Discovered : 1860 by R. Bunsen and G. R. Kirchoff in Heidelberg, Germany Origin : The name is derived from the Latin caesius, ‘sky blue’. Description : A soft, gold-coloured metal that is quickly attacked by air and reacts explosively in water. It is used in industry as a catalyst promoter, to make special glass, and in radiation monitoring equipment. The ‘caesium clock’ (atomic clock) is the standard measure of time: the electron resonance frequency of the caesium atom is exactly 9,192,631,770 cycles per second. Image : Atomic clock.