The year 1870 in science and technology involved some significant events, listed below.

• January 18 – Gerhardt Krefft first describes the Queensland lungfish, in The Sydney Morning Herald.
• Charles Valentine Riley confirms Phylloxera as the cause of the Great French Wine Blight.^[1]
• Heinrich Wilhelm Gottfried von Waldeyer-Hartz postulates that the number of ova in the female is fixed.

• Norman Lockyer and Edward Frankland propose that the gas detected in solar observations should be called 'helium'.^[2][3]

• Felix Klein constructs a model for hyperbolic geometry establishing its self-consistency and the logical independence of Euclid's fifth postulate. (Note: Eugenio Beltrami had previously given such a model in 1868.)
• W. Stanley Jevons publishes the popular textbook Elementary Lessons on Logic.^[4]

• Louis Pasteur and Robert Koch establish the germ theory of disease.
• Henry Maudsley publishes his lectures on Body and Mind: an Inquiry into their Connection and Mutual Influence.
• Frances Morgan becomes the first British woman to receive a Doctor of Medicine degree from a European university, the University of Zurich.

• November 1 – In the United States, the newly created Weather Bureau (later renamed the National Weather Service) makes its first official meteorological forecast: "High winds at Chicago and Milwaukee... and along the Lakes".

• Eustreptospondylus oxoniensis juvenile dinosaur fossil found in Summertown, Oxford.^[5]

• Rudolf Clausius proves the scalar virial theorem.

• Ludimar Hermann observes the Hermann grid illusion.^[6]

• February 26 – The Beach Pneumatic Transit subway in New York City is opened.
• March 8 – Joy valve gear for steam locomotives is patented in the United Kingdom by David Joy.
• August 2 – Official opening of the Tower Subway beneath the River Thames in London, first use of the cylindrical wrought iron tunnelling shield devised by Peter W. Barlow and James Henry Greathead^[7] and of a permanent tunnel lining of cast iron segments.^[8]
• Svend Foyn receives a Norwegian patent for the grenade harpoon cannon for whaling.
• Henry R. Heyl receives a United States patent for a magic lantern movie projector.
• A practical stock ticker is introduced by Thomas Edison.
• First known use of weapons for anti-aircraft warfare, at Paris during the Franco-Prussian War.

• Ellen Swallow Richards becomes the first woman admitted to study at the Massachusetts Institute of Technology.
• December 20 – Missouri University of Science and Technology established as the Missouri School of Mines and Metallurgy.

• Copley Medal: James Prescott Joule^[9]
• Wollaston Medal for geology: Gerard Paul Deshayes

• January 9 – Joseph Strauss (died 1938), American bridge engineer.
• January 13 – Ross Granville Harrison (died 1959), American physiologist.
• February 7 – Alfred Adler (died 1937), Austrian psychotherapist.
• March 17 – Horace Donisthorpe (died 1951), English entomologist.
• May 20 – Arthur Korn (died 1945), German inventor.
• May 27 – Anna Stecksén (died 1904), Swedish scientist, physician and pathologist.
• June 21 – Clara Immerwahr (suicide 1915), German chemist.
• August 25 – Mihran Kassabian (died 1910), American radiologist.
• October 23 – George Newman (died 1948), English public health physician.

• January 25 – Janet Taylor (born 1804), English mathematician and navigational instrument maker.
• March 9 – 'Granny' Maria Ann Smith (born 1799), English-born Australian horticulturalist.
• March 12 – Charles Xavier Thomas (born 1785), French inventor of the first mass-produced calculator.
• July 12 – Alexander Henry Haliday (born 1806), Anglo Irish entomologist.
• November 14 – Karl Weltzien (born 1813), German inorganic chemist.
• December 27 (O.S. December 15) – Nikolai N. Kaufman (born 1834), Russian botanist.