1721 in science

Medicine

• The use of ether is developed as a pain-killer.
• Lady Mary Wortley Montagu introduces the Ottoman Turkish method of inoculation against smallpox - variolation - to London.
• Thomas Guy founds Guy's Hospital in London to treat "incurables" discharged from St Thomas'.

  Psychology

• A suggestion box is developed under the eighth shōgun of Japan, Yoshimune Tokugawa.

  Technology

• Richard Newsham of London obtains his first patent for a manual fire pump.

  Deaths

• September 11 – Rudolf Jakob Camerarius, German botanist