Zehnder studied mechanical engineering in Zurich from 1873 to 1875. After that, he ran a factory for electrical equipment in Basel for 15 years. However, this did not satisfy him in the long run and he went to Berlin in 1885 to study physics with Hermann von Helmholtz.^[1]

Zehnder was a student of Wilhelm Röntgen, professor of physics at the universities of Freiburg and Basel. He produced the first pictures of the human skeleton in 1896 by shining x-rays through the human body.^[1]