 While attending the University of Halle, he studied physics under Friedrich Ernst Dorn.Repeating the cosmic ray experiments of Victor Hess, in 1913-14 Kolhörster ascended by balloon to an altitude of 9 km, where he confirmed Hess' result that the ionization rate from cosmic rays was greater at that altitude than at sea level.This was evidence that the source for these ionizing rays came from above the Earth's atmosphere.