In 1803 Oersted returned to Copenhagen and applied for the university's chair in physics but was rejected because he was probably considered more a philosopher than a physicist. However, he continued experimenting and lecturing, publishing the results of his experiments in German and Danish periodicals. In 1806 his ambition was realized and he became professor of physics at the Copenhagen University, though not realizing full professorship (ordinarius) until 1817.

During Oersted's attendance at the university, it was poorly equipped with physical apparatus for experimenting in the sciences. He was, however, fortunate in his contact with Prof. J. G. L. Manthey (1769 -- 1842), teacher of chemistry, who, in addition to his academic chair, was also proprietor of the ``Lion Pharmacy'' in Copenhagen where Oersted assisted him. Manthey maintained a valuable collection of physical and chemical apparatus which was at Oersted's disposal during and after his graduation. In 1800, Manthey went abroad and Oersted was appointed manager of the Lion Pharmacy. In February 1801, Oersted did manage to experiment with physical apparatus and reported experiments made with a voltaic battery of 600 plates of zinc and silver and of later experiments with a battery of 60 plates of zinc and lead. In the following year, 1803, Oersted, simultaneously with Davy, discovered that acids increased the strength of a voltaic battery more than did salts. Eager as he was to pursue this promising line, he was so loaded down with the management of the pharmacy and lectures in the medical and pharmaceutical faculties at the university that he could devote only Sunday afternoons to ``galvanizing.''