The year 1842 in science and technology involved some significant events, listed below.

• Nathaniel Bagshaw Ward publishes On the Growth of Plants in Closely Glazed Cases in London, promoting his concept of the Wardian case.^[1]

• Antarctic explorer James Clark Ross charts the eastern side of James Ross Island and on January 23 reaches a Farthest South of 78°09'30"S.^[2]

• January – American medical student William E. Clarke of Berkshire Medical College becomes the first person to administer an inhaled anesthetic to facilitate a surgical procedure (dental extraction).^[3]
• March 30 – American physician and pharmacist Crawford Long administers an inhaled anesthetic (diethyl ether) to facilitate a surgical procedure (removal of a neck tumor).^[4][5]
• English surgeon William Bowman publishes On the Structure and Use of the Malpighian Bodies of the Kidney,^[6] identifying Bowman's capsule, a key component of the nephron.
• Edwin Chadwick's critical Report on an inquiry into the Sanitary Condition of the Labouring Population of Great Britain is published by the Poor Law Commission.^[7]

• Palaeontologist Richard Owen coins the name Dinosauria, hence the Anglicized dinosaur.^[8]

• Christian Doppler proposes the Doppler effect.^[9]
• Julius Robert von Mayer proposes that work and heat are equivalent.^[10] This is independently discovered in 1843 by James Prescott Joule, who names it "mechanical equivalent of heat".

• January 8 – Delft University of Technology established by William II of the Netherlands as a 'Royal Academy for the education of civilian engineers'.^[11]
• February 21 – John Greenough is granted the first U.S. patent for the sewing machine.^[12]
• June – James Nasmyth patents his design of steam hammer in England and introduces an improved planing machine.^[13]
• John Herschel discovers the cyanotype (blueprint) photographic process in England.^[14]

• September 14–17 – English naturalist Charles Darwin and his family settle at Down House in Kent.

• Copley Medal: James MacCullagh^[15]
• Wollaston Medal: Leopold von Buch

• February 2 – Julian Sochocki (died 1927), Polish mathematician.
• February 10 – Agnes Mary Clerke (died 1907) Irish astronomer and author.^[16]
• February 22 – Camille Flammarion (died 1925), French astronomer.
• March 17 – Rosina Heikel (died 1929), Finnish physician.^[17]
• March 23 – Susan Jane Cunningham (died 1921), American mathematician.
• April 4 – Édouard Lucas (died 1891, French mathematician.
• May 7 – Isala Van Diest (died 1916), Belgian physician.
• May 8 – Emil Christian Hansen (died 1909), Danish fermentation physiologist.
• June 11 – Carl von Linde (died 1934), German refrigeration engineer.
• August 23 – Osborne Reynolds (died 1912), Irish-born physicist.
• September 9 – Elliott Coues (died 1899), American ornithologist.
• September 20
  • James Dewar (died 1923), Scottish-born chemist.
  • Charles Lapworth (died 1920), English geologist.
• October 17 – Gustaf Retzius (died 1919), Swedish anatomist.
• October 24 (O.S. October 12) – Nikolai Menshutkin (died 1907), Russian chemist.
• November 12 – John William Strutt, 3rd Baron Rayleigh (died 1919), English Nobel Prize-winning physicist.
• December 3 – Ellen Swallow Richards (d. 1911), American chemist.
• December 17 – Sophus Lie (died 1899), Norwegian mathematician.

• February 15 – Archibald Menzies (born 1754), Scottish-born botanist.
• April 28 – Charles Bell (born 1774), Scottish-born anatomist.
• May 8 – Jules Dumont d'Urville (born 1790), French explorer.
• June 9 - Maria Dalle Donne (born 1778), Bolognese physician
• June 30 – Thomas Coke, Earl of Leicester (born 1754), English agriculturalist and geneticist.
• July 19 – Pierre Joseph Pelletier (born 1788), French chemist.
• July 25 – Dominique Jean Larrey (born 1766), French military surgeon, pioneer of battlefield medicine.