Simplify the following text for a Grade 10 native English-speaking person.
Original: In 1812 , Mohs became professor in Graz ; in 1818 , professor in Freiberg , Saxony ; in 1826 , professor in ViennaIn 1817 , Mohs replaced his mentor Werner , who had died , as a tutor at the mining academy in Freiberg , where he worked for nine more years , until he was appointed as a professor of Mineralogy at the University of Vienna .
Simplified: In 1812 , Mohs became professor in Graz ; in 1818 , professor in Freiberg , Saxony ; in 1826 , professor in Vienna .