1778-1829. English chemist. As a laboratory 
assistant in Bristol in 1799, he discovered 
the respiratory effects of laughing gas 
(nitrous oxide). He discovered, by 
electrolysis, the elements sodium, potassium, 
calcium, magnesium, strontium, and barium. He 
invented the `safety lamp' for use in mines 
where methane was present, enabling the 
miners to work in previously unsafe 
conditions. In 1802 he became professor at 
the Royal Institution, London. He was elected 
President of the Royal Society in 1820.