Complex sentence: In 1850 he returned to the United states and became a professor at Brown University he left in 1852 to take the place of the retiring Professor John P. Norton at Sheffield Scientific School (then Yale Scientific School).
Split into simpler sentences: In 1850 he returned to the United states and became a professor at Brown University. He left in 1852 to take the place of the retiring Professor John P. Norton at Sheffield Scientific School (then Yale Scientific School).