APA (7th ed.) Citation

Walpole, H., & Walpole, S. (1902). Some unpublished letters of Horace Walpole. Longmans, Green.

Chicago Style (17th ed.) Citation

Walpole, Horace, and Spencer Walpole. Some Unpublished Letters of Horace Walpole. London, New York: Longmans, Green, 1902.

MLA (9th ed.) Citation

Walpole, Horace, and Spencer Walpole. Some Unpublished Letters of Horace Walpole. Longmans, Green, 1902.