While crossing a public highway in the city, Joel was struck by a horse-drawn cart driven by Morison’s agent. The agent was traveling between Burton Crescent Mews and Finchley on his employer’s business and was not supposed to go into the city. Apparently, the agent was on a detour to visit a friend when the accident occurred. Joel brought this action against Morison for the injuries he sustained as a result of the agent’s negligence. Morison argues that he is not liable for his agent’s negligence because the agent had strayed from his assigned path. Who is correct? Why?