In 1830 Belgium declared itself independent from The Netherlands and there was a treaty discussion going on to determine the status of the regions.

[1] The treaty placed Venlo back in The Netherlands so his father moved to Liège as he was in the military and a captain in the Belgian artillery.

In Belgium, his father was put in charge to teach pyrotechnics and artillery advancements to the army.

[4] Folie was the Administer at the University of Liège from 1872 to 1884, it was under his administration that most of the buildings of science and medicine were built.

Because of the increase in size of Brussels it was no longer a good city to do astronomy and he built an observatory at Uccle.

[2] He visited the Bonn observatory several times where he worked on astronomy with Friedrich Wilhelm Argelander and Adalbert Krüger.