Where any person ("the principal") would be liable under this Act to any punishment or penalty for any act, omission, neglect or default, he shall be liable to the same punishment or penalty for every such act, omission, neglect or default of any employee or agent of his, or of the employee of such agent, if such act, omission, neglect or default was committed by the principal's employee in the course of his employment, or by the agent when acting on behalf of the principal, or by the employee of such agent in the course of his employment by such agent or otherwise on behalf of the agent.