when did the aforementioned professor start teaching at the university?
In 1920.
Harold Innis
In 1920, Innis joined the department of political economy at the University of Toronto. 
who was harold innis? He was a professor and an author. what subjects did he teach? Political economy. in which university did he teach? University of Toronto. what is the origin of the subject mentioned above? It originated in moral philosophy, to explore the administration of states' wealth, with "political" signifying the Greek word "polity" and "economy" signifying the Greek word "oikonomía" (household management).. what are some of the new approaches to the subject? Modeling economic policy and political institutions concerning interactions between agents and economic and political institutions.
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Harold Innis [SEP] "Dirt" research
In 1920, Innis joined the department of political economy at the University of Toronto. He was assigned to teach courses in commerce, economic history and economic theory. He decided to focus his scholarly research on Canadian economic history, a hugely neglected subject, and he settled on the fur trade as his first area of study. Furs had brought French and English traders to Canada, motivating them to travel west along the continent's interlocking lake and river systems to the Pacific coast. Innis realized that he had to search out archival documents to understand the history of the fur trade and also travel the country himself gathering masses of firsthand information and accumulating what he called "dirt" experience.