Charles Mackay, David J. Schneider, Extraordinary Popular Delusions and the Madness of Crowds, Barnes & Noble Publishing, 2004, p. 238
Eleanor Margolies, Ventriloquism: Kantor, Templeton, and the Voices of the Dead, p. 206, in New Theatre Quarterly 63: Volume 16, Parte 3, Cambridge University Press, 2001.