1891 in science

Biology

• March 3 – Yellowstone Timberland Reserve, predecessor of Shoshone National Forest, in Wyoming is established as the first United States National Forest.
• The New Zealand government sets aside Resolution Island in Fiordland as a nature reserve.
• The New York Botanical Garden is founded in The Bronx largely due to the efforts of Nathaniel Lord Britton.
• Jane Willis Kirkaldy and Catherine Pollard become the first women to sit final examinations in biology at the University of Oxford.

Chemistry

• Agnes Pockels first publishes the results of her researches into surface tension.
• The Fischer projection is devised by German chemist Hermann Emil Fischer,

Geology

• Hans Reusch describes what comes to be known as Reusch's Moraine in northern Norway; tillite from a Precambrian glaciation.

Environment

• The Japan Meteorological Agency begins taking records of the global average temperature.

Mathematics

• Fyodorov–Schoenflies theorem concluded by Yevgraf Fyodorov and Arthur Schoenflies from their work on crystallographic groups.
• Édouard Lucas first formulates the ménage problem.

Paleontology

• October – Eugène Dubois finds the first fragmentary bones of Pithecanthropus erectus (later redesignated Homo erectus), or 'Java Man', at Trinil on the Solo River.

Physiology and medicine

• Julius Ludwig August Koch begins publication of in Ravensburg, introducing the concept of psychopathology.
• Arnold Pick first uses the term dementia praecox in this form.
• Heinrich Wilhelm Gottfried von Waldeyer-Hartz names the neuron.
• Myxedema is first treated successfully, by George Redmayne Murray using thyroid extract.
• The earliest recorded attempt at hip replacement is carried out by Themistocles Gluck in Berlin, using ivory to replace the femoral head.
• Viennese pathologist Hans Chiari describes a form of Chiari malformation.

Technology

• March 10 – Almon B. Strowger, an undertaker in Topeka, Kansas, is granted a patent in the United States for an automatic telephone exchange using the Strowger switch.
• May 20 – First public demonstration of the Kinetograph moving picture system developed by W. K. L. Dickson under the direction of Thomas Alva Edison, a showing of the film known as Dickson Greeting. Edison files patents on the camera and peephole viewer on August 24.
• Crompton & Co. introduce the electric kettle, in the United Kingdom.
• Michelin patent the removable pneumatic bicycle tire.
• Panhard et Levassor produce the first Système Panhard automobile layout, consisting of four wheels with front-engine, rear-wheel drive and a sliding-gear transmission, designed by Émile Levassor.
• William Le Baron Jenney develops the construction of steel frame skyscrapers in Chicago with the Ludington, Manhattan and Second Leiter Buildings.
• The modern taximeter is invented by Friedrich Wilhelm Gustav Bruhn in Germany.

Awards

• Copley Medal: Stanislao Cannizzaro
• Wollaston Medal for Geology: John Wesley Judd

Births

• January 8 – Walther Bothe, German physicist, winner of the Nobel Prize in Physics .
• January 26 – Wilder Penfield, American-born neurosurgeon.
• April 22 – Harold Jeffreys, English mathematician.
• May 15 – Fritz Feigl,, Austrian-born Brazilian chemist
• July 5 – John Howard Northrop, American biochemist, winner of the Nobel Prize in Chemistry
• July 27 – Jacob van der Hoeden, Dutch-Israeli veterinary scientist
• August 17 – Aly Tewfik Shousha, Egyptian bacteriologist.
• September 14 – Ivan Matveyevich Vinogradov, Russian mathematician.
• September 24 – W. F. Friedman, Bessarabian-born cryptanalyst.
• October 24 – Ernest Melville DuPorte, Caribbean-born Canadian insect morphologist.
• November 14 – Frederick Banting, Canadian discoverer of insulin, winner of the Nobel Prize in Physiology or Medicine.

Deaths

• January 6 – Hugh Owen Thomas, British orthopaedic surgeon.
• February 10 – Sofia Kovalevskaya, Russian mathematician.
• March 9 – Amalie Dietrich, German naturalist.
• May 11 – Edmond Becquerel, French physicist.
• June 9 – Henry Edwards, English-born American entomologist and actor.
• June 23
• * Sir Norman Pogson, English-born astronomer.
• * Wilhelm Eduard Weber, German physicist.
• August 30 – Emanoil Bacaloglu, Romanian polymath.
• September 18 – William Ferrel, American meteorologist.
• October 3 – Édouard Lucas, French mathematician.
• November 18 – Joseph Wolstenholme, English mathematician.
• December 21 – William Cavendish, 7th Duke of Devonshire, English landowner and promoter of science.