May 17, 1861 – James Clark Maxwell obtains the first authentic color photographic image.

March 30, 1861 – William Crookes discovered the element thallium.

August 7, 1861 – Ernest Solvay develops an ammonia-chloride process for the production of soda ash.

August 15, 1861 - the first description of the fossil Archaeopteryx from a few remains. In September, the first fully identified skeleton was found near Langenalthheim in Germany.

At the end of 1861, Richard Gatling invented Gatling’s rifle gun, the first machine gun.

March 3, 1861 – Emperor of the Russian Empire Alexander II manifesto “On the Most Merciful Granting of the Rights of Free Rural People to Serfs” abolished serfdom in Russia.