 The last element "fossen," the definite form of "foss" (waterfall), is a later addition.The waterfall was hardly known by anyone other than locals until 1821.In that year professor Christopher Hansteen, who was on his way to the Hardangervidda plateau to make astronomical observations, estimated the height of the waterfall to be about by throwing stones down from the edge and measuring the time they took to fall with his pocket watch.