Complex sentence: Then he was a demonstrator at École pratique des hautes études and a lecturer to the Faculty of Science of the University of Paris.In January 4,1887, he was made assistant professor of that university, then in 1899, full professor.
Split into simpler sentences: Then he was a demonstrator at École pratique des hautes études and a lecturer to the Faculty of Science of the University of Paris. On January 4,1887, he was made assistant professor at that university, then in 1899, full professor.