Samuel Taylor Coleridge (1856). “The Complete Works of Samuel Taylor Coleridge: With an Introductory Essay Upon His Philosophical and Theological Opinions”, p.145
Gaston Leroux (2016). “The Phantom of the Opera & The Mystery of the Yellow Room (Mystery Classics): The Ultimate Gothic Romance Mystery and One of the First Locked-Room Crime Mysteries”, p.10, e-artnow