Complex sentence: From 1899 to 1902 he lectured on law at Columbia Law School; he was a professor there from 1902 to 1905; and eventually became the school's dean from 1910 to 1923.
Split into simpler sentences: From 1899 to 1902 he lectured on law at Columbia Law School. He was a professor there from 1902 to 1905 and eventually served as the school's dean from 1910 to 1923.