 Complete the following phrase:  Petronijević retired from the university in 1927. He served as secretary of the Serbian Royal Academy from February 1932 to February 1933 and founded the Serbian Philosophical Society in 1938, together with Vladimir Dvorniković, Justin Popović and others. The third volume of his Principles of Metaphysics was destroyed in an air raid in April 1941. He held lectures at the German Scientific Institute during the 