir William Ramsay
• Medicine – Ivan Pavlov

• January 21 – Edris Rice-Wray Carson (died 1990), American-born physician, pioneer in family planning.
• January 26 – Ancel Keys (died 2004), American nutritionist.
• March 13 – René Dumont (died 2001), French agronomist.
• March 20 – B. F. Skinner (died 1990), American behavioral psychologist.
• April 11 – Arthur Mourant (died 1994), Jersiais hematologist.
• April 22 – J. Robert Oppenheimer (died 1967), American physicist.
• June 3 – Charles R. Drew (died 1950), African American physician, pioneer in blood transfusion.
• July 5 – Ernst Mayr (died 2005), German-born evolutionary biologist.
• August 5 – Kenneth V. Thimann (died 1997), English-American plant physiologist and microbiologist known for his studies of plant hormones.
• August 17 – Cornelis Simon Meijer (died 1974), Dutch mathematician.
• August 28 – Secondo Campini (died 1980), Italian jet pioneer.
• August 29 – Werner Forssmann (died 1979), German physician, recipient of the Nobel Prize in Physiology or Medicine.
• November 11 – J. H. C. Whitehead (died 1960), British mathematician.
• Sven Sømme (died 1961), Norwegian ichthyologist and resistance worker.

• March 7 – Ferdinand André Fouqué (born 1828), French geologist, petrologist and volcanologist.
• May 10 – Henry Morton Stanley (born 1841), Welsh-born explorer and journalist.
• July 3 – John Bell Hatcher (born 1861), American paleontologist.
• September 24 – Niels Ryberg Finsen (born 1860), Icelandic/Faroese/Danish physician and scientist, recipient of the Nobel Prize in Physiology or Medicine.
• October 7 – Isabella Bird (born 1831), British explorer, writer, photographer and naturalist.
• October 21 – Isabelle Eberhardt (born 1877), Swiss–Algerian explorer.

{{reflist}}

{{DEFAULTSORT:1904 In Science}}

Category:20th century in science

Category:1900s in science