Simplify the following text for a Grade 6 native English-speaking person.
Original: In 1860 , Robert Bunsen and Gustav Kirchhoff discovered caesium in the mineral water from DÃ 1\/4 rkheim , Germany .
Simplified: Caesium was first described in 1861 , by Gustav Robert Kirchhoff and Robert Wilhelm Bunsen . They were testing mineral water , from Bad DÃ 1\/4 rkheim .