Sir Humphry Davy, English chemist, 1801.

UNITED KINGDOM - APRIL 20: Mezzotint by C Turner after a painting by Henry Howard. Whilst at the Pneumatic Institute in Bristol, Davy (1778-1829) discovered the anaesthetic effects of laughing gas (nitrous oxide). In 1801, he was appointed lecturer at the Royal Institution, where he isolated the metals barium, calcium, magnesium, potassium, sodium and strontium, and investigated, with his assistant Michael Faraday (1791-1867), his theory of volcanic action. It is his invention in 1815 of the miners' safety lamp (which enabled deeper, more gaseous seams to be mined without risk of explosion) for which he is perhaps best known. (Photo by SSPL/Getty Images)