Complex sentence: In 1841, he returned to France, in the Domanican habit, theoretically illegal according to revolutionary laws, and on the 14th of February 1841, preached successfully at Notre-Dame.
Split into simpler sentences: In 1841, he returned to France, in the Dominican habit, which was theoretically illegal according to revolutionary laws. On the 14th of February 1841, preached successfully at Notre-Dame.