1915 in science
- March 19 – Pluto is photographed for the first time but is not classified as a planet.
- Einstein's new theory of general relativity is used to explain Mercury's strange motions that baffled Urbain Le Verrier.
- Robert Innes discovers Proxima Centauri, the closest star to Earth after the Sun.
- May 22 – Lassen Peak, one of the Cascade Volcanoes in Northern California, erupts, sending an ash plume 30,000 feet in the air and devastating the nearby area with pyroclastic flows and lahars. It is the only volcano to erupt in the contiguous United States between 1900 and 1980.
- Alfred Wegener publishes his theory of Pangea, which he calls Urkontinent.
- undated - German paleontologist Ernst Stromer published an article assigning the specimen to a new genus and species Spinosaurus aegyptiacus.
- A global pandemic of encephalitis lethargica begins.
- Walter Bradford Cannon coins the term fight or flight to describe an animal's response to threats.
- Thomas Hunt Morgan, demonstrates non-inherited genetic mutation (in Drosophila melanogaster), undermining the conceptual basis of eugenics.
- Reginald Punnett's Mimicry in Butterflies is published in Cambridge (U.K.)
- Clara H. Hasse publishes a paper identifying the cause of citrus canker which leads to the development of methods for controlling the disease, saving the citrus crops in the southern United States from being wiped out.
- Emmy Noether proves her theorem that any differentiable symmetry of the action of a physical system has a corresponding conservation law.
- Wacław Sierpiński describes the Sierpinski triangle.
- August – Ada Hitchins' experimental results indicating that radium is formed by the decay of uranium are published.
- November 25 – Albert Einstein presents to the Prussian Academy of Sciences the Einstein field equations of general relativity. He abandons his hole argument for general relativity.
- Arnold Sommerfeld develops a modified Bohr atomic model with elliptic orbits to explain relativistic fine structure.
- Danish psychologist Edgar Rubin publishes Synsoplevede Figurer ("Visual Figures") introducing the optical illusion which becomes known as the Rubin vase.
- January 19 – Georges Claude patents the neon discharge tube for use in advertising.
- February 4 – John G. A. Kitchen patents the reversing rudder.
- March 3 – The National Advisory Committee for Aeronautics, the predecessor of NASA, is established in the United States.
- July 1 – First use of synchronization gear in aerial warfare.
- September 9 – William Foster & Co. of Lincoln in England complete the first prototype military tank "Little Willie".
- Wolfgang Gaede invents the diffusion pump.
- William Mills patents, develops and manufactures the Mills bomb, a hand grenade, at the Mills Munition Factory in Birmingham, England.
- Dagobert Müller von Thomamühl produces a form of hovercraft.
- Nobel Prize
- January 11 – Lucille Farrier Stickel (died 2007), American wildlife toxicologist.
- March 15 – Laurent Schwartz (died 2002), French mathematician.
- March 16 – Kunihiko Kodaira (died 1997), Japanese mathematician.
- May 30 – Henry Aaron Hill (died 1979), American fluorocarbon chemist and first African American president of the American Chemical Society.
- June 15 – Thomas Huckle Weller (died 2008), American virologist and co-recipient of the Nobel Prize in Physiology or Medicine (1954) for his work on polio.
- June 19 – Katherine Sanford (died 2005), American cell biologist.
- June 24 – Fred Hoyle (died 2001), English astronomer and science fiction writer.
- July 28 – Charles Hard Townes (died 2015), American physicist and co-recipient of the Nobel Prize in Physics (1964) for developing the maser.
- October 1 – Jerome Bruner (died 2016), American developmental and educational psychologist.
- October 26 – Lu Jiaxi (died 2001), Chinese physical chemist.
- November 30 – Henry Taube (died 2005), Canadian-born recipient of the Nobel Prize in Chemistry (1983).
- December 5 – Ren Xinmin (died 2017), Chinese rocket scientist.
- December 22 – A. E. Wilder-Smith (died 1995), English-born organic chemist.
- April 19 – Sir Thomas Clouston (born 1840), Scottish psychiatrist.
- March 21 – Ambrosius Hubrecht (born 1853), Dutch zoologist.
- March 24 – Margaret Lindsay Huggins (born 1848), Irish-born astronomer.
- May 2 – Clara Immerwahr (born 1870), German chemist (suicide).
- May 7 – Marie Depage (born 1872), Belgian nurse (died in sinking of the RMS Lusitania).
- May 13 – Morgan Crofton (born 1826), Irish-born mathematician.
- July 22 – Sir Sandford Fleming (born 1827), Canadian engineer and surveyor known as the "father of time zones".
- August 10 – Henry Moseley (born 1887), English physicist (killed in action on the Gallipoli Campaign).
- September 26 – Tsuruko Haraguchi (born 1886), Japanese psychologist (tuberculosis).
- October 11 – Jean Henri Fabre (born 1823), French entomologist.
- October 15 – Theodor Boveri (born 1862), German geneticist.
- December 19 – Alois Alzheimer (born 1864), German neuroscientist.
- Die Entstehung der Kontinente und Ozeane ("The Origin of Continents and Oceans").
- synd/3356 at Who Named It?
- von Economo, K. (1917-05-10) "Encepahlitis lethargica". Wiener klinische Wochenschrift 30: pp. 581–585; (1918) Die Encephalitis lethargica. Leipzig; Vienna: Franz Deuticke.
- "Encephalitis lethargica" at Dorland's Medical Dictionary
- Cannon, Walter Bradford (1915). Bodily Changes in Pain, Hunger, Fear and Rage: an Account of Recent Researches into the Function of Emotional Excitement. Appleton.
- Blom, Philipp (2008). The Vertigo Years: Change and Culture in the West, 1900-1914. Toronto: McClelland & Stewart. pp. 336–337. ISBN 978-0-7710-1630-1.
- In Journal of Agricultural Research. Harding, Thomas Swann (1980). Two Blades of Grass: A History of Scientific Development in the U.S. Department of Agriculture. Ayer Publishing. p. 324. ISBN 0-405-12547-X.
- Noether, E. (1918). "Invariante Variationsprobleme". Nachrichten von der Königliche Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-Physikalische Klasse. 1918: 235–257. Reprinted in: Noether, Emmy; Tavel (1971). "Invariant Variation Problems". Transport Theory and Statistical Physics. 1 (3): 186–207. arXiv: . Bibcode:1971TTSP....1..186N. doi:10.1080/00411457108231446.
- Soddy, Frederick; Hitchins, A. F. R. (August 1915). "XVII. The relation between uranium and radium. Part VI. The life-period of ionium". Philosophical Magazine. 6. 30 (176): 209–219. doi:10.1080/14786440808635387.
- Einstein, Albert (1915-11-25). "Die Feldgleichungen der Gravitation". Sitzungsberichte der Preussischen Akademie der Wissenschaften zu Berlin: 844–847. Retrieved 2006-09-12.
- van Dongen, Jeroen (2010). Einstein's Unification. Cambridge University Press. p. 23. ISBN 9780521883467.
- Wilson, Paul N. (1972). "J. G. A. Kitchen, 1869-1940, and his inventions". Newcomen Society Transactions. 45: 15–43.
- Gaede, W. (1915). "Die Diffusion der Gase durch Quecksilberdampf bei niederen Drucken und die Diffusionsluftpumpe". Annalen der Physik. 46 (3): 357–392. Bibcode:1915AnP...351..357G. doi:10.1002/andp.19153510304.
- U.S. Patent 1,178,092 U.S. copy of the 1915/1916 Mills grenade patent.