The rhetorical device identified in the excerpt is the use of rhetorical questioning, specifically in the line, “I wish to know what there has been in the conduct of the British ministry for the last ten years to justify those hopes.”
The author’s purpose for using this rhetorical device is to make a clear connection between the past and the future. By referencing the actions of the British ministry over the past decade, Henry seeks to challenge the audience's optimistic views and to underscore the lack of justification for hope in positive change. This connection emphasizes the inevitability of consequences based on past behavior, thereby arguing for a call to action for liberty.