cæsium, cesium

Cæsium, or cesium as it is usually spelled in the United States, is the fifty-fifth element. It was discovered by German scientists Robert Bunsen and Gustav Kirchhoff in 1860. Cæsium is the neuter form of the Latin adjective cæsius, meaning bluish-gray. It is so called because spectral analysis of the element reveals two bright lines in that portion of the spectrum. From an 1861 issue of the London, Edinburgh, and Dublin Philosophical Magazine:

A faint blue line not due to strontium or potassium or to the lately discovered cæsium.1

Cæsium has the chemical symbol Cs.

1Oxford English Dictionary, cæsium, 2nd Edition, 1989, Oxford University Press, accessed 11 October 2009, http://dictionary.oed.com/cgi/entry/50031116.

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