 After doing his military service in Cologne, he became an assistant high school teacher there in 1852 at the Friedrich-Wilhelms-Gymnasium. After failing to be promoted from assistant teacher to teacher after three years, he resigned and received his habilitation (qualification as a university lecturer) at the University of Bonn. In 1855 he became a Privatdozent of Philosophy and Pedagogy at the University of  Bonn.[2]  His inaugural lecture was on the relation between the education systems and dominant world views of various time periods (Lange  1855).[3]  He gave lectures on psychology and pedagogy. He began lecturing on the history of materialism during the summer of 1857. This was the beginning of the research that would eventually yield his book, The History of Materialism, many years later. He also gave lectures on “Moralstatistik”, the view popular in some circles in the nineteenth century that there are statistical correlations between the rates of certain kinds of morally significant behavior such as crimes, marriages, and suicides. Lange’s thoughts about how to reform logic also begin during this period even though his book, Logical Studies, that eventually emerged from his investigations, was only published posthumously. It is presumably significant for his later views that during this time he heard Hermann von Helmholtz lecture on the “Physiology of the Sense  Organs”.[4]